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The description of oil absorption behavior of potato chips during the frying
Abstract
The oil absorption during frying is a complex phenomenon and how the oil permeated into the sample is still not clear. The oil absorption behavior of potato chips was investigated by combined the dyed oil methods, digital photo analysis, confocal laser scanning microscopy, low field nuclear magnetic resonance imager and mercury porosimeter. The relationship between the oil absorption with frying time, microstructure and pore formation was discussed. The results showed that the content of total oil and structural oil of potato chips increased with the increasing of frying time, and it reached 40.44% and 6.44% at 2 min, respectively. Penetrated surface oil reached the maximum at 2 min and then decreased. The oil infiltration was in accordance with the sequence from outside to inside of potato chips and the oil was distributed along the contours of the cells and filling cell interstitial. The oil absorption was closely related to the pore properties, and the total pore volume and porosity of potato chips increased but bulk density decreased during the first 8 min, which remained constant at 1.63 mL g⁻¹, 0.42 g mL⁻¹ and 68.7% during 8–12 min. The results could provide scientific guidance for the production of low-fat and healthy fried food.
... During frying, the hot oil acts as a medium of heat transfer, and the water evaporates from the surface while the oil is absorbed into the product. Simultaneously, changes in the cellular structure of carbohydrates, proteins, and fats (Zhang et al. 2018) as well as some other chemical reactions such as Maillard reaction, caramelization reaction, and oxidation reactions occur. The moisture in the surface evaporates during frying, forming the outer crust. ...
... The moisture is also transmitted from the inner core through molecular diffusion which results in the formation of various channels that are later filled with oil (Krokida et al. 2000). Several studies have reported that most of the oil is absorbed while removing the product from the oil bath since the rapid escape of water vapor would hinder the oil penetration during frying (Dana and Saguy 2006;Zhang et al. 2018;Touffet et al. 2020). The extent of oil absorption depends on various factors such as pretreatments (pre-drying, blanching), processing parameters (temperature, time, and method) as well as product characteristics including surface roughness, composition, the thickness of the layer, and oil properties (Zhang et al. 2018;Xu et al. 2020;Dehghannya and Ngadi 2021). ...
... Several studies have reported that most of the oil is absorbed while removing the product from the oil bath since the rapid escape of water vapor would hinder the oil penetration during frying (Dana and Saguy 2006;Zhang et al. 2018;Touffet et al. 2020). The extent of oil absorption depends on various factors such as pretreatments (pre-drying, blanching), processing parameters (temperature, time, and method) as well as product characteristics including surface roughness, composition, the thickness of the layer, and oil properties (Zhang et al. 2018;Xu et al. 2020;Dehghannya and Ngadi 2021). These factors also play a crucial role in developing crispy crust, golden brown color, and distinct flavors and aromas making fried food appealing to the consumers (Fellows 2017;Ghaitaranpour et al. 2018). ...
The present study was focused on the optimization of process parameters and quality characterization of Khaja. A full factorial design 53 was applied using different levels of fat proportions (5-25%), frying temperature (160-200 °C), and frying time (1-5 min). The response optimizer function in Minitab 18 software was used to select five samples with the highest desirability which were then subjected to sensory analysis. The lightness of the samples decreased significantly (P ˂ 0.05) from 68.59 to 43.33 whereas, redness increased significantly (P ˂ 0.05) from 0.26 to 11.48 with increasing levels of all independent variables. Water activity and moisture content of the samples decreased significantly (P ˂ 0.05) from 0.75 to 0.21 and 14.41-1.40%wb respectively, whereas total fat content increased significantly (P ˂ 0.05) from 25.05 to 45.7% with increasing levels of independent variables. The hardness of the samples significantly (P ˂ 0.05) varied from 60.45 to 7.69 N. The sensory analysis revealed that the sample with 20% fat proportion, fried at 180 °C for 4 min, scored maximum in overall acceptability. The microstructural images revealed the structural damage and formation of pores in fried samples. The fatty acid analysis showed higher saturated fatty acids in market samples than in optimized samples. The results of the study concluded that fat proportion and frying parameters (temperature and time) are crucial for a better understanding of the deep-frying process of Khaja in order to achieve good quality.
Supplementary information:
The online version contains supplementary material available at 10.1007/s13197-022-05509-x.
... Frying is considered to be one of the oldest thermal techniques in cooking and is widely used at both domestic and industrial scales. The process involves the simultaneous transfer of mass (water loss and oil uptake) and heat [1]. During atmospheric frying at high temperatures (150-200 °C), heat from the oil is transferred to the food surface by convection and continuously transferred into the center by conduction [2]. ...
... Many studies have reported that oil absorption occurs mainly during the post-frying cooling period [5]. For example, Zhang et al. [1] reported that total oil uptake could increase by as much as 40% during the frying of potato chips for 2 min while about 60% of the total oil remained on the chip surface. The reverse situation has been presented by Durán et al. [6] who reported that almost 65% of the total oil content was absorbed by potato chips during the cooling stage and only 35% remains at the surface. ...
... The oil uptake during frying is affected by many factors, including food composition, surface roughness, frying conditions, and frying medium [1]. Several attempts have been made to reduce the oil content in atmospheric fried products using pre-frying treatment, modifying frying conditions, the hybrid fry method, and post-frying treatment [9]. ...
The effects of pressure (21.3, 41.3, 61.3, 81.3, and 101.3 kPa) and temperature (174–184 °C) applied during the post-frying centrifuge stage on the physico-chemical characteristics of atmospheric fried plantain chips were studied. Results showed that the surface temperature dropped very fast during the cooling process while the total oil content gradually increased. The oil uptake in the plantain chips increased by 7.7% after 9 min of post-frying cooling. Though an alteration in moisture and oil content was significantly affected (p<0.05) by either vacuum pressure or temperature control applied during the post-frying centrifuge step, a higher reduction (p<0.05) of moisture content by 79.1% and total oil content by 44.9% was observed when the combination of vacuum pressure (21.3 kPa) and temperature control was employed, comparing to the control of atmospheric pressure (101.3 kPa). Plantain chips centrifuged under vacuum pressure at 21.3 kPa without temperature control had higher total extractable phenolic acids and lower acrylamide content when compared to control sample. A reduction of pressure alone produced lighter color, higher crispness, and less volume shrinkage of plantain chips; however, no significant difference (p>0.05) was observed among the samples centrifuged at different pressures. The application of vacuum pressure at 21.3 kPa together with temperature control for 5 min during the post-frying centrifuge stage was significantly effective (p<0.05) in reducing moisture and oil content, while samples were less crispiness, shrunk more, and a higher bulk density.
... Pore properties. The pore properties of fried apple slices were analyzed using mercury intrusion porosimetry (Poremaster GT-60, Quantachrome Instruments, USA) [22]. Fried samples were sliced into small tube that were less than 10 mm in length and width following the removal of oil and water, and subjected to poremaster with pressures ranging from 0.006 to 69.431 MPa. ...
... The total oil content (TOC) in fried apple slices was determined using the Soxhlet extraction method with petroleum ether (30-60 • ) as solvent [23]. The oil fractions, including surface oil (SUOC) and structural oil (STOC) were analyzed using staining method with Sudan I fluoresce according to the report of Zhang et al. [22]. ...
The effects of integrated ultrasonic infrared frying (USIF) on the oil absorption of apple slices and the oil deterioration were studied with frequency of 28 and 40 kHz, respectively. Results showed that the heat transfer and moisture migration was accelerated by the integrated ultrasound in IF. The soluble Gal-A content and esterification degree of pectin was increased, the damages of pectin crystal structure and chemical structure in side chain was aggravated. These damages to pectin were intensified with higher frequency (40 kHz) of ultrasound. Lower retention of phenols was found in USIF apple slices, but the flavonoids content had no significant change compared to CF samples. USIF samples showed a smoother morphology, and the pore volume and porosity were reduced by ultrasonication applied with 28 kHz but increased with 40 kHz. The largest volume fraction of pores was changed from 100-250 μm in IF to 0.02–10 μm and 10–100 μm by the integrated ultrasound at 28 kHz and 40 kHz samples, respectively. The total oil uptake in USIF samples was reduced by 24.9 %–33.2 % compared to the conventional fried (CF) samples, and achieved the lowest with the frequency of 40 kHz. The surficial and structural oil were also decreased by 39.2 %-51.3 % and 20.9 %–32.3 %, respectively. The peroxide value, acid value, carbonyl value, polar component, and the saturated fatty acids ratio of oil in repeated frying for 16 h was reduced in USIF, especially with ultrasonication 40 kHz. These results indicate that USIF is a promising method for producing novel low-oil apple fries.
... With increasing frying time, the water content of all samples showed a trend of decreasing dramatically and gradually flattening, and they reached equilibrium water contents (Me) in 9, 10, 10, and 11 min, respectively. Zhang, Zhang, Fan, Li, and Fan [29] reported that the water content of fried chips decreased from 82% to 2% after frying for 6 min, and there was no significant difference between other samples. The changes in water content with frying time indicated that water loss of fries during frying was divided into three stages: (1) at the beginning of frying process, the heat in the frying oil was transferred to the surface of the food in the form of convection, and at this time, there was no water evaporation. ...
... With increasing frying time, the water content of all samples showed a trend of decreasing dramatically and gradually flattening, and they reached equilibrium water contents (M e ) in 9, 10, 10, and 11 min, respectively. Zhang, Zhang, Fan, Li, and Fan [29] reported that the water content of fried chips decreased from 82% to 2% after frying for 6 min, and there was no significant difference between other samples. The changes in water content with frying time indicated that water loss of fries during frying was divided into three stages: (1) at the beginning of frying process, the heat in the frying oil was transferred to the surface of the food in the form of convection, and at this time, there was no water evaporation. ...
The effect of frying temperature on heat transfer, water loss kinetic, oil uptake kinetic, and quality of French fries was evaluated. With increasing frying temperature, the core temperature of fries increased, and the Biot number and heat transfer coefficient (h) first decreased and then increased significantly (p < 0.05). The water loss rate (kw) and water effective diffusion of fries increased with the increasing frying temperature. The kw of fries fried at 150–190 °C were 0.2391, 0.2414, 0.3205, 0.3998, and 0.3931, respectively. The oil uptake rate (ko) first increased and then decreased with increasing frying temperature, and the ko of samples fried at 150–190 °C were 0.2691, 0.2564, 0.4764, 0.3387, and 0.2522, respectively. There were significant differences in the a*, L*, ΔE, and BI between fries with different temperatures (p < 0.05), while there was no significant difference in the b* (p > 0.05). The hardness and crispness of fries increased with increased frying temperature. The highest overall acceptability scores of fries were fried at 170 °C. Therefore, the changes in color, texture overall acceptability, and oil content were due to the Maillard reaction and the formation of porous structure, which was induced by h and water evaporation of fries when they changed.
... Besides, the surface cellular structure of IF samples partially maintained intact and well-organized morphology. The continuous heat transfer and water migration in the tissue made the vaporization front move from the surface to the core at a relatively low speed, and led to the destruction of the cellular structure and formation of the porous structures (Zhang, Zhang, Fan, Li, & Fan, 2018). The modifications on the morphology would attribute to the enhanced moisture evaporation and heat transfer during the infrared frying. ...
... Since the evaporation rate of the surface water was much higher than that of the water migrating from the interior to the surface, a more compact layer (crust) was formed close to the surface of the fried samples (Yao, Fan, & Duan, 2020). The denser and smoother surface cellular morphology produced by the infrared frying also accounted for the reduced oil uptake in fried apple slices (Zhang, Zhang, Fan, Li, & Fan, 2018). ...
The influence of infrared frying (IF) on the physicochemical properties of fried apple slices and the oil deterioration was investigated, considering conventional frying (CF) as a reference. IF had a more favorable impact on the heating rate and thermal efficiency, which subsequently resulted an accelerated moisture removal rate. The oil uptake in infrared-fried apple slices were reduced by 12.9%-17.3%, when compared to the CF, as attributed to the denser and smoother morphological microstructure. The color of apple slices was better preserved in IF and the total phenolic and flavonoid contents had a higher retention rate with the optimal infrared power (2000 W in this study). Additionally, infrared frying was proved to be a promising technology to slow down the oil deterioration rate as was observed from lower values of acid value, and carbonyl value, which was also supported by the results of gas chromatography, FT-IR, and LF-NMR analysis.
... Besides, industrial frozen meat in the thawing process causes flavor loss, resulting in fried-coated food products lacking meat flavor [3]. Simultaneously, the reduced crispiness and quick loss of texture are the non-negligible challenges in deep-fried coated food products, which are attributed to the starch type in the coating, the frying process, and freezing procedures [4,5]. Researchers have explored various innovative strategies to address these challenges, such as enhancing crispiness, reducing oil absorption by cross-linked and pregelatinized modified starches [6,7], and improving meat flavor stability by introducing ethyl maltol. ...
The study delved into the interaction between corn starch and ethyl maltol during innovative repeated-continuous heat-moisture treatment (RCHMT), and its impact on the quality of fried chicken nuggets. The results revealed that the complexation ratio of ethyl maltol in the corn starch-ethyl maltol complex remained stable, and the complex created dense microporous structures. Native starch and complex samples exhibited an A-type crystal structure, while the physical mixture sample showed a Ca-type. Additionally, the peak of C-O-H def., CH2 of the complex sample was red-shifted, and the hydrogen bond structure was enhanced. Moreover, the complex exhibited a higher resistant starch content and lower hydrolysis rate than the physical mixture sample. The starch-ethyl maltol formed by RCHMT is a non-inclusion complex. It has been shown to reduce oil absorption and enhance the crispness of fried chicken nuggets, matching that of commercial products. This finding provides a direction for the development of innovative coating powders.
... 11 The morphology of fried banana slices was photographed using a scanning electron microscope (JSM-5610LV, JEOL Corporation, Mitaka, Japan). 18 The fried banana slices were completely de-oiled by Soxhlet extraction and dehydrated with liquid nitrogen. After they were sputter coated with a thin layer of gold-palladium, the samples were observed and visualized using SEM with an acceleration voltage of 10 kV. ...
Background
The crust characteristics of fried crisps determine their oil absorption. Starch structures, as the main components of fried starchy fruits and vegetables, influence their crust formation and properties. This study investigated the reduction of oil uptake and acrylamide content in infrared‐fried (IF) banana slices by modifying starch structures at varying infrared power levels.
Results
Infrared heating improved heat transfer and surface moisture removal in fried banana slices. It facilitated crust formation in the IF samples and produced increased crust uniformity, crust ratio, and hardness. Analysis of the porous properties showed that the volume fraction of pores sized 100–250 μm was reduced in IF samples but the proportion of pores with a diameter ranging from 0.02 to 10 μm was increased. Infrared frying reduced the total oil uptake, surface oil, and structural oil content in banana slices, and each of these measures decreased as infrared power levels increased. Characterization of the starch structures suggested that the damage to the crystalline structure was increased in IF samples and more starch‐lipid complexes were generated, which would be responsible for the formation of a denser and thicker crust. The acrylamide content in the IF sample was reduced, as determined by liquid chromatography–tandem mass spectrometry (LC–MS/MS).
Conclusion
Modifications to starch structures (crystalline structures and chemical structures) play a crucial role in oil absorption in fried starchy fruits and vegetables. Infrared frying can be used as an alternative method to produce low‐fat fruits and vegetable crisps with reduced acrylamide content. © 2024 Society of Chemical Industry.
... Moreover, industrial frozen meat in the thawing process causes flavor loss, resulting in fried-coated food products lacking a meaty flavor [3]. Simultaneously, the reduced crispiness and quick loss of texture are the non-negligible challenges of deep-fried coated food products, which are attributed to the starch type in the coating, the frying process, and freezing procedures [4,5]. Researchers have explored various innovative strategies to address these challenges, such as enhancing crispiness, reducing oil absorption by cross-linked and pregelatinized modified starches [6,7], and improving meat flavor stability by introducing ethyl maltol. ...
This study delved into the interaction between corn starch and ethyl maltol during innovative repeated continuous heat-moisture treatment (RCHMT) and its impact on the quality of fried chicken nuggets. The results reveal that the complexation ratio of ethyl maltol is about 31.6%, and the complex creates dense microporous structures. Native starch and complex samples exhibited an A-type crystal structure, while the physical mixture sample showed superposition peaks of starch and ethyl maltol. Additionally, the peak of C-O-H def., CH2 of the complex sample was blue-shifted to the larger wave number, and the hydrogen bond structure was enhanced. Moreover, the complex exhibited a higher resistant starch content and lower hydrolysis rate and amylose content than the physical mixture sample. The starch–ethyl maltol complex has been demonstrated to be a non-inclusion compound. It has been shown to reduce oil absorption and enhance the crispness of fried chicken nuggets, matching that of commercial products. This finding provides a direction for the development of innovative coating powders.
... Numerous factors influence oil absorption during frying (Figure 2), including oil composition and viscosity , frying temperature/duration (Millin et al., 2016), food chemical composition, pre-frying processing (Zhang et al., 2018), food microstructure (Alam & Takhar, 2016), and oil removal after deep-frying (Devi et al., 2021). ...
During frying, oils can deteriorate due to autoxidation and hydrolytic alterations, processes influenced by the oil's fatty acid composition (FAC) and antioxidant content. However, there are different techniques to improve fried food quality and reduce oil absorption. This review aims to assess existing literature on the interactions between frying methods, oil selection, and the chemical composition of foods. To achieve this goal, the article examines the impact of oil FAC, antioxidants, pretreatments, and alternative frying technologies. A literature search was conducted from 2016 to 2023. The keywords used were (AND/OR) frying, fried foods, oil, oil absorption, and fatty acids. Oils rich in monounsaturated fatty acids and antioxidants, such as olive oil, are recommended for their nutritional benefits and improved oil stability. The water content and structure of the food also play a significant role in oil absorption. Pretreatments to diminish food moisture content contribute to a lower oil absorption in the fried food while mitigating excessive accumulation of lipid oxidation products. Proper selection of frying oils, incorporation of antioxidants, and the use of pretreatments could help prevent chemical changes and minimize oil absorption during frying. These measures contribute to maintaining the nutritional quality and safety of fried foods while also enhancing their overall sensory appeal.
... Reduction in oil content about 21.5%, 30.6%, and 34.9% with the addition of 1%, 3%, and 5% pullulan (polysaccharide), indicated that the addition of pullulan successfully exerted the reduction in fat absorption in a dose-dependent manner. Zhang et al. (2018) reported the reason may be because of the higher moisture content of the potato chips and vigorous vaporization hindered the oil absorption of the interior in the initial stage of frying. With the frying process continuing, the pore or voids volume increased due to the evaporation of water. ...
Bananas blossom or known as bananas flowers are one of the Musa genus and can be discovered in many parts of the world, especially in Southeast Asia. It has a wide variety of benefits such as promoting heart health, anti-microbial, improves digestion and also slow aging process. However, some people especially kids and teenagers do not like it as the flower is starchy and slightly bitter, with more vegetal flavors, entirely different than the mature banana fruit. Thus, this study was conducted to evaluate physicochemical properties and consumer preference of Banana blossom nugget, BBN formulated with different percentage of banana blossom and potato flour. Three formulations of BBN were prepared with the percentage of banana blossom to potato flour of BBN were: A (65:25), B (60:30) and C (50:40). Data obtained was analyzed using SPSS software version 17.0. Results found that BBN with formulation C was significantly higher (p<0.05) in hardness compared to A and B, A was significantly lower in chewiness compared to B and C. However, there was no significant differences found in cohesiveness. Meanwhile, all BBN were found significantly different in oil absorption. All BBN were also significantly different (P<0.05) in total protein and fat content. No significant difference (p>0.05) observed in the sensory scores of BBN for colour and texture. However, there was significantly higher (p<0.05) for aroma and lower for flavor of formulation A compared to another BBN. However, hedonic test found that consumers preferred (p<0.05) formulation A and B compared to C. The BBN which contained percentage of banana blossom to potato flour (65:25) was the most preferred by consumer in term of colour, aroma and flavor compared to all BBN. This finding showed that formulation of BBN with banana blossom and potato flour could be accepted by consumers but further research should be focused on the optimized amount of banana blossom in the BBN. Thus, the physicochemical and sensory analysis should be improved by compared to a commercial brand of chicken or beef nugget.
... 4 However, lowering the oil content in potato chips has been challenging due to the complex physical process of oil transportation during the frying process. The oil content in each piece of potato chip could also be affected by the potato chip size, thickness, frying time, oil temperature, chip pore characteristic, bulk density, and porosity, 5 resulting in high variability piece to piece. Therefore, the snack food industry has been looking for a nondestructive and real-time approach to monitor the oil content in potato chips to ensure consistency of product quality. ...
... These get absorbed by the food and are associated with cardiovascular diseases, cancers, obesity, diarrhea, type 2 diabetes and gastrointestinal discomfort in humans (Hamsi et al., 2015;Karaman et al., 2014;Ma et al., 2021;Wu et al., 2019). Additionally, the volatile compounds such as polycyclic aromatic hydrocarbons and heterocyclic amines generated during frying, when inhaled over time expose food processors to respiratory tract cancer (Zhang et al., 2018). Overly recycled cooking oils are less nutritious to consumers since essential nutrients such as vitamin A and E are degraded over time. ...
... In some brands of potato chips found on the market in Romania, the saturated (SFA), cis-monounsaturated (MUFA) and polyunsaturated (PUFA) fatty acid contents have a large range of variation, namely between 6.4 and 48.8% for SFA, 41.7 and 84.5% for MUFA, and 5.5 and 28.2% for PUFA. Since potatoes possess low amounts of fat, the fat incorporation occurs during the frying process and is strongly influenced by the duration of frying [28,29]. ...
Food composition issues represent an increasing concern nowadays, in the context of diverse food commodity varieties. The contents and types of fatty acids are a constant preoccupation among consumers because of their reflections of nutrition and health problems. This study aims to find the best tool for the rapid and reliable identification of similarities and differences among several food items from a fatty acid profile perspective. An acknowledged GC-FID method was considered, while, for a better interpretation of the analytical results, machine learning algorithms were used. It was possible to develop a recognition model able to simultaneously differentiate, with an accuracy of 79.3%, nine product types using the bagged tree ensemble model. The low number of samples or some similarities among the classes could be responsible for the wrong assignments that occurred, especially in the biscuit, wafer and instant soup classes. Better accuracies values of 95, 86.1, and 97.8% were obtained when the products were grouped into three categories: (1) sunflower oil, mayonnaise, margarine, and cream cheese; (2) biscuits, cookies, margarine, and wafers; and (3) sunflower oil, chips, and instant soup.
... The rapid evaporation of moisture in MF samples led to a less cohesive crust and a denser interior with smaller pore diameters. These changes resulted in a decrease in oil absorbency after microwave frying, as reported by Parikh and Takhar [33] and Zhang [34]. In the case of MF, the dielectric properties of the food, particularly water content, greatly influence the heating process. ...
ABSTRACT
Background: This study aimed to compare the effects of three different frying methods, namely air frying (AF),
microwave frying (MF), and deep frying (DF) in corn oil, on the moisture and texture, as well as the content and
absorption of oil, carbohydrates and acrylamide in French fries.
Materials and Methods: For the DF, the fresh potatoes were fully dipped in corn oil and the oil temperature was set at
160 °C for three intervals of 3, 5, and 7 minutes. In the MF, the oil was preheated to 180 °C for three time intervals of
160, 180, and 200 seconds. The AF was set at a temperature of 170 °C for three time intervals of 8, 10, and 12 minutes,
without adding oil.
Results: The results showed that AF resulted in a lower acrylamide content (21.8 ppm) after 8 minutes at 170°C compared
to the other frying methods. However, DF in corn oil was preferred in terms of color, flavor, and overall acceptance in
the sensory evaluation of the French fries. MF resulted in the hardest French fry texture due to excessive evaporation of
moisture.
Conclusion: The findings suggest that AF may be a healthier option with a lower acrylamide content, while DF in corn oil
may be preferred for its superior sensory characteristics.
... It constitutes an essential ingredient in lebanese dishes such as fries and tradition cuisine [6]. Recently, potato has a very important role in the food industry ; processing companies producing crisps, frozen french fries, chips, dehydrated products, canned foods and ready-made meals have been developed contributing to potato marketing and the improvement of national economy [7]. However, due to the competition with potato imported from neighbor countries to meet the needs of the lebanese population, potato cultivation in Lebanon must ensure that tubers are of good technological quality. ...
The effect of potassium fertilization and time of application on yield and tuber quality of potato (Solanum tuberosum L., cv. Agria) was studied in Bekaa region in Lebanon. Potassium was applied in one split at tuber initiation (T1) and at tuber bulking (T2) in four different rates: K0 (0 kg/ha), K1 (100 kg/ha), K2 (200 kg/ha) and K3 (300 kg/ha). Results showed that aerial dry matter decreased and tuber dry matter increased during the growing period. The dry matter accumulation was dependent on potassium fertilization. Potassium concentration gradually decreased in leaves and increased in tubers during the growing period, while the most potassium treatment (K3) has accumulated at harvest, higher potassium concentrations in leaves and tubers, with more emphasis to application time T2 with respect to T1. Moreover, potassium has accelerated significantly (p<0.05) tuber dry matter accumulation. This was revealed by growth rate and harvest index values that were significantly higher (p<0.05) in K3 treatment with comparison to other treatments. Results also showed that fresh tuber yields increased with potassium fertilization and were more pronounced with T2 application whereas K3 had significantly (p<0.05) the highest value of 62.9 t/ha (K3). Yield augmentation was primarily due to an increase in tuber size in the larger (> 60 mm) and the medium (35 – 60 mm) grades. In addition, results showed that tuber dry matter content and specific gravity were statistically dependent on potassium fertilization and application time (p<0.05). The highest potassium treatment K3, regardless of application time, gave the best tuber quality of industrial potato by having the highest dry matter and the lowest reducing sugar contents. Finally, the results of this study suggest that maximum potato yield was obtained with K3 treatment (300 kg/ha) applied during tuber bulking stage (T2).
... It constitutes an essential ingredient in lebanese dishes such as fries and tradition cuisine [6]. Recently, potato has a very important role in the food industry ; processing companies producing crisps, frozen french fries, chips, dehydrated products, canned foods and ready-made meals have been developed contributing to potato marketing and the improvement of national economy [7]. However, due to the competition with potato imported from neighbor countries to meet the needs of the lebanese population, potato cultivation in Lebanon must ensure that tubers are of good technological quality. ...
The effect of potassium fertilization and time of application on yield and tuber quality of potato (Solanum tuberosum L., cv. Agria) was studied in Bekaa region in Lebanon. Potassium was applied in one split at tuber initiation (T1) and at tuber bulking (T2) in four different rates: K0 (0 kg/ha), K1 (100 kg/ha), K2 (200 kg/ha) and K3 (300 kg/ha). Results showed that aerial dry matter decreased and tuber dry matter increased during the growing period. The dry matter accumulation was dependent on potassium fertilization. Potassium concentration gradually decreased in leaves and increased in tubers during the growing period, while the most potassium treatment (K3) has accumulated at harvest, higher potassium concentrations in leaves and tubers, with more emphasis to application time T2 with respect to T1. Moreover, potassium has accelerated significantly (p<0.05) tuber dry matter accumulation. This was revealed by growth rate and harvest index values that were significantly higher (p<0.05) in K3 treatment with comparison to other treatments. Results also showed that fresh tuber yields increased with potassium fertilization and were more pronounced with T2 application whereas K3 had significantly (p<0.05) the highest value of 62.9 t/ha (K3). Yield augmentation was primarily due to an increase in tuber size in the larger (> 60 mm) and the medium (35 – 60 mm) grades. In addition, results showed that tuber dry matter content and specific gravity were statistically dependent on potassium fertilization and application time (p<0.05). The highest potassium treatment K3, regardless of application time, gave the best tuber quality of industrial potato by having the highest dry matter and the lowest reducing sugar contents. Finally, the results of this study suggest that maximum potato yield was obtained with K3 treatment (300 kg/ ha) applied during tuber bulking stage (T2).
... Nevertheless, oil uptake is a complicated process and is impacted by various factors other than moisture loss. Previous research has reported that surface roughness and porous structures could also influence the oil uptake of fried materials (Su et al., 2020;Zhang et al., 2018). It is likely because PFB had a rougher surface and structure, entrapping more surrounding oil during frying. ...
... Ghaderi et al. [31] reported ca. 35 % reduction in total fat content by increasing the frying temperature from 150 to 190 • C. According to previous studies, the extension of frying time results in higher fat content [115,123]. In this regard, the optimal frying time to minimize fat content in potato chips was found to be 3.5 min, while optimal frying temperature was either 160 or 180 • C depending on frying oil type [16]. ...
Potato chips production is a traditional food process. To achieve uniform product quality, raw materials are usually rigorously sorted. Traditionally, the process is conducted in a single stage approach leading to high quality losses. Recently, dynamically optimized frying processes have been found to result in higher product quality. Consequently, industrial continuous deep-fat fryers convey potato disks through several zones pre-set at different temperatures.
However, these improved systems still do not take the variabilities in frying kinetics among potatoes into consideration. To address this issue and decrease uncertainties in end-product quality, frying conditions of each zone must be optimized, physiochemical properties of the various raw tubers and their frying kinetics taking into account.
This paper, therefore, presents a novel approach for an intelligent frying process with embedded computer vision systems providing continuous monitoring of product quality and, therefore, facilitate dynamic control of frying conditions in order to meet desired quality attributes in the final product. An extensive literature review of the key physiochemical attributes of raw potato tubers is presented, followed by an introduction to novel pre-treatment technologies, and the importance of optimal frying conditions. An overview of the potentials for using computer vision systems for the assessment of said quality criteria is given, followed by a detailed description of the envisioned frying process. The paper concludes that the realization of intelligent frying processes necessitates the development of fully fledged digital twins of the process and the products, combining physics based and data driven modelling with real time sensing and control.
Terminology: Chips refer to thin slices of potato while French fries refers to wedges/stripes
... It was shown that the oil content absorbed during frying was significantly lower than the one absorbed during cooling (p < 0.05). This was consistent with the results of Garmakhani et al. [30] and Zhang et al. [31]. ...
The purpose of this study was to investigate the effects of konjac glucomannan (KGM) on oil absorption and the formation of safety hazard factors in fried battered fish nuggets by measuring advanced glycation end products (AGEs) and acrylamide contents. Other physicochemical properties were determined to explore the reason for oil absorption and formation of safety hazard factors. The acrylamide was found mainly in the crust. The addition of 0.8% KGM could significantly reduce the acrylamide content (p < 0.05). For the battered sample, the AGEs content was far lower than the unbattered. The addition of 0.8% KGM could significantly reduce the AGEs content in the inner layer (p < 0.05). The microstructure showed that the sample with 0.8% KGM had the most compact crust. The compact crust reduced oil and malondialdehyde contents. Combined with the other indicators, the inhibitory effect of 0.8% KGM on acrylamide was closely related with the decreased extent of oil oxidation and Maillard reaction in the samples with 0.8% KGM. The inhibitory effect of 0.8% KGM on AGEs might originate from its lower oil content.
... This is mainly related to the increase in total oil in chips with increasing frying time. 37 Hence the changes of pesticide concentrations in oil during processing of chips are collectively determined by three factors: pesticide degradation, transfer to chips and concentration. To our best knowledge, this is the first report of transfer of pesticide from contaminated oil to fried food, and the repeated use of edible oils containing pesticides could lead to increasing dietary risks. ...
BACKGROUND
Pesticide contamination in oil crops and processed products is an important food safety concern. The study was aimed to investigate the pesticide residue changes in press processing of peanut oil and frying of chips.
RESULTS
Five pesticides – chlorpyrifos, deltamethrin, methoxyfenozide, azoxystrobin and propargite – which are often applied during growth period in peanut plants, were selected to investigate their residue changes in cold press processing of peanut oil and frying of potato chips. Results showed that the residues of the five pesticides were decreased by 3.1–42.6% during air‐drying before oil pressing. The residues of chlorpyrifos, deltamethrin, methoxyfenozide and propargite in peanut oil were 2.05–3.63 times higher than that in peanut meal after cold pressing of the oil, except for azoxystrobin having a slightly lower residue in peanut oil, with 0.92 times that in peanut meal. The processing factors of the five pesticides in peanut oil ranged from 1.17 to 2.73 and were highly related to the log Kow of the pesticides. The higher the log Kow, the more easily was the pesticide partitioned in the peanut oil. Besides, as frying time increase during preparation of chips, the concentration of pesticides in peanut oil decreased gradually by 6.7–22.1% compared to the first frying. In addition, 0.47–11.06% of the pesticides were transferred to the chips through frying with contaminated oil.
CONCLUSION
This is first report showing that pesticides can transfer from contaminated oil to chips. There exists a potential dietary health risk by using pesticide‐contaminated oil for frying chips. This work could provide basic data for accurate dietary risk assessment of pesticide residues in peanut oil and its frying products. © 2021 Society of Chemical Industry.
... The oil uptake values of ethanol and US + ethanol pre-treated samples were 39.7 and 43.5 (g/100 g db), respectively at the end of the frying (12 min), while that of ultrasonic pre-treated and untreated samples were 58.5 and 60.5 (g/100 g db), respectively. The oil absorption of fried products was mainly affected by the porous structures and the surface roughness of the crust (Su et al., 2020;Zhang et al., 2018). The oil penetrates into the intercellular spaces, cellular structures, or adhere to the surfaces of the fried products, the final oil uptake depends on the equilibrium between draining and suction of oil through the porous structure . ...
Presently, the effectiveness of combined ultrasonic and ethanol (US + ethanol) pre-treatment was evaluated with an aim to reduce the oil uptake and enhance the frying efficiency of deep-fried apple slices. The US + ethanol pre-treatment was conducted by immersing apple slices in 95% ethanol and ultrasonic treatment (40 kHz, 300 W) for 30 min. Results revealed that the permeability of cells was greatly increased and the mass transfer during the pre-treatment was significantly enhanced by the US + ethanol pre-treatment. Subsequently, the heat transfer and moisture loss kinetics of fried apple slices were significantly improved by the US + ethanol pre-treatment. The oil uptake was achieved the lowest value and reduced by 34.5% and 28.2% in the fried samples pre-treated by 95% ethanol and US + ethanol, respectively, compared with the untreated samples (60.5 g/100 g db). The appearance, total phenolic and flavonoid contents in fried apple slices were also improved by the US + ethanol pre-treatment. The morphology observation revealed that the US + ethanol pre-treatment induced a denser and smoother surface and more micron-sized pores on the crust of fried apple slices. Conclusively, the US + ethanol pre-treatment would be a promising method for the reduction of oil uptake in fried fruits and vegetables with an enhanced frying efficiency.
... The structural oil is the fraction that the food itself contains before frying. The absorbed oil is further divided into the residual surface oil and the penetrated oil according to the frying stage (Zhang, et al., 2016;Zhang et al., 2018). The residual surface oil is the part that is extracted by soaking in petroleum ether for 5-20 s. ...
Fried food is popular because of its attractive aroma, colour and taste. However, its high oil content may cause cardiovascular diseases, such as high cholesterol and high blood pressure. Therefore, it is of great significance to reduce the oil uptake of fried food. It is found that water‐oil replacement, surfactant theory and the cooling‐phase effect are the main mechanisms of oil uptake in fried food. According to these mechanisms, improving the frying technology, changing the frying medium and coating treatment can reduce the amount of oil in fried foods. Among these methods, coating treatment is the most common method to reduce the oil content. Protein coatings usually have better performance than polysaccharide coatings. The performance of protein coatings depends on the type of food and protein. In addition, oil resistance of protein coatings can be improved by adding the plasticiser, combination with other components and cross‐linking treatment.
... The results indicated that UPT reduced the PSO content of potato chips. The change of PSO content in potato chips was related to the cooling-phase effect mechanism of oil absorption (Zhang, Zhang, Fan, Li, & Fan, 2018). When samples contained a lot of STO fraction, most pores and cracks were occupied by STO, therefore the oil could not penetrate the microstructure of samples during the cooling stage. ...
The present work applied the ultrasound pretreatment (UPT) to reduce oil absorption and improve quality features (texture) of potato chips. The oil content, oil fractions, cell viability, cell morphology, oil distribution, color changes, and texture of potato chips were discussed. UPT (360 W, 60 min) significantly decreased penetrated surface oil content of potato chips, causing the 27.66% decrease in total oil content. The changes in cell viability induced by ultrasound resulted in variations of oil distribution at a macro level. Higher ultrasound power destroyed more cells on the edge, which further resulting in more oil absorption on the edge of potato chips. Disrupting cell structure changed oil distribution at a micro level. When the ultrasound power was increased to 600 W, the oil showed more uneven distribution because of the destroyed cellular structure. Texture testing pointed out that UPT decreased the hardness of potato chips.
... The oil absorption of D and UD pretreated potato chips was observed by using MRI to monitor the oil macroscopically distribution at various zones. The signal intensity of MIR is strongly affected by oil content in different regions of samples, and the MIR images can visually provide oil distribution of the whole samples [40]. As shown in Fig. 5, the color bar on the right represented a relative scale for the oil content of samples. ...
The initial water content was closely related to the oil absorption and properties of fried food. The effects of convective air drying (D) and ultrasound combined convective air drying (UD) pretreatment on the properties and oil absorption of potato chips have been investigated. The oil contents were 48.48 ± 1.42% and 39.78 ± 3.08% for control samples (without D and UD pretreatment) and ultrasound treated samples (without D pretreatment). When the mass loss of samples was reached the proportion of quality to without drying samples quality 80%, 50%, and 20%, the oil contents of D pretreated samples decreased by 12.67%, 28.24% and 62.07%, respectively, and the oil contents of UD pretreated samples decreased by 7.42%, 24.10% and 51.76%, respectively. By applying ultrasound before frying, more cracks and pores were exhibited of fried potato chips. After drying process, potato chips exhibited less disruption of cell structure and deformation of cell irregular. The hardness of the D and UD pretreated potato chips increased with the extension of drying. The FTIR analysis stated the formation of amylose-lipid complexes. This research could contribute to providing evidence for the development and application of the pretreatment strategy.
The effect of vacuum pressure mode has not been studied depth yet. Effect of vacuum pressure on the quality of vacuum‐fried banana slices was studies in this work. Three vacuum frying processes were conducted and tested. Classically, two constant vacuum pressures 80 (CVF‐80) and 180 mmHg (CVF‐180) were applied in the frying process at 90°C. One novel frying method with gradient vacuum pressure (GVF) changed from 760 to 80 mmHg was conducted and adapted. The frying temperature was kept at 90°C. The frying processes were monitoring by moisture contents and 4% was generally accepted as moisture content of final product. Meanwhile, the frying times of CVF‐80, CVF‐180 and GVF were 50, 80 and 60 min, whereas the brightness values (L*) were corresponded to 71.07, 71.36, 67.25, respectively. The GVF samples were brightest with lowest hardness value (30.8 N) and the CVF‐180 was darkest with highest hardness value (36.87 N). The microstructure analysis showed that the GVF increase in both size and number of pores in comparison with CVF. Additionally, based on the paired comparison sensorial test the GVF fried banana slices were crisper than CVF samples. Our results revealed that the GVF method improves the quality of vacuum‐fried banana slices, thus it can be good alternative method for production of banana snack.
Deep-fat frying is a popular cooking method known for its quickness, simplicity, and ability to impart desirable culinary characteristics to a variety of foods. The process involves complex heat and mass transfer mechanisms, which cause physical and chemical changes in both the food and the frying oil. Excessive consumption of fried foods, on the other hand, has negative health consequences due to increased oil absorption and the formation of harmful compounds.
Microwave frying combines microwave heating with conventional frying to increase heat and mass transfer efficiency. Shorter frying times, lower oil content, enhanced product texture and color, and lower acrylamide concentrations are all advantages of microwave frying. This chapter gives insight into microwave frying as an alternative cooking method.
Flour-based fried foods are among the most commonly consumed foods worldwide. However, the sensory attributes and nutritional value of fried foods are inconsistent and unstable. Therefore, the creation of fried foods with desirable sensory attributes and good nutritional value remains a major challenge for the development of the fried food industry. The quality of flour-based fried foods can sometimes be improved by physical methods and the addition of chemical modifiers. However, enzyme modification is widely accepted by consumers due to its unique advantages of specificity, mild processing conditions and high safety. Therefore, it is important to elucidate the effects of enzyme treatments on the sensory attributes (color, flavor and texture), oil absorption and digestibility of flour-based fried foods. This paper reviews recent research progress in utilizing enzyme modification to improve the quality of flour-based fried foods. This paper begins with the effects of common enzymes on the physicochemical properties (rheological property, retrogradation property and specific volume) of dough. Based on the analysis of the mechanism of formation of sensory attributes and nutritional properties, it focuses on the application of amylase, protease, transglutaminase, and lipase in the regulation of sensory attributes and nutritional properties of flour-based fried foods.
Purpose
This review aims to examine the potential of oleogels as a frying medium to decrease oil absorption during deep-frying and enhance the nutritional and energy content of foods. By investigating the factors influencing oil incorporation during deep-frying and examining the application of oleogels in this process, we seek to provide insights into using oleogels as an alternative to traditional cooking oils.
Scope
Deep-frying, a widely used cooking method, leads to the retention of large amounts of oil in fried food, which has been associated with health concerns. To address this issue, researchers have investigated various methods to minimize oil absorption during frying. One promising approach is the use of oleogels, which are thermo-reversible, three-dimensional gel networks formed by entrapment of bulk oil with a low concentration (<10% of weight) of solid lipid materials known as oleogelators. This review will focus on the following aspects: a) an overview of deep-fried foods, b) factors influencing oil uptake and underlying mechanisms for oil absorption during deep-frying, c) the characterization and application of different frying oils and their oleogels in deep-fried foods, d) components of the oleogel system for deep-frying, and e) the health impact, oxidative stability, and sensory acceptability of using oleogels in deep-frying.
Key findings
The review highlights the potential of oleogels as a promising alternative frying medium to reduce fat absorption in deep-fried foods. Considering the factors influencing oil uptake during deep-frying, as well as exploring the properties and applications of different frying oils and their oleogels, can result in improved product qualities and heightened consumer acceptance. Moreover, oleogels offer the advantage of lower fat content in fried products, addressing health concerns associated with traditional deep-frying methods. The capacity to enhance the nutritional and energy profile of foods while preserving sensory qualities and oxidative stability positions oleogels as a promising choice for upcoming food processing applications.
Fried foods occupy a large portion of the fast-food market. However, growing consumer health awareness is driving research to minimize the oil content of products. The use of specific barriers such as hydrocolloid coatings can avoid high oil absorption. Herein, the physicochemical characteristics of banana fruit cultivars and the effects of hydrocolloid coatings on the quality attributes of banana chips were evaluated. The unripe fruits were analyzed for length, diameter, mass, pulp/peel ratio, firmness, and color. The pulps were analyzed for moisture, total and reducing sugars, crude fat, total soluble solids, pH, titratable acidity, and maturation index. Pulp slices were coated before frying with four hydrocolloid solutions: guar gum, carboxymethylcellulose, sodium alginate, and maltodextrin. The fruits of the cultivar BRS Platina were larger, with a more yellowish pulp and those of FHIA 18 had smaller lengths and diameters. After frying, higher moisture losses were observed in the control and in the treatment with maltodextrin. Hydrocolloids promoted reductions in oil absorption from 26.54 to 9.14%, in addition to changes in the color and hardness of the chips. A coating pretreatment can be used to produce low-fat banana chips, with better results using guar gum. Our results are useful in expanding the commercialization of fruits that fall easily and the chip coating technology can be applied in snack industries.
Excessive oil uptake and formation of carcinogens, such as acrylamide (AA), heterocyclic amines (HCAs), and polycyclic aromatic hydrocarbons (PAHs), during deep‐frying are a potential threat for food quality and safety. Cellulose‐ and chitosan‐based edible coatings have been widely applied to deep‐fried foods for reduction of oil uptake because of their barrier property to limit oil ingress, and their apparent inhibition of AA formation. Cellulose‐ and chitosan‐based edible coatings have low negative impacts on sensory attributes of fried foods and are low cost, nontoxic, and nonallergenic. They also show great potential for reducing HCAs and PAHs in fried foods. The incorporation of nanoparticles improves mechanical and barrier properties of cellulose and chitosan coatings, which may also contribute to reducing carcinogens derived from deep‐frying. Considering the potential for positive health outcomes, cellulose‐ and chitosan‐based edible coatings could be a valuable method for the food industry to improve the quality and safety of deep‐fried foods.
Non‐thermal food processing technologies (NTFPT) are appealing to food scientists, processors, and consumers due to their minimal impact on the nutritional and sensory qualities of foods while extending shelf life by suppressing or destroying microbes. NTFPT are more energy efficient and maintain better quality than traditional thermal methods. The food industries are undergoing continuous transformation as part of its ongoing evolution. The evolution to meet the demands and address the major issues posed by an ever‐increasing global population and food claimants in terms of both quantity and quality. Magnetic fields (MF) are one of the NTFPT that are widely used in the food industry to protect food quality. It has numerous advantages in terms of ease of use, such as the fact that it is non‐toxic, non‐polluting, and safe. Magnetic fields have a broad array of applications in the food processing sector due to the favorable biological effects. Weak magnetic fields are more effective at activating bacteria and stimulating their proliferation in food processing than strong magnetic fields, which are commonly used as a physical non‐thermal sterilizing method. Depending on how they behave in food systems over time, magnetic fields can be classified as oscillating magnetic fields, static magnetic fields, or pulsed magnetic fields. The ability to apply various types of magnetism requires a thorough understanding of how materials react to magnetic fields. The background information on the generation of magnetic fields, the basic principle of magnetism, and the classification of magnetic fields was presented in this chapter. In addition, this chapter focuses on magnetic field research and applications in the food processing and preservation industries. It provides an overview of current experimental results for the compositional and structural analysis of various food constituents using a magnetic field. Following a discussion of compositional and structural analysis, the use of the magnetic field in various food processing methods such as freezing, drying, frying, fermentation, and quality inspection of various commodities is discussed. The effect of the magnetic field on microbes and enzymes was discussed in relation to food preservation. Magnetic fields as an alternative food processing technique have not gained widespread commercial acceptance due to conflicting results on microbial growth and death kinetics. Furthermore, there is a significant knowledge gap in the field of machine development. However, there is a significant research gap in these areas, and future progress is expected to bring solutions to unsolved issues.
This study unveiled the effect of the suspected precursors of acrylamide (asparagine, glutamine) combined/separated with different formulations of glucose, fructose, and sucrose. To better understand the interaction between acrylamide precursors, cooking technique (deep vs air frying), and temperature (170 °C vs 190 °C), seven potato models from starch, sugars, amino acids, water and hydrocolloids (alginate and agar) were formulated. In line with previous findings, the present results showed that asparagine, glucose and fructose played an important role in acrylamide formation in these synthetic potato models. Furthermore, glutamine and sodium alginate might have an inhibitory effect on acrylamide formation. A significant impact of frying technique was also revealed. On the other hand, GC-FID analysis detected acrylamide in only these three models, (glucose-fructose, sucrose and asparagine-glucose/fructose/sucrose models > LOD 333.33 µg.kg-1).
Vacuum frying has proven to be the most feasible technique to obtain safe and nutritious deep‐fried food without compromising its organoleptic and textural properties. This frying system has a lot of benefits over conventional frying such as reduced acrylamide content, lower oil content and better preservation of nutritious compounds. The most promising advantage of vacuum frying is its ability to produce foods with a low glycemic response. Optimization of vacuum frying technology is, however, a prerequisite to attain a fried product with desirable quality. Microwave‐assisted vacuum frying, ultrasound‐assisted microwave vacuum frying, and pulse‐spouted microwave vacuum frying are some of the novel frying techniques which improve the quality of fried products with enhanced nutrient retention, reduced oil uptake, and reduced starch digestibility. In addition, various pretreatments, posttreatments, packaging, and storage conditions have a profound effect on the quality of vacuum‐fried foods. This review aims to address the advantages vacuum frying offers over conventional frying, providing an overview of recent developments in this technology, and the effects of vacuum frying on the nutritional qualities of food.
Practical Applications
Frying industry all over the world is in boom as frying provides unique flavor and texture to the food products. However, the consumption of fried foods has been related to the development of various diseases due to the generation of harmful compounds at higher temperatures employed during deep‐frying. Vacuum frying has been suggested to overcome this limitation of atmospheric frying by maintaining low‐temperature conditions, thus producing safe foods. This review will focus on the developments done in vacuum fryer over the past few years and evaluate what enhancements in final fried products can be observed upon modifying the vacuum frying unit. Replacement of atmospheric fried products with vacuum‐fried products could further boost the frying sector by producing toxin‐free products without sacrificing sensorial or organoleptic properties.
Acrylamide is a potential carcinogen produced at higher temperatures while frying, roasting and baking. Starch‐rich foods like potatoes are known to produce acrylamide in increasing concentrations than other kinds of foods. This study focuses on mitigation of acrylamide in sweet potato, taro and cassava samples subjected to various heat‐treatment processes like oil frying, air frying and baking. Dipping of tuber slices in solutions of garlic, green tea, sodium chloride, yeast, distilled water, whey and blanching prior to frying the tubers were found to be effective pre‐treatment methods. However, the effect of the treatments depended on the sample and mode of processing. Yeast was found to produce a significant reduction in the acrylamide production in taro (98.64%) and garlic pretreatment reduced acrylamide in deep fat fried cassava samples up to 95.62%. Similarly, air fried taro samples dipped in distilled water was found to significantly reduce the browning reaction up to 96.51%; primarily due to the fact that distilled water was found to block the reaction between precursors like asparagine and reducing sugars, thereby preventing the formation of acrylamide. Influence of reducing sugar on the formation of acrylamide, when fried at different temperatures was analyzed using Response Surface Methodology (RSM), clearly indicating that the amount of reducing sugars decreased at higher temperatures with increase in acrylamide content. The attempts in the study clearly shows that simple and cost effective pretreatments can be successful applied to produce healthy tuber products with reduced concentration of acrylamide.
The effect of chitosan (CS) coating on oil absorption, water migration, starch structure and morphology in French fries was evaluated. The penetrated surface oil, structure oil, total oil content, and a* of coated fries decreased, while the water content, L*, b*, and hardness significantly (P < 0.05) increased compared to uncoated samples. 1 % CS-coated fries had the lowest oil content, which decreased by 43.0 % compared to uncoated samples. CS-coated fries had higher free water, and lower T2 relaxation time, immobile and binding water than the control. CS coating reduced the pores on the fries' surface and the interaction between oil and the component of fries, which was observed by confocal laser scanning microscopy and scanning electron microscopy (SEM). As for starch morphology, the pores and cracks of starch granules in the coated samples reduced. As for the starch structure, the relative crystallinity, R1047/1022 respectively increased by 47.2 % and 2.35 times, and ΔH of CS-coated fries increased from 0 to 2.09 J/g, indicating that the long-range crystalline structure, short-range ordered structure, and hydrogen bonds between the double helices in starch increased. Therefore, CS coating reduced oil penetration into fries by reducing water migration and increasing starch ordered structure and morphological integrity.
Isotope-labeled four polycyclic aromatic hydrocarbons (PAH4-d12) were applied to study the migration and distribution of PAH4 in oil to French fries during frying. The results showed that the mobilities of PAH4-d12 showed a downtrend within 0-6 h and then an uptrend, and PAH4-d12 were mainly distributed in the crust of the French fries, especially five-ring PAHs-d12. The correlation analysis showed that PAH4-d12 migration was mainly caused by oil absorption of French fries. The low fluidity of the oil slowed down the PAH4-d12 migration, which was accelerated as the total polar component increased (higher than 15-20%). Additionally, higher frying temperature enhanced the crust ratio and porous structure of French fries, which explained the abundant five-ring PAHs-d12 distributed in the crust. This study provided references for optimizing the frying parameters: the exposure of PAH4 in French fries to humans can be reduced by controlling the oil quality and weakening the crust of the French fries.
Lemon juice is used to enhance the flavor of dishes prepared with fish, which is more prone to oxidation than other flesh food. This study evaluated the impact of treating sardine fillets (Sardina pilchardus) with Tahiti lemon juice and submit them to different domestic cooking methods (air fryer, grill, and deep-fat fryer), regarding the oxidation of unsaturated fatty acids and cholesterol. The juice extract was characterized by its antioxidant capacity and bioactive constituents by UHPLC-MS. Cooking caused the degradation of polyunsaturated fatty acids (PUFAs), such as eicosapentaenoic (EPA, C20:5) and docosahexaenoic acids (DHA, C22:6), and increased the cholesterol oxides level. However, for most treatments, degradation of PUFAs and formation of cholesterol oxides were more pronounced in samples treated with juice. Lemon juice induced cholesterol oxidation, mainly in air-fried sardines where the total content of cholesterol oxides increased from 700 ± 4 (control) to 1333 ± 5 µg/g (10% lemon juice, in dry basis). Thus, the overall data suggest that potential antioxidant compounds may have degraded during heating and the acid environment may have induced oxidative reactions.
Hot air frying is one of the newest processing methods that can make healthier fried foods. The mechanism of frying using this method is not understood entirely yet. There is no model available to describe the oil absorption for air-fried foods. In this research, an agent-based model was extended to describe the oil penetration procedure and study the different effects of the cellular structure of crust on oil distribution during hot air frying. Netlogo software was used for the model simulation. The simulation results of oil penetration were in good agreement with experimental data. Obtained results show that the oil penetration procedure divided into three main steps named latent phase, acceleration phase, and deceleration phase. The acceleration phase is the most critical step in doughnut oil absorption. Simulated data also show that oil penetration starts from the thinner parts of the crust. Therefore, it seems that the structure of the crust has an important effect on oil absorption pattern.
Quick and accurate determination of oil content is extremely important to control the oil content of vacuum fried fruit and vegetable chips. This article uses fresh Pleurotus eryngii as raw materials to explore the influence of different vacuum frying times (0–14 min) on the moisture distribution, oil changes and quality of Pleurotus eryngii strips. The results show that as the frying time increases, the lateral relaxation time required for the taro strips to drop from the highest point of the signal amplitude to smooth becomes shorter and shorter, and the decay rate becomes faster and faster, that is, when the frying time is 14 minutes, The attenuation curvature and velocity are the largest. The oil content and brittleness of Pleurotus eryngii strips are significantly increased (P < 0.05); the water content is significantly reduced (P < 0.05); the hardness first decreases and then increases (P < 0.05); the brightness L* value does not change much, and the color is not Significant change (P > 0.05). At the same time, low-field NMR shows that the high-degree-of-freedom water in the pleurotus eryngii strips migrates to the low-degree-of-freedom water during the vacuum frying process. Among them, the free water in the pleurotus eryngii strips has a large degree of freedom. It has been removed, resulting in poor mobility and increased inability to flow. Part of the free water migrates to the semi-bound water, and most of the semi-bound water migrates outward as free water and then is removed. From this, all peaks are gradually removed. Moving to the left, the total peak area decreases. During the frying process, the T2 relaxation time of Pleurotus eryngii strips all shifted to the left, the total peak area is continuously reduced, the water content is getting less and less, the fat content is getting higher and higher, and the fat content distributed in the edge shell is always higher than Other locations. Low-field nuclear magnetic resonance technology can provide a fast, accurate, and non-destructive method for detecting moisture and grease for the vacuum-fried fruit and vegetable chips. As the frying time increases, the inner contour of the MRI image of Pleurotus eryngii strips gradually becomes blurred, the brightness gradually decreases, the volume shrinks, the less water, and the image interior is close to the background color (blue), indicating that the sample has reached the end of drying; and The grease content is distributed in the edge shell layer higher than other positions. Therefore, the water is continuously removed, the oil signal becomes stronger and stronger, and the oil content of the sample becomes higher and higher.
Crust property is an important factor in affecting the oil absorption of potato strips. The present study aimed at illustrating detailed crust characteristics in relation to oil uptake of potato strips during frying as a function of hot-air pre-drying time. Results showed that oil content decreased with the increasing hot-air pre-drying time. Oil distribution determined by LF-NMR and CLSM confirmed pre-drying could reduce oil uptake of potato strips. Structural and textural analysis of crust revealed the increase in crust ratio, roughness and texture (Fm, Nwr, fwr, Wc), and decrease in crust uniformity. Results of microscopic structure unraveled that the crust of fried strips after pre-drying for 180 min became thick and compact with almost no pores. Our results suggested that hot-air pre-drying caused the formation of harder and denser crust, and oil uptake of fried potato strips after pre-drying largely depended on crust texture rather than morphology.
Background
A more frequent consumption of deep-fat fried food is believed to be linked with a higher risk of subsequently developing obesity and higher severe diseases. However, the evidence from long-term randomized trials or prospective epidemiological studies is scarce. Dietary management for a healthier consumption of food with low fat intake gives high contributions to health.
Scope and approach
Despite the changes in lifestyle that acquire more favourable type of deep-fat fried food as the main dish, a dietary fibre-formulated batter could be the most suitable substitute without changing the taste to keep the health benefits within. Dietary fibre-formulated batter consists the same benefits as resistant starch that can reduce the blood cholesterol level, the glycaemic index and influence in digestive tract. In this review paper, we discuss the factors, properties, background and applications of fibres in batter formulations for oil uptake reduction.
Key findings and conclusions
With high potential of health benefits, different types of dietary fibre have been explored as batter formulations. Dietary fibres are proven to reduce the oil uptake of fried food products as well as improving the textural and overall acceptability. The application of dietary fibre as batter rich in nutrients could be product-friendly for deep-fat fried food products.
Background
Due to the increasing trend in consumer habits to use healthy food products with low fat content, reduction of oil uptake during different frying processes is necessary. Recent studies have clearly revealed that microstructural changes occurred during frying operations significantly impact oil uptake. These variations are assessed for better comprehension of the mechanisms involved in oil absorption of fried products to minimize oil uptake without sacrificing organoleptic and textural properties of the foods. Different strategies such as state-of-the-art computational simulations based on numerical analysis of simultaneous momentum, heat and mass transfer modeling during frying have been attempted by several researchers to better control the process.
Scope and approach
This review paper presents a comprehensive and up-to-date review of microstructure variations covering all existing methods of frying operations comprising deep-fat frying, vacuum frying, hot-air frying, non-fat frying and microwave frying together with post-frying treatments and process modeling of frying.
Key findings and conclusions: Oil uptake can be controlled during frying by proper process design regarding different products and frying operations. Textural and organoleptic characteristics of fried foods are affected by applying various frying processes. Microstructural changes and post-frying treatments influence oil uptake during frying. In addition, suitable design and optimization of frying using process modeling is important to produce fried food products with high quality.
Effects of the addition of rice starch and dietary fibres (pectin and Fibrex) on the porosity of basic frying mixture formulations (corn flour, salt, spices) and oil uptake of coated chicken meat have been evaluated. Porosity of the fried breaded chicken meat was calculated from particle and bulk density. Pore size and particle size distribution were determined using microscopy image analysis and particle density by mercury intrusion porosimeter (MIP). Since there is a wide range of particle diameters, significant differences in pore size distribution were found. Also, pore structure appeared to be affected by oil absorption. Mercury entrapment in pores decreased significantly during 8 min of frying. The obtained results show that porosity of the samples is different for different frying mixture formulations and indicate that there is a difference in the extent of oil uptake for different formulations due to film forming capabilities of dietary fibres (pectin and Fibrex).
During frying process, whether and how moisture content in materials affects oil absorption remain unclear. Herein, we provided direct evidence suggesting that although the initial moisture content had no significant effect either on the final oil content or oil fraction, the moisture content did greatly affect the rate of oil absorption. We analyzed the total oil (TO), surface oil (SO), structural oil (STO), penetrated surface oil (PSO), and oil distribution during frying process in once-fried and twice-fried potato chips, and found that SO fraction was lowest (about 0.90-1.66 %) among three different fractions of TO, while PSO was the dominant section (about 50 %) for TO. Surprisingly, there were no significant difference among the final TO, SO, STO, and PSO for two kinds potato chips (P > 0.05), a finding suggesting that the initial moisture content itself might have no effect on oil absorption. Compared with once-fried potato chips, twice-fried chips much quicker (around sevenfold) reached equilibrium at 180 °C, which might be attributed to no inner resistance of water evaporation in twice-fried potato chips. More importantly, our confocal laser scanning microscopy (CLSM) inspection established that oil of twice-fried chips entered the core faster than once-fried chips. Oil followed the cell shapes and located in cell walls and inside the intercellular spaces for both samples. Taken together, this study provided compelling new data to clarify the relationship between the initial moisture content and oil absorption during frying process, and laid the groundwork for introducing a pre-drying strategy to frying process in food industry.
Response surface methodology was used to investigate the effects of frying temperature, time and maltodextrin (MD) levels on the moisture, oil and beta‐carotene contents of the vacuum‐fried apricot slices. Based on the results, the moisture content of vacuum‐fried apricot slices decreases with increasing frying temperature and frying time. Generally, the oil content of vacuum‐fried apricot slices decreases with decreasing frying temperature and frying time. The beta‐carotene content of vacuum‐fried apricot slices increases with increasing frying temperature. But the trend of increase in the beta‐carotene content of the product with frying temperature was higher at lower MD level. When processing vacuum‐fried apricot slices, a frying temperature of 100 °C, frying time of 72.5 min and an MD level of 70% must be used to achieve a product of acceptable moisture, oil and beta‐carotene contents.
The objective of this study was to evaluate the effect of different batter formulation on mass transfer during deep fat frying of shrimp nuggets prepared without a pre-frying step. The effects of soy and corn flour (5, 10%) addition to the batter formulation, frying temperature and time on mass transfer were determined. The results showed an interaction effect of these processing conditions on mass transfer. The most reduction in fat absorption was observed when samples were coated with batter contained 10% soy flour and fried at 190 ˚C. The first order kinetic based on the Fick’s law were used to describe moisture transfer data. The effective moisture diffusivity ranged between 2.05×10-8 to 5.71×10-8 m2/s with R2 between 0.91 to 0.98, and fat transfer rate constant was between 3.5×10-3 to 7.8×10-3 s-1 with R2 from 0.82 to 0.99. Activation energy obtained from the Arrhenius plot for the effective moisture diffusivity ranged between -18.42 and -23.84 kJ/mol.
The objective of this study was to investigate the possibility of using ultrasound-assisted osmotic dehydration (UAOD) as a pretreatment prior to frying and to study its effects on the quality of fried potatoes. The quality parameters, moisture content, oil uptake, color, texture, and microstructure of fried potatoes, were chosen. Quality of fried potatoes treated with UAOD was also compared with the ones treated with osmotic dehydration (OD). Potato slabs (40 × 40 × 7 mm) were pretreated with different osmotic solutions (15 % sodium chloride and 15 % sodium chloride/50 % sucrose solutions) at different temperatures (25, 45, and 65 °C) with and without ultrasonic waves for different treatment times. The pretreatment conditions which are OD for 90 min and UAOD for 30 min using 15 % sodium chloride/50 % sucrose solution were applied prior to frying at 170 °C for 2, 4, and 6 min. UAOD reduced the oil content of fried potatoes by 12.5 % (db) as compared to untreated fried potatoes at the end of frying. There was no significant difference between OD and UAOD in reduction of oil uptake in fried potatoes. However, UAOD was found to have the advantage of improving the color of French fries. In addition, it shortened the pretreatment time of OD by about 67 %. Cell structure of fried potato was damaged in the presence of pretreatments of OD and UAOD.
Deep fat frying is an important, ubiquitous and highly versatile process, which has been used since antiquity to cook a wide spectrum of products. Its unique contribution to sensory characteristics, together with the relatively low cost of large-scale frying, has made fried foods the staples of the ever growing late 20th century fast food industry. Despite its considerable fat content and intensified consumers’ awareness of the relationships between food, nutrition and health, frying remains a principal cooking method. Oil consumption especially saturated fat is considered a major factor increasing health risks such as coronary heart disease (CHD), cancer, diabetes and hypertension, and even linked to increased causes of deaths. Fried foods contribute a significant proportion of the total fat consumed in the Western world. Yet, aside from their high caloric value, fried foods can be nutritious and favourably compared with other cooking methods such as baking and boiling. Fried foods are popular due to their taste, distinctive flavour, aroma and crunchy texture. Misconceptions about frying extend beyond nutrition to the fundamental aspects of the process, such as the role of water and oil quality during frying. The water released during frying enhances heat transfer, may cause oil deterioration, and also can prevent oxidation. Improving oil quality, the mechanism of oil, coating, engineering considerations of residence time and design, are typical examples of frying technology that is still evolving. To provide quality products that meet consumers’ expectations and satisfaction, and simultaneously improve their quality characteristics, a new paradigm is required. These topics are discussed and data presented to suggest that fried foods do not have to be a health risk in a balanced diet, when frying technology and oil quality are carefully maintained. Future research needs are also highlighted.
The objective of this research was to study the kinetics of oil absorption and distribution in the structure of potato slices during frying, considering the effects of three oil temperatures and a blanching pre-treatment. Either raw or blanched potato slices (Desirée variety, diameter: 30 mm, thickness: 3.0 mm) were fried at three constant (±1 °C) oil temperatures: 120, 150 and 180 °C. The blanching pre-treatment was accomplished in hot water at 85 °C for 3.5 min. Raw potato slices were used as the control for the experiments. The amount of oil absorbed was quantified during frying at four time intervals. The following fractions of the total oil (TO) content of potato slices were determined: (i) structural oil (STO); (ii) penetrated surface oil (PSO); and (iii) surface oil (SO). PSO constituted the highest fraction of the total oil content and this was the case for the control as well as the blanched slices, confirming that oil absorption in potato chips is mainly a surface phenomenon. Contrary to expectation, the blanched potato chips absorbed more oil than the control chips. The higher the frying temperature, the lower the oil absorbed by chips. Confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) allowed studying the surface topography of potato chips, and in some cases, the location of oil on the surface.
The objective of this study was to evaluate the effect of microwave precooking on mass transfer during deep-fat frying of chicken nuggets. The effect of microwave power level, frying temperature and time on mass transfer in the breading coating and the core parts were determined. The results showed an interaction effect of these processing conditions on mass transfer. The most reduction in fat absorption was observed when samples were precooked at 6.7 W/g and fried 170 °C. The first order kinetic model fitted the moisture and fat transfer data well except for fat transfer in the core portion. The effective moisture diffusivity for the breading coating and core portion ranged between 6.39 × 10−10 to 14.7 × 10−10 m2/s and 1.77 × 10−10 to 14.0 × 10−10 m2/s, respectively, and the R2 values were between 0.86 and 0.99. Fat transfer rate constant in the breading region was between 0.04 and 40.96 s−1 with R2 from 0.67 to 0.97. Activation energy obtained from the Arrhenius plot for the effective moisture diffusivity ranged between 13.65 and 54.93 kJ/mol.
Literature on the crispy/crunchy behavior of cellular solid foods with a crust is discussed. The emphasis is on products with a dry crispy or crunchy crust as bread and various snacks and especially on mesoscopic and macroscopic aspects. Successively, the sensory sensations involved, the mechanical and fracture behavior of crispy/crunchy products, morphological aspects, and the relation between crispy and crunchy behavior and mobility of the macromolecules and plasticizer (primarily water) involved, are discussed. Finally, some ideas for an integrated approach of crispy/crunchy behavior of cellular solid foods with a dry crust will be discussed.
Effects of guar gum with glycerol coating on the oil absorption of fried potato chips were investigated using dye oil methods, confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). The results showed that coating with guar gum and glycerol could effectively hinder the oil absorption of fried potato chips and have no negative effects on its breaking force. Compared with control or samples coated with guar gum, potato chips with guar gum and glycerol produced a reduction of oil absorption by 51.8% and 34.8%, respectively. Both for control or coated potato chips, penetrated surface oil (PSOs) was dominant in total oil (TOs), followed by structural oil (STOs) and surface oil (SOs). Coating treatment with guar gum and glycerol could significantly reduce the SOs and PSOs of potato chips (P < 0.05). PSOs was the main factor which attributed to the TOs reduction of fried potato chips after coating. CLSM photographs revealed the oil distribution pattern for control or coated sample, and confirmed that PSOs obviously reduced after coating with guar gum and glycerol, followed by SOs. SEM photographs indicated that guar gum, guar gum and glycerol coatings were effective in preventing oil penetration into the potato tissue during frying process. Coating formulations not only enhance the barrier properties of fried potato chips, but also avoid pores and cracks in the fried products with higher toughness.
This work determines pore characteristics of the French-fry crust and their development at two time intervals during frying. dynamic wicking (DW) and scanning electron microscopy (SEM) are used for that reason. DW is used to determine the effective mean pore radius of the crust. SEM is used to observe the microstructural characteristics of the crust interior and surface. The shapes and sizes of openings/pores in the crust and surface and cell sizes in the crust and core are determined by analysis of the SEM images. Except from new to the literature data on pore sizes in French-fry crusts the above observations provide insight on phenomena occurring in the crust during frying. In addition, the behavior of the interconnected crust porous network during capillary penetration is assessed by DW. Finally, an approximate rate of frying oil uptake in the crust region is estimated considering a capillary penetration theory for oil uptake.
We investigated the applicability of microwave-assisted vacuum frying in producing potato chips. Three microwave power levels (600, 800, 1000 W) were used for frying times of up to 360 s. The moisture loss and oil uptake histories were measured as a function of the microwave power levels. The textural crispness (breaking force) and color parameters (lightness, redness, and yellowness) were also measured as a function of microwave power levels and frying time. The application of microwave-assisted vacuum frying significantly increased the moisture evaporation and oil uptake rates in potato chips. At the same time, the amount of oil uptake was similar to that in vacuum-fried chips not assisted by microwave. The chips produced using microwave-assisted vacuum frying were crispier (lower breaking force), visually appealing, and could be produced in a shorter time.
Confocal laser scanning microscopy (CLSM) was used in fluorescence mode for oil and cell wall detection, and in reflective mode to observe the surface morphology of potato chips. Oil distribution in chips fried at 170°C in oil mixed with the thermoresistant probe Nile Red was studied as the crust developed during frying. Oil was trapped only in intercellular spaces for short frying times while at longer times it was strongly linked to the developed crust microstructure (not only in intercellular spaces but also over some cells) and not easily extractable by hexane washing. Chips infiltrated with a solution of the dye Congo Red (CR) before frying revealed drastic changes in cell walls but no signs of rupture during frying at the magnification used in this research (20X). Topographical data acquired by CLSM in reflective mode confirmed that several cells are broken during the cutting operation. Image representation of the reconstructed surface of a fried chip (170°C, 3 min) allowed observe oil location in potato surface after frying.
The aim of this work was to characterize the inner microstructure of different fried formulated products to understand its relationship to oil absorption. Two product categories, which were either based on potato-flakes or wheat gluten, were analyzed. A non-invasive double staining procedure to perform a two channel observation using confocal scanning laser microscopy was set-up. The dough was directly stained during preparation with fluorescein-5-isothiocyanate (FITC), laminated and fried in oil stained with Nile Red. Thereafter, samples were observed without further intrusion. Pore size, porosity and oil were quantified using image analysis. A direct relationship between porosity and oil absorption was found in gluten-based products, but, no relationship was detected in potato-flakes-based ones. Further, gluten-based products were less porous but retained, in general, more oil. Parameters such as pore tortuosity and/or connectivity, as well as oil wettability, might explain such differences. In addition, the developed microscopy technique developed herein may be used in other food systems.
Crust microstructure plays a critical role in oil uptake of atmospheric fried food and seems to play an important role in vacuum fried products. The objective of this study was to understand the relationship between key microstructural parameters and oil absorption, after atmospheric and vacuum frying of different vegetable tissues. The effect of drainage and centrifugation in oil-uptake reduction was also analyzed. Key microstructural parameters were determined using gas adsorption at cryogenic temperatures, while oil location and surface roughness were studied using confocal laser scanning microscopy and area-scale fractal analysis, respectively. Overall, we found a linear relationship between porosity and final oil content in vacuum and atmospheric fried chips. However, this relationship could not be extended when analyzing the whole set of data, since oil absorption was significantly higher in atmospheric fried chips. Centrifugation allowed reducing oil-uptake up to 73% in atmospheric fried chips and up to 64% in vacuum fried ones.
The effect of frying oil temperature and frying times on pore structure was investigated, while the primary focus of this study was directed towards pore structure characterization by using mercury intrusion porosimeter. The samples were cut into rectangular shapes and deep-fat-fried at different frying oil temperatures (170, 180, and 190 °C) in an industrial fryer for periods ranging from 5 to 360 s and subsequently freeze-dried. Pore structure characterization was conducted by using mercury porosimeter. The cumulative pore volumes decreased by 24% from 2.13 to 0.51 ml/g and with a corresponding porosity of 0.71–0.37 after 360 s of deep-fat frying. Pore structure appeared to be affected by oil absorption, evidently, increased mercury entrapment in pores increased from 0.97% to 10% after 360 s of frying, which implied development of inkbottle shapes. The inter-fiber (planer) pore diameter was about 10.2 μm while the intra-fiber (internal) pores vary from 0.006 to 10 μm in diameter and over 84% of the pores were capillary pores.
Deep-fat frying is a popular process that has been studied essentially to clarify the complex mechanisms of fat decomposition at high temperatures and to assess their effects on human health. The aim of this paper is to show how the application of process engineering methods has recently improved our understanding of the basic principles and mechanisms involved at different scales and different times during the process: pretreatment, frying, and cooling.New results concerning the understanding of the frying process have been obtained as a result of major breakthroughs in on-line instrumentation (heat, steam flux, and local pressure sensors), in the methodology of microstructural and imaging analysis (NMR, MRI, SEM) and in software tools for the simulation of coupled transfer and transport phenomena. Such advances have opened up the way for the creation of a major database of the behavior of various materials and to the development of new tools to control frying operations via final product quality in real conditions. Lastly, this paper promotes an integrated approach to the frying process including various competencies such as those of chemists, engineers, toxicologists, nutritionists, and materials scientists as well as of the catering and industrial sectors.
Frying is one of the oldest unit operations and is used not only in industry but also at home. The most commonly fried vegetable is potato, for important commercial products such as potato chips, par-fried potatoes, and french fries. Quality parameters of interest for fried potatoes include physical and chemical properties such as color, mechanical properties (e.g., crispness, hardness, etc.), structural properties (e.g., porosity and roughness), oil content, and water content, among others. Some chemical contaminants such as acrylamide and furan are heat-generated during the frying of potato slices or strips, leading to final fried pieces with considerable amounts of these contaminants. The controllable variables in industrial frying processes are generally potato variety, oil type, frying time, and frying temperature. Therefore, the study of the quality changes during frying is critical because knowledge regarding kinetics parameters will enable prediction of the final quality in fried potatoes and improvements in the final product value by selecting properly the processing conditions. Finally, modern techniques such as computer vision provide valuable tools to quantify and predict physical and chemical properties of potato pieces during frying in a fast and noninvasive way. In addition, computer vision can allow us to classify fried potatoes in different quality classes previously determined by sensorial panels.
Changes in the structure of food products play important role in the various mass transfer processes during deep-fat frying. The relationship between moisture loss and pore formation were investigated at frying oil temperatures of 170, 180, and 190°C and frying times up to 900 s. Porosity and pore structure were characterized by using mercury intrusion porosimetry and helium displacement pycnometer. Moisture transfer in the samples was modeled using Fick's law and effective moisture diffusivity was computed from experimental data. Pore formation changes significantly (P
Porosity and pore size distribution are very important microstructural properties of fried foods needed in process optimization and product development. The objective of this study was to characterize the pore properties and quantify fat distribution in deep-fat fried chicken nuggets batter coating using confocal laser scanning microscopy. Samples were fried at three temperatures namely 170, 180 and 190 °C. Detached batter coatings were stained non-covalently and 2-D images were obtained at fluorescence and reflection modes of the microscope. The images were analyzed for fat and pore distribution. Fat distribution obtained from image analysis was significantly (P < 0.05) affected by the frying temperature and time, and it decreased within the depth of the sample thickness. There was a strong correlation between fat distribution and fat content obtained by the conventional method at two temperatures, 180 and 190 °C. Porosity ranged between 4.97% and 32.7% and was significantly influenced by frying temperature. Pore size varied approximately between 1.20 and 550 μm. Frying process led to the formation of more micropores (pores < 40 μm) and bigger (pore ⩾ 216 μm) pores.
Differential scanning calorimetry (DSC) was used to determine the oil uptake of commercial frozen par-fried potatoes after frying at 180 °C in colza/soybean oil. The enthalpy and temperature range of the crystallization peak for the pure frying oil were 47.2 J/g and −44 to −50 °C, respectively. DSC was performed by cooling samples of crust and core of fried potatoes from 10 to −60 °C at 1 °C/min and the oil content calculated from the peak area. The crust contained almost 6 times as much oil as the central core (23.6% vs 4%, dry weight basis), as visualized by light microscopy. Only 87% of the oil in the intact crust can be removed by solvent extraction, the rest being extractable only after grinding. Deviation between DSC and Soxtec extraction methods was less than 3%. The DSC method is fast, specific, and reliable, does not use solvents, requires smaller samples (<100 mg) than conventional solvent extraction methods, and can also detect freezable water. Keywords: Differential scanning calorimetry; oil; frying; fried potatoes; microstructure
The objective of this work was to study certain physical properties of French fries, such as density and porosity, and their relationship with oil absorption during the frying process. The effects of oil temperature and frying time on moisture loss, oil content and crust thickness were first studied. Changes in apparent density, absolute density as well as porosity during two successive periods of frying process (frying and cooling) were then investigated, and possible reasons for these changes were discussed. Finally, the porosity changes were related to oil uptake. Potatoes were cut into rectangular shapes and were fried at different oil temperatures (140, 155, 170 and 185C) for periods ranging from 60 to 240 s. Results showed that during frying, the porosity of the product increases, reaching a maximum at the end of frying, whereas during the cooling period, it decreases because of oil absorption and collapse phenomena.
This study shows some physical changes that can be related to oil absorption during the frying process of French fries. Many food research projects attempt to understand oil uptake during the frying process in order to control and reduce the fat content of fried products. The results of this work may lead to finding the way(s) to produce less greasy fried products.
The objective of this study was to characterise the pore properties of deep-fat-fried chicken nuggets coating under different processing conditions namely frying temperatures (170, 180 and 190 °C) and time (0–240 s) using porosimetry technique. Porosity range obtained was between 39.93 and 68.99%. Porosity of the freeze-dried samples decreased with frying time. The main effect of temperature on porosity was significant (P < 0.05). Porosity showed a high positive and negative correlation with moisture and fat contents, and the correlation coefficients ranged between 0.88 and 0.96 and 0.78 and 0.8, respectively. Bulk density increased with frying time, while apparent density was relatively the same. Pore distribution showed bimodality. There was no significant effect of temperature on pore size distribution. Over 70% of the pore volume is made up of pores greater than 1 μm. Pore volume ranged between 0.54 and 1.5 cm3 g−1, and it decreased with frying time. Mean pore diameter was between 0.006 and 389 μm, while with frying time, it ranged between 0.25 and 8.32 μm. Total pore area was between 2.53 and 16.53 m2 g−1. Hysteresis phenomenon showed that some of the pores were not perfectly cylindrical in shape.
Frying induces major structural changes in the surface of foods influencing oil uptake. This work discusses the use of several different methods of microscopy as well as techniques of image analysis to study frying at the microstructural level. Hot-stage video microscopy was instrumental in assessing geometrical changes in cells of potato tissue and in starch in real time. The swelling of starches inside cells appeared to be retarded compared with that in starch suspensions. Confocal laser scanning microscopy (CLSM) permitted ‘optical’ sectioning of the crust, revealing that oil was located in the interior in pockets or surrounding intact cells. The manipulation of microscopy data by image processing is also presented.
The purpose of the study was to determine some changes in the structure of potato tissue and the contents of non-starch polysaccharides and lignin in potatoes at particular stages of French fries production. The samples for laboratory studies were taken from potato tubers, strips and French fries collected from six locations of the technological line. Immediately after the samples were collected from the processing line, the texture of potatoes was determined using an Instron 5544. Structural changes in the tissue were determined using a Leo-435VP scanning electron microscope. Dry matter and non-starch polysaccharide contents were determined in the samples of processed potatoes. It was found that the texture of potato was changing during the technological process due to water losses and damages of potato tissue and consequent changes in non-starch polysaccharides and lignin. The greatest changes in potato tissue resulted from thermal processes: blanching, pre-drying and frying. Increases of non-starch polysaccharide and lignin contents were observed during these processes, owing to water losses in potato strips. The ultimate texture of French fries was developed during frying, by penetration of fat primarily into the external layer of strips.
Deep-fat frying is a popular cooking method, particularly for potato based snack products. While fats and oils are known to add unique flavour, texture and overall palatability to foods, the absorption and distribution of oil is not well established. This work examines the absorption of oil in fried potato products with a range of nuclear magnetic resonance and magnetic resonance imaging techniques. We investigate the oil and water contents in French fries based upon the distribution of relaxation times. Relaxation times from different oil and water environments overlap precluding a simple analysis. We develop several techniques for isolating the oil signal from the water signal, and present images mapping the oil absorption as a function of the degree of cooking. Lastly, we present an image derived T2 map. Spatially resolving the relaxation times permits quantification of the oil and water contributions in the crust and in the core.
Ways of removing the adhered surface oil, while the product is still in the fryer, has been the subject of many studies and patents for deep-fat frying processes. In the case of vacuum frying, this problem is exacerbated by the pressurization step, which causes a quick increase in pressure in the pore space thus forcing most of the surface oil into the product pore spaces. Therefore, for vacuum frying, a de-oiling mechanism is required to reduce the excessive oil absorption at the surface of the product. The main objective of this study was to establish the effect of de-oiling and frying temperature on potato chips quality attributes and oil absorption.
During the last decade much attention has been given to investigating oil absorption during frying. Several studies have suggested the key role of the dehydrated crust, which is thought to control the main mechanisms in oil absorption, that is drainage and capillary suction during post-frying cooling. To contribute to a better understanding of these mechanisms, we have used infrared microspectroscopy at the Synchrotron Radiation Source at Daresbury (UK) to monitor the oil distribution in fried potato cylinders. We report what we believe to be the first quantitative data on oil distribution within a fried product. Results show that the oil distribution within the crust reflects the anisotropic nature of the porous region in accordance with the proposed mechanism of oil absorption.
The variations in moisture content and oil content of samples of 1.5-mm thick slices of potato (c.v. Record U.K.) were examined after various frying times at frying temperatures of 145, 165 and 185°C. The loss of moisture and the uptake of oil were found to be interrelated and both were linear functions of the square root of frying time. Within the temperature range examined, moisture loss and oil uptake were found to be independent of frying temperature. From the data and visual observations the mechanism of moisture loss and its influence on oil content in the final product were discussed. Suggestions are made for means of reducing the total oil content by modifications in the frying process.
ABSTRACT Analysis of the oil-absorption process in deep-fat fried potato cylinders (frying temperatures of 155°C, 170°C, and 185°C) allowed to distinguish 3 oil fractions: structural oil (absorbed during frying), penetrated surface oil (suctioned during cooling), and surface oil. Results showed that a small amount of oil penetrates during frying because most of the oil was picked up at the end of the process, suggesting that oil uptake and water removal are not synchronous phenomena. After cooling, oil was located either on the surface of the chip or suctioned into the porous crust microstructure, with an inverse relationship between them for increasing frying times.
The quality and marketability of many fried food products is a function of the internal distribution of oil and water. French fries, for example, are well received when they are both crisp and moist, but not when they are soggy. A rapid technique for the measurement of local oil and water content is therefore highly desirable to guide the development and processing of fried food materials.Time-domain nuclear magnetic resonance (TD-NMR) has proven to be a quick, reproducible, accurate, and non-invasive technique, which is particularly well suited to measurements of oil and moisture content. Nuclear spin–spin relaxation times (T2) are an excellent probe of molecular mobility, which in turn can be directly correlated to moisture content.In this work, a precursor to spatially resolved measurements, we measure T2 in a model fried food crust sample as a function of moisture level. We observe multi-exponential behavior, which we assign to specific liquid constituents. We find a direct correlation between the component weightings and the known oil and water contents.By systematically varying the moisture level of the sample, we explore the nature of water uptake in these materials. Absorption is modeled with a modified BET sorption isotherm.These results provide a basis upon which magnetic resonance imaging (MRI) techniques can be applied to investigate cooked starch food crusts.
Over the past 5 years growing demands for reducing fat content of fried foods have greatly stimulated the amount of research spent on the issue of fat uptake during deep-fat frying. The results of these efforts are summarized in this review. Most of the increased understanding of the mechanism of fat uptake has been brought about by improved imaging techniques. It turns out that fat uptake is basically determined by two mechanisms: the condensation effect and the capillary effect. Major reductions claimed in literature and patents are found for coating and batter formulations using various types of biopolymers.
Literature on the crispy / crunchy behaviour of cellular solid foods with a crust is discussed. The emphasis is on products with a dry crispy or crunchy crust as bread and various snacks and especially on mesoscopic and macroscopic aspects. Successively, the sensory sensation involved, the relation to fracture behaviour, morphological aspects, and the relation between crispy and crunchy behaviour and mobility of the macromolecules and plasticizer (primarily water) involved, are discussed. Finally we will discuss some ideas for an integrated approach of crispy / crunchy behaviour of cellular solid foods with a dry crust.
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