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Densities, shrinkage and porosity of some vegetables during air drying
Drying Technology
Abstract
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.
... It has been also observed that, irrespective of the drying method used, the apparent density of apple decreased with decrease in moisture content. In the case of garlic [6], potato and carrot [7], the apparent density values were found to increase with the removal of water during drying. ...
... The porosity of a material may affect the diffusion coefficient, the rehydration rate and the final moisture content after rehydration, adsorption or absorption [5]. Krokidaet et al. [5], Zogzas et al. [7], Witrowa-Rajchert and Rząca [1] observed a noticeable increase in apple porosity during drying. On the contrary, almost fruits and vegetables developed low porosity values during drying such as garlic [6], carrots and potatoes [7], banana, pineapple and mango [9]. ...
... Krokidaet et al. [5], Zogzas et al. [7], Witrowa-Rajchert and Rząca [1] observed a noticeable increase in apple porosity during drying. On the contrary, almost fruits and vegetables developed low porosity values during drying such as garlic [6], carrots and potatoes [7], banana, pineapple and mango [9]. The porosity of apple depends strongly on the drying method used. ...
The evolution of physical properties (shrinkage, density and porosity) of cylindrical shaped apple samples (Golden Delicious) during convective drying was investigated. For this purpose, the weight and the dimensions (diameter, height) of apple samples were monitoring at regular time intervals of the drying process. A constant drying rate period was not detected although considering the reduction of the exchange surface area. Apple exhibited a clear anisotropy behavior of the shrinkage coefficients. The volume shrinkage of apple samples showed a linear relationship with moisture content (R2 = 0.996). A theoretical relation between the surface ratio and the volume ratio was determined (R2 = 0.956). During drying process, the apparent density of apples decreased with decrease in moisture content following a second-degree polynomial curve (R2 = 0.991), whereas the true density aggrandized with removal of water. The porosity of apple samples was showed to increase as drying progressed. At the starting of the drying process, the porosity changes resulted from the reduction of the total volume. Then, the porosity changes during drying were found to be a consequence of a loss of water and a simultaneous reduction of gaseous volume.
... [13,14] Several researchers proposed mathematical expressions to predict the porosity of food materials as a function of the moisture content. These models can be grouped into two categories: (i) theoretical models that are built based on the understanding of the fundamental physics and mechanisms that may be involved in pore formation, [15][16][17] and (ii) empirical models that are built by fitting the model's parameters to the experimental data [18][19][20] . The majority of the previous studies regarding shrinkage are either experimental or empirical; however, such studies cannot provide a realistic understanding of the physical phenomena behind the material shrinkage. ...
... As shrinkage coefficient is not constant, real time experimental values are required for this model. Zogas et al. [16] e ...
... Based on the moisture content and temperature, effective diffusivity (D eff ) can be expressed as the function of both temperature and moisture (db) as presented in Equation (16). ...
Pore formation and evolution is a common physical phenomenon observed in food materials during different dehydration processes. This change affects heat and mass transfer process and many quality attributes of dried product. Many mathematical models ranging from emperical to classical models proposed in the literature for predicting porosity during drying of food materials. Classical model is in its infancy as the required materials properties during drying are not avaiable for the material charecterisation. Empirical and semi-empirical models are reasonably well developed in establishing relationships between pore evolution and moisture content and determining experimental based coefficients. However, there are no simplistic models that considered process conditions and material properties together to predict the porosity. The purpose of this work is to develop a simplistic theoretical model for pore formation taking both process parameters and changing material properties during drying into consideration. A new “shrinkage velocity” approach has been introduced and the model has been developed based on this shrinkage velocity taking into account the main factors that influence the porosity including the glass transition temperature. Experimental results show good agreement with simulated results and thus validated the model. This study is expected to enhance the current understanding of pore formation of deformable materials during drying.
... Volatile compounds were also reduced in dried parsley (Diaz-Maroto et al., 2002). Shrinkage, density, porosity, and rehydration ability of dried vegetables are among the most studied physical indicators of quality (Lozano et al., 1983;Madamba et al., 1994;Zogzas et al., 1994;Krokida et al., 2003;Martynenko, 2011;Lopez-Ortiz et al., 2013). Color of vegetables is recognized as one of the key indicators of quality for carrot (Lin et al., 1998;Prakash et al., 2004;Zielinska & Markowski, 2012), potato (Krokida et al., 2001;Pedreschi et al., 2006;Wang et al., 2010), onion (Mongpraneet et al., 2002;Arslan & Özcan, 2010), pepper (Vega-Gálvez et al., 2009;Guiné & Barroca, 2012), pumpkin (Guiné & Barroca, 2012), parsley (Soysal, 2004), and dasheen leaves (Maharaj & Sankat, 1996). ...
... However, it was found that monitoring of product quality in real-time manner allows optimization of drying process with respect to quality (Martynenko & Yang, 2007;Jin et al., 2014). Wang and Xi (2005) Rehydration ratio, quality Slices Nahimana and Zhang (2011) Color, shrinkage Cubes Zogzas et al. (1994) Shrinkage, porosity, density Cubes Zielinska and Markowski (2012) Color, carotene Discs Lewicki and Duszczyk (1998) Color Cylinders Krokida et al. (1997) Color Cylinders Lozano et al. (1983) Density, shrinkage, porosity Cylinders Marabi et al. (2006) Rehydration, flavor, texture Whole Krokida et al. (2003) Diffusivity Tomato Slices Davoodi et al. (2007) Rehydration, color Cuts Toor and Savage (2006) Antioxidants, color ...
Computer vision for industrial control has been developed since the early 1980s, mostly for robotic applications. Some of the motivations for using computer vision in the industrial workplace included automated visual inspection and robot vision. Recent advances in computer and digital processing technologies have made it available for food and agricultural applications.
... La densidad aparente de los granos fue determinada aplicando el método de desplazamiento de líquido descrito por Zogzas et al. (1994). En la Fig. 1 se muestra el instrumento utilizado para esta medición; el cual es una réplica de elaboración propia, del instrumento descrito por dichos autores. ...
... El procedimiento de medición (Zogzas et al., 1994) consistió en agregar un volumen previamente establecido de agua en el compartimento para la muestra ( Fig. 1). Luego se introdujo una muestra de granos previamente pesada (masa cercana a los 10 g), mgrano. ...
Se estudió el comportamiento fluidodinámico de cuatro granos (sorgo, frijol, arroz y maíz) en dos secadores de escala de laboratorio: uno de lecho fluidizado y otro de lecho de chorro. Los secadores consistían en una columna de plástico transparente a la cual se adaptaron dos bases diferentes, una para cada secador, conectado a un ventilador. Adicionalmente, se determinaron experimentalmente las propiedades físicas (diámetro, esfericidad y densidad aparente) relacionadas con la fluidización como función de la humedad del grano. Además, se calculó la porosidad del lecho para cada uno de los granos a su máxima humedad. Solo fue posible fluidizar los cuatro granos en el lecho de chorro. Este estudio fluidodinámico es el primer avance en cuanto a la determinación de las propiedades físicas y de fluidización de los granos más consumidos en Nicaragua.
... The effect of sample compactness on shrinkage is not conclusive as the elaborate varieties of foods. The pattern of shrinkage varies with change of sample varieties [11,12]. ...
... Different types of plant-based food materials like Brinjal, Carrot, and Radish were collected from the local market in Rajshahi, Bangladesh. The initial moisture content of the fresh food materials was measured by oven drying method [12]. The initial mass of the Brinjal, Carrot and Radish samples were about 4.5 gm, 9 gm, and 8.5 gm respectively. ...
The shelf life of food materials can be extended by removing water through heat and mass transfer phenomena which is known as drying. Along with taking immense energy, food quality deteriorates significantly throughout drying. Literature depicts that both drying conditions, as well as food properties, affect the degree of quality degradation. Although extensive research has been carried out on the effect of drying conditions on drying kinetics and quality, minimal study exists which adequately covers the effect of sample compactness on mentioned consequences. To attain a correlation between sample geometry and quality aspect, three typical shapes with constant volume of selected food materials have been investigated in this study. The colors and aesthetic appearance are also viewed in this experiment. With the variation of sample geometry, the overall food quality during drying of Brinjal, Carrot, and Radish varies significantly. Minimum quality deterioration was occurred for sliced samples of selected food materials; whereas, cylindrical-shaped samples deteriorate significantly higher than other samples. It can be concluded that sample compactness remarkably affects food quality and energy consumptions.
... It is worth noticing that, after the DIC texturing, since the drying occurred close to or within the vitreous step, shrimps did not shrink as stated by Ratti. [49] Since the most key physical, functional, and sensorial properties of dried food products are expressed through the specific density q spec and porosity u, [50] IMAD and DIC-IMAD processes were studied under these response parameters. Figure 3b allows noticing the weak impact of microwave power density level _ } and the dramatically high effect of DIC saturated steam pressure and processing time (P, t) on q spec and u of shrimp snacks. ...
... It is worth specifying that by increasing _ } to 12 and even 24 W/g wb, coupled to the most severe DIC conditions, q spec decreased between 97 and 130 kg m À3 , respectively. This means even less shrinkage [50] with a statement more concordant with the behavior reported by Devahastin et al. [51] for carrot dried by low pressured superheated steam. ...
Effects of operating parameters of the instant controlled pressure drop (DIC) texturing process followed by intermittent microwave (MW) and airflow drying were studied for the manufacture of novel swell-dried shrimp snacks. The DIC processing parameters were the absolute pressure of saturated steam (P ¼ 0.4, 0.55, and 0.7 MPa) and the treatment time (t ¼ 70, 100, and 130 s). Intermittent MW drying with active time t ON of 30 s and tempering time t OFF of 60 s followed DIC-texturing of blanched shrimp samples (30 g cubes of 1 cm 3). The MW density power _ } levels tested were 6, 12, and 24 W/g wb (wet basis). The airflow condition was fixed at 3.2 m/s, 20 C, and 276 Pa water vapor pressure. Drying performance along with the organoleptic, structural, and functional quality parameters was measured for the dried product. The results showed that the highest DIC processing parameters of P ¼ 0.7 MPa for 170 s were the best texturing conditions, while the MW power level of 24 W/g wb yielded the most effective drying performance when 90% of moisture was removed in 10 min, with organoleptic quality attributes and structural properties better than those of conventionally dried shrimp. Furthermore, the aroma was better preserved, and the exceptionally high absolute expansion ratio (Ɛ abs ¼ 13.84) and porosity (u ¼ 92.83%) allowed enhancement of the desired crispness of the snacks as well. The highly porous microstruc-ture also results in improved rehydration performance. ARTICLE HISTORY
... For larger size, the number of fish in the tray is smaller. This phenomenon resulted in an increase in density with weight loss, as expected from the literature (Karathanos et al., 1996;Zogzas et al., 1994). In observing the interaction of the catfish size mixture design with the loaded fish, it was observed that with low water content, a significant weight loss relative to the volume of the tray was noted. ...
... In observing the interaction of the catfish size mixture design with the loaded fish, it was observed that with low water content, a significant weight loss relative to the volume of the tray was noted. Several authors (Zogzas et al., 1994;Wang and Brennan, 1995;Krokida and Maroulis, 1997) observed an increased density, because agricultural products lose water during drying. Wang and Brennan (1995) also explained this as a consequence of shrinkage reduction in the final stages of drying. ...
Fish smoking is widely used in the fish processing industry, especially in the post-harvest catfish product due to its simple operating technique. The objective of this study was to optimise the tray loading capacity of a smoking kiln for catfish. A mixture design was employed to investigate the effects of varied fish size (0.25, 0.30 and 0.35 kg) component tray loading on the loading capacity, drying rate and moisture ratio during smoking process. The results showed that the loading capacity of the kiln was between 190 and 198 pieces of fish at minimum and maximum 50 and 52 kg. High moisture ratio was observed at equal size combination at low drying rate. The catfish weight mixtures of 0.25, 0.30 and 0.35 kg used to evaluate the kiln load capacity optimization were significant ( P < 0.05). The smoking kiln worked optimally at catfish size (50, 50 and 0 %) with maximum desirability of 0.63 resulted in weight of fish loaded of 51.30 kg, moisture ratio of 0.21 and drying rate of 0.5 kg ⁻¹ h. This study brings new knowledge about the loading capacity and confirms that the smoking kiln is an acceptable technology for processing fish.
... Process flowchart for iron fortification of fresh-cut French beans using VI m i -mass after VI. Shrinkage (S) was determined by the method suggested by Zogzas et al. (1994). Length (L) and diameter (D) of the cut beans were determined by a vernier caliper (Mitutoyo, Japan) and the volume of the fresh (Vf) and vacuum impregnated (Vi) beans was calculated. ...
The present study was carried out to enhance the iron content of the fresh-cut French beans through vacuum impregnation (VI). For fortification, five iron salts, namely, ammonium ferrous sulphate, ferrous sulphate, ferric pyrophosphate, anhydrous ferric chloride and ferric ammonium citrate were tested as fortificant. Fresh-cut green French beans were dipped in variable concentrations (0.025%, 0.05% and 0.1%) of the iron salts for imbibitions at different time periods (5, 10 and 15 min) under atmospheric pressure. On basis of least colour change and maximum iron absorption, ammonium ferrous sulphate at 0.025% was selected for further study. For VI, different levels of vacuum pressure (50, 75 and 100 mmHg), vacuum time (5, 10 and 15 min) and ascorbic acid (0, 0.5 and 1%) were evaluated for iron impregnation through Box-Behnken design. Maximum iron infusion in fresh-cut beans was achieved at 50 mmHg vacuum pressure, 6 min vacuum time and 0% ascorbic acid. At optimized condition, iron content of the bean increased by 64.05%. The infused beans were stable for a week at 6 ± 1 °C without any discolouration and were microbiologically safe for consumption. Overall, the present study demonstrated that VI has the potential to develop iron fortified fresh-cut ready-to-use French beans.
... High shrinkage is a result of extremely distorted and dehydrated cells, which could explain increased water loss and decreased solid gain [58,59]. However, some studies show that shrinkage is proportional to the water loss during the drying process, which is in agreement with the findings of our study [59,60]. Sample 2 (67.76 ± 0.271 %) shrank more than sample 4 even before the drying stage, and sample 2 will continue to shrink more after drying. ...
The increasing global demand for tropical fresh cut products is driven by their convenience, quality, and health benefits, highlighting the need for effective preservation methods. Pineapple slices were treated with antioxidant solution, osmodehydrated (OD) and edible sodium alginate coating was applied in different methods to investigate the effect of edible coating on osmotic dehydration, convection drying phenomena, and quality parameters of dried pineapple slices. The findings showed that edible coatings influenced drying kinetics and physicochemical properties of pineapple slices. The optimal drying temperature was identified as 60 °C, while color degradation occurred at 65 °C. Pineapple slices treated with sodium alginate after OD required the highest activation energy (65.93 kJ/mol) for moisture diffusion. Coatings enhanced ash content and moisture retention while reducing shrinkage and improving the rehydration ratio, vitamin C, and total phenolic content (TPC). Sensory assessment indicated improvements in color, flavor, texture, and overall acceptability for all coated samples. Notably, samples coated with sodium alginate after OD exhibited the most favorable physicochemical properties at 60 °C and the highest overall acceptability up to the 15th day of post-processing storage. These results underscore the potential of edible coatings to enhance the preservation and quality of pineapple slices, suggesting scopes for future research in pre-treatment technologies for drying.
... The mean temperature range recorded was 47.8 to 68.2 °C for PSSD and 39 to 47.5 °C for OSD. It is ideal to dry tomatoes between 55 and 60 °C to reduce case hardening [20]. The relative humidity of the dryer throughout the drying period was (15.6 to 65.4%) for PSSD as compared to ODS which ranged (from 31.9 to 75%) respectively as seen in Figs. 3 and 4. The higher temperature and lower relative humidity in the PSSD agree with the observations made by [21] in the drying of bell peppers which showed a temperature range of (35 to 52 °C) and relative humidity of (46 to 65%) for PSSD as compared to (30 to 43 ℃) and (48 to 72%) for OSD. ...
This study aimed to evaluate the performance of a Parabolic Shaped Solar Dryer (PSSD) developed at Nigerian Stored Products Research Institute (NSPRI) Kano for drying Tomatoes compared to traditional Open Sun Drying methods. During the experiment, 139.3 kg of Tomato slices of Eka variety with 5 mm thickness were dried in the Parabolic Shaped Solar Dryer. The drying rate, physiochemical properties, functional properties, and bacteria count were determined. The result showed that Parabolic Shaped Solar Dryer recorded a maximum temperature of 68.2 °C, and a drying rate of 5.2 kg/day leading to a moisture content of 14.5% within the 6 days drying period. In contrast, Open Sun Drying resulted in a slightly higher moisture content of 17.8%, a lower drying rate of 1.3 kg/day, and a maximum temperature of 47.5 °C. The result also indicates an increase in Titratable acidity while Vitamin C retention significantly declines in both drying systems. A decrease in pH and Total Soluble solids was also observed. Oil Absorption capacity was observed to be 10% higher in a Parabolic Shaped Solar Dryer than in Open Sun Drying while Water Absorption capacity was also highest in samples dried in Parabolic Shaped Solar Dryer. Compared to Open Sun drying; Parabolic Shaped Solar dried tomatoes showed a much better nutrient retention for all quality parameters.
... Convective drying, a widely used method involving hot air, often requires high temperatures and extended durations, which trigger chemical and biochemical reactions that alter color, flavor, aroma, and nutritional properties [2][3][4][5]. Drying can also cause excessive shrinkage and/or shape deformation [6][7][8], making the product less appealing to consumers. ...
Convective drying is one of the most commonly employed preservation techniques for food. However, the use of high temperatures and extended drying times often leads to a reduction in product quality and increased energy consumption. To address these issues, hybrid processes combining convective drying with more efficient methods are frequently employed. This study investigates the convective rotary drying of carrot (cv. Nantes), assisted by microwaves and ultrasound, using a hybrid rotary dryer. In total, four distinct drying programs—comprising one convective and three hybrid approaches—were evaluated. The study assessed drying kinetics, energy consumption, and product quality. The use of ultrasound increased the drying rate by 13%, microwaves by 112%, and microwaves and ultrasound together by 140%. The use of microwaves reduced energy consumption by 30%, whereas ultrasound resulted in a slight increase. All processes resulted in a significant reduction in water activity. Ultrasound decreased the color difference index, while microwaves increased it compared to convective drying.
... The initial volume fraction of oil, , in the porous matrix was taken to be 0 as raw potatoes have negligible oil content. The initial volume fraction of gas in raw potato, , is about 0.05 (113,148). The initial mass fraction of liquid water on a dry basis can be represented as ...
Physics-based modeling of deep fat frying is daunting given the intricacies involved in the transport of different phases (liquid water, gas, and oil) in a continuously deforming unsaturated porous matrix. To simplify model development, previous models for frying either ignored volume changes or used empirical relations. The model developed in this study solved the hybrid mixture theory-based unsaturated transport equations and mechanistically accounted for the volume changes of the porous food (potato) matrix. Pore pressure, the effective pressure on pore walls, was used as the driving force governing the volume changes. A good agreement was found between the model predictions and experimental results. The % mean absolute error for moisture content, oil content, and temperature is 5.57%, 22.42%, and 13.35%, respectively. Evaporation and gas expansion during frying led to high pressures in the porous matrix with a peak gauge pore pressure of approximately 19.16 kPa at the center of the sample. The high pressure restricted the frying oil from penetrating beyond the surface layers. Oil uptake mainly occurred during the early stages of frying (t<50 s) when the pressure in the core was low, and towards the end of frying when the matrix was more susceptible to oil penetration because of decreasing pressure. The potato cylinder shrunk by 18.55% for a frying time of 300 s. The gauge pore pressure near the surface became negative, which led to the rapid contraction of the surface layers, and as a result, the porosity near the surface decreased. The average porosity was predicted to decrease by 5.06% after 300 s of frying. The evaporation zone expanded with frying time, and its peak progressively moved towards the core. The insights generated from the discussed mechanisms will guide the industry in optimizing frying techniques.
... The mean temperature range recorded was 47.8 -68.2 °C for PSSD and 39 -47.5 °C for OSD. It is ideal to dry tomatoes between 55 and 60°C to reduce case hardening [30]. The relative humidity of the dryer throughout the drying period was (18.2 -65.5 %) for PSSD as compared to ODS which ranged (from 31.9 -75%) respectively as seen in Figure 4b. ...
This study evaluated the performance of a Parabolic Shaped Solar Dryer (PSSD) developed at Nigerian Stored Products Research Institute Kano (NSPRI) and compared it with an Open Sun Drying (OSD) - Ambient. The evaluation was carried out using Tomatoes ( Eka ). After sorting and washing the fresh tomatoes were sliced into 15 mm thickness and then spread on trays in PSSD and OSD. A thermo-hygrometer was used to record daily temperature and relative humidity. The dried Tomatoes' average drying temperature and relative humidity were 68.2 o C and 50.5% for PSSD, 47.5 o C, and 66.6% for OSD. The average drying rate was 31.6 kg/day for PSSD and 19.7 kg/day for OSD. The result showed that PSSD recorded the highest temperature variation and drying for drying of Tomatoes when compared to OSD. Initial moisture of 89.12% was reduced to a final moisture content of 14.5% for PSSD and 17.8% for OSD after six days of drying. Physiochemical and functional properties of the dehydrated tomato were also carried out. The bacteria count was lower in PSSD (5.8 x 103 Cfu/ml) compared to OSD (7.6 x 10 ³ Cfu/ml). However, no fungal growth was observed in OSD where 4.1 x 10 ³ Cfu/ml was recorded in PSSD.
... During drying often pore development occurs, as during drying of polymeric food materials [1][2][3][4] , or conventional air drying of vegetables [5][6][7][8] . A requirement for this pore formation is the development of an elastic skin 4 , which can happen either via gelling or via entering the glassy state 9 . ...
In this paper we present a numerical model that can describe the pore formation/cavitation in viscoelastic food materials during drying. The food material has been idealized as a spherical object,...
... Due to the heterogeneity of biomaterials and the simultaneous heat and mass transfer involved, food drying results in nonlinear multifactorial problems, which complicates its modeling. Several attempts have been made to model the bulk density of dried foods (Khalloufi et al., 2010;Koç et al., 2008;Lozano et al., 1983;Zogzas et al., 1994). They are classified into two categories: empirical and theoretical models. ...
Bulk density is among the fundamental properties for defining quality attributes of dehydrated foods. Mathematical models offer elegant tools for predicting bulk density and therefore optimizing dehydration processes. In this contribution, three machine learning techniques, namely extreme learning machine (ELM), support vector machine (SVM), and evolutionary polynomial regression (EPR), were assessed for predicting bulk density. Comprehensive experimental data including eight variables (product, initial moisture content, initial bulk density, pretreatment, technology, temperature, pressure, and microwave power) from 191 datasets were used to feed the models. All possible combinations of input variables were examined with ELM to obtain the optimum models involving three to eight input variables. The latter were ranked from one to eight according to their impact on the performance of the models in predicting bulk density. The results showed that the product and drying technology are the essential variables for predicting bulk density. The minimum impact on predictions was observed for pretreatment and power. The initial moisture content was shown to be relevant for predicting the bulk density of freeze-dried products. In addition, the best models obtained by ELM were examined and compared with SVM and EPR models. The SVM showed the highest accuracy, but the EPR had the best performance when both the accuracy and simplicity of the models were considered simultaneously. The developed equations can be used as tools for predicting bulk density and exploited in optimizing dehydration processes without needing costly, time-consuming, and energy-demanding experiments. Opportunities and limitations of artificial intelligence have also been discussed.
... The same was depicted by Sargent 1988;Tortoe & Orchard 2006 for apples and bananas, respectively, concluding that dehydration caused the movement of water and deformation of the pectin, hemicellulose, and cellulose of the cell structure plasma membrane and middle lamella, resulting in the collapse of the cell and plasmolyzed cells. A study also showed that the level of cell wall collapse during drying is proportional to the amount of water lost during the drying process (Zogzas et al. 1994). This is comparable to what Mavis et al. 2014 found in a study on the structure of oven dried tomatoes. ...
Apple pomace, which makes up 20–30% of all processed apples, is an accessible source of bioactive ingredients that could be used in the food industry. A research of the impact of drying techniques on the quality characteristics of apple pomace powder was carried out to efficiently utilize this waste. The pomace was dried at 50 °C and 60 °C in a vacuum-assisted microwave dryer and an oven dryer, respectively. The different temperatures chosen for the drying of apple pomace were selected based on preliminary tests. Microwave drying resulted in reducing the drying time and improving the physicochemical, functional and morphological properties of the powder. The TPC (Total phenolic content) and AA (antioxidant activity) of pomace powder were found to be considerably influenced by the drying technique. Maximum TPC, DPPH and FRAP values observed for the apple pomace powder dried in the microwave were 5.21 ± 0.09 mg GAE/g, 93 ± 1% and 3.22 ± 0.04 µg/mg, respectively while as in oven drying, the values were 3.14 ± 0.06 mg GAE/g, 89 ± 1% and 2.22 ± 0.02 µg/mg. Microwave drying led to increasing bulk density (0.55 ± 0.01 g/cc), water hydration capacity (3.35 ± 0.09 mL/g), oil binding capacity (0.95 ± 0.04 g/g), solubility index (14.0 ± 0.9%), and emulsion capacity (60.0 ± 1.0%) of the powder. Lower values for bulk density (0.50 ± 0.01 g/cc), water hydration capacity (3.04 ± 0.08 mL/g), oil binding capacity (0.70 ± 0.03 g/g), solubility index (10.0 ± 0.8%), and emulsion capacity (48.0 ± 0.9%) were observed in oven-dried powder. Microwave drying resulted in a more disordered, crystalline and porous structure of apple pomace powder as compared to oven-dried powder as confirmed by SEM (Scanning electron microscopy) and XRD (X-ray diffraction). Microwave-dried powder also had a higher vitamin C content (20.00 ± 0.12 mg/100 mg) than oven-dried powder (12.53 ± 0.08 mg/100 mg). This study may be helpful in the preprocessing of apple pomace for bioconversion processes and extraction of valuable components from apple pomace.
Graphical abstract
... The mean temperature ranged recorded was 30-41°C for sun drying and 36-66°C for solar drying. It is ideal to dry tomato between 55 and 60°C to reduce case hardening [35]. Tomato slices with initial moisture content of 95-96% were reduced to 14-15% final moisture content for solar-dried tomato and 19-22% for sun-dried tomato over 23-25 h. ...
Tomato (Lycopersicon esculentum) is an important vegetable used in cooking most local foods in Ghana. At the peak season of harvesting, high loses are incurred because of the absence of tomato processing facilities to store, process, and extend the shelf life of fresh tomatoes. Solar drying has been proven to be a more efficient and low-cost method of enhancing quality and adding value to tomato and other vegetables. However, there are concerns about the functionality and quality of the dried products by consumers due to the methods of drying used. In this study, a passive mixed-mode solar dryer suitable for drying tomato was adapted and used to investigate the dehydration characteristics and microbiological quality of the dried tomato. The efficiency of a passive solar dryer was evaluated and used in the processing of fresh tomato to powder. The processing involved the pretreatment of 6 mm slices of fresh Roma variety of tomato by dipping in potassium metabisulfite solution and ascorbic acid solution. The moisture content, moisture ratio, and dehydration rate of solar-dried tomato were assessed. The 24 h dryer efficiency of 24.2% facilitated the drying process of tomato (final moisture content of 12-14%). Aerobic mesophile counts were lower in solar-dried tomato pretreated with potassium metabisulfite (3.90 CFU/g) compared with sun-dried samples (4.85 CFU/g). Solar-dried tomato powder is safer for consumption compared with open sun-dried tomato samples.
... The liquid displacement method has been widely used to determine the volumes of food materials because of easy operation. [3][4][5][6] Nowadays, some non-intrusive imaging techniques are used to measure shrinkage parameters yielding surface area, shape parameters and perimeter. Gulati et al. 6 measured and analyzed area shrinkage in situ during microwave drying utilizing a digital camera and ImageJ software. ...
Shrinkage parameters of highly shrinkable materials such as length, diameter and surface area during drying are difficult to quantify in situ. However, these are significant components of an accurate model. In this study, an attempt to isolate the surface area effect is reported in order to fetch the REA model (reaction engineering approach) parameters without knowing it a priori. Carrot cube and cabbage leaf were selected as experimental material and dried with hot air under a range of conditions. Shrinkages was calculated using an optical method which is used to qualitatively compare with that “calculated” using the current approach. By matching the experimental temperature and moisture content profiles against time after obtaining REA parameters for both samples without knowing the surface area, the surface areas can be “calculated” numerically. Surface area was found to be affected by sample temperature as well as the moisture content. Drying simulations can be well carried out when correlating the surface area against sample moisture content X and temperature T, and it provides the best accuracy in predicting data on T and X vs. time. In addition, carrot cube can shrink ideally while cabbage leaf cannot. The overall relative errors of predicted moisture content and temperature were less than 1%.
... The dimension of samples (cubes) was measured with a calliper, and the volume of the cubes were calculated (V o ). The volume of dried gels (V f ) was measured using the toluene displacement method [62]. The pycnometric (true) density was measured using a helium stereopycnometer (Quantachrome Instruments, Boynton Beach, FL, USA). ...
This study aimed to determine the effect of the addition of apple juice concentrate (AJC) on the properties of agar gel and dried materials. Agar gels with the addition of apple juice concentrate in the range of 5–20% were prepared with or without the addition of maltodextrin. The gels were also soaked in the solution of AJC. The water content, water activity, densities, some mechanical and acoustic descriptors of gels, and the freeze-dried gels were analysed. The porosity and shrinkage of dried products were also investigated. The addition of AJC significantly changed mechanical and acoustic properties of gels. The hardness of gels decreased with a higher addition of concentrate. Dried samples with a lower concentration of sugars (the lower addition of AJC) were characterised by lower shrinkage and higher porosity, as well as crispness and glass transition temperature. The investigated mechanical and acoustic properties of dried gels showed the addition of apple concentrate at the level of 5% to agar solution was optimal.
... For example, for cork μ≈0.0 and for natural rubber μ≈0.5 (Kawabe, 2019). Relatively high value of μ for untreated carrot can be explained by the small initial porosity (ε≈0) of carrot (Madiouli et al., 2007;Zogzas et al., 1994). ...
Typically, the carrot tissues have rather high initial moisture content and low porosity. Expression of juice from such tissue may be rather complicated and include different stages. In this work, a simple creep tests with carrot tissue treated by pulsed electric fields (PEF) were performed. The samples were compressed for 15 min in a special jig using a constant load of F = 0.5 kg (initial pressure p0 = 1.89 bar) or 1 kg (initial pressure p0 = 3.78 bar). PEF treatment was done using electric field strength E = 0, 483, 838, and 1037 V/cm and pulse duration of ti = 10 ms to different levels of tissue disintegration Z. Effect of PEF on volumetric shrinkage V* and Poisson ‘s ratio μ of have been evaluated for the first time. Different stages were observed for time behavior of V* and μ. From time evolution of V* presence of the primary (initial) and final (secondary) creep relaxation processes was suggested. It was demonstrated that the damage of cells induced by PEF resulted in redistribution between contributions of primary and secondary stages. The time evolutions of Poisson ratio’s was described by first order kinetic equation. It was shown that PEF treatment decreased the value of Poisson ratio’s. Significant effects of PEF treatment on volumetric shrinkage and Poisson ‘s ratio were not accompanied with large changes in moisture content inside the carrot tissues.
... The functional properties of biopolymers encompass any physicochemical property that exerts an effect on the characteristics of the foods to which they have been applied during their production, processing, storage, and/or consumption, thus contributing to their final quality (Dehnad et al., 2016). These properties include the water retention capacity of the food, the emulsifying properties, solubility, viscosity, porosity, swelling, elasticity, adsorption, among others (Zogzas et al., 1994;Fazaeli et al., 2012). Agudelo et al. (2017), in a previous study, optimized the formulation of a grapefruit puree or liquidized added with GA and BF as to obtain, in each case, a powdered product with the best nutritional and sensory quality, established on the basis of its color, mechanical properties, hygroscopicity, solubility, total phenols, flavonoids, vitamin C and antioxidant activity, and even with the highest dry matter yield. ...
Freeze‐drying and spray‐drying are two techniques used to produce dehydrated food products. Both techniques are easy to use and offer high sensory, nutritive value, and functional quality to foods. However, both processes become difficult for foods with high sugar and acid content, such as fruits. This is because these products, once dehydrated, moisten quickly, causing a change in their physical properties, mainly in the mechanical aspects related to the start of a caking phenomenon. Therefore, incorporating high molecular weight biopolymers that act as facilitators or processors, prevent the structural collapse of the product. The aim of this study was to select the best process, between freeze‐drying or spray‐drying, to obtain a powdered grapefruit product with the higher quality. The impact of the biopolymers used to stabilize the powdered product was also tested. The properties analyzed were the solubility, wettability, hygroscopicity, porosity, and color of the powder together with the flow behavior, both in air and water. The results of this study show that using the freeze‐drying technique, products have a better flow behavior, greater porosity, and a color more like fresh grapefruit. Biopolymers, especially when in combination, have a positive effect on the quality parameters studied.
Practical Application
The results of this study allow freeze‐drying to be proposed as a process to obtain a grapefruit product with better properties, both powdered and rehydrated, than that obtained by spray‐drying. On the other hand, although the incorporation of biopolymers is necessary to facilitate the process and stabilize the product, no significant differences have been found between the different formulations tested, although it seems that their combination favours some of the properties of the powder, such as solubility, hygroscopicity, wetting time and dispersibility.
... The determining features are porosity and permeability in the models of diffusive flux of the gas phase and pressure driven flux of the liquid phase; porosity is described respectively in Eq. (4) [57] and permeability is described in Eq. (5), with the index's 'g' denotes gas phase and 'l' denotes liquid phase and 's' denotes the solid part: ...
Heat and moisture transfer of two moving moist objects in a channel with convection of hot dry air is investigated numerically. A moving mesh approach is used for providing movement by means of the Arbitrary Lagrangian-Eulerian (ALE) framework. Governing equations for flow field and porous objects are solved by finite element discretization method for the 3D transient problem. Effects of drying air velocity and temperature are simulated by means of temperature, moisture content and heat transfer distributions. Results showed the importance of varying parameters on drying behavior. It was observed that the air velocity also has an increasing effect on evaporation and most reduction in moisture content is obtained at 0.8 m/s air velocity with 63.12% loss. Besides, there are insignificant differences between heat transfer values for fixed and moving objects, differences in average heat transfer values calculated between 6 and 13% for static bed and moving bed.
... Heat transfer coefficient was computed by utilizing the lumped system analysis while mass transfer coefficient was evaluated using the analogy for different boundary layers. Zogzas et al. [19] determined bulk density, porosity and shrinkage of potato, apple and carrot cubes in hot air drying experimentally and achieved effective results to be used in numerical studies. A steady model of convective drying based on Fick's law of diffusion was developed for investigating the moisture transfer from apple and carrot slices by Srikiatden and Roberts [20]. ...
The aim of this study is to investigate heat and mass transfer during convective drying of a moving porous medium in a 2D rectangular channel with laminar flow conditions. Finite element method is used with ALE to model the movement of the porous moist object. Hot dry air with different temperatures flowed in the channel with varying velocities and the porous object also has a movement with parallel direction to the flow. The code is validated by using experimental results. Results indicated that the heat transfer coefficient of the moving porous moist object is time dependent and varying locally. Significant impacts of increasing values of air temperature and velocity on the heat and mass transfer features are observed.
... Another research conducted by Rathnayaka et al. (2017) focused on the alterations in the morphology of food tissues during drying and also reviewed the current advances in the numerical modeling of foodstuffs. The effect of vacuum and conventional drying on the color attributes of potato, banana, apple, and carrot was reported by Krokida et al. (1998) whereas Zogzas et al. (1994) examined the influence of drying on the physical characteristics like particle density, bulk density, porosity, and shrinkage of potato and apple cubes to determine the quality of food materials. ...
... Porosity Porosity was calculated using the data for true and apparent densities (Zogzas et al. 1994) as expressed by Eq. 7. ...
Modification of the surface properties of materials is a promising approach to reduce the uptake of oils during frying. In this work, the quality characteristics of plantain chips subjected to a pretreatment consisting of osmotic drying in sugar solutions (29 and 45° Brix; 40 and 80 °C) were evaluated. True density, apparent density, porosity and moisture content were measured in pretreated samples (PS) before frying. Image ESEM was used to evaluate microstructural changes on the surface and in cross-sections at different depths. Global oil absorption (GOA) and fatty acid profile were monitored in surface and deep cross-sections (DCS). The color parameters of chips (L*, a*, b*, ΔE), browning index, crispness, crunchiness and hardness were evaluated during frying. Oil absorption in the crust was lower in samples subjected to pretreatments with a higher temperature. PS showed high gelatinization in both the surface and DCS, thus changing crust physical properties, total oil uptake and fatty acid profile. An exponential correlation between porosity (ε) and GOA was found, while a second order correlation was found between ε and the fatty acid profile. The characteristics of texture and color, as desired by the consumer, were reached more quickly in the PS at 29° Brix and 40 °C.
... In such a system, moisture content has a strong relationship with the cell turgor pressure and similarly [10], drying temperature has a relationship with the relative humidity. To derive the most appropriate relationship among such driving forces, cellular morphogenesis and underlying transport phenomena; various microscale theoretical [11,12] and empirical [3,5,13] models have been developed. ...
Food drying is a global industry focused on producing various types of dried food products, mainly sourced from plant food materials. In this regard, optimisation of food drying processes demands a thorough knowledge of the corresponding transport phenomena in plant food cellular structures. Based on this need, this research has developed a three-dimensional (3-D) numerical model to investigate the morphological changes and related solid and fluid dynamics of a single apple parenchyma cell during drying. This numerical model was developed by coupling a meshfree particle based method: Smoothed Particle Hydrodynamics (SPH) and a Discrete Element Method (DEM). The plant cell model is composed of a cell fluid model and cell wall model. The cell fluid model is based on SPH and approximates the cell protoplasm to a homogeneous Newtonian liquid. The cell wall model is based on DEM and approximates the real cell wall to an incompressible Neo-Hookean solid material. A series of simulations were conducted to mimic the gradual geometrical shrinkage during drying as a function of the moisture content. Compared to conventional grid based numerical modelling techniques such as Finite Element Methods (FEM), Finite Difference Methods (FDM) and Finite Volume Methods (FVM); the proposed meshfree-based model can simulate physical deformations and shrinkage of cells within a wide range of moisture content, effectively replicating their realistic behaviour during drying.
... The whole process occurs when the product temperature is lower than the water boiling point. To simplify all these phenomena, the whole transfer can be expressed by similar-Fick diffusion law, with an effective diffusivity (D eff ) [25]. Thus, by adopting the formulation of Allaf (1982), it can be expressed as: ...
... For carrot (Figure 8b), on the other hand, no pores were observed even at a resolution of 1 μm suggesting that pores inside the carrot are either very few or are smaller than 1 μm. Experimental gas porosity of carrot (Zogzas, Maroulis, & Marino-Kouris, 1994) was found to be negligible (<0.01) as well. ...
Selective or enhanced heating of a solid in a solid–liquid mixture in microwaves that can lead to enhanced boiling and possibly bumping was studied. A soup containing broth and particulate foods was heated in a cylindrical container in a standard domestic microwave oven. Heating patterns were obtained using a coupled three dimensional thermal‐electromagnetic model, as well as an infrared camera, and boiling was visually observed. Selective heating of the solid particulates over the broth depends on their dielectric and thermal property differential. Enhanced and early boiling on the surface resulting from selective heating also depends on factors that aid in bubble formation and growth such as the surface roughness and porosity (gas pockets) in the solid. For quick prediction of the potential for enhanced heating in product design, a characteristic number was developed that can predict situations that are more prone to enhanced heating than the surrounding liquid.
Practical applications
When microwave heating of a soup or a soup‐like multicomponent mixture of solid and liquid foods, for example carrot or corn pieces in a broth, the solid can end up heating faster than the surrounding liquid, leading boiling to be initiated preferentially at the solid surface, as opposed to in the bulk broth. Depending on the solid material and its surface properties, such a boiling can be further enhanced and sudden, leading to possible bumping during the heating process. A simple design parameter, based on easily available dielectric and thermal properties of the solid and liquid, was developed to quickly predict the possibility of such an enhanced heating of the solid surface (that could eventually lead to bumping). When designing microwaveable products like soups, this simple parameter can be of particular help, reducing the time and resources for experimentation by providing a quick estimate of the probability of enhanced boiling and thus bumping.
... For some materials are available! [37,68,69] Bulk/App density, ...
Effective moisture diffusivity provides an easy and expeditious route to understanding many moisture transport processes involving food materials. Instead of making the moisture diffusivity a parameter obtained from curve-fitting a given experimental data that severely restricts its predictive value for the different sets of conditions, a simple but mechanistic approach is provided that for its prediction uses very little empirical information. This approach is based on treating the food as porous media and using parameters such as relative permeability, porosity, tortuosity, and constrictivity. The parameters are predicted using well-known relationships. The model is a combination of liquid and vapor diffusion-weighted by the respective volumes present in the porous medium that provides effective moisture diffusivity. Our model is compared to a mechanistic model that is backboned by Kelvin’s capillary pressure equation and experimental isotherms data. In addition, the prediction is thoroughly validated against available experimental data and the general understanding of liquid/vapor transport in porous media literature. The more mechanistic approach enables prediction over a broader range of moisture content and a greater range of food materials with acceptable RMSE compared to other literature models.
... The whole process occurs when the product temperature is lower than the water boiling point. To simplify all these phenomena, the whole transfer can be expressed by similar-Fick diffusion law, with an effective diffusivity (D eff ) [25]. Thus, by adopting the formulation of Allaf (1982), it can be expressed as: ...
The increasing demand for functional foods requires the design, simulation, and further optimization of preservation processes of food with the purpose of keeping as high as possible the functionality of food products. Many studies have shown that the high consumption of fruit and vegetables prevent chronic diseases such as obesity, type 2 diabetes mellitus, cancer, among others. Fruits and vegetables are important sources of nutrients, dietary fibers, and phytochemicals. However, after harvest, they are highly perishable because of their high moisture content of almost 3-9 g H 2 O/g db. Solar and airflow drying processes have been the most popular methods to increase the shelf life of these products. Nevertheless, low organoleptic and nutritional quality, hygiene problems, and long drying periods constitute significant barriers to a more widespread use. "Swell-drying" is a special drying process convective airflow drying (CAD) to the instant controlled pressure-drop (DIC) expansion. This process is well-known as guaranteeing (1) the preservation of functional properties; (2) the organoleptic quality; (3) the effective microbio-logical/fungi decontamination; and (4) a reduced energy consumption and a lower drying time. DIC treatment is a high temperature/short time (HTST) process that improves both performance of drying process and high-quality functional foods.
... Because heat transfer and temperature distribution was excluded in the simulation, temperature rise along the ISD tunnel was neglected. The wire mesh bottom of the trays and the layer of drying material resting on it was assumed as a porous medium with a porosity of 0.6 [24]. The resulting resolution was set at level 8, which is the highest level. ...
The technical performance of an inflatable solar dryer (ISD) to dry amaranth leaves (Amaranthus spp.) was investigated. To handle the drying of lightweight materials, modification was made by adding an air deflector and trays inside the ISD. Computational performance of the ISD solar energy system was evaluated using MATLAB Simulink. The estimated air mass flow in the inlet of the ISD was 0.75 kg/s. Using computational fluid dynamics (CFD), the uniformity of air distribution in the ISD was evaluated. The solar radiation reported during good drying performance ranged between 510 and 950 W/m². In a controlled charging system, a 100 Wp PV module typically generated voltage between 10.22 and 18.75 V. Drying conditions at temperatures of 40 °C or above were typically achieved in the ISD from 12:00 to 16:00. Temperature inside the ISD could reach up to 69.4 °C during the day and 13.4 °C during the night. The highest relative humidity of 97.4% was recorded during the night. Opening the ISD while mixing the product could lead to considerable heat loss. Fluctuation of solar radiation and shaded areas in the ISD appeared to be the major factors affecting the drying performance.
... ICMIEE18-144-2 2.1 Materials Different types of plant-based food materials like Brinjal, Carrot, and Radish were collected from the local market in Rajshahi, Bangladesh. The initial moisture content of the fresh food materials was measured by oven drying method [13]. The initial mass of the Brinjal, Carrot and Radish samples were about 4.5 gm, 9 gm, and 8.5 gm respectively. ...
Drying is a simultaneous heat and mass transfer phenomena, primarily remove water to extend the shelf life of food materials. Over the course of drying, food quality deteriorates significantly along with taking huge energy. From the literature, it is found that both food properties and drying conditions affect the energy consumption criteria. However, there is a very limited number of research found that conducted investigation on the effect of sample geometry on energy requirement to dry. In this study, three typical shapes with a constant volume of selected food materials have been investigated to attain a correlationship between sample geometry and energy requirements. The amount of energy requirement during drying of Brinjal, Carrot, and Radish varies significantly with the variation of sample geometry. The minimum energy was required for sliced samples of selected food materials; whereas, cylindrical shaped samples took higher energy. The minimizing amount of energy also reduces the environmental pollution and GHG (Green House Gas). It can be concluded that sample compactness remarkably affects the energy requirement.
... Pengukuran Densitas (Liu et al., 2012dan Madiouli et al., 2012 Densitas atau massa jenis adalah suatu besaran kerapatan massa benda yang dinyatakan dalam berat benda per satuan volume benda dalam satuan kg/m 3 atau g/cm 3 . Pengukuran densitas selain berdasarkan formula dari Liu et al. (2012), dan Madiouli et al. (2012), juga menggunakan formula dari Zogzas et al. (1994), Krokida et al. (1997Krokida et al. ( dan 2000, Koc et al. (2008), Martynenko (2008), Khalloufi et al. (2009) Pengukuran Warna (deMan, 1999) Warna pempek lenjer instan diukur dengan menggunakan Colour Reader CR-300. Colour reader dinyalakan dan tombol fungsi diaktifkan untuk memilih dan menentukan nilai dan angka yang digunakan, tekan tombol calibarate (warna kuning), tetapkan kondisi a* dan b* harus nol dan L (lightness)=100, sampel dimasukkan ke dalam wadah transparan (plastik bening/blanko), posisikan penembak warna (colour reader) di atas blanko, tekan measure sekali dan tunggu sampai terpotret 3 kali, tempelkan sampel ke alat pemotret dan akan muncul angka L (%), H ( o ), dan C (%) yang tertera pada alat dan dilakukan pencatatan. ...
Pempek is a typical food of Palembang, South Sumatra, Indonesia, mostly processed in the form of wet with a moisture content of 50-60%, so that it only lasts for 3-4 days. In order for pempek to long last, it was processed into instant pempek using the freeze drying method. Pempek had tube form with a size of 3 cm in high and 4 cm in diameter. This study was aimed to see the freeze drying pressure and time to length of cooking, density, and lightness of instant pempek. Stored pempek at temperature of -50° C was carried out freeze drying with a pressure of 0.002 bar, 004 bar, 0.006 bar, and 0.008 bar for 38 hours, 40 hours, 42 hours, and 44 hours with a methodology of Split the Duncan Real Distance Difference Test Plot Design. The result showed that the pressure and time had very significant effect on the length of cooking, density and lightness of pempek. P3 (0.006 bar) pressure treatment affected shorter cooking time of pempek about 10.83 minutes, L2 treatment has 14.17 minutes for cooking times and the P3L2 treatment combination has low density of 0.71 g / cm3 and color brightness (lightness) about 85.38, almost resemble with white color. Making instant pempek with freeze drying method gave better results in ways of shorter and faster cooking time than instant pempek by other drying methods. Keywords: cooking length, freeze drying, instant pempek
This research intended to investigate the transport phenomena that occur during microwave freeze‐drying (MFD) of potato slices using drying kinetics and finite element analysis (FEA). The impacts of microwave power levels and potato slice thickness on drying rate constant (DR) and average moisture diffusion (DAVG) were analyzed using MFD kinetics and were then incorporated in the simulation. It was found that the DR and DAVG were in the range of 301.3 × 10⁻³–775.4 × 10⁻³ min⁻¹ and 1.045 × 10⁻¹⁰–3.336 × 10⁻¹⁰ m²/s, respectively. In the sublimation phase, the DR and DAVG were higher than those in the desorption phase. The DR and DAVG increased as the microwave power level increased but decreased as the thickness increased. The FEA of temperature and moisture distribution within the potato slices demonstrated the outward transfer of heat and mass from the center to the exterior and closely matched the experimental data with an error margin of within 5%, leading to the proposed schematic shrinkage model corresponding to the MFD simulation.
In this paper, we describe a model for pore formation in food materials during drying. As a proxy for fruits and vegetables, we take a spherical hydrogel, with a stiff elastic skin, and a central cavity filled with air and water vapour. The model describes moisture transport coupled to large deformation mechanics. Both stress and chemical potential are derived from a free energy functional, following the framework developed by Suo and coworkers. We have compared Finite Volume and Finite Element implementations and analytical solutions with each other, and we show that they render similar solutions. The Finite Element solver has a larger range of numerical stability than the Finite Volume solver, and the analytical solution also has a limited range of validity. Since the Finite Element solver operates using the mathematically intricate weak form, we introduce the method in a tutorial manner for food scientists.
Subsequently, we have explored the physics of the pore formation problem further with the Finite Element solver. We show that the presence of an elastic skin is a prerequisite for the growth of the central cavity. The elastic skin must have an elastic modulus of at least 10 times that of the hydrogel. An initial pore with 10% of the size of the gel can grow to 5 times its initial size. Such an increase in porosity has been reported in the literature on drying of vegetables, if a dense hard skin is formed, known as case hardening. We discuss that models as presented in this paper, where moisture transport is strongly coupled to large deformation mechanics, are required if one wants to describe pore/structure formation during drying and intensive heating (as baking and frying) of food materials from first principles.
Shrinkage and collapse phenomena are the two mechanisms involved in the evolution of pores within food products during dehydration. These phenomena can be mathematically represented by shrinkage and collapse functions, which can be derived from theoretical models of porosity, bulk density, or volume reduction coefficient. In this contribution, these two functions were simplified to capture four extreme scenarios of dehydration, which consist in the combination of total or no shrinkage with total or no collapse. The four simplified equations were used to generate theoretical maps characterized by three distinct zones that are associated with pore evolution. Each of these zones represents a key dehydration situation. By superimposing experimental data of porosity, bulk density, or volume reduction coefficient on these theoretical maps, it is possible to assess dehydration processes, i.e., drying technologies and/or dehydration conditions, in terms of pore formation and evolution over time. These theoretical maps can be constructed for each food product before starting the dehydration processes. Therefore, when the experimental data is available, the suggested mapping approach is a simple, fast, and reliable tool to: (i) assess the performance of a given dehydration process versus specific cases of pore formation, and (ii) compare different dehydration processes in terms of their ability to promote pore formation. This practical tool can be used by the industry and academia to quantitatively evaluate how far a drying technology and/or its dehydration conditions are from the ideal scenario in terms of pore formation. This gap quantification will provide a basis for converging towards the ideal scenario by fine-tuning the dehydration conditions or choosing the appropriate drying technology.
Pore formation efficiency can be defined as the volume of pores formed and/or remained vs. the maximum volume of pores that could have been formed and/or remained during processing. This contribution proposes new mathematical tools to estimate four different and complementary types of pore formation efficiencies, named here the overall efficiency, the specific efficiency, the conservation efficiency, and the instant efficiency. Published experimental data of porosity, bulk density, and volume reduction coefficient were used to assess the efficiencies of various dehydration processes. In terms of overall efficiency, for 88% of the dehydration processes investigated in this study, the final products contained less than 20% of the maximum air volume that would theoretically have been present if all the initial air had been conserved and if all the water removed had been entirely replaced by pores. The instant efficiency, which allows evaluating pore formation at one precise moment of drying, enabled the detection of punctual anomalies and critical periods of dehydration for some food products investigated. The results of conservation and specific efficiencies revealed that, in some specific cases, there was no pore formation despite an increase in porosity. This mathematical toolkit of pore formation efficiencies can be used for comparing dehydration technologies and/or process conditions in terms of their potential for pore formation.
Vegetable production in the Republic of Serbia accounts for about 3.5% of total
crop production, within which there is a constant trend of declining areas where vegetables are
grown, primarily due to the great need for hiring labor, which is decreasing. One of the most
common vegetable crop grown in the Republic of Serbia is watermelon, which according to the
Republic Statistical Office, along with quince, was grown on 5,700 hectares in 2019, while the
largest areas under these vegetables were recorded in 2017 when they amounted to about 8,300
acres. The aim of this paper is to present the economic and financial aspects of watermelon
production on farms in the Republic of Serbia in the period between 2015 and 2019, based on data
from Statistical Office of the Republic of Serbia and the income and expense survey on the family
farms, which represents calculations based on variable costs, conducted by the Institute for the
Application of Science in Agriculture. Sensitivity analysis shows the price and yield influence on
gross margin amounts in watermelon production. The obtained results indicate a variation in the
amount of gross margin in watermelon production in the analyzed period, due to changes in
prices, yields and variable costs. Data obtained on sensitivity analysis, determinate that changes in
price and yield have a significant impact on the amount of gross margin in watermelon production.
Hot air drying of ginger (Zingiber Officinale) samples (10 mm × 10 mm × 5 mm) having an initial moisture content of 84.89% (wet basis) were carried out at 60℃. Effect of treatment prior to drying was studied at different concentrations of calcium chloride (CaCl2) of 3, 3.5, 4, and 4.5 Mol per liter and compared with the samples dried without pretreatment. Also, process intermittency was applied with a pulse ratio of 1.5 by keeping the sample in vacuum or open atmosphere. During intermittent drying, the products were dried in hot air dryer for 40 min, followed by either vacuum drying or open-air drying at ambient conditions for 20 min. It was observed that calcium chloride with higher concentrations had a significant effect on the moisture extraction rate. Open-air intermittency exhibited better rehydration ability and lowest shrinkage ratio, which facilitated a higher drying rate during the falling rate period.
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.
The study was aimed to investigate the mathematical modeling of drying kinetics and quality of shrimp (Metapenaeus dobsoni) dried under a solar–LPG (liquefied petroleum gas) hybrid dryer. The major components of the dryer were a solar water collector, insulated water storage tank, LPG burner with cylinder, drying chamber, stainless steel trays, axial flow fan, and heat exchanger. Initially, shrimps were treated by dipping in a salt solution (3% w/v, water to shrimp ratio of 1:1) at 80°C for 3 mins. The treated shrimps (76.71%, w.b) were dried to the final moisture content of 15.38% (w.b) within 6 h of drying. Mathematical modeling of the drying kinetics showed that the page model could accurately predict the drying behavior of shrimp. An effective moisture diffusivity value of 1.04 × 10⁻⁹ was obtained based on the Fick’s equation. Proximate and biochemical composition of dried shrimps were not significantly affected by drying process. The total plate count of dried shrimp was found to be within the acceptable limit (10⁴ CFU/g). It was observed that dried shrimp had a shrinkage rate of 13.28% and a rehydration ratio of 2.48. In the sensory analysis, the color attribute received a significantly higher sensory score.
This study deals with the use of the innovative swell-drying process in the case of two different proveniences of thyme (Thymus capitatus); KEF and BEJA. This process is based on two successive stages: texturing by instant controlled pressure drop (DIC) and drying performed by hot airflow. DIC consists of subjecting the vegetable matrix to a high temperature/high pressure for a few seconds followed by an almost instantaneous pressure drop toward a vacuum of about 5 kPa. It normally causes an adequate autovaporization within the product, a controlled expansion, and a cooling of the vegetable matrix. This new structure allows the final drying step to reach much lower water content. In the two considered cases of thyme, the product structure (thickness of the leaf), the functional behavior, and drying technology aptitudes were studied. The impact of DIC conditions of total treatment time and a number of cycles was statistically analyzed using a two-factor, five-level central composite design of experiments (DoE), through the response surface methodology (RSM). DIC treatment allowed achieving four times better drying efficiency. The range of negligible external resistance (NER) allowed defining the two coupled steps of superficial starting accessibility and water internal diffusion (SAWID) phenomenological drying model. Swell-drying implied the effective diffusivity to increase up to 10 times and the starting accessibility up to twice better than the conventional hot air drying for a relative expansion ratio of almost 2. The highest DIC treatment parameters were measured to be 1 cycle/60 s for Deff and 7 cycles/20 s for δWs for both thyme proveniences (KEF and BEJA).
The purpose of this study was to analyse the impact of blanching, the atmosphere of nitrogen and storage time on carotenoids content, colour and sorption properties of freeze-dried carrot. The material was stored for up to 16 weeks, in the dark, at room temperature. The colour was measured on the surface and in cross sections. As the storage time increased, there was a continual decrease in the carotenoids content in the carrot packed in atmospheric air. In the carrots packed in the atmosphere of nitrogen, no changes in carotenoid content were observed. The colour parameters correlated with the changes in the carotenoids content. The colour parameters changed on the surface and in cross sections in the same manner. During storage, a significant decrease in sorption properties of freeze-dried carrots was noted after 2 weeks of storage.
Sun is a clean and available sustainable energy source. The usage of sustainable energy in various industries such as agriculture is taking into consideration during the early years. One application is dehydration by using an indirect solar dryer, which was adopted in this study. A dynamic model was presented in which the calculation of the solar radiation received in the tiled surface of the collector, temperature variation along the collector, the kinetics of moisture reduction and temperature variation of the drying material were taken into consideration. The model was validated and confirmed with high accuracy by test results in three states of mass flow rates of air. The effects of air velocity, the glass cover thickness and the length of the collector took into consideration in the analysis as effective parameters. The thermal analysis was accomplished by using energy and exergy analysis. To energy analysis, the values of received and used energy were calculated in addition to energy utilization ratio and for exergy analysis, the irreversibility at collector was calculated as well as the exergy efficiency of drying in the chamber. Energy and exergy analysis revealed more stream exergy for higher speed air and hence, lower irreversibility. Besides, the defined exergy efficiency was independent of the material mass despite the exergy destruction or energy efficiency, which means a suitable criterion for the system analysis. The model was in good agreement with the experiments so that the deviation from the best fit line (y = x) in the model-experiments curves were 2.37% for radiation estimation, 4% for the outlet air temperature of the collector, 1% for the material temperature and 4.8% for the moisture ratio of the drying material. The model also revealed two critical moisture ratio of 0.75 and 0.23 in the drying process so that the maximum exergy destruction was observed at the first one and the maximum exergy efficiency was 22% for the dryer.
This chapter discusses tunnel dehydrators, as used to dehydrate certain fruits and vegetables. It provides a general introduction to the subject, primarily for the use of students, food technologists, and engineers. Although it goes into a number of matters concerned with the design and operation of this kind of equipment, it is, in no sense, a manual either of design or of operation. Emphasis has been laid on the discussion of underlying principles and the more recent advances in application of these principles. An effort has been made to bring together published information from many different sources, some of which are not widely available. Tunnel dehydrators, as a class, are frequently called tunnel-and-truck, truck-and-tray, or simply tunnel driers. Principles pertaining to their use have been discussed. All tunnel-and-truck dehydrators for fruits and vegetables have a common feature that distinguishes them from other kinds of drier. Numerous factors govern the selection of the drying system, or type of dehydrator, for a particular plant. Economic factors, such as initial and installation costs and operating labor costs, although important, are not the only criteria for proper selection. Some of the other important considerations have been listed in the chapter.
True density, bulk density and apparent density of the seeds, kernels and hulls of commercial varieties of muskmelon, longmelon and watermelon were determined. There is a significant difference between the apparent densities of kernels and of seeds. Kernels are denser than water whereas seeds are less dense; hence kernels sink while seeds float in water. A suitable water separation tank, either batch or continuous, based on this property can be designed for separation of the kernel and seed fractions obtained by mechanical dehulling of the melon seeds.
The thermal properties of sultana grapes and raisins were investigated in the moisture content range 14–80% (wet basis) near room temperature. The density of the berries increased from 1080 to 1460 kg/m3 as the grapes were dried, following the model of an ideal mixture of dry solids and water. The specific heat and the effective thermal conductivity of the raisins were found to vary linearly with the moisture content. The effective thermal conductivity did not change significantly in the temperature range 39–51 °C and the porosity range 0.4 – 0.5.
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.
Regular regime theory was used to evaluate the effective moisture diffusivity of a commercial white bread, plain sheet muffin, and baking powder biscuit as a function of moisture content based on desorption experiments. Volume shrinkage during drying was also monitored. The existence of regular regime periods in desorption processes for porous baked products was experimentally verified. Effective moisture diffusivity at temperatures between 20 and 100°C ranged from 2.5×10−5 to 5.5×10−3 cm2/s in the moisture range of 0.1–0.7 g of H20/g of solid for bread, 9.35×10−6 to 9.7×10−4 cm2/s in the moisture range of 0.1–0.65 g of H20/g of solid for biscuit, and 8.4×10−6 to 1.54×10−3 cm2/s in the moisture range of 0.1–0.9 g of H20/g of solid for muffin. The effect of temperature on effective moisture diffusivity was adequately modeled by the Arrhenius relationship. Activation energies for bread, biscuit, and muffin were found to be independent of moisture content and were 51, 51, and 55 kJ/mol, respectively. Mathematical models to relate the effective moisture diffusivity to temperature and moisture content were developed.
Mathematical models for heat and moisture transfer-related properties of intermediate moisture apples were developed. The models of thermal properties were based on a linear dependence of thermal conductivity on temperature and moisture content, a logarithmic dependence of bulk density on moisture content, and a linear dependence of specific heat on moisture content. The effect of moisture content and temperature on moisture diffusivity was modeled by an exponential relationship. The sorption data were adequately fitted by the Modified Henderson's equation.
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.
The physical structure, developed during drying, affects the transport of water and the quality of processed solid foods. the effective diffusivity of water in starch-based systems was estimated from drying data at moisture 3–50% and temperatures 40-100°C. Hydrated granular or gelatinized starches and their mixtures with sugars or inert particles were used to produce different structures during air drying. the physical structure was characterized by the bulk porosity, estimated from the bulk and solid densities of the samples. the water diffusivity was influenced strongly by the porosity, developed during drying. Mechanical compression, starch gelatinization or addition of water-soluble sugars reduced the water diffusivity in granular starches. Incorporation of inert particles or extrusion cooking resulted in higher water diffusivities, due to higher porosities of the starch/inert mixtures or the expanded extrudates.
The particle density of granular and gelatinized corn starches was determined in the moisture range 0 to 1 kg water/kg dry solids, using a gas stereopycnometer. The bulk porosity (void fraction) of spherical starch samples at various moisture contents was estimated from the bulk and particle densities during air drying at 60°C. The particle density data fitted a polynomial function of moisture content (X), passing through a maximum value of 1500 kg/m3 at X = 0.15. The bulk porosity of the starch samples increased linearly during drying, reaching a value of 0.45 near dryness. Differences in structure between granular and gelatinized starches during drying were observed by stereomicroscopy. The changes in porosity could be related to variations of the effective moisture and thermal diffusivities of starch materials.
Bulk porosity and pore size distribution were measured for granular, heat-gelatinized and extruded starch materials, using helium stereopycnometry and mercury porosimetry. Most of the pores of granular materials had a radius of 1–3 μm and bulk porosity about 0·6. About 20% of the total porosity is due to the 6–8-μm voids between starch agglomerates, about 60% is due to the voids around starch granules (1–3·5 μm) and 10% is due to the very small pores. The remaining 10% of the total porosity might be due to pores larger than 150 μm. Gelatinized starches had average pore sizes of 0·8–1·5 μm and bulk porosity lower than 0·1. Extruded starches had pores varying from 1 to 120 μm and bulk porosity 0·1–0·95, depending on the experimental extrusion conditions. High porosity and large pores resulted when starch was extruded at high temperatures and/or low moisture contents. Mechanical compression reduced the bulk porosity and the size of the pores. The porosity and the mean pore size of starches increased during the drying process. Porosity and pore size distribution are important parameters in the transport (diffusion) of water in starch materials and starch-based foods.
Most algorithms for the least-squares estimation of non-linear parameters have centered about either of two approaches. On the one hand, the model may be expanded as a Taylor series and corrections to the several parameters calculated at each iteration on the assumption of local linearity. On the other hand, various modifications of the method of steepest-descent have been used. Both methods not infrequently run aground, the Taylor series method because of divergence of the successive iterates, the steepest-descent (or gradient) methods because of agonizingly slow convergence after the first few iterations. In this paper a maximum neighborhood method is developed which, in effect, performs an optimum interpolation between the Taylor series method and the gradient method, the interpolation being based upon the maximum neighborhood in which the truncated Taylor series gives an adequate representation of the nonlinear model. The results are extended to the problem of solving a set of nonlinear algebraic e