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Drying kinetics for some fruits: Predicting of porosity and color during dehydration
Drying Technology
Abstract
Drying kinetics of four fruits (prune, quince, fig and strawberry) were studied by using a simple mass transfer mathematical model involving a characteristic parameter (K) as a function of process variables. The model was tested with data produced in a laboratory air dryer, using non-linear regression analysis. The investigation involved three values of sample thickness (5, 10, 15mm) and three different air temperatures (50, 60, 70 °C).The parameters of the model were found to be greatly affected by sample thickness and air temperature. The effect of moisture content on the porosity of three fruits (namely avocado, prune and strawberry) was also investigated. A simple mathematical model was used to correlate porosity with moisture content. It was found that porosity increased with decreasing moisture content.Samples of three fruits (avocado, prune and strawberry) were investigated to estimate color changes during conventional drying at 70 °C. A first order kinetic model was fitted to experimental data with great success. It is found that the color of avocado and strawberry change while the color of prune remains the same.Furthermore, the water sorption isotherms of three fruits (avocado, prune and strawberry) at 25° temperature were determined experimentally and the parameters at the GAB equation were evaluated by means of non-linear regression analysis. The use of the above equation produced a very good fit.
... Devahastin and Niamnuy [21] have put forward a review on modelling quality changes of fruits and vegetables including color degradation kinetics. More specifically, the influence of hot-air drying on color changes has been studied by applying zero or first order kinetic models for basil, [22] apple, [23] hazelnut, [24] potato, [25] avocado, [26] prune, [26] strawberry, [26] grape juice and leather, [27] and onion [28] while the impact of microwave drying for kiwi, [29] okra, [30] spinach, [31] and basil [32] has been studied. The effects of the drying medium, [33] pre-treatment, [34] and drying method [35] on the kinetics of color changes have also been investigated for some fruits and vegetables. ...
... Devahastin and Niamnuy [21] have put forward a review on modelling quality changes of fruits and vegetables including color degradation kinetics. More specifically, the influence of hot-air drying on color changes has been studied by applying zero or first order kinetic models for basil, [22] apple, [23] hazelnut, [24] potato, [25] avocado, [26] prune, [26] strawberry, [26] grape juice and leather, [27] and onion [28] while the impact of microwave drying for kiwi, [29] okra, [30] spinach, [31] and basil [32] has been studied. The effects of the drying medium, [33] pre-treatment, [34] and drying method [35] on the kinetics of color changes have also been investigated for some fruits and vegetables. ...
... Devahastin and Niamnuy [21] have put forward a review on modelling quality changes of fruits and vegetables including color degradation kinetics. More specifically, the influence of hot-air drying on color changes has been studied by applying zero or first order kinetic models for basil, [22] apple, [23] hazelnut, [24] potato, [25] avocado, [26] prune, [26] strawberry, [26] grape juice and leather, [27] and onion [28] while the impact of microwave drying for kiwi, [29] okra, [30] spinach, [31] and basil [32] has been studied. The effects of the drying medium, [33] pre-treatment, [34] and drying method [35] on the kinetics of color changes have also been investigated for some fruits and vegetables. ...
In the present work, the effects of drying air temperature and pre-treatment on color changes and texture of Boletus edulis (Bull.: Fr.) mushrooms were investigated during convective drying. The drying experiments were conducted in a laboratory hot-air dryer at temperatures of 50, 60, and 70 °C under thermal (water or steam blanching) and chemical (solution of potassium metabisulfite or citric acid) treatments. Changes in color were evaluated by the CIELAB color system and the experimental color parameters (L* a* b*) were fitted to a first order kinetic model. Values of total color difference (ΔE*), hue angle (h*), and chroma (C*) were also calculated. The texture of dried mushrooms was measured by an Instron texture analyzer and expressed as hardness. The model fitted the experimental a* and b* values sufficiently. The results showed that during convective drying, lightness decreased slightly while yellowness and redness increased. Chemical pre-treatments did not influence the color of mushrooms positively while blanching caused intensive color deterioration. Moreover, the ΔE* value could contribute to the assessment of color change effectively. Hardness increased as drying proceeded and was found to be greater at higher temperatures. Mushrooms subjected to water or steam blanching were harder in texture. A temperature limit of 60°C is imposed for the dehydration of B. edulis mushrooms. Thermal treatment prior to drying is not recommended for B. edulis mushrooms when color and texture are desirable quality criteria.
... where is the volume-shrinkage coefficient Avocado, prune and strawberry slices (Tsami and Katsioti, 2000) Banana, apple, carrot and potato cylinders pores (Lewis, 1987). It is expected that, as the food loses water, the value of the particle density ranges between the water density and the dried material density. ...
... Avocado, prune and strawberry slices (Tsami and Katsioti, 2000) Banana, apple, carrot and potato cylinders Figure 4. Typical variation of density with water content. (Potter and Hotchkiss, 1998). ...
... Avocado, prune and strawberry slices (Tsami and Katsioti , 2000) Banana, apple, carrot and potato cylinders Garlic cloves (Madamba et al., 1994) b ¼ i 1 þ i 2 expði 3 X 2 Þ ð 12Þ Potato slabs (Wang and Brennan, 1995) Structural Changes During Air Drying 205 ...
This work aims at reviewing structural changes occurring in convective air drying of fruits and vegetables. These include changes in physical properties, such as volume, porosity and bulk and particle density, which directlyaffect textural attributes of the products. Models relating with water content physical properties are also summarised. At microscopic level, the phenomena observed byprevious authors is described, focusing on shrinkage. In particular, a new approach on modelling kinetics of microstructural modifications is presented. Although the air drying process is relatively well studied, there is a lack of research concerning changes in structural properties. Modelling mass transfer during drying frequently does not include those effects and, there has not been established a standard methodologyfor predictive purposes. Correlating microstructure, texture measurements and sensoryanalysis would be an attractive area to be exploited for drying processes of fruits and vegetables. Although this is a wide working field, much is still to be done.
... Oil content in avocado complicates the drying kinetics of avocado. It is the major factor that affects the drying kinetics (Alzamora and Chirife, 1980) It has been reported that the effective diffusivity is inversely correlated with oil content of the avocado pulp (Tsami and Katsioti 2000). Pre-treatment processes like blanching and freezing only Mechanical pretreatment Sensitive to heat ...
... Ceylan et al, (2007) reported the drying kinetics of avocado subjected to heat pump assisted drying with thickness of 5 mm, that 360 min was required to dehydrated avocado slice to a moisture content of 0.35 g H2O/ g DM. Hot air drying of avocado resulted in significant color change in the dehydrated product (Tsami and Katsioti 2000). Grajales-Lagunes et al. (2009) reported findings on spray drying of avocado juice with the inlet temperature and outlet temperatures of 190°C and 80°C, respectively, with air velocity of 27 m/s. ...
... The deterioration of the color attributes with drying condi- tions has been widely studied in a large number of vegetables, mainly in apple ( Mandala et al., 2005); banana, carrot and potato ( Krokida et al., 1998); kiwi fruit (Maskan, 2001); cher- ries ( Ohaco et al., 2001); quince, prune and strawberry (Tsami and Katsioti, 2000), among others. Pineapple color is a decisive factor in the judging of product acceptability since a pale yel- low is associated with ripening and development of the flavour characteristic of the fruit ( Bartolome et al., 1996). ...
... In addition, an important dispersion of measured L values was observed. Similar observations about of L values (notable dispersion of measured values; without tendency to change during the process; independence of the drying tem- perature) were reported by Krokida et al. (1998) during apple, banana, carrot and potato drying and by Tsami and Katsioti (2000) during the drying of strawberries. Pineapple slices tend to get darker ("more red") as drying proceeds (as a result of non-enzymatic browning reactions) as indicated by the progressive increasing of a values, without change of L values. ...
Pineapple (Anana comosus) slices were dried by hot-air convective drying technique at fixed temperature (45, 60 and 75°C) and constant air velocity of 1.5m/s. The effect of drying conditions (drying time and air temperature) on the pineapple quality was evaluated. The quality of dehydrated pineapple was analyzed by color and texture changes, l-ascorbic acid loss and the ability of water uptake during rehydration procedure. Water uptake during rehydration was described by Page model. Statistical analysis of data revealed not significant difference (p>0.05) among color and mechanical characteristics of pineapple samples dried at different drying temperatures to preset moisture content. Pineapple samples dried at 45°C had better rehydration ability and more l-ascorbic acid retention than those obtained by air drying 75°C. Hence, 45°C drying temperature was best condition for pineapple quality preservation.
... • D is calculated using Eq. (20). ...
... Experimental observation shows that the lag factor G and the drying coefficient S are 1.0086 and 7:91389 Â 10 À5 , respectively. It is also observed that the experimental drying time for a 10% centerline moisture content of the initial value is 28 800 s as obtain from Tsami and Katsioti [20]. Let us estimate the moisture diffusivity D and the moisture transfer coefficient h m of this prune slab. ...
In this paper a simple graphical method is proposed to determine the drying moisture transfer parameters such as moisture diffusivity and moisture transfer coefficient for solid products. Once the lag factor and the drying coefficient are obtained from the experimental moisture content data, the proposed graphical method can be used to estimate the drying moisture transfer parameters in a quick and efficient manner. Drying time can also be easily determined for a solid whose drying process parameters are known. Two illustrative examples are given to highlight the importance of the topic and validate the use of the present methodology for practical drying applications.
... × 10 −7 m·s −1 , at 10 −7 m·s −1 , at 60˚C -110˚C)[21] and eggplant (6.478 -2.190 × 10 −7 m·s −1 , at 50˚C -70˚C)[29]. Ours results were also in accordance with those from Markowski[66] who determinates an average mass transfer coefficient value of 1.371 × 10 −7 m·s −1 during drying of fresh carrot slices, those by Elbert et al.[67] with a value of 4.81 × 10 −7 m·s −1 during parboiled rice drying, those by Tsami and Katsioti[68] with 4.026 × 10 −7 m·s −1 during drying of prune slices, and those by Ruiz-Cabrera et al.[69] with 6.608 × 10 −7 m·s −1 during carrot drying. Examination of the relative magnitude of the mass transfer coefficient for onion showed a variation A.Compaoré et al. ...
In the present work, the mass transfer characteristics, namely moisture diffusivity and moisture transfer coefficient of “Violet de Galmi” variety of onions were evaluated using the analytical model. Onions were dried in a single layer at different temperatures (40 ̊C, 50 ̊C, 60 ̊C, and 70 ̊C) and for a relative humidity of drying air of 20%. The results showed a reasonably good agreement between the values predicted by the correlation and the experimental observations. This model computed the Biot number, effective moisture diffusivity, and mass transfer coefficient. Effective diffusion coefficient values are obtained between 0.2578 × 10−9 m2·s−1 and 0.5460 × 10−9 m 2·s−1. Mass transfer coefficients of “Violet de Galmi” onion drying vary between 3.37 × 10−7 m·s−1 and 13.38 × 10−7 m·s−1. Numbers of mass transfer Biot are found between 0.9797 and 2.9397. The activation energy Ea is 31.73 kJ·mol −1
... Figure 2 shows that the color of the dried product became darker (decrease in L* value), less green (increase in a* value), and more yellow (increase in b* value), indicating an increase in browning pigments and a loss of natural pigments in products (see Figure 3). For hot air drying of sliced avocados [52] and infrared-vacuum drying of grapefruit slices [53], the same trend was observed, with an increase in a* value and a decrease in L* and b* values. This study found each investigated factor showed a significant impact on the change of color parameters. ...
Featured Application
Avocado powder was first produced from avocado pulp using infrared drying. Drying with 9% maltodextrin at 70 °C retained 95% antioxidant contents and activity.
Abstract
In this study, avocado pulp with a good nutritional profile and economic value was dehydrated using infrared drying to produce pulp powder, which shows potential application in nutritional supplements. An experimental design with two factors, namely maltodextrin level (0% and 9%) and infrared temperature (ranging from 65 to 80 °C), was used. Responses related to the physicochemical properties of the resulted powder were observed, including peroxide value, total polyphenols, total chlorophylls, antioxidant activity, and color parameters (L*, a*, and b* values). The quality of dried products may be harmed by drying either at a high temperature or for an extended period of time. The coating substance maltodextrin was found to be beneficial in limiting unexpected changes in avocado pulp subjected to infrared drying. The highest quality of dried avocado could be obtained via infrared drying of avocado pulp with 9% maltodextrin at 70 °C, as illustrated by the exceptional retention of total polyphenols, total chlorophylls, and antioxidant activity, being 95.1, 95.2, and 94.4%, respectively. Moreover, the short drying time (35–55 min) led to the minimization of lipid oxidation and the absence of peroxide compounds in all samples.
... Attempts have been made to produce a dried avocado pulp to extend the shelf life and make available yearround. Drying techniques have included hot air (oven) drying, heat pump assisted drying and drying with superheated steam [2][3][4][5][6]. Works on the hot air drying of avocado pulp slices and cubes investigated drying (5-8h) at temperatures ranging from 50 to 80°C [2,5]. ...
This work investigated the technique of vacuum freeze drying of avocado pulp (Persea americana var. Pollock) to produce a dried cake which could be blended into a powder to be used in various food applications. Frozen, mashed avocado pulp samples were dried in a Benhay SB-4 vacuum freeze dryer. For comparison, fresh pulp samples were also oven-dried in a Unitemp drying cabinet at 60°C. Samples were dried until constant weight was achieved after which they were blended into powders and analysed. Analyses included determination of moisture content, water activity, pH and total soluble solids content, colour assessment, proximate analyses, physical properties, rehydration behaviour and a preliminary storage assessment. Drying data was used to generate rate and Moisture Ratio (MR) curves and thin layer models applied to the MR data. The moisture content and water activity values of the fresh pulp averaged 3.16 g H2O/g dry matter (76.0% wet basis) and 0.889, respectively. Samples were successfully dried in the freeze dryer to an average moisture content of 0.02 g H2O/g dry matter (2.1% wet basis) after 72h, and a final average water activity of 0.356. Drying occurred in the falling rate period and the drying rate constant (k1) averaged 0.2496 1/h. The Verma model was found to best fit the Moisture Ratio (MR) data. Compared with oven-dried samples, the freeze-dried samples dried to lower equilibrium moisture values, did not show any signs of browning and was higher in protein and fat content. The freeze-dried 'cake' was easier to blend to a light, free-flowing powder which easily rehydrated to a form which closely resembled fresh avocado puree. Freeze drying is therefore an attractive option to produce a high-quality Pollock avocado powder, without the use of heat or the application of chemical preservatives to preserve colour.
... The avocado powder can be useful for off-season for several purposes such as coloring agent, cosmetic industry, etc. There are few studies on the drying of avocados such as heat pump drying (Ceylan et al., 2007) and convective drying (Tsami and Katsioti, 2000). From the authors' knowledge, there is a paucity of the literature producing foam mat dried avocado powder and investigating the effect of foam mat drying processes and conditions on the physical, functional, and powder properties of the avocado powder. ...
The aim of this study was to produce hot air (60-80°C and 20% ventilation rate) and microwave (120-700W) assisted foam mat dried avocado powders and to determine the effect of different drying temperatures and microwave powers on physical, functional, and powder properties of avocado powders. Significantly lower drying times were observed for the microwave assisted foam-mat dried avocado powder (p<0.05). Microwave assisted foam-mat dried avocado powders have superior properties in moisture content and flow properties (p<0.05), whereas comparatively better results were obtained for hot air assisted foam mat dried avocado powder for wettability and solubility times. The changes in ash content, pH, water holding capacity, bulk and tapped densities, Carr Index and Hausner Ratio values followed a quadratic trend depending on both drying temperature and microwave power. Principal component analysis indicated that there is a convenient relation between the avocado powders which were dried at different drying techniques and conditions.
... Kurutma sıcaklığı arttıkça L* ve b* değerlerinde daha fazla düşüş, a* değerlerinde ise daha fazla artış gerçeklemiştir. Avokadoların sıcak hava ile kurutulması esnasındaki kütle transferinin matematiksel olarak modellendiği çalışmada da benzer şekilde kurutma işlemi ilerledikçe L* ve b* değerleri azalırken a* değerlerinde artış görülmüştür (opali ve Katsioti, 2000). Bu çalışmaya benzer olarak sıcak hava ve vakumla kurutmanın karalahanaların renk değerleri üzerine etkisinin araştırıldığı bir çalışmada kullanılan karalahanalarda vakumlu kurutucu ile kurutulmuş örneklerin L* ve b* değerlerinde daha az düşüş gerçekleşmiştir (Alibas, 2009 ...
Besides limiting microbiological and chemical activity in fruits, drying is a practical method that provides healthy snacks nowadays, when culture of nutrition with snacks is increasingly common. It is very important to choose a method that preserves both nutritional values and physical and sensory properties of foods in the drying process. In this study, the comparison of quality characteristics of dried avocados using vacuum dryer and fluidized bed dryer was investigated. Avocados with initial moisture content of 72±09 % were dried until their moisture content reached 13±1 %. The drying process in the fluidized bed dryer was completed at 50 °C, 60 °C and 70°C with 1.5 m/s speed in 8 hours, 7 hours and 6 hours respectively, while the vacuum drying process was completed at 10 Kpa pressure at 50 °C, 60 °C and 70 °C temperatures in 10 hours, 9 hours and 8 hours respectively. In order to compare the physical, chemical and sensory properties of dried avocados, color, water activity, rehydration capacity, shrinkage rate, pH, antioxidant activity, total phenolic content measurements and sensory analysis tests were conducted. (p<0.05). In the result of this study, it has been revealed that vacuum drying is a method that better preserves the physical and chemical properties of avocados as well as their sensory properties.
... In this study, the total phenolic compounds concentration expressed as gallic acid equivalent was investigated at different drying temperatures as heat treatment causes irreversible reaction of phenolic compounds. At certain pH and moisture content, phenolic compounds are trapped in the pores (Tsami and Katsioti, 2007). During drying, all parts of the thin layer of onion slice came in contact with hot air; hence, oxygen was in excess. ...
Onion, a very common season ingredient, is useful as an antioxidant and optimal conditions are required for its drying while ensuring the best quality is retained. This study evaluated the effect of drying temperatures and relative humidity on both drying rate and onion quality. Onions with an average diameter of 20.125 ± 0.025 mm were peeled and sliced into a thickness of 1.233 ± 0.029 mm. They were then dried for 120 min under various temperatures ranging from 40 to 70 °C. Both moisture content and total phenolic compounds were measured and analyzed as responses, and the data obtained were used for estimating the kinetic parameters of drying rate and total phenolic compounds degradation. The results show that the drying kinetics followed Fick's model. Moreover, the total phenolic compounds degradation can be properly expressed using a first-order reaction model, and the optimization using response surface method revealed that the optimum conditions of onion slice drying were achieved at 49.6 °C and relative humidity of 0.65%. These conditions can significantly reduce drying time with phenolic compounds retention of up to 96%.
... The rapid expansion of pores and the possibility of generating superheated vapor could rupture pores and cause internal collapse and eventually sample shrinkage. [95] A microwaved cranberry sample reveals that a dried sample heated in a higher-power microwave requires greater cutting force than a dried sample heated in a lower-power microwave. [96] This result might be explained by reference to internal collapse and sample shrinkage. ...
The complexity of food materials can be attributed to their hygroscopic, amorphous, heterogeneous, and porous structure. During processing, the microstructure of food materials changes; this significantly affects the structural and transport properties of food. A comprehensive understanding of the microstructure and its dynamics during food processing is critical to optimizing food processes and making food quality more predictable and controllable. This review critically assesses the product and process parameters that influence the modification of microstructure in the course of food processes such as pre-treatment, cooking, convective drying, freeze-drying, microwave heating, deep-frying, and baking. An extensive review of the literature indicates that food quality significantly and interchangeably depends on 1) the transport and structural properties of raw material, 2) the evolution of properties, and 3) processing parameters. A porous media framework allows a broader (and deeper) understanding of food microstructure evolution during its processing across many processes and products. This should help speed-up process optimization and novel and hybrid process development.
... During pineapple drying, variations in the L* values were not statistically significant; hence, it can be stated that this it was not affected by process temperature. Tsami and Katsioti [21] reported the similar observations during apple, banana, carrot and potato drying for L* values (notable scattering of values measured; without any inclination to change during the process). While, on the other side, the control sample contained significantly lower a* values. ...
Demands for processed food products are rising worldwide and, consumers nowadays have adopted a healthy lifestyle and are always looking for the products which are advantageous for their health and have the characteristics and taste of a fresh commodity at the same time. Many techniques or combination of techniques have been tried to expand the shelf life of the perishable food commodities. One of the simplest methods which do not require sophisticated equipment is osmotic dehydration. Osmotic dehydration is an excellent phenomenon in which removal of water happens from an area of higher concentration to an area where concentration is lower through a membrane known as a semi-permeable membrane. Since osmotic dehydration lowers the water activity of food item; it has found broad application in the field of food material preservation. In this study pineapple cubes were dehydrated with osmotic dehydration followed by tray drying at 60℃ were assessed for physicochemical properties such as moisture, ash, rehydration ratio, ascorbic acid, water activity, color parameters and sensory properties. Sucrose solution, honey solution and honey-sucrose solution were used as osmotic agents. Duncan’s test was used to analyze the obtained data. Results showed that the pineapple sample cubes treated with honey sucrose solution at 50⁰C temperature were found to have better rehydration characteristics and lowest moisture content value as compared to the other samples. Sensory evaluation of all the samples revealed that highest scores were obtained by the sample containing both sucrose and honey (50⁰C). Highest ascorbic acid content after the osmotic dehydration was found in sample with sucrose and honey. Hence, sample with combination of sucrose and honey solution at 50⁰C proved to be the best in terms of nutritional quality, shelf stability and all other tested parameters. Therefore, many products with enhanced shelf life can be prepared using this rapid and economical technique.
... In recent years, drying consumes a lot of energy, up to 70% for wood industry and 50% for the textile (Minea, 2013), whereas the food industry consumes about 15% (Perussello et al., 2014), although an inappropriate drying can increase this consumption and decrease the final product quality. The quality concept can be characterized by microbiological activity, the shrinkage, nutritional control and the sensory characteristics (Tsami and Katsioti, 2000;Chua et al., 2000;Cui et al., 2008) which are directly related to product moisture content and temperature (Kalbasi and Mehraban, 2000). During drying, the product dehydrates on the surface faster unlike the heart (Wang and Brennan, 1993;Srikiatden and Roberts, 2008;Mihoubi et al., 2009). ...
This study concerns a purely convective drying of parallelepiped un-blanched potato slices. A numerical model for heat and mass transfer has been developed in Lagrangian referential to overcome the structural changes. The thermo-physical properties of the slices vary with the temperature and moisture content. The finite volume method combined with a typically implicit time pattern was used to solve the model equations. The evaporated mass flux was calculated using the transfer surface area by which the water evaporates, and heat transfer coefficient was estimated using Nusselt number; The inverse method was used in this computation. The experiments were carried out under several thermo-aeraulics conditions in order to determine the most influent operating variable on the drying kinetic. A good agreement between experimental and simulated results was obtained with a moisture content determination coefficient (R2) higher than 0.9980; Whereas, the surface and center temperatures are higher than 0.9328 and 0.9305 respectively. The results have shown that the air temperature is the most important parameter that controls the drying kinetic.
... Values obtained of moisture transfer coefficient (h m ) ( Table 4) ranged between 7.113 x 10 -7 to 13.290 x 10 -7 m/s, and 2.863 x 10 -7 to 5.539 x 10 -7 m/s, respectively for slab and cylinder shape. These results are in the same range of those available by several authors for different foods and drying conditions, such as reported by Tsami & Katsioti (2000) for drying of prune slices (4.026 x 10 -7 m/s), by Elbert et al. (2001) for drying of parboiled rice (4.81 x 10 -7 m/s), by Demirel & Turhan (2003) for drying of banana slices (6.0 x 10 -7 to 15.10 x 10 -7 m/s), by Dincer & Hussain (2004) for drying of onion slices (12.226 x 10 -7 m/s), by Tripathy & Kumar (2009) for drying of potato in cylindrical shape (1.61 x 10 -7 to 4.17 x 10 -7 m/s) and by Bezerra et al. (2015) for drying of passion fruit peel (4.530 x 10 -7 to 8.702 x 10 -7 m/s). This is an important drying parameter that depends on moisture diffusivity, viscosity, velocity of the fluid and the geometry of the transfer system (Saravacos & Maroulis, 2001). ...
By the analytical model proposed by Dincer and Dost, the mass transfer parameters (moisture transfer coefficient and moisture diffusivity) of shrimp samples were determined. Three sets of drying experiments were performed with three samples of shrimp: without boiling (WB), boiled in salt solution (SB) and boiled in salt solution and subjected to liquid smoking process (SBS). The experiments were performed under controlled conditions of drying air at temperature of 60°C and velocity of 1.5 m/s. Experimental dimensionless moisture content data were used to calculate the drying coefficients and lag factors, which were then incorporated into the analytical model for slab and cylinder shapes. The results showed an adequate fit between the experimental data and the values predicted from the correlation. The boiling is the most recommended pretreatment, because provided a shorter drying time, with high values of moisture transfer coefficient and moisture diffusivity.
... Heat and mass transfer rate changes with reduction in area which is dictated by shrinkage pattern (May and Peree, 2002) and it increases with increase in average pore size (Karathanos et al., 1996). These events ultimately affect the structural, textural, and sensory quality of food, which determines its acceptance in market (Tasami and Katsioti, 2000). ...
Fruits and vegetables are porous in nature and undergo pronounced shrinkage during convective drying process. Therefore, shrinkage and porosity should be taken into consideration while predicting heat and mass transfer. This work was conducted to study shrinkage and porosity changes along with simultaneous heat and mass transport during the process. Potato slices were subjected to drying for 7 h at 62 �C. It was observed that shrinkage varies linearly with respect to moisture content and reduction in radial dimension of potato slices was around 35%. Porosity undergoes rapid increase after attaining certain moisture content in final stages of drying. The work was extended to study the influence of shrinkage and porosity on heat and mass transfer. Simulated results were validated with experimental values. This model can be employed to predict temperature, moisture, density profiles and to study shrinkage and porosity of various fruits and vegetables.
... The decrease in antioxidant activity observed is associated with the degradation of the main antioxidative compounds in strawberries and alterations to their chemical structures. Moreover, Jankovié (1993) reported that during air drying of strawberries, an 80.26% volume reduction was noted and the porosity increased dramatically when the water content was less than 3 g water /g ds (Tsami & Katsioti, 2000). These changes in the physical structure of the material increase its exposure to oxygen and its contact with components that degrade the bioactives responsible for antioxidant activity. ...
The thermal drying effects on strawberries were investigated in terms of the kinetics of antioxidant activity (AA), anthocyanins (A) and total phenolic compound content (TPC), as well as the final colour. The evaluated drying temperatures were 50 and 60 °C with an air rate of 1.5 m/s. The 2,2-diphenyl-2-picryl-hydrazyl, pH differential and Folin–Ciocalteu methods were used to assess the antioxidant properties. The kinetics of TPC and AA showed an initial and final period of degradation attributed to inhibition of enzymes. A plateau between these two periods suggests that under certain conditions of temperature and water content, no degradation reactions occurred. Final losses of up to 74, 45 and 78% were found for AA, A and TPC, respectively. The total colour change (ΔE) was lesser degree at 60 than 50 °C. Thermal degradation of the antioxidant compounds followed a first-order reaction kinetics and the degradation rate constants (k) were calculated.
... In addition, mulberry fruit was a solid system with cellular structure, the anthocyanins were enclosed in vacuoles, which was different with the disperse status of anthocyanins in the liquid. As the drying time prolonged and moisture content decreased, the cellular structure was gradually destroyed and the porosity was increased (Tsami & Katsioti, 2017). This may lead to the disparate degradation kinetic of anthocyanins in solid food system. ...
The aim of this study is to ascertain the degradation kinetic of anthocyanin in dehydration process of solid food system. Mulberry fruit was treated by hot air and vacuum drying at 60 and 75 °C. The contents of cyanidin 3-O-glucoside and cyanidin 3-O-rutinoside were determined by using high performance liquid chromatography. Kinetic and thermodynamic parameters were calculated for analysing the degradation characteristics. Model fitting results showed monomeric anthocyanin degradations were followed the second-order kinetic. Vacuum drying presented high kinetic rate constants and low t1/2 values. Thermodynamic parameters including the activation energy, enthalpy change and entropy change appeared significant differences between hot air and vacuum drying. Both heating techniques showed similar effects on polyphenol oxidase activities. These results indicate the anthocyanin degradation kinetic in solid food system is different from that in liquid and the oxygen can be regarded as a catalyst to accelerate the degradation.
... Important quality changes during drying mainly depend on the two parameters air temperature and drying time. The color for instance is subject to the drying conditions (Tsami and Katsioti 2000), with the temperature as highest impact parameter (Argyropoulos et al. 2011;Krokida et al. 1998;Mujumdar 2000). Color changes also depend on drying time (Arslan and Özcan 2011;Vega-Gálvez et al. 2012). ...
Besides energy efficiency, product quality is gaining importance in the design of drying processes for sensitive biological foodstuffs. The influence of drying parameters on the drying kinetics of apples has been extensively investigated; the information about effects on product quality available in literature however, is often contradictory. Furthermore quality changes obtained applying different drying parameters are usually hard to compare. As most quality changes can be expressed as zero, first or second order reactions and mainly depend on drying air temperature and drying time, it would be desirable to cross-check the results in function thereof. This paper introduces a method of quality determination using a new reference value, the cumulated thermal load. It is defined as the time integral of the product surface temperature and improves the comparability of quality changes obtained by different experimental settings in drying of apples and tomatoes. It could be shown that quality parameters like color changes and shrinkage during apple drying and the content of temperature sensitive acids in tomatoes vary linearly with the integral of product temperature over time.
... [14] Liquid displacement Samples are placed in a container with known volume liquid, volume is measured by displacement. [7,9,[15][16][17][18][19][20][21][22] Similar to the buoyancy force method, coating is necessary due to possible absorption of the material in the liquid. An estimation of bulk volume of pears using liquid displacement compared to dimensional measurements was performed by Guine et al. [7] Liquid displacement was found to be more accurate due to consistent replication. ...
The accuracy of imaging for bulk volume estimation of apple slices in the process of drying at temperatures from 40 °C to 80 °C was investigated and compared with physical caliper measurements. The initial hypothesis was to estimate bulk volume of cylindrically-shaped apple slices from diameter and thickness imaging. Imaging of diameter showed strong agreement with caliper measurements throughout the entire drying process, however imaging of thickness was not accurate due to the irregular shrinkage and bending phenomena. A linear model reflecting the relationship between diameter and bulk volume was developed and validated at temperatures of 40 °C, 60 °C and 80 °C. It showed good correlation between imaging diameter and bulk volume changes in the range of moisture contents from 9.1 g/g to 0.25 g/g. The relative percentage error of the prediction model was approximately 6.45%, which suggests that imaging can be used as a robust tool for bulk volume estimation of apple slices during convective drying.
... Conversely, other convective air-drying treatment reported scores lower than for control figs. Regarding color, the low scores obtained for some treatments such as E1 (40°C) and E3 (60°C) could be related to the negative effect of high temperatures on color and firmness parameters during the drying process, as described by other authors (Boudhrioua, Michon, Cuvelier, & Bonazzi, 2002;Demirel & Turhan, 2003;Tsami & Katsioti, 2000) due to the caramelization of sugar and Maillard reactions. Leitea, Mancinia, and Borges (2007) reported similar results for banana slices dried at 60°C and 70°C, resulting in a diminution of sugars due to these reactions. ...
The aim of this work was to study the effect of different drying systems on the quality characteristics of dried figs as an alternative to sun drying. Fresh figs were dried as follows: drying in a convection oven at different temperatures; pre-treatment by soaking in osmotic solutions at different concentrations; pre-treatment with K2CO3 + olive oil, combined or not with osmotic solutions; pre-treatments with ultrasound combined or not with osmotic solutions; sun drying (control). Moisture, water activity, microbial counts, firmness and sensory quality were measured at the beginning, at the mid-way and at the end points of the drying process. The figs dried with all the artificial drying systems tested needed between 1 and 3 days to reach the required moisture content of 24% wet basis (w.b.), while the sun dried figs needed 15 days to reach the optimal moisture. Regarding mold counts, firmness and sensory quality, the best results were observed for the treatments with ultrasound combined with osmotic solutions. Thus, this treatment could be a good alternative to the sun drying process.
... Different types of food materials, different varieties of the same species, and different degrees of maturity of the same variety have all been observed to give considerably different responses under identical drying conditions. Eventually, varying fi nal food Guiné ( 2006 ), Liu et al. ( 2012 ), Karathanos et al. ( 1996 ), , Vincent ( 2008 ), , , Martí et al. ( 2009), Yan et al. ( 2008, Tsami and Katsioti ( 2000 ), Boukouvalas et al. ( 2006 ), , Katekawa and Silva ( 2004 ), and Djendoubi Mrad et al. ( 2012 ) Water Content ...
The drying of an agricultural product affects its structural orientation because of the simultaneous transfer of heat and mass. Pore formation and evolution are among the important structural changes that occur during drying. However, the mechanisms of pore formation in food materials over the course of drying are very complicated because of the structural complexity of plant-based products. In general, the development of voids resulting from water migration and structural mobility is a more pronounced phenomenon causing pore formation and evolution during drying. This chapter lays out the theoretical mechanisms of pore formation and evolution and looks at how they are affected by food properties and drying conditions.
... Different types of food materials, different varieties of the same species, and different degrees of maturity of the same variety have all been observed to give considerably different responses under identical drying conditions. Eventually, varying fi nal food Guiné ( 2006 ), Liu et al. ( 2012 ), Karathanos et al. ( 1996 ), , Vincent ( 2008 ), , , Martí et al. ( 2009), Yan et al. ( 2008, Tsami and Katsioti ( 2000 ), Boukouvalas et al. ( 2006 ), , Katekawa and Silva ( 2004 ), and Djendoubi Mrad et al. ( 2012 ) Water Content ...
Drying causes severe structural changes in plant-based food materials owing to the simultaneous transfer of heat and mass. Pore formation is one of the critical structural changes that occur during drying. Pore characteristics affect heat and mass transfer mechanisms significantly. In addition to this, the degree of porosity of food materials notably influences the nutritional, sensorial, mechanical, and chemical quality of dried food products. This chapter presents the findings of research focusing on the effect of porosity on transfer mechanisms and other quality attributes of foodstuffs.
... The simultaneous transfer of heat and moisture during drying leads to local tension and shrinkage, which influences the texture of the dehydrated products. [35][36][37] Force-displacement data generated in compression and puncture tests of crunchy foods lead to mechanical signatures characterized by sharp force oscillations. In porous and brittle materials, penetration force fluctuates during breaking and crumbling of the wall structure. ...
This study is about how to control the microstructure of dehydrated banana during drying by a multi-flash drying process. The influence of different drying methods and process variables on the formation of fruit microstructure and texture were evaluated. These processes were: a conductive multi-flash drying process, conductive multi-flash drying combined with classical vacuum drying, convective drying in an oven, and vacuum drying. Density, porosity, and shrinkage of dehydrated fruit were strongly influenced by the drying process being applied. Results showed that it is possible to control the porous structure of dehydrated banana by choosing the correct dehydration process.
... Heat and mass transfer rate changes with reduction in area which is dictated by shrinkage pattern (May and Peree, 2002) and it increases with increase in average pore size (Karathanos et al., 1996). These events ultimately affect the structural, textural, and sensory quality of food, which determines its acceptance in market (Tasami and Katsioti, 2000). ...
Fruits and vegetables are porous in nature and undergo pronounced shrinkage during convective drying process. Therefore, shrinkage and porosity should be taken into consideration while predicting heat and mass transfer. This work was conducted to study shrinkage and porosity changes along with simultaneous heat and mass transport during the process. Potato slices were subjected to drying for 7 hours at 62°C. It was observed that shrinkage varies linearly with respect to moisture content and reduction in radial dimension of potato slices was around 35%. Porosity undergoes rapid increase after attaining certain moisture content in final stages of drying. The work was extended to study the influence of shrinkage and porosity on heat and mass transfer. Simulated results were validated with experimental values. This model can be employed to predict temperature, moisture, density profiles and to study shrinkage and porosity of various fruits and vegetables.
... Anthocyanins degradation may be modelled using the Arrhenius relationship (Ahmed et al., 2004). Tsami & Katsioti (2000) suggested that the colour of the dehydrated product can be predicted by controlling the process conditions. Other studies have reported anthocyanin degradation in cherries, cherry juice and jams, but the kinetic parameters have not been estimated (Forni et al., 1993;Kim & Padilla-Zakour, 2004). ...
Anthocyanins (ACY) and colour changes in cherry pomace under non‐isothermal processing were investigated. Pomace at moisture levels of 70% (MC‐70), 41% (MC‐41) and 25% (MC‐25) was heated at 126.7 °C in a retort for 25, 40 and 60 min. Total ACY, Hunter colour values, total colour difference (ΔE), chroma, hue angle (h°) and browning index (BI) were analysed. Thermal degradation kinetics for colour parameters were determined using zero‐ and first‐order models. ACY degradation increased with heating time and ranged from 34 to 68% for 25 and 60 min heating, respectively. The half‐life of ACY was 38, 33 and 27 min for MC‐70, MC‐41 and MC‐25 pomace, respectively. The ΔE increased with increasing heating time, whereas BI exhibited an inverse trend. Except for ΔE for MC‐70, the zero‐order kinetic model showed better fit (R 2 = 0.85–0.97) to experimental data than the first‐order kinetic model for Hunter colour b values and ΔE.
... OLIVEIRA, L. F. et al. www.ital.sp.gov.br/bj discutido por Tsami e Katsioti (2000), Demirel e Thuran (2003) e Leite et al. (2007). ...
Os frutos da jaqueira (Artocarpus heterophyllus Lam.) são consumidos na forma innatura pelas mais diversas camadas da população e sua alta perecibilidade leva a um índice elevado de perda pós-colheita, acarretando prejuízos para os produtores dessa frutífera. Sendo assim, o objetivo desse trabalho foi avaliar o efeito da temperatura de secagem (50, 60 e 70°C) e do teor de umidade final (20 e 25%) sobre as características químicas e sensoriais da jaca desidratada. Foram realizadas análises de matéria seca, cinzas, proteínas, lipídeos, carboidratos, além da avaliação sensorial. Os resultados globais obtidos mostraram que a jaca desidratada possui teor de matéria seca de 74,2 a 80,9%, cinzas de 3,1 a 3,8%, proteínas de 3,2 a 6,6%, lipídeos de 0,09 a 1,2% e carboidratos de 89,8 a 92,4%. A avaliação sensorial mostrou que o produto de maior aceitação (média de 5,95) foi aquele desidratado a 50°C e com 20% de umidade final, demonstrando que este pode ser uma alternativa alimentar para as regiões produtoras de jaca.
... The simultaneous transfer of heat and moisture during drying leads to local tension and shrinkage, which influences the texture of the dehydrated products. [35][36][37] Force-displacement data generated in compression and puncture tests of crunchy foods lead to mechanical signatures characterized by sharp force oscillations. In porous and brittle materials, penetration force fluctuates during breaking and crumbling of the wall structure. ...
The morphology of the drying front at pore-scale was studied to gain a better understanding of the mass transport mechanisms that occur at pore-level. Therefore, a glass micromodel was built using a photolithographic technique. Micromodels can be defined as transparent networks of pores (pore bodies) and constrictions (pore throat) that capture the complexities of natural porous media. The micromodel was saturated with distilled water and frozen at −85 °C and then put into a laboratory lyophilizer maintained at −42 °C. Pore-level distribution of ice and vapor as the mass transport process advances were reported. Ice distribution in the bidimensional porous medium was slightly influenced by pore structure disorder. Two different sublimation regimes were also observed (fast front advance and slow front advance). Preliminary results show that the drying front for the slow front regimes scaling over time with an exponent of 0.577.
... In this period, gradients of water are higher and also the diffusivity. Such behavior is largely published in drying works (Kouris & Vagenas, 1991;Tsami & Katsioti, 2000;Queiroz & Nebra, 2001;Krokida et al., 2003;Sacilik, 2007;Silva et al., 2008;Simioni et al., 2008).This can be corroborate by the parameter of experimental adjustment, k 1 (Table 1), which corresponds to a rate between ln(Y st /Y 0 ) and t and is presented in equation 3. Table 1 shows that the difference with respect to the shape is more evident at 70º C. Except for banana 'Prata' without blanching, the disk shape carried out to a higher k 1 . However, if the average standard error of the experimental values of Y is considered as 10%, the disk shape presented a significant higher drying rate for banana cv. ...
The influence of variables as temperature, solid shape, temperature, branching and cultivar on drying of bananas were studied. Bananas from cv. Prata and D'água, on disk and cylindrical shape, blanched or not, were dehydrated in a tray dryer in natural convection at 40 and 70 o C. Drying behavior was analyzed by using a mathematical model. The exponential model showed good agreement to experimental data (r 2 0.93 -0.99 and standard error: 0.01-0.05). Temperature presented positive influence on drying rate in all the tested conditions. With respect to the sample shape, the disk shape carried out to significantly higher drying rates only for D'água cultivar without blanching. Blanching was significantly influent, with positive influence, on drying rate of banana cv. Prata at 40º C. The influence of the cultivar did not present a defined tendency. Index terms: Fruit, dehydration, pretreatment. RESUMO No presente trabalho, estudou-se a influência de variáveis como temperatura, formato do sólido, branqueamento e cultivar na secagem de bananas. Bananas cultivares Prata e D'água, nos formatos disco e cilindro, branqueadas ou não, foram desidratadas em secador de bandejas com convecção natural nas temperaturas de 40 e 70 o C. O comportamento da secagem foi analisado utilizando– se modelagem matemática. O modelo exponencial mostrou bom ajuste aos resultados experimentais (r 2 : 0,93 -0,99 e erro de estimativa padrão: 0,01 -0,04). A temperatura apresentou influência positiva na taxa de secagem em todas as condições testadas. Com relação ao formato das amostras, o formato disco conduziu a taxas de secagem significativamente maiores somente para o cultivar D'água e sem branqueamento. O branqueamento se mostrou significativamente influente, com influência positiva na taxa de secagem da banana Prata a 40º C. A influência da cultivar não apresentou uma tendência definida. Termos para indexação: Fruta, desidratação, pré-tratamento.
... Through the appropriate selection of the right equipment and operating parameters, it is possible to generate products having different visual appearance (shape, color) and physical properties (physical state, porosity, density). [3][4][5][6][7][8] These properties will have a direct impact on the performance of the final product, e.g., flowability or dissolution time of powders. ...
In this contribution, we discuss a scientific approach to controlling the freeze-drying process in order to obtain products with desired attributes, using two examples.In the first part, the freeze-drying kinetics of a model food are recorded and represented using a state diagram, which was then used to optimize a strategy to preserve the physical structure and minimize the drying time of the product. The second part focuses on the application of freeze drying to produce amorphous sucrose coatings. In this study, model food materials have been coated with a liquid sucrose solution, and freeze-dried on a laboratory scale. The drying kinetics have been measured and plotted on a sucrose state diagram in order to optimize the process conditions and to minimize possible crystallization. Analysis of the physical state of the sucrose (using DSC, NIR, and microscopy) showed that a dominantly amorphous coating was obtained. Compared to a crystalline reference, the amorphous sucrose dissolved more quickly in a liquid, inducing a faster sweetness perception. This result also opens new opportunities for sugar reduction in food due to an enhanced sweetness perception.
In the context of post-harvest pest management in agricultural products, the adoption of modified atmospheres presents an eco-friendly alternative to conventional pesticides. This study focuses on nitrogen gas as a potential agent for insect control in stored commodities, utilizing computational simulations (by employing the convection–diffusion equation) to investigate its penetration and distribution within two common storage configurations: chamber-contained pallets and silos. The results highlight the influence of boundary conditions, commodity porosity, and convection effects on nitrogen dispersion. In chamber scenarios, the first boundary condition considers that pallets are placed inside a chamber with uniform (99.5%) nitrogen concentration, whereas in the second one, the concentration gradually increases from 78% to 99.5%. The average duration required for O2 concentration to reach 1% is approximately 10.7 h and 133.3 h for the two boundary conditions, respectively. Among the agricultural commodities, walnuts (kernels) exhibit the shortest duration, while prunes require the longest time. In silos, convection and diffusion interact to establish a consistent diffusion layer thickness. Most agricultural products exhibit similar behavior, with average times of 13.5 h, 25.4 h, and 37.0 h for three heights (10 m, 20 m, and at the silo’s top at 30 m), respectively.
In the context of post-harvest pest management in agricultural products, the adoption of modified atmospheres presents an eco-friendly alternative to conventional pesticides. This study focuses on nitrogen gas as a potential agent for insect control in stored commodities, utilizing computational simulations to investigate its penetration and distribution within two common storage configurations: chamber-contained pallets and silos. By employing the convection-diffusion equation, the simulations reveal insights into nitrogen distribution dynamics and duration required for oxygen reduction. The results highlight the influence of boundary conditions, commodity porosity, and convection effects on nitrogen dispersion. In chamber scenarios, boundary condition type significantly affects oxygen reduction time, while in silos, convection and diffusion interact to establish a consistent diffusion layer thickness. This research enhances the understanding of modified atmosphere techniques and their potential for sustainable pest management. It provides practitioners with valuable quantitative insights, paving the way for optimized modified atmosphere strategies in real-world agricultural contexts.
Ivy gourd with a good amount of potassium (K) and calcium (Ca) offers greater benefit to human health. Studying the drying mechanism of fresh ivy gourd is very important for subsequent processes and the quality of the product. The present study is intended to perform a mineral analysis (K and Ca), ash content and color parameter (L*, a*, b*, C*, H*, and whiteness and yellowness index) of solar‐dried ivy gourd. Drying experiments are performed in a single slope solar dryer and open sun drying. During the drying process, the temperature of the dryer is maintained from 45 to 75°C, undergoing forced convection drying (air velocity of 1 m/s). Fresh and dried ivy gourd samples had high amounts of Ca (379.26–4992.24 mg/kg) and K (330.63–14690.24 mg/kg). The highest mineral values were determined in the ivy gourd samples dried inside a forced convection solar dryer. Open sun (L*43.29, a*−0.57, b*16.78, C*16.78, h*88.05), natural convection (L*41.74, a*−1.74, b*15.82, C*15.98, h*83.54) and forced convection (L*41.72, a*−2.02, b*15.81, C*15.94, h*82.72) revealed better color values in the dried ivy gourd samples. The moisture is reduced from 93.5% to 10% wet basis in the natural and forced convection solar dryer within 9 and 6 h, whereas it took 10 h under open sun drying. Forced convection solar dryer dried the ivy gourd sample in a minimal time with better mineral retention and color parameter values when compared to natural and open sun‐dried samples.
Porosity is generally used to monitor the evolution of pore formation during dehydration. However, in some cases of dehydration, porosity could increase without involving pore formation, resulting in misleading interpretation. To avoid this misleading interpretation, this contribution suggests a new concept, which is the normalized air content (NAC). NAC is defined as the volume of air (mL) contained in a matrix per g of dry matter composing the same matrix. Based on this definition, it is possible to calculate the NAC using experimental data of porosity, bulk density, or volume reduction coefficient during dehydration. An extensive validation of this concept was performed by using experimental data. Porosity and NAC profiles as a function of moisture content were compared for some relevant cases. In addition, porosity and NAC values were calculated for more than 80 fresh and dehydrated products obtained by several research groups, diverse drying technologies, and under different operating conditions. The results revealed that, in several cases, porosity increases while NAC decreases. In 75% of the cases investigated, with the exception of freeze-drying technology, the NAC does not increase when the porosity increases. This analysis led to the conclusion that, in some cases, the increase of porosity may not be the consequence of pore formation within the dehydrated products but would rather be due to the removal of water during dehydration. The NAC profiles allowed distinguishing whether there is an actual pore formation within the food products investigated. One practical use of NAC is that it could be exploited to select promising technologies and/or drying conditions for producing porous products.
Moisture adsorption isotherms of the freeze-dried powders containing avocado, maltodextrin and inulin with different ratio, were determined using gravimetric static method of saturated salt solutions at 25 °C and the range of the water activity from 0.11 to 0.86. The data obtained were evaluated using sorption models: BET (Brunauer-Emmett-Teller), GAB (Guggenheim, Anderson and deBoer), Peleg, Lewicki, Oswin and Henderson. The goodness of the fit evaluated on the basis of criteria such as coefficient of the determination and root mean square values. Sorption isotherm of the pure avocado powder was III type while curves plotted for others powders showed sigmoid shape. It was found that the Peleg model was the most adequate for representation of the sorption data of all analyzed blends. In order to characterize the research material, chemical composition of the edible part of the avocado fruit was determined. Main component of the dry matter was fat.
Essentials & Applications of Food Engineering provides a comprehensive understanding of food engineering operations and their practical and industrial utility. It presents pertinent case studies, solved numerical problems, and multiple choice questions in each chapter and serves as a ready reference for classroom teaching and exam preparations.
The first part of this textbook contains the introductory topics on units and dimensions, material balance, energy balance, and fluid flow. The second part deals with the theory and applications of heat and mass transfer, psychrometry, and reaction kinetics. The subsequent chapters of the book present the heat and mass transfer operations such as evaporation, drying, refrigeration, freezing, mixing, and separation. The final section focuses on the thermal, non-thermal, and nanotechnology-based novel food processing techniques, 3D food printing, active and intelligent food packaging, and fundamentals of CFD modeling.
Features of this textbook:
Features 28 case studies to provide a substantial understanding of the practical and industrial applications of various food engineering operations.
Includes 178 solved numerical problems and 285 multiple choice questions.
Highlights the application of mass balance in food product traceability and the importance of viscosity measurement in a variety of food products.
Provides updated information on novel food processing techniques such as cold plasma, 3D food printing, nanospray drying, electrospraying, and electrospinning.
The textbook is designed for undergraduate and graduate students pursuing Food Technology and Food Process Engineering courses. This book would also be of interest to course instructors and food industry professionals.
Dehydrofreezing process involves water partial removal before freezing. This treatment has been proposed in order to reduce the negative impacts of conventional or even accelerated freezing, especially on the textural quality of high water content fruits and vegetables. Indeed, in such cases, freezing and thawing processes result in severe damage of the integrity of product’s cell structure due to the formation of ice crystals. For this purpose, quince fruits (7 g H2O/g db) were subjected to convective air drying of 40 °C and 3m/s to reach different water content levels of 2, 1, and 0.3 g H2O/g db. Freezing profiles obtained at various freezing rates (V1, V2, and V3) for different water contents allowed the main freezing characteristics such as the Initial Freezing Temperature (IFT), the Practical Freezing time (PFt), and the Specific Freezing time (SFt) to be assessed. The impact of freezing rate was important on PFt and SFt, and more pronounced for high water contents (W between 7 and 2 g H2O/g db (dry basis)). Furthermore, IFT decreased sharply when initial sample water content decreased. Indeed, it started at −0.8 °C for W = 7g H2O/g db, while it reached a value of −8.2 °C for samples of W = 1g H2O/g db. Since convective air drying normally triggers shrinkage which causes a detrimental deformation of fruit structures, instant controlled pressure drop (DIC) treatment was used to improve the texture and enhance the whole dehydrofreezing performance and the final frozen-thawed product quality. Moreover, DIC implied a slight increase of PFt compared to untreated ones. On the other hand, quality attributes were estimated through the assessment of thawed water exudate (TWE g H2O/100 g db), color and texture (maximum puncture force as index of firmness): freezing rate and water content had great impacts on TWE. Hence, the lower the water content, the weaker the TWE. Furthermore, the TWE of the pre-dried quince (0.3 g H2O/g db) had higher value for DIC-textured samples than for the un-treated ones. Indeed, DIC-texturing leads to a well-controlled structure expansion of the cell wall. These textural changes resulted in more lixiviation of residual water. Consequently, water becomes more available, hence more releasable after thawing. Finally, the partial removal of water by air drying before freezing remarkably reduced the negative impact of freezing/thawing processes on final quince color. Decisively, the firmness of quince fruit increased with the decrease of water content level.
Abbreviations: DMC: Dry Matter Concentration (%); DIC: Instant controlled pressure drop; W: Water content dry basis (g H2O/g db); IFT: Initial Freezing Temperature (°C); PFt: Practical Freezing time (min); SFt: Specific Freezing time (min); TWE: Thawed Water Exudate (g H2O/100 g db); L, a, and b: Color coordinates; (L): The degrees of lightness; (a) and (–a): The redness (a) or greenness (−a), respectively; (b) and (−b): The yellowness (b) or blueness (−b), respectively; ΔE*ab: Total color difference; L0, a0, and b0: Color coordinates of fresh or dried quince samples; SD: Standard Deviation; ANOVA: Analysis of variances; LSD: Least Significant Differences; cp: Specific Heat of the product depending on composition (dry material and water content)(KJ/kg K); cpd: Specific Heat of the dry material (KJ/kg K); cpW: Specific Heat of water (KJ/kg K); V1: Freezing rate without insulation; V2: Freezing rate with a food stretch film insulation with thickness e2 = 3 mm and thermal conductivity λ2 = 0.17 W/m K; V3: Freezing rate with a versatile flexible insulation (Armacell) with thickness e3 = 13mm and weak thermal conductivity λ3 = 0.036 W/m K; vd: Volume of dry material of quince sample (mm³); vH2O: Volume of quince sample water (mm³); vt: Total volume of quince sample (mm³); e0: Quince sample thickness (mm); e2: Insulation thickness in the case V2; = 3 mm; ; e3: Insulation thickness in the case V3; = 13 mm; ; λ0: Quince sample conductivity (W/m K); λ2: Insulation conductivity in the case V2; = 0.17 W/m K; ; λ3: Insulation conductivity in the case V3; = 0.036 W/m K; λd: Conductivity of quince sample dry material (W/m K); λH2O: Conductivity of water (W/m K); λequiv: Equivalent conductivity of quince sample versus water content (W/m K); mi and mf: Weights of the frozen and thawed samples, respectively
Vacuum frying of fruits enables frying at lower temperatures compared to atmospheric frying, thereby improving quality attributes of the fried product, such as oil content, texture, retention of nutrients, and color. Producing high-quality vacuum-fried fruit is a challenge, especially because of the high initial water content of fruits that requires long frying times. Factors influencing vacuum-fried fruit quality attributes are the type of equipment, pre-treatments, processing conditions, fruit type, and fruit matrix. Pre-treatments such as hot air, osmotic drying, blanching, freezing, impregnation, anti-browning agents, and hydrocolloid application strongly influence the final quality attributes of the products. The vacuum-frying processing parameters, namely frying time, temperature, and vacuum pressure, have to be adjusted to the fruit characteristics. Tropical fruits have different matrix properties, including physical and chemical, which changed during ripening and influenced vacuum-fried tropical fruit quality. This paper reviews the state of the art of vacuum frying of fruit with a specific focus on the effect of fruit type and matrix on the quality attributes of the fried product.
This chapter reviews the production and consumption, postharvest physiology, storage and shelf-life, physicochemical and nutritional characteristics, as well as the major value-added products made from avocado. Avocado has healthy lipid composition. In addition, it is rich in minerals, vitamin E, and health promoting phytochemicals. Avocados have a long history of production and consumption, especially in Mexico, and North and Central America. Avocados are commercially grown by grafting. The three major races have different growing conditions and characteristics, which are stated as follows: Mexican race; Guatemalan race; and West Indian race. To enhance shelf-life, most producers size avocados by weight or separate by firmness. It is important to sort avocados in lots of different ripening stages and employ postharvest measures to extend shelf-life and quality, as ethylene production from some avocados in a lot can trigger ripening that, once initiated, is hard to stop.
The simultaneous transfer of heat and mass significantly affects the mechanical and physicochemical properties of food materials. Pore formation is an important structural change that takes place during drying. The degree of porosity depends on the properties of the food materials and drying process conditions. The material composition, fresh structure, moisture size, and shape of the sample are the critical material characteristics that significantly affect pore formation during drying. In addition, drying process parameters, such as temperature, pressure, coating treatment, noticeably influence structural changes over the course of drying. This chapter is concerned with the effects of material properties and drying process parameters on pore development during the drying process. Following this is a discussion of the pattern of pore formation during five major types of drying process.
In the present investigation, the drying kinetic of Erythroxylum minutifolium Griseb leaves was studied. The milling leaves were dried in a tray dryer at selected temperatures (50-70°C), air flow speed (2-4 m/s) and bed depth (10-20 cm). The sorption isotherm of the fresh product was mathematically described by the Guggenheim, Anderson and de Boer (GAB) model, giving as a result monolayer moisture of 0.23 g /g d.b. The results indicated that the drying process takes place in the falling rate period and both the bed depth and the temperature of air are the parameters with most influence in the drying of E. minutifolium leaves. The diffusivity coefficient increased with the temperature from 4.30-5.56 10 -07 m 2/s, for a range of temperatures between 50 and 70°C, with an estimated activation energy of 204.13 kJ/mol. Three equations were used for modelling of drying kinetic of leaves. The Page's model was found the best to fit of the data, showing that this equation correctly simulates the E. minutifolium leaves dehydration process and represents an excellent tool for estimating its drying time.
In the present work, the mass transfer characteristics, namely moisture diffusivity and moisture transfer coefficient, of passion fruit peel were evaluated using the analytical model proposed by Dincer and Dost. Passion fruit peels were dried in a single layer at different temperatures (50, 60, and 70 °C) and air velocities (2.0 and 3.5 m/s). The results showed a reasonably good agreement between the values predicted from the correlation and the experimental observations. The Biot number, effective moisture diffusivity, and mass transfer coefficient were computed and ranged between 0.1018 and 0.3199, 0.632 × 10−8 and 1.994 × 10−8 m2/s, and 4.53 × 10−7 and 8.702 × 10−7 m/s, respectively.
In this research the effect of drying condition on optical properties of apple slices was investigated. Hunter values (L, a, b) were used to measure the color parameters. Effect of various coating materials such as Carboxymethylcellulose (CMC), Starch and Pectin and drying condition including microwave treatment in presence of coating materials on optical properties with respect to microstructural changes, was studied. Some of microstructural properties and its effects on optical properties were discussed. So scanning electron microscopy (SEM) technique were used to analyze the effects of these processes on microstructure. Color changes values including total color difference (ΔE), and browning index (BI) were measured. Results showed that optical properties of samples were affected by drying condition and coating material. So that coated samples by pectin had a lower L and higher BI, but different results in presence of starch were achieved. Microwave treatment in presence of appropriates coatings could improve optical properties of dried slices.
High-temperature and short-time pre-drying followed by vacuum drying was carried out in order to dry carrot slices. In a pre-drying process, a central composite rotatable design was tested where drying air temperature (114–156C) and time (540–1,740 s) were independent variables of effective diffusivity, and water activity and rehydration capacity were dependent variables. Then absolute pressure (0.09 MPa) and drying temperature (70C) were kept constant. For rehydration capacity optimal conditions, the color and β-carotene degradation were evaluated and compared with fresh samples. The effective diffusivity values with and without shrinkage effect ranged from 5.37 × 10−12 to 6.55 × 10−11 and from 8.50 × 10−12 to 8.44 × 10−11, respectively. Water activity of dried products ranged from 0.39 to 0.44 and rehydration capacity between 58.16 and 84.40%. Dried carrot brightness values were noticed to be lower than those of fresh samples, besides the reduction of red and yellow values. The β-carotene degradation was also observed.Practical ApplicationsIn studying the drying process of biological materials, the shrinkage effect must be analyzed for a better understanding of transport phenomena. For processed products, the knowledge of shrinkage, water activity, rehydration capacity as well as property changes (color and β-carotene) caused by drying process is very important. These properties can provide an important information set to determine the process conditions in order to obtain a good quality of food, as well as their characterization and stability prediction.
The acceptance of processed or minimally processed food products by consumers is highly dependent on several quality and nutritional attributes as well as their organoleptic characteristics. Shelf-life is an additional factor that influences consumer behavior. Moreover, consumers now demand high-value food products that are healthier and have high nutritional value. The quality, nutrition level, and perception of processed foods is governed, among other attributes, by the structure of the dried product. Hence, examination of the structure of dried foods is of significant importance. Dehydration methods have a great impact on the structural properties of most food products. The effect of various dehydration methods on shrinkage and porosity of dried foods is discussed in this article following a comprehensive review of the available literature. Novel drying processes and combination of various conventional drying methods are discussed with regard to their expected impact on food structure. Finally, aspects of food formulation during diverse drying processes and recommendations for future research are presented.
Vacuum dehydration technique (VDT) is known as a rapid evaporative technique for moist and porous solid products. Known advantages of VDT is short processing time, extension of products shelf life and improvement of product properties related to quality and safety issues. In this study, animal feed wheat-based diets with different particle size distributions, ground by hammer-mill, through 1, 3 and 5 mm screen size was manufactured through different pellet-die hole diameters (2, 3.5 and 5 mm). Moisture was removed by traditional air dehydration technique (ADT) or VDT. Measuring the dry matter was done immediately after the dehydration of feed pellets. Pellet durability index (PDI %) and hardness analysis were done 30 days after the dehydration. Successive dynamics of water loss performed better while using the VDT compared to ADT, where VDT appeared to reach the industrial moisture equilibrium much faster. It was not observed a clear pattern of influence on dehydration efficiency of different feed structure represented by particle size distribution. The volume increase of the product was confirmed to have negative influence on moisture removal from feed pellets when conventional ADT was used, whereas no clear outline was confirmed for VDT. This indicated that an increase of feed pellets diameter can limit the moisture removal using both VDT and ADT. The VDT demonstrated positive influence on PDI when compared to traditional ADT. Pellet hardness analysis did not show a clear influence of the different dehydration techniques on manufactured feed solids.
The drying kinetics of four varieties of chillies (Pb-Lal, Pb-Guchhedar, Pb-Surkh, and CH-1) was studied. The chillies (pricked and unpricked) were pretreated in the dip sol solution. The treated chillies were dried in an automatic weighing experimental dryer at selected temperatures (45°, 50°, 55°, 60°, and 65°C). The results indicated that drying took place in the falling rate period. Out of three models considered, Page's model was found to be the most suitable for describing the drying behavior of chillies. The dependence of drying constant on temperature was analyzed using an Arrhenius equation. The variety Pb-Lal has the maximum value of activation energy (42.59 kJ/mol), which is also reflected in the reduced drying time for this variety. The results of quality studies of dried chillies in terms of capsaicin content and coloring matter indicated that the Pb-Lal variety had acceptable capsaicin content of 532.08 µg and coloring matter of 73.8 ASTA.
An understanding of the sorptional equilibrium of food systems is an important objective in food engineering. In particular, a knowledge of the equilibrium characteristics of foodstuffs is an essential prerequisite for interpretation of the mass transport phenomena during drying. The equilibrium moisture content of a food system is developed as a result of the interaction between the material and the environment. A standard static gravimetric technique was adopted to evaluate the moisture sorption characteristics of the model food gels. The high-starch systems displayed Type II isotherm characteristics, while the high-sugar systems presented Type III behaviour. Adequate quantitative evaluation of the sorption characteristics was realized on the basis of the Guggenheim-Anderson-de Boer model.
The effect of drying method on bulk density, particle density, specific volume and porosity of banana, apple, carrot and potato at various moisture contents was investigated, using a large set of experimental measurements. Samples were dehydrated with five different drying methods: conventional, vacuum, microwave, freeze and osmotic drying. A simple mathematical model was used In order to correlate the above properties with the material moisture content. Four parameters with physical meaning were incorporated in the model: the enclosed water density pw, the dry solid density ps, the dry solid bulk density pbo and the volume shrinkage coefficient β'. The effect of drying method on the examined properties was taken into account through its effect on the corresponding parameters. Only, dry solid bulk density was dependent on both material and drying method. Freeze dried materials developed the highest porosity, whereas the lowest one was obtained using conventional air drying.
The effect of drying conditions on color changes of apple, banana, carrot and potato during conventional and vacuum drying was investigated. The Hunder color scale parameters redness, yellowness and lightness were used to estimate color changes during vacuum and conventional drying at 50, 70 and 90°C. Air humidity during conventional drying was regulated at 15, 30 and 40%. Air temperature and humidity affected redness and yellowness, but not lightness. A first order kinetic model was fitted to experimental data adequately for both redness and yellowness. The rate of color deterioration was found to increase as temperature increased and air humidity decreased, for both drying methods and all the examined materials.
Four mathematical models, describing the moisture transfer during Virginia tobacco curing under varying air-temperature and humidity were tested using experimental data from an industrial dryer.The model, based on the assumption that the major resistance to moisture transfer is at the air boundary layer and that the driving force is the water activity difference, was found to be the most accurate. The appropriate mass transfer coefficient was determined.An empirical equation, predicting the equilibrium moisture content of Virginia tobacco as a function of temperature and water activity of the surrounding air, was proposed and experimentally tested.
Drying kinetics of four Fruits (namely, apple, pear, kiwi and banana) were studied by introducing an one-parameter empirical mass transfer model, involving a characteristic parameter (drying constant), as a function of process variables. The model was tested with data produced in a laboratory dryer, using non-linear regression analysis. The investigation involved a wide range of characteristic dimensions of samples and air conditions (temperature, humidity, and superficial velocity). The parameters of the model considered were found to be greatly affected by sample characteristic dimension and air temperature. The model also involved the equilibrium material moisture content which was formulated in the form of the GAB equation. Its parameters were evaluated by means of non-linear regression analysis to independent experiments covering two process variables (temperature and water activity of the surrounding air).
The effect of drying conditions, namely, microwave power, vacuum pressure, as well as sample geometry, on the drying kinetics and rehydration characteristics of five microwave vacuum dehydrated fruits (apple, avocado, mushroom, pear and strawberry) was studied. The investigation involved a wide range of microwave power, vacuum pressure and sample size levels. The drying rate and the rehydration ratio, a measure of rehydration characteristics, were found to depend on the drying conditions. An empirical mass transfer model, involving a characteristic parameter for each process (drying and rehydration( as a function of process variables, namely, microwave power, vacuum pressure and sample size, was also tested with the data obtained in a microwave oven equipped with vacuum apparatus. Furthermore, a comparison of rehydration properties of microwave vacuum and conventionally dehydrated products, was conducted.
Bulk density, particle density, shrinkage and porosity were experimentally determined at various moisture content during air drying for apple, carrot and potato cubes. A simple mathematical model was used to predict the above properties versus material moisture content. Four parameters were incorporated in the model: enclosed water density, dry solids' density, bulk density of dry solids, and volume-shrinkage coefficient. The model was fitted to experimental data satisfactorily, and the parameters were estimated. The influence of varying drying conditions was also investigated.
Shrinkage of rectangular slabs of squid flesh during air drying at 70°C and 15% relative humidity was determined. A material balance equation considering dry fibre, water and air phases can predict the bulk shrinkage and apparent density of squid flesh.
Dependable data on bulk density, volumetric shrinkage due to water loss and porosity are needed to model processes such as drying, packaging and storing. Experimental data are presented for all three properties. It is possible to model the water-loss-based bulk shrinkage coefficient to obtain a predictive equation based on composition of the foodstuff. From this, a generalized correlation is obtained which predicts bulk shrinkage coefficient knowing only the initial moisture content of the food. Porosities for the foodstuffs considered can be predicted through suitable correlations, but there is no generalized equation spanning all foods.
SUMMARY—The method of drying apple and potato affects primarily the rate of sorption of water of the dehydrated product, and to a lesser degree the equilibrium isotherms. The freeze-dried products adsorbed more water vapor than the puff-dried and air-dried materials. The apparent diffusivity of water vapor was considerably higher in the freeze-dried samples than in the air-dried materials. In puff-dried samples, the diffusivity had an intermediate value. The diffusivity in freeze-dried apple and potato decreased at higher relative humidities, and the effect was opposite in air-dried samples.
Moisture sorption isotherms of dried fruits [Sultana raisins, Corinthian (black) currants, figs, prunes, and apricots] were determined at 15, 30, 45, and 60°C, using the standard static gravimetric method developed by the European Cooperation Project COST 90. Experimental curves showed an inverse effect of temperature at high moisture content due to high sugar content of dried fruits. The hysteresis between adsorption and desorption was verified experimentally. The GAB equation was used to predict experimental data for water activity range 0–0.95.
Pectin-sugar gels were dehydrated with four different drying methods: freeze, microwave, vacuum and conventional drying to a moisture content of about 5%. The effect of the drying method on the water sorption properties of dehydrated products was evaluated at 25 °C. Freeze-dried gel adsorbed more water vapour than microwave-dried gel, which had a higher sorption capacity than vacuum- and conventional-dried product. The sorption isotherms were in agreement with the reported shape for high sugar foodstuffs. Three different equations proposed in the literature (GAB, Oswin, Hasley) were used to fit the sorption data. The GAB equation gave the best fit to the experimental data. The porosity of the dehydrated products depended on the drying method, ranging between 0.2 and 0.5. Freeze- and vacuum-dried pectin developed the highest porosity, whereas the lowest porosity was obtained using conventional and microwave drying. Hunter colour parameters (L, a, b) also depended on the drying method. The colour of freeze- and vacuum-dried pectin was close to that of commercial pectin, while the colour of the conventional- and microwave-dried product changed significantly.
Three cookies and two corn snacks were analyzed for major components and their moisture adsorption characteristics were evaluated at 25, 35 and 45 °C. The main composition differences were in fat and total carbohydrate content. The isotherms of each product were different (p < 0.05) and significantly affected by temperature. The mathematical description of the adsorption data was obtained applying some of the most common sorption equations. Peleg's model gave the best description of the experimental data, followed by GAB equation. The mean relative deviations for Peleg's equation were higher as the temperature increased and varied from 2.81 to 10.60%. Monolayer moisture content evaluated with BET and GAB models were in general lower for the cookies. The maximum net isosteric heats of adsorption were lower than 11 kJ/mol.
The equilibrium moisture content of potato, carrot, tomato, green pepper and onion was determined within the range of 10 to 90% water activity at three different temperatures (30, 45 and 60°C), using the standard static gravimetric method developed by the European Cooperation Project COST 90. The GAB equation was fitted to the experimental data, using the direct nonlinear regression analysis method and the agreement between experimental and calculated values was satisfactory. The net isosteric heat of desorption of water was determined from the equilibrium desorption data, using the Clausius-Clapeyron equation. An empirical exponential relationship between the net isosteric heat of sorption and the moisture content was proposed and validated.
The colour change in concentrated apple, peach and plum pulp due to extended heat treatment was investigated. Colour differences (ΔE) and Hunter L parameters were used to estimate the severity of damage during heating of the fruit pulp at 56, 66, 80 and 94 °C for 700 min. The results indicate apparent first-order kinetics. Hunter a and b and CIE x and y parameters provided information on changes in chromatic attributes after severe heat treatment. The analysis of data concerning the rate of colour deterioration in concentrated fruit pulps as a function of temperature suggests that more that one mechanism is involved.
Drying of carrots. Drying Models, Drying Technology
- A Mulet
- A Berna
Mulet, A,, Berna, A. and Rosello, 1989, Drying of carrots. Drying Models, Drying Technology, 7 (3). pp. 537 -557