No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Mechanistic Understanding of Case-hardening and Texture Development During Drying of Food Materials
Abstract
A mechanistic framework for quality development such as shrinkage and case hardening in drying would allow new insights making the final quality in a drying process more predictable and controllable. A poromechanics model that includes multiphase (solid matrix/liquid water/vapor) transport and large deformation using hyperelastic constitutive relationship between the stress and strain is developed. Moisture and state (rubbery/glassy) dependent mechanical and transport properties are used. A complex shrinkage pattern that is not simply equal to the amount of water lost is observed at low moisture contents due to glass transition of the material. For high drying rates, the surface dries out faster than the core and forms a case-hardened layer resulting in early deviations in shrinkage. In contrast, for low drying rates, deviations in shrinkage occur at extremely low moisture contents due to a gradual rubbery/glassy transition. Key quality attributes, such as degree of crust formation, are predicted from fundamentals.
... Thus, FD facilitates milling, resulting in a smaller particle size and promoting fibres' breakdown and soluble compounds' release. On the contrary, HAD can cause crusting phenomena, also known as case-hardening, which generates rubbery cores that make subsequent milling more difficult, resulting in powders with a lower soluble solids content [10,51,52]. Figure 3 shows the antioxidant properties values of the fresh and fermented stems before and after dehydration by the two techniques tested. ...
... 0 Statistically significant differences in moisture content values (p-value < 0.05) were observed, with higher values in the HAD powders, indicating differences in water removal mechanisms depending on the drying technique used. During convective drying, water is transferred from inside the product to the product-air interface and then removed from the surface in the vapour state, leading to tissue shrinkage that can limit further moisture transfer [52,116]. This process results in the formation of a surface layer with increased resistance, which results in a dry surface, while the inner side remains moist [52,77]. ...
... During convective drying, water is transferred from inside the product to the product-air interface and then removed from the surface in the vapour state, leading to tissue shrinkage that can limit further moisture transfer [52,116]. This process results in the formation of a surface layer with increased resistance, which results in a dry surface, while the inner side remains moist [52,77]. This phenomenon is more pronounced as the drying rate increases [11,117]. ...
Fruit and vegetable industrialisation is a major contributor to food waste; thus, its integral transformation into functional powders has gained attention. Pretreatments can be incorporated into valorisation processes to generate structural or biochemical changes that improve powders’ characteristics. This study deepens into the impact of biological (fermentation, FERM) and thermophysical (autoclaving, AUTO; microwaves, MW; ultrasound, US; and pasteurisation, PAST) pretreatments, combined with dehydration (hot air-drying, HAD; or freeze-drying, FD) on the characteristics of powdered products obtained from broccoli stems. The impact of pretreatments on physicochemical (moisture, water activity, total soluble solids) and antioxidant properties (phenols, flavonoids, antioxidant capacity by ABTS and DPPH) on residue and powdered products was studied, together with their impact on plant tissue structure (Cryo-SEM) and the powders’ phenolic profile (HPLC). Probiotic viability was also determined on the fermented samples. The pretreatments applied, particularly the ultrasound, improved the antioxidant properties of the broccoli stems compared to the unpretreated samples, in line with microscopic observations. Dehydration did also improve the antioxidant attributes of the broccoli wastes, especially drying at 60 °C. However, pretreatments combined with dehydration did not generally lead to an improvement in the antioxidant properties of the powders. Probiotic properties were preserved in the freeze-dried products (>10⁷ CFU/g). In conclusion, pretreatments may be applied to enhance the antioxidant attributes of broccoli wastes, but not necessarily that of dried powdered products.
... For vegetables, the skin formation is called case-hardening, where the biopolymer network of the cell wall material densifies with an increase in the elastic modulus. The case-hardened skin can even get into the glassy state 10 . ...
... In this paper, we like to extend our previous model towards viscoelastic food materials. Pore formation happens in several food applications: a) spray drying of maltodextrin, where pore formation happens via cavitation, if a gel-like skin is formed 4 , b) pore formation in pre-dried vegetable snacks via instant pressure drop (DIC) 23 , and c) pore formation during hot air drying of vegetables, as induced by case hardening 10 , d) pore formation during drying of seeds, e) puffing of bubbles in heated starchy snacks 10,24 . The interplay between pressure drop and time development of porosity also plays a role in DIC treatment of nonpredried mushrooms 25 , but this system is different from above, as the mushroom is a porous system with high interconnectivity, while the other systems have closed pores. ...
... In this paper, we have studied numerically the pore formation during the drying of a spherical viscoelastic core-shell system with a central gas-filled cavity, which approximates food materials like vegetables and fruits. For these materials, it is known that porosity increases during drying after the event of case hardening, i.e. the formation of a hard, elastic skin 10 . Case hardening occurs if the dried material gets into the glassy state. ...
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,...
... However, the a w of the crumb portion of plain bagels remained unchanged during the baking and cooling process (0.933 to 0.933). The drastic differences in the a w of the crust and crumb of plain bagels could be attributed to case hardening [32,33]. The case hardening is a phenomenon where the product's outer layer dries much faster than the core or crumb portion during the baking process [33]. ...
... The drastic differences in the a w of the crust and crumb of plain bagels could be attributed to case hardening [32,33]. The case hardening is a phenomenon where the product's outer layer dries much faster than the core or crumb portion during the baking process [33]. Similar trends were observed by earlier researchers. ...
A study was conducted to validate the plain bagel baking process as an effective kill-step in controlling Shiga toxin-producing Escherichia coli (STEC) in the event of pre-baking contamination originating from flour. Unbleached bread flour was inoculated with five strains of STEC and dried back to its original water activity levels. The inoculated flour was used to prepare the bagel dough, proofed, boiled for 2 min, and baked at 232.2 °C (450 °F) for 14 min mimicking the commercial manufacturing process. Additionally, water activity (aw) and pH in plain bagels during baking, and thermal inactivation kinetics (D- and z-values) of STEC in plain bagel dough were studied. The results clearly demonstrated that baking plain bagels at 232.2 °C (450 °F) for 14 min will result in at least a >5 log reduction in the STEC population, thus providing an effective kill-step assuring the safety of the finished food products. The pH of plain bagels increased significantly from pre-proofed plain bagel dough to seven min into the baking process, reaching a final value of 5.83. The water activity of the crust and crumb portions of plain bagels was significantly different during the baking process. The D-values of STEC in plain bagels at, 56, 59, and 62 °C were 26.3 ± 1.55, 9.0 ± 0.27, and 2.50 ± 0.15 min with a z-value of 5.8 ± 0.16 °C.
... The dynamic changes of heat load and moisture load in the drying process are particularly complicated because of the porosity and biological characteristics of shiitake mushrooms [4]. On the one hand, excessive energy supply not only accelerates nutrient loss [20], shrinkage [21], and hardening [22], but also results in energy waste. On the other hand, insufficient energy supply leads to insufficient dehydration and longer drying time [23]. ...
... Therefore, shiitake mushrooms are rubbery and show viscoelastic behaviors during drying. The Poisson's ratio is taken as 0.49 according to [22]. The initial water saturation is calculated from the initial moisture content, solid matrix density, and liquid water density [50]. ...
Variable-temperature convective drying (VTCD) is a promising technology for obtaining high-quality dried mushrooms, particularly when considering rehydration capacity. However, accurate numerical models for variable-temperature convective drying and rehydration of shiitake mushrooms are lacking. This study addresses this gap by employing a model with thermo–hydro and mechanical bidirectional coupling to investigate five dehydration characteristics (moisture ratio, drying rate, temperature, evaporation rate, and volume shrinkage ratio) and a drying load characteristic (enthalpy difference) during VTCD. Additionally, a mathematical model combining drying and rehydration is proposed to analyze the effect of VTCD processes on the rehydration performance of shiitake mushrooms. The results demonstrate that, compared to constant-temperature drying, VTCD-dried mushrooms exhibit moderate shrinkage rates and drying time (16.89 h), along with reduced temperature variation and evaporation rate gradient (Max. 1.50 mol/(m³·s)). VTCD also improves enthalpy stability, reducing the maximum drying load by 58.84% compared to 338.15 K constant-temperature drying. Furthermore, drying time at medium temperatures (318.15–328.15 K) greatly influences rehydration performance. This study quantitatively highlights the superiority of variable-temperature convective drying, offering valuable insights for optimizing the shiitake mushroom drying processes.
... Therefore, it is essential to propose a comprehensive coupled multiphase transfer model, as illustrated in Figure 13. [113][114][115] Achieving uniform heating in microwave ovens has been a persistent challenge in their design. [116,117] Ahmad Zauzi et al. [100] attempted to use azodicarbonamide (ADC) as a foaming agent for microwave foaming of natural rubber (NR), but encountered significant difficulties due to the uneven cell structure produced internally. ...
... Schematic diagram of the physical process of steam-assisted foaming. [113][114][115] moderate increase in internal pressure, aiding the transport of vapor from the center to the surface (Figure 14(c)). The internal cell structure during foaming using convection heating and simultaneous microwave and convection heating is depicted in Figure 14(d). ...
... In line with previous studies, chopping before drying led to coarser particle sizes than grinding [9,11]. Chopping usually implies shorter drying times due to a less compacted bed which facilitates water migration through the inter-particle spaces; however, faster drying rates together with larger particles being dried have been related to case-hardening phenomena which makes it more difficult to reach low moisture content in the core of the particle and leading to rubbery materials, less crispy and more difficult to mill [12]. FD implied finer particle size powders than HAD. ...
... In contrast, in vegetables dried at 60 °C, only celery and leek samples followed this trend. This would confirm that faster drying rates and larger particles may lead to case-hardening phenomena, thus limiting water migration from the core of the particles [12]. Crusting phenomena are significantly influenced by the vegetable matrix structure but also by soluble solids content, since it implies the accumulation of non-volatile compounds carried away by water diffusion [11]. ...
Vegetable wastes are generated during harvesting, processing, and distribution, which implies a wastage of nutrients and evidence inefficiencies in present food systems. Vegetable residues are rich in bioactive compounds, for which their valorisation and reintroduction into the food chain are crucial towards circular economy and food systems sustainability. In this work, upcycled powdered ingredients were obtained from vegetables wastes (carrot, white cabbage, celery, and leek) through a disruption, dehydration and milling process. Disruption pre-treatment at different intensities was followed by freeze-drying or hot-air drying (60 and 70 °C), and final milling to produce fine powders. Powdered products were characterized in terms of physicochemical, antioxidant and technological properties (water and oil interaction), after processing and during four months of storage. Antioxidant properties were generally favoured by hot-air drying, particularly at 70 °C, attributed to new compounds formation combined to less exposure time to drying conditions. The powders showed good water interaction properties, especially freeze-dried ones. Storage had a negative impact on the quality of powders: moisture increased, antioxidant compounds generally diminished, and colour changes were evidenced. Upcycled vegetable waste powders are proposed as ingredients to fortify foods, both processing and storage conditions having an impact on their properties.
... During osmodehydration, the permeation of a hypertonic solution into the fruit tissue can occur heterogeneously (Fernando et al., 2008;Gulati and Datta, 2015). The heterogeneous impregnation entails a concentration disparity of solutes, with a marked accumulation of solids on the product's external surface (Martínez-Vera and Vizcarra-Mendoza, 2022). ...
... This condition occurs when the product's outer layer dries faster than the inner layers, forming a hard, impermeable layer on the surface. The hardened layer traps moisture inside the product, leading to non-uniform drying and the proliferation of mold and bacteria (Gulati and Datta, 2015). To prevent case hardening, it is important to ensure a drying process that is slow and uniform, facilitating sufficient airflow and humidity control. ...
... [110] Conventional heated air drying contributes to reducing moisture levels but poses safety concerns and the potential for case hardening. [112] Infrared drying minimizes quality reduction while rapidly drying food material and eliminating harmful mold spores. Nevertheless, improvements are needed to enhance the throughput of the drying process to meet the producers' requirements. ...
... One of the challenges posed by hot air drying is the formation of case hardening on the surface of the food materials during drying (Gulati and Datta, 2015). The crust formation usually resists the escape of moisture from the internal structure of the samples during drying (Portanguen et al., 2014). ...
... Before baking, the dough starts in a rubbery state. As it bakes, moisture evaporates, causing the dry matter content to increase with time resulting in a state transition to either a rubbery-glassy or fully glassy state (Gulati & Datta, 2015;Sinha & Bhargav, 2020a). Subsequently, when the snack is cooled down to room temperature, it becomes stiffer (i.e. higher Young's modulus). ...
Customized textures can be achieved using extrusion-based 3D food printing by varying composition and processing parameters, e.g., printing designs and post-processing conditions. This study aims to design textural properties of customized pea-based snacks by investigating the effects of composition and multiple processing parameters on fracture behavior. Macronutrient composition of printing materials (i.e. starch-to-protein ratio), geometric design, and post-processing conditions (i.e. steaming or baking time) were systematically varied. The fracture behavior of freshly printed and post processed structures was analyzed. Samples showed elastic deformation and plastic deformation after steaming and baking, respectively. This difference in fracture behavior could be linked to microstructural changes indicated by confocal laser scanning microscopic imaging. Starch-to-protein ratio of the printing material and the geometric design also influenced the fracture behavior, but to a relatively minor extent. Moreover, fracture stress and Young’s modulus were strongly influenced by the dry matter content of the samples. Statistical analysis using ANOVA was performed to establish the significance of the effect of composition and processing parameters on Young’s modulus and dry matter content of samples. Based on this understanding, we propose different strategies to effectively design textural properties of snacks using 3D printing. By considering multiple factors, this study provides valuable insights into designing healthy snacks with customized textures using 3D food printing.
... The exclusion of water during treatment is a factor in the fineness of cowpea leaves (Mythili et al., 2021). Initial high moisture content can cause rapid initial drying rates causing hardening of the outer layer but rubbery inner core with higher moisture content, making them difficult to mill (Bas-Bellver et al., 2022;Gulati & Datta, 2015). Bas-Bellver et al. (2022) reported finer particle size with higher drying temperatures for cabbage and the opposite for broccoli. ...
Indigenous fruits and vegetables can improve food security and biodiversity. However, their use is hindered by perishability, seasonal availability, cooking losses, lack of nutritional composition data, and connections to low socioeconomic status. This study aimed to process cowpea leaves into powder and determine the effect of five home‐cooking methods on their protein, functional, physicochemical, and heavy metal profiles. Cowpea leaves were boiled, blanched, steamed, sous‐vide cooked, and stir‐fried, at 5, 10, and 15 min before dehydration at 60°C. Cowpea leaves contain protein up to 20 g/100 g. The leaves are rich in calcium, potassium, and zinc, providing up to 70% of the adult recommended dietary allowance for calcium and potassium per 100 g of powder. Cowpea leaf powder exhibited good water/oil absorption and rehydration capacities. Sous‐vide and steamed cowpea leaves provided an overall superior nutritional profile (p ≤ 0.05). Heavy metals in the cowpea leaf powders were below the WHO permissible limits except for aluminum and high arsenic levels. This study demonstrated that cowpea leaf powders could be potentially incorporated into foods to improve functional properties and nutrient intake.
... In general, the processing of satay komoh is still conventional or traditional, namely using charcoal grilling. The constraints of conventional processing are uneven product doneness and case hardening often occurs (Gulati and Datta, 2015). This problem also occurred in satay Thunnus sp. from Small and Medium Enterprises (SMEs) Poklahsar Mina Jaya Mandiri, Kondang Merak Beach, South Malang, so that an alternative idea emerged using a microwave oven to overcome this problem. ...
Satay as a traditional Indonesian product is still sold directly in fresh processed form and none has been sold in frozen processed form. So far, various types of satay have been found based on raw materials, processing, spices used, and region of origin. One type of traditional satay is komoh. Inspired by products that can be sold in frozen processed form such as nuggets sold in frozen semi-cooked processed form, it is necessary to conduct research on satay products. The aim of this study to determine the right conditions for processed satay meat that can be stored frozen. The research method applied was an experimental method carried out in the form of treating raw satay conditions, semi-cooked satay conditions, and cooked satay conditions stored frozen. Satay was made in 2 ways, namely the traditional charcoal grilling process and the microwave grilling process. The results showed that satay komoh from Thunnus meat made with a microwave was organoleptically preferred over conventional satay komoh, both in terms of color, aroma, taste, and texture attributes. Microwave-satay has lower texture, peroxide value, Thio-barbituric Acid, and water content than conventional-satay. Satay komoh that stored frozen in half-cooked and cooked conditions is preferred over raw conditions. Satay komoh that stored frozen with increasing doneness has an effect on the texture, peroxide, Thio-barbituric Acid, and water content. The best treatment in frozen storage of satay komoh was grilling with a microwave in half-cooked conditions.
... The porous tissue structure of samples can be promoted at higher drying temperatures due to the faster moisture migration and evaporation rate in comparison to the lower temperatures. At higher drying temperatures, a transition from a rubbery state to a glassy state prevails on the outer surface of the samples than the core due to the faster removal of water [32]. This results in the formation of a porous rigid crust, known as case hardening, on the surface which promotes the development of a highly porous interior structure [10]. ...
... This finding also can be explained by the glass transition theory. The mechanical properties of SAM in its rubbery state (initial period of drying) are too low to generate stress which can offset the hygroscopic stress induced by capillary pressure, and afterwards as drying progressed, the anti-plasticization effect of water leads to an increase in T g , which significantly (p < 0.05) influence the mechanical properties of a material (Gulati & Datta, 2015). Contrary to this study, Ozturk and Takhar (2020) reported that the highest relaxation modulus value was observed in fresh carrots due to its compact and hard texture, but it was decreased to the lowest value after 1-h drying and afterwards increased with increasing drying time. ...
The effects of ultrasound (US) pretreatment, heat pump drying temperature and drying time on the water status and viscoelastic properties as well as the correlation between them of scallop adductors were investigated. As drying progressed, the transverse relaxation time (T2) of tightly and loosely bound water maintained a relatively stable state, while the T2 of free and immobilized water shifted leftwards with US pretreatment and increasing drying temperature. The creep compliance was increased, but the relaxation modulus decreased with US pretreatment and an increase in drying temperature. However, the creep compliance exhibited a decreasing trend, but the relaxation modulus showed an increase tendency as drying proceeded, viz., decreasing moisture content. Burger’s model and the three-element generalized Maxwell model achieved the best fit to describe the creep behavior and stress relaxation, respectively. The storage modulus (G′) and loss modulus (G″) were decreased with US pretreatment, increasing the drying temperature and moisture content. The T2 of all water components and peak area fraction of immobilized water were positively correlated with the creep compliance but significantly negatively correlated with the stress relaxation modulus, G′ and G″. Low-field nuclear magnetic resonance provided reliable viscoelastic properties of scallop adductors by monitoring the water status during the drying process, which can be used to accurately control the final product quality.
... However, the a w of crumb portion of English muffins increased slightly (0.9470-0.9557), which could be attributed to case hardening and toughening of crumb during baking. Gulati and Datta (2015) studied the poromechanics model that includes multiphase (solid matrix/liquid water/vapor) transport and explained case hard- ening as a phenomenon where the outer layer of the food material dries much faster than the core during the drying of the food materials. The a w of the crust and crumb samples of English muffins follows the same trend as reported by various other baking validation studies. ...
... This content was influenced by the applied drying process (p > 0.05), as samples subjected to lyophilization showed a higher flavonoid content compared to those subjected to hot air drying at 60°C with an air velocity of 2 m·s −1 , demonstrating the beneficial effect of lyophilization on extraction. Additionally, Gulati and Datta [41] report that the sonication process enhances the rate of water removal within the material's surface by creating microscopic channels through compression and expansion. Hence, in the present study, UAE was employed for improved extraction of bioactive compounds. ...
The research investigates the extraction of antioxidant phenolic compounds from grape pomace, a wine fermentation byproduct. Ultrasound-assisted extraction (UAE), varying parameters such as solute:solvent ratio, power, and time were utilized. UAE was specifically applied to Vitis vinifera L. using high-intensity ultrasound with ratios of 1:18 and 1:42 g:mL, 250 and 400 W power levels, and extraction times of 15 and 20 minutes. Total phenolic content was quantified via the Folin–Ciocalteau reagent, and total flavonoids were determined using quercetin as a standard. Antioxidant capacity was evaluated through ABTS, FRAP, and DPPH Radical Scavenging Assays, with Trolox equivalent antioxidant capacity (TEAC) for comparison. Results indicated a total phenolic content of 50 to 80 μmol GAE/g d.w., with no significant differences among treatments. Total flavonoid concentration ranged from 2.5 to 4 μmol QE/g d.w. Importantly, the solute:solvent ratio impacted antioxidant capacity, with higher ratios showing increased ABTS radical capacity. Treatment 1, with the highest flavonoid content, exhibited the greatest antioxidant capacity against DPPH radicals. This study underscores the intrinsic correlation between cumulative bioactive compound content and the inherent antioxidant capacity of grape pomace extracts. This highlights the potential application of these extracts as antioxidant reservoirs, poised for integration into functional foods and biomedical nutraceuticals.
... The results highlight that both lentils and yellow peas experience a higher initial loss of moisture during the early stages of IR exposure, followed by a gradual decrease with prolonged exposure. This phenomenon may be attributed to the rapid removal of surface or free moisture from lentils, leading to a "case-hardening" effect on the exterior surface as it reaches a glass transition stage (Gulati & Datta, 2015). This exterior hardening could be more pronounced in lentils due to their smaller kernel size and relatively larger surface area, facilitating faster removal of free moisture. ...
... Furthermore, no experimental evidence of casehardening, which is associated with the transition from a rubbery to a glassy state of the outer layers [58] , was observed within the moisture content ranges used in this study. The transition from the rubbery to the glassy state and vice versa is also linked with stress cracking during the drying of food materials [59] . ...
... Szymanek et al. (2020) suggested that blanching can increase the sample's moisture content, thereby increasing the drying time required. Gulati and Datta (2015) suggested that higher moisture content in dried materials can lead to lower yields due to the materials' rigid texture, complicating the crushing and milling process. This finding is consistent with the results presented in Table 2, which show that jicama flour, with a higher moisture content than cassava flour, resulted in a lower yield (7.73±0.16%) ...
Biscuits are a commonly consumed bakery product typically using wheat flour as a primary ingredient, rendering them unsuitable for gluten-intolerant consumers. Using cassava as a gluten-free alternative for composite flour in bakery products has been proven effective. Furthermore, jicama, which has high total dietary fiber contents, including inulin, can enhance total dietary fiber content. However, high-fiber ingredients can often produce a tough texture. To address this, fats such as butter and margarine are typically used to enhance the texture of baked products, although the use of shortening still needs to be explored. Both margarine and shortening are vegetable-based, making them more widely consumable. The production of jicama flour and gluten-free biscuits was the focus of this study. This study uses a completely randomized design with two factors: the ratio of composite flour (100:0, 90:10, 80:20, 70:30, 60:40) and the type of fat (margarine and shortening). Analyses were performed on the gluten-free biscuits to determine the total dietary fiber, inulin, fat, moisture, spread ratio, color and hardness. Results indicated that biscuits made with shortening with a flour ratio of 90:10 of cassava to jicama flour are the best formulation, yielding 2.54±0.00% inulin, 6.50±0.10% total dietary fiber, 19.88±0.17% fat, 2.20±0.10% moisture content, 10.03±0.20 spread ratio, lightness (L*) value of 52.53±0.37, °Hue value of 66.78±0.51, and 869.88±16.07 g hardness. This study shows that jicama flour can be an alternative to producing composite flour for gluten-free products. Shortening, which is not commonly used in biscuit making, may be considered an alternative fat source.
... On the other hand, high drying rates promote rapid moisture depletion and consequently more diffusion of vitamin C. However, the case-hardening effect due to quick removal of water allowed conservation of vitamin C (Gulati & Datta, 2015). On the other hand, the low porosity and high apparent density of the dehydrated fruit resulting from this technique exerts a protective effect on the vitamin, allowing little oxygen inside the sample, low partial pressure of oxygen close to the sample surface and low breakage of cell walls during drying (Lewicki & Pawlak, 2003;Oikonomopoulou & Krokida, 2013). ...
Food insecurity is a major global challenge. Food preservation, particularly through drying, presents a promising solution to enhance food security and minimize waste. Fruits and vegetables contain 80%–90% water, and much of this is removed during drying. However, structural changes across multiple length scales occur during drying, compromising stability and affecting quality. Understanding these changes is essential, and several modeling techniques exist to analyze them, including empirical modeling, physics‐based computational methods, purely data‐driven machine learning approaches, and physics‐informed neural network (PINN) models. Although empirical methods are straightforward to implement, their limited generalizability and lack of physical insights have led to the development of physics‐based computational methods. These methods can achieve high spatiotemporal resolution without requiring experimental investigations. However, their complexity and high computational costs have prompted the exploration of data‐driven machine learning models for drying processes, which involve comparatively lower computational costs and are more straightforward to execute. Nonetheless, their poor predictive ability with sparse data has restricted their application, leading to a hybrid modeling approach: PINN, which merges physical insights with data‐driven machine learning techniques. This method still holds significant potential for advancements in food drying modeling. Therefore, this study aims to conduct a comprehensive literature review of state‐of‐the‐art conventional drying modeling techniques, such as empirical, physics‐based computational, and pure data‐driven machine learning techniques, and explores the potential of the PINN approach for overcoming the limitations associated with conventional drying modeling strategies.
Karasumi, a salted-dried mullet (Mugil cephalus) roe, is consumed worldwide. Anjo is widely utilized to increase the drying rate of Karasumi during the manufacturing process. However, the detailed influence of different Anjo processes (pressing, wrapping, and pressing-wrapping) on the water behavior and quality of Karasumi during drying remains unclear, and thus, their effects were investigated. Moisture content and ¹H T2-enhanced images obtained from magnetic resonance imaging (MRI) analysis clarified that the pressing Anjo method was the most effective in promoting the drying of Karasumi. An increase in Young’s modulus and acceleration of browning were observed in the pressed sample with the progress of drying. Furthermore, the pressed sample did not exhibit the surface irregularities and internal cracking observed in the control sample. Therefore, the pressing Anjo process during the production of Karasumi is effective not only in accelerating drying, but also in improving its visual properties, such as shape and prevention of cracking.
Drying is a complex process of simultaneous heat, mass, and momentum transport phenomena with continuous phase changes. Numerical modelling is one of the most effective tools to mechanistically express the different physics of drying processes for accurately predicting the drying kinetics and understanding the morphological changes during drying. However, the mathematical modelling of drying processes is complex and computationally very expensive due to multiphysics and the multiscale nature of heat and mass transfer during drying. Physics-informed machine learning (PIML)-based modelling has the potential to overcome these drawbacks and could be an exciting new addition to drying research for describing drying processes by embedding fundamental transport laws and constraints in machine learning models. Based on a comprehensive literature review, this paper presents two types of information: fundamental physics-based information about drying processes and data-driven modelling strategies to develop PIML-based models for drying applications. The current status of physics-based models and PIML-based models and their limitations are discussed. A sample PIML-based modelling framework for drying application is presented. Finally, the challenges of addressing simultaneous heat, mass, and momentum transport phenomena in PIML modelling for optimizing the drying process are presented at the end of this paper.
Deformation during drying is a major physical change influencing drying kinetics and final product quality. Therefore, accurate prediction of shrinkage kinetics is essential for determining the optimal drying conditions for these foods. Shrinkage kinetics is greatly influenced by their structural mobility (rubbery-glassy transition) and
viscoelastic properties. The current deformation models lack a comprehensive integration of structural mobility and viscoelasticity concepts, resulting in limitation in attaining insights on physiochemical state variations and viscoelastic stresses developed during drying. In order to overcome this limitation, this study proposes a novel mechanistic shrinkage model that combines solid matrix mobility-based shrinkage velocity and viscoelasticity consideration, incorporating variable mechanical properties to simulate deformation arising from moisture loss
and pressure gradient respectively. Comparison between predicted drying kinetics and shrinkage evolution with experimental observation yielded close agreement, achieving low mean absolute error values. As the drying process progressed, a distinct anisotropic shrinkage pattern emerged, which is attributed to varied structural mobility based on temperature and moisture distribution across the food sample. Notably, shrinkage driven by moisture loss significantly outweighed that induced by pressure, exerting a predominant influence on overall volume change. Furthermore, the model demonstrated heightened sensitivity to water transport parameters compared to mechanical factors, which indicates the significance of moisture dynamics in shaping the drying process. Combined consideration of physiochemical changes and viscoelastic concept in the developed deformation
model extends new possibility towards optimizing the drying process as well as quality aspect evaluation.
Biological materials always exhibit heterogeneous physical properties, both mechanical and chemical, which give them a rich phenomenology that poses significant challenges in the developing of effective models. The Flory–Rehner theory revolutionized our understanding of the dynamics of the liquid-polymers coupling in soft swollen gels, recognizing polymers as elastic networks stretched by the presence of liquid. Despite its foundational role, applying this theory to bodies with non uniform physical properties requires further improvements. This article proposes a unified approach to address mechano-diffusion challenges in multi-domain bodies, that is in material bodies made of regions having different chemo-mechanical properties, and focuses on the dehydration and remodeling of biological-like materials. Drawing inspiration from natural systems, we integrate principles from nonlinear mechanics and swelling theories; in particular, what is specifically new is the idea of applying the notion of the multiplicative decomposition of the strain–developed for plasticity–to model the swelling properties of a body made of two or more materials. The article gives a systematic presentation of the subject, and guides readers through key concepts and practical insights, aiming to provide a robust framework for modeling chemo-mechanical interactions. Moreover, it paves the way for the modeling of heterogenous bodies having spatially-varying properties.
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.
Four different drying methods, hot-air-drying (HAD), vacuum-drying (VD), ultrasound-assisted vacuum-drying (US-VD), and freeze-drying (FD), were used to obtain dried plums (Prunes domesticaL.). These prunes were evaluated for their physical properties (such as color, rehydration ratio, and microstructural properties), phenolic compounds, and antioxidant activities before and after being subjected to in vitro digestion. TPC (total phenolic content) of plums ranged from 196.84 to 919.58 mg of GAE (gallic acid equivalent)/100 g of dw, and neochlorogenic acid was the most abundant phenolic compound. FD prunes had the highest levels of phenolics, whereas US-VD caused the most significant loss. During in vitro digestion, the phenolics were present at higher levels at the gastric medium but failed to maintain their stability at the small intestinal stage. Among the samples, FD along with HAD prunes exhibited a higher bioaccessibility index for most of the phenolic compounds. The ratios of TPC, TFC (total flavonoid content), and individual phenolics determined in the digested residues to the initial values of the undigested samples ranged from 0.23 to 31.03%. It could be concluded that the majority of the phenolics were extracted during digestion. Our findings showed that the different drying methods would alter the microstructure, which would affect the extractability and release of phenolics in the simulated digestion model.
A significant part of the world's population still has problems in accessing food. The growing world population will exacerbate this issue in the future. Innovative studies conducted in this field play a crucial role in addressing the issue of drying and storage of foods. Atmospheric drying methods, such as rotary, tunnel, conveyor, cabinet, tower, and kiln dryers, offer advantages in relation to high production capacities, cost‐effective initial setup, and economical operating conditions. However, concurrently, the weaknesses of these methods arise from factors such as drying duration, uneven moisture content, and space requirements. The solar dryer method is especially effective in dehydrating agricultural products, offering an energy‐saving advantage compared to other methods. However, it is important to note that this approach, which involves exposing crops to direct sunlight, comes with several drawbacks affecting both food quality and health. In cases where the quality of highly valued foodstuffs is crucial, subatmospheric drying methods like vacuum, freeze, and microwave freeze are typically preferred. However, the primary drawback of this approach lies in its high operating costs, particularly in terms of energy consumption. Artificial neural networks (ANNs) can be used for predictive modeling, helping to forecast drying behavior and optimize process parameters in food drying applications especially nonlinear connections among variables. ANNs are adept at managing nonlinearities, offering a more precise depiction of the intricate interactions within food drying systems. This review examines articles from the last 5 years in the literature, synthesizing research conducted in food drying. The findings indicate a predominant interest among researchers in methodologies with lower environmental impact, prompting increased attention to studies addressing this aspect. There is a notable emphasis on the frequent exploration of energy‐efficient systems. The ongoing research focuses on the development of methods utilizing ultrasonic, infrared radiation, and electrohydrodynamic techniques to achieve more effective, shorter‐duration, energy‐efficient drying processes with enhanced control over the final product.
In this paper, we review the physical/chemical phenomena, contributing to the final texture of French fries, as occurs in the whole industrial production chain of frozen par-fried fries. Our discussion is organized following a multiscale hierarchy of these causal factors, where we distinguish the molecular, cellular, microstructural, and product levels. Using the same multiscale framework, we also discuss currently available theoretical knowledge, and experimental methods probing the relevant physical/chemical phenomena. We have identified knowledge gaps, and experimental methods are evaluated in terms of the effort and value of their results. With our overviews, we hope to give promising research directions such to arrive at a multiscale model, encompassing all causal factors relevant to the final texture. This multiscale model is the ultimate tool to evaluate process innovations for effects on final textural quality, which can be balanced against the impacts on sustainability and economics.
The popularity of gluten-free (GF) pasta has increased dramatically as more individuals become aware of the adverse health effects of gluten-containing diets caused by gluten sensitivity or celiac disease. In GF pasta, starch and some added proteins are the main polymeric ingredients, and they determine the structural, textural properties and cooking qualities. However, drying temperature is a challenging factor in the production of GF pasta, and it is crucial to optimize drying conditions to achieve the desired GF pasta properties. Industrial production of GF pasta requires careful observation in controlling heat and mass transfer processes in order to ensure improved quality and morphological attributes of end-product. Drying is a crucial step in the GF production line; thus, the proper understanding and effective implementation of all engineering knowledge should be followed to maximize production with minimum quality loss. This chapter provides an overview of how drying temperature affects different properties of GF pasta with paramount consideration for achieving a desirable product.
This chapter reviews the factors that contribute to the texture of fish. We review the methods used to assess the texture of fish from both an instrumental and a sensory perspective. Fish is easily spoiled and hence frequently processed to extend the shelf life; such products as surimi, dried fish, smoked fish, fermented fish, and canned fish are described in this chapter. For each product, we examine how it is processed and how the texture is affected.
Instant rice is well-suited for ready-to-use applications as low-moisture, light-weight military ration and emergency food for our Armed Forces, offering longer shelf life with rapid rehydration characteristics. Present investigation demonstrated the effect of different salt pretreatment during soaking as precooking operation on the physico-chemical, cooking and rehydration kinetics of instant rice. Application of salt pretreatment reduced bulk density and damaged grain percentage, while enhanced the porosity, volume expansion percent, weight gain percentage, and rehydration characteristics. The grain elongation ratio was not affected significantly by the application of salt pretreatments; however, water uptake and chemical composition were significantly affected. Soaking pretreatment with 1% calcium chloride, followed by open pan cooking and subsequently freeze-thaw-dehydrating until attainment of 5–6% moisture content was found to be the optimal processing condition for developing instant rice with less than 2 min of rehydration time by mere addition of hot water. Modelling of water absorption behaviour revealed that both Peleg (R2 0.980–0.999) and Singh and Kulshrestha (R2 0.966–0.999) models fitted well.
The authors start with an introduction to the concepts involved in physics giving the equations of flow through porous media and the deformation characteristics of soils and rocks. Succeeding chapters deal with the practical implications of these phenomena and explain the application of theory in both experimental and field work. Details are given of actual incidents, such as the subsidence experienced in Venice and Ravenna. The authors have also formulated a consolidation code, which is detailed at the end of the book, and provide instructions on how to modify the given program.
Microwave (MW) drying is a rapid dehydration technique that can be applied to specific foods. Increasing concerns over product quality and production costs have motivated the researchers to investigate and the industry to adopt microwave drying technology. The advantages of microwave drying include the following: shorter drying time, improved product quality, and flexibility in producing a wide variety of dried products. Drying is influenced by heat and mass transfer between drying airflow and product, as well as the complex moisture transport processes which take place in the product.. This paper presents an analytical approach for the drying of potato. The laws of moisture content change in the food product as a function of mass transfer are used for the theoretical approach. The study gives a brief description of efforts made to obtain basic drying parameters under different microwave drying conditions. This computational method can be used as a tool for microwave drying of potato slabs more efficiency.
In the present work the moisture content and apparent density of pears were measured during the drying of pears under different conditions: peeled uncut pears dried by direct sun exposure (a traditional method used in Portugal) and small slices of pear pulp dried in a ventilated drying chamber at constant temperature of 30°C.
Using the experimental results obtained was possible to estimate the parameters of the model proposed by Zogzas et al. (1994), and make previsions of bulk and particle densities as well as porosity variations during drying.
It was possible to conclude from this work that, in spite of being substantially different, the two drying procedures used can be considered equivalent with respect to the structure product developed. In fact, the model parameters were very similar in the two situations tested and the evolution of porosity was also very analogous. Furthermore, it was possible to conclude that the pears developed relatively low porosities during drying, as a consequence of the slow drying rates used in both situations, and the high degree of shrinkage observed.
Volumetric and thickness shrinkage evaluated by direct measurement and n-heptane displacement were determined during convective and freeze drying of Golden delicious apples. For convective drying, the influence of blanching and diameter/thickness ratio of the apple disks used were analysed at different levels of moisture content under constant conditions. It was found that shrinkage of dried samples, both by convection and by freeze-drying, is anisotropic to a level which depends on sample geometry (ratio diameter/thickness) used. Blanching did not affect shrinkage results.Based on results obtained a new model to predict bulk density of materials during drying is proposed, showing a better fit to experimental data than previous models reported in the literature. This model was further used to predict changes in apple porosity during drying.
The present work aimed, on one hand, to study of the drying of onions in terms of drying kinetics, which was evaluated at 30°C, 50°C and 60°C. The experimental data was fitted to different empirical kinetic models from the literature, and this kinetic study was then complemented with the modelling if terms of Fick's diffusion equation, for estimation of the diffusion coefficients. On the other hand, the chemical characterization in fresh and dried onions at different temperatures (varying from 30°C to 70°C) was analysed, to evaluate the effect of drying and drying temperature on the chemical composition of the product. In this way, the analyses of moisture content, sugar content, crude protein, ash, fat, crude fibre, acidity and vitamin C were made and reported in this paper.From the results obtained it was verified that some chemical components of the onions are not affected by drying (ash, fat, protein and fibre) whereas some others are considerably influenced by drying (sugars, acidity and vitamin C). The present work allowed concluding that the three empirical models tested (Newton, Modified Page and Logarithmic) all describe relatively well the dehydration kinetics at the three temperatures analysed. Moreover, from the experimental data it was possible to estimate the diffusivities, which range between 3.33×10−09m2/s at 30°C and 8.55×10−09m2/s at 60°C.
State diagram is a map of the different states of a food as a function of water or solids content and temperature. The main advantage of drawing map is in identifying different states of a food, such as freezing point and glass transition, which helps in understanding the complex changes when food's water content and temperature are changed. it also assists in identifying food's stability during storage as well as selecting suitable conditions of temperature and moisture content for processing. This paper provides an overview and critical assessment on the basic concepts of the state diagram with their terminologies, selected measurement techniques, and their use. Glass transition alone could not be considered as generic rules for food stability criteria since numbers of instances, such as pore formation, diffusion, microbial stability, non-enzymatic browning, other factors or mechanisms play important role. However, it is definitely one of the factors affecting the stability, and a future challenge to combine the glass concept with other mechanisms or factors.
Using thin discoid and slender cylindrical potato samples, the shrinkage data in all three dimensions were obtained experimentally at a temperature of 60°C, a relative humidity of 5%, and an air velocity of 1.6m/sec. The results are expressed as percentage change of lengths in axis and radius during drying. The relationships between volume and directional shrinkage were discussed. Directional shrinkage was correlated to volumetric shrinkage and moisture removal direction. It was observed that the shrinkage coefficient in the axis was significantly different from that in the radius during air-drying. On the other hand, data describing the mechanical characteristics of cylindrical potato samples were experimentally determined at the above drying conditions. The Young's modulus (E), yield stress (μc), fracture stress (μf) were expressed as a function of bulk moisture content (M). These data for the moisture ranges used in conventional potato drying can help to optimize the drying conditions and the drier design. © 2001, Japan Society for Food Engineering. All rights reserved.
Collapse of structure of foodstuffs during air drying affects quality. In many materials the soluble components, mainly sugars, are an important part of the tissue in which case collapse may be related to their glass transition temperature (Tg). It has been speculated that collapse occurs at a temperature (Tc) related to, but greater than, Tg. Plant tissues with high moisture contents, such as celery, have low Tgs. Therefore considerable collapse is expected at drying temperatures. The aim of this study was to determine how air drying temperature affected the quality characteristics of the tissue. Celery, air dried at temperatures between 5 and 80 °C, was examined for volumetric shrinkage, rehydration characteristics and porosity changes. Significant shrinkage occurred at all drying conditions. At low water content collapse was limited, probably due to a higher collapse temperature. Porosity development was insignificant during drying until the sample was very dry. Lower air-drying temperatures gave a product with improved quality characteristics.
Several researchers have developed mathematical models, which can be used to predict the thermal properties of liquid food products. However, they are for specific liquid foods with little application to all the physical situations in food processing. For a model to have broad applications, it should account for temperature and composition changes. Because in food processing these two variables are commonly encountered. Therefore, the following objectives are developed for this study: to collect as much literature data on thermal properties of liquid foods as possible; to develop general mathematical models to predict the thermal conductivity, thermal diffusivity, density and specific heat of liquid foods based on the literature data.
The effect of shrinkage on moisture diffusion during drying of biological products has been considered by numerically solving simultaneously for shrinkage and moisture content, assuming a density and concentration dependent mass diffusivity. The moisture diffusion equation for remoistened soybeans, simulated by spherical bodies, has been solved by a finite-element technique.
The purpose of this study is to develop a mathematical methodology to qualify corn kernel breakage caused by drying processes. Stresses, predicted for a viscoelastic sphere with the physical properties of horny endosperm, were calculated as functions of predicted moisture and temperature gradients in the sphere. Combined processes of drying, tempering (holding the grain at elevated temperatures), and cooling were evaluated. The moisture gradients and, to a lesser degree, the temperature gradients, were sig- nificant in stress development and relaxation. Since the results indicate that the predicted stresses follow the same trends as published experimental results for the breakage susceptibility of corn, the potential exists for this method to be used as a design tool to estimate the extent of kernel stress and breakage caused by a drying process.
Drying is one of the most complex and energy-consuming chemical unit operations. R&D efforts in drying technology have skyrocketed in the past decades, as new drivers emerged in this industry next to procuring prime product quality and high throughput, namely reduction of energy consumption and carbon footprint as well as improving food safety and security. Solutions are sought in optimising existing technologies or developing new ones which increase energy and resource efficiency, use renewable energy, recuperate waste heat and reduce product loss, thus also the embodied energy therein. Novel tools are required to push such technological innovations and their subsequent implementation. Particularly computer-aided drying process engineering has a large potential to develop next-generation drying technology, including more energy-smart and environmentally-friendly products and dryers systems. This review paper deals with rapidly emerging advanced computational methods for modelling dehydration of porous materials, particularly for foods. Drying is approached as a combined multiphysics, multiscale and multiphase problem. These advanced methods include computational fluid dynamics, several multiphysics modelling methods (e.g. conjugate modelling), multiscale modelling and modelling of material properties and the associated propagation of material property variability. Apart from the current challenges for each of these, future perspectives should be directed towards material property determination, model validation, more complete multiphysics models and more energy-oriented and integrated “nexus” modelling of the dehydration process. Development of more user-friendly, specialised software is paramount to bridge the current gap between modelling in research and industry by making it more attractive. These advanced computational methods show promising perspectives to aid developing next-generation sustainable and green drying technology, tailored to the new requirements for the future society, and are expected to play an increasingly important role in drying technology R&D.
Magnetic resonance imaging (MRI) was used to obtain moisture profiles of a model food gel during drying. A cylinder of gel, 1 cm in diameter, with an initial moisture content of 76% was imaged while drying at room temperature. Moisture profiles were obtained from the imaging data by imaging calibration samples of known moisture content. Signal intensity of the images was found to be highly proportional to solids content. The moisture profiles were compared to profiles predicted by a finite difference solution of Fickian radial diffusion in a cylinder. Actual moisture profiles obtained by MRI were much flatter near the center of the cylinder, with a steeper moisture profile near the edge, compared to the typical parabolic shape of the Fickian model. The Fickian model was found to be an inaccurate predictor of the interior moisture profile of the model food gel, since effective diffusivity was found to not be solely a function of moisture content. The moisture profiles obtained provide for a method to evaluate other mass transfer models, and the methods outlined provide a technique to explore mass transfer within actual food materials during processing.
A numerical model is developed for prediction of transient moisture content of food materials. The moisture transfer is modeled considering diffusion of liquid water from inner layer to outer surface of the food material followed by evaporation of water from the surface to the dry air which flows over the moist food material. Discretization of transient heat and mass transfer governing equations are done using the finite-volume method (FVM). A 3-D code in MATLAB is developed to solve the simultaneous heat and mass transfer equations. The flow field over the moist food material is assumed to be turbulent and SST k–ω turbulence model is used for prediction of heat transfer coefficient using a computational fluid dynamics (CFD) commercial code. The sample moist food material is considered to be a rectangular shaped potato and the effects of temperature and velocity on drying behavior of the same are predicted. Different drying rate periods are identified. The numerical model is validated with experimental data with a reasonable agreement.
The aim of this work was to study the effect of temperature and air velocity on the drying kinetics and quality attributes of apple (var. Granny Smith) slices during drying. Experiments were conducted at 40, 60 and 80 °C, as well as at air velocities of 0.5, 1.0 and 1.5 m s−1. Effective moisture diffusivity increased with temperature and air velocity, reaching a value of 15.30 × 10−9 m2 s−1 at maximum temperature and air velocity under study. The rehydration ratio changed with varying both air velocity and temperature indicating tissue damage due to processing. The colour difference, ΔE, showed the best results at 80 °C. The DPPH-radical scavenging activity at 40 °C and 0.5 m s−1 showed the highest antioxidant activity, closest to that of the fresh sample. Although ΔE decreased with temperature, antioxidant activity barely varied and even increased at high air velocities, revealing an antioxidant capacity of the browning products. The total phenolics decreased with temperature, but at high air velocity retardation of thermal degradation was observed. Firmness was also determined and explained using glass transition concept and microstructure analysis.
This updated and expanded edition of the bestselling textbook provides a comprehensive introduction to the methods and theory of nonlinear finite element analysis. New material provides a concise introduction to some of the cutting-edge methods that have evolved in recent years in the field of nonlinear finite element modeling, and includes the eXtended finite element method (XFEM), multiresolution continuum theory for multiscale microstructures, and dislocation-density-based crystalline plasticity.
Nonlinear Finite Elements for Continua and Structures, Second Edition focuses on the formulation and solution of discrete equations for various classes of problems that are of principal interest in applications to solid and structural mechanics. Topics covered include the discretization by finite elements of continua in one dimension and in multi-dimensions; the formulation of constitutive equations for nonlinear materials and large deformations; procedures for the solution of the discrete equations, including considerations of both numerical and multiscale physical instabilities; and the treatment of structural and contact-impact problems.
The multiphase porous media model, developed in the companion paper, has been applied to frying of a restructured potato slice to obtain temperature, pressure, moisture, oil content, acrylamide content and evaporation rate profiles, providing valuable insight into the frying process. The model is validated by comparing temperature, moisture content and crust thickness profiles from literature experimental results. A novel non-equilibrium formulation, different from the existing food literature, is able to describe well the evaporation process. Post-frying cooling is included through appropriate changes in boundary conditions. It is seen that the oil pickup mostly takes place during post-frying cooling and is due to capillary suction created by the negative pressures from condensation of water–vapour. Acrylamide is formed primarily in the crust region where temperature exceeds 100°C. Sensitivity analyses of the process to surface mass transfer coefficient, evaporation rate constant and oil diffusivity show that they all have significant effects on the process. Development of this mechanistic model that is also more easily implementable than previous models should make computer-aided design and optimization of frying processes closer to reality.
A fundamental-based model of the frying process that can also be solved in a commercially available software would provide tremendous benefit to design of fried food products and frying processes by making the power of simulation available for design. Quality and safety issues such as crust development, oil pickup and acrylamide formation can be addressed with such a model. However to achieve the above without sacrificing the fundamental physics behind the process, significant reformulations are needed, that require mathematical as well as physical insight into the process. An improved multiphase porous media model involving heat and mass transfer has been developed and solved numerically with careful consideration given to selection of input parameters. Non-equilibrium formulation for evaporation is used which describes the physics better and is easier to implement in a typical CFD software as it can explicitly express the evaporation rate in terms of concentration of vapor and temperature. External heat transfer and mass transfer coefficients are estimated to accurately reflect the different frying phases, i.e., the non-boiling phase and surface boiling and falling rate stages in the boiling phase. This paper discusses model development, while the results, validation and the sensitivity analysis are presented in the companion paper.
A differential scanning calorimeter was used to determine the Tg of papaya pieces equilibrated with several water activities. Thermograms revealed the existence of two Tg. The first, which presented lower value, is due to the matrix formed by sugar and water. The second one, less visible and less plasticized by water, probably corresponds to macromolecules. The data of Tg were satisfactory correlated by the Gordon–Taylor model. A convective tray dryer was used for the drying experiments, which were carried out at air temperatures of 40 °C and 70 °C and air velocity of 1.0 m/s. The shrinkage behavior was accomplished by total area and apparent volume alterations along drying. Samples were photographed during process, and their length and lateral areas were measured using the ImageJ® software. As result, the effect of air temperature on shrinkage was significant and the highest temperature (70 °C) induced higher extent of shrinkage values. At this condition, papaya sample was in a rubbery state, characterized by great matrix mobility, and remained so until the end of process, since product temperature (Tp) was above the Tg along the process. At lower temperature (40 °C), shrinkage stopped at a critical value of moisture content (0.21 g/g, wet basis), which coincided with the point in which the Tg was close to Tp.
A framework for fundamental physics-based prediction of texture was developed whereby changes in Young’s modulus in potato strips during frying could be predicted by combining modulus changes with temperature and moisture with predictions of the latter from fundamental physics-based process model. Moisture and temperature dependence of Young’s modulus was obtained from experiment. Process model for frying was based on multiphase porous media based transport equations. Effective value of Young’s modulus for a potato strip was obtained from local values of modulus predicted by the model through homogenization. The predictions were validated using measured Young’s modulus during frying. Such a model-based prediction providing insight into texture development during a frying process (both as function of time as well as spatially) within the potato strip will be difficult to achieve from direct experimentation alone. Precise effects of increased sample size and reduced oil temperature in slowing down the texture development are shown. Since the model is physics-based, the prediction framework can be extended to processes other than frying, allowing fundamental-based quality prediction in general.
Texture is one of the most important quality parameter, which influences the acceptability of food products. The kinetics of texture development which was evaluated using a Stevens-LFRA Texture Analyzer in terms load in grams, has been studied over a temperature range of 50–120 °C (isothermal process), and also during normal open pan cooking, pressure-cooking and a cooking in a newly developed and patented fuel-efficient ‘EcoCooker’ (non-isothermal heating process). The texture development followed first order kinetics in potato cubes, whole green gram and red gram splits, the food samples used in this study. A mathematical model was developed using the rate constants of texture development at fixed temperatures and the time–temperature profile of the processing method.
Water loss of fruit during storage has a large impact on fruit quality and shelf life and is essential to fruit drying. Dehydration of fruit tissues is often accompanied by large deformations. One-dimensional water transport and large deformation of cylindrical samples of apple tissue during dehydration were modeled by coupled mass transfer and mechanics and validated by calibrated X-ray CT measurements. Uni-axial compression–relaxation tests were carried out to determine the nonlinear viscoelastic properties of apple tissue. The Mooney–Rivlin and Yeoh hyperelastic potentials with three parameters were effective to reproduce the nonlinear behavior during the loading region. Maxwell model was successful to quantify the viscoelastic behavior of the tissue during stress relaxation. The nonlinear models were superior to linear elastic and viscoelastic models to predict deformation and water loss. The sensitivity of different model parameters using the nonlinear viscoelastic model using Yeoh hyperelastic potentials was studied. The model predictions proved to be more sensitive to water transport parameters than to the mechanical parameters. The large effect of relative humidity and temperature on the deformation of apple tissue was confirmed by this study. The validated model can be employed to better understand postharvest storage and drying processes of apple fruit and thus improve product quality in the cold chain.
In Part I of this series, a method was presented for analysis of the stresses that develop during drying of a porous body, such as a gel. That formulation did not take propert account of the effect of local variations in network shrinkage on the pressure in the liquid. In this paper, an improved analysis is presented. The form of the original equations is generally preserved, except that the pressure in the liquid is shown to depend on both the shear and bulk moduli (or viscosities), rather than simply on the bulk modulus (or viscosity). The present modification is most important for the case of a warping plate or a film on a rigid substrate. The connection of this model with those of Biot and others is discussed.
This paper presents a study on the impact of baking conditions on crumb staling. Breads were baked at 220 °C, 200 °C and 180 °C corresponding to 6, 8 and 10 min to rise the temperature to 98 °C in the crumb (heating rates 13, 9.8 and 7.8 °C/min respectively with an initial temperature of 20 °C). A new protocol has been developed, consisting in baking a slab of degassed dough in a miniaturized oven to mimic the baking conditions of conventional bread making. Texture tests were done during staling on degassed crumb and on conventional crumb. Calorimetry tests showed that during storage, amylopectin recrystallisation occurred before crumb stiffening. A first order kinetics model was used to fit the evolution of the crumb texture (Young's modulus) and of the recrystallisation of amylopectin. The results showed that the hardening of the crumb during staling occurred after retrogradation of amylopectin. In addition, the staling rate was faster for faster baking kinetics. A mechanical model showed that the relative Young modulus is proportional to the square of the relative density of the crumb.
A modernized baking industry needs accurate information on materials and processes for manufacturing products with textures suited to consumer demands. Texture assessments of bread have been mostly directed to measuring the firmness of bread crumb—a mechanical property related to fundamental mechanical parameters such as elastic modulus and critical stress, which, in turn, are related to the macro- and microstructure of the crumb. While the contribution of the macrostructure, such as cells and cell walls, has been extensively investigated, the contributions of the microstructure and the irregularity of the structures remain to be explored. This review discusses the hierarchical structures that are present from macroscale to microscale within bread crumb, and examines how structures at the different hierarchical levels affect the mechanical properties of the bread crumb. Predictions of mechanical properties of bread crumb using various approaches such as empirical models, Gibson and Ashby's theory, fractal characterizations, theories on colloidal linkage mechanisms and finite element methods are discussed. Although the cellular solids approach of Gibson and Ashby's theory can predict the mechanical properties of bread crumb reasonably well, the other approaches are more physically realistic because they do not assign a periodic structure to the bread crumb.
Great effort has been devoted towards developing models that describe cooking processes. A difficulty towards developing such models arises from the fact that during cooking, the physical properties and quite often sample geometry are time dependent. In this work a finite element model describing cooking of rice and water uptake using a Fickian diffusion model was developed, assuming axisymmetric conditions. Effective diffusivity was considered a function of moisture content. The numerical model compared favorably with experimental results. The value of the effective water diffusivity was estimated to be in the order of 7×10−10m2/s, by minimizing the error between experimental and numerically predicted results.The effect of grain size on the cooking was also investigated using the model. Cooking time, i.e. the time to reach about 70% moisture content (wet basis), appeared to be a strong function of the initial size distribution.
Potato cubes were blanched and partially dried in a cabinet drier prior to puffing in a Torbed 500, high-temperature fluidised bed drier. It was established that formation of a partially dried layer (PDL) on the surface of the cubes was necessary to achieve puffing. The influence of blanching and drying conditions on this layer was investigated. It was concluded that blanching for 2 min in water at 100°C followed by drying in air at 90°C for 40 min resulted in the maximum increase in volume of the puffed cubes.
Compressive strength properties of three different varieties of rice, namely Akitakomachi (Short grain variety), Delta and L201 (Long grain varieties) were determined in their natural state. Rough rice was compressed between two rigid plates using a stress–strain tester and the force–deformation curves recorded. Determinations made included initial yield point, yield point, initial yield stress and strain, Young's modulus and Poisson's ratio. Stress was determined by considering the variation of contact area with compression force whereas Poisson's ratio was computed based on the Boussinesq's theory. Initial yield force and Young's modulus were found to be about 18 N and 543 MPa, respectively for the three varieties of rice. Initial yield point and yield point occurred after almost the same deformation of about 0.16 and 0.60 mm, respectively. However, short grain rice had higher Poisson's ratio and lower yield stress compared to long grain rice. Consideration of variation in contact area during compression gave representative apparent compressive strength properties for rough rice.
The particle density of calamari mantle meat powder decreased with increasing water content and apparent density gave a peak at low water content, then decreased with increasing water content. The shrinkage and porosity were derived from the experimental density data and were correlated empirically. The empirical models were used to predict the density data. An attempt was made to apply the theoretical model proposed by Rahman (1991, Ph.D. Thesis, University of New South Wales, Australia) based on conservation of mass and volume, and modified to include excess volume and air pore formation. The uncertainty in the true density measurement, which is a common difficulty in this area, has made it impossible to predict accurately the excess volume, thus limiting Rahman's model.
Texture degradation kinetics of carrots during traditional thermal and novel high-pressure/high-temperature (HP/HT) processing were compared. Carrots were thermally (0.1MPa) or HP/HT (600MPa) treated in a temperature range from 95 to 110°C. The residual texture (hardness) was determined using a texture analyzer. Kinetic parameters were estimated using a fractional-conversion model. In comparison to the thermal treatments, the HP/HT treatments resulted in a 10-fold slower texture degradation. The retarded texture loss was accompanied by a significantly lower degree of methyl-esterification (DM) of the cell wall pectin. Additionally, the effect of lowering the DM (by applying an HP pretreatment) and adding exogenous calcium ions prior to the HP/HT treatment on the texture of carrots was investigated. It was observed that this combined pretreatment resulted in a notably harder texture of HP/HT-treated carrots. However, a similar outcome was obtained by HP/HT treating carrots directly in a calcium chloride solution without preceding DM reduction and calcium soak. Excluding a separate pretreatment step will lead to time savings and a lower cost. This study demonstrated that HP/HT processing has great potential, concerning texture preservation of processed fruits and vegetables.
A study of the pysical structure and quality potatoes during microwave and air drying war undertaken. The effect of various experimental variables on volumetric shrinkage including microwove power levels, air temperature and velocity as well as sample geometry was investigated. In both microwave and air drying, the shrinkage of potatoes showed a linear behaviour in relation to different moisture content levels. Experimental data showedthat air velocity and microwave power had a major effect on the degree of shrinkage, also the shrinkage behaviour was independent of sample geometry and air temperature. The use of microwave produced smaller changer in volume (less shrinkage) and henee a better quality finished product.
Drying processes affect the quality of the final food biopolymer product. The texture, density, wetability, caking, rehydration capacity and mechanical properties of the dried food biopolymer depend on: the product properties, the drying process conditions and the product residence time distribution in the dryer. The interrelationship between dried product quality and drying process conditions is not sufficiently explored in literature because of limited understanding of the physico-chemical mechanisms affecting product quality, and of the effect of these mechanisms on transport properties. Recent ad- vances in material and polymer science research, however, provide the tools and methodologies needed to understand in depth the quality changes dur-ing drying. The current work reviews the approaches of conventional drying theories and presents recent advances in polymer science on modelling solvent absorption by glassy polymers based on the glass-transition theory. Oppor- tunities presented by the glass transition theory towards explaining quality changes during drying are identified and the framework of a recent rnathe- matical model that can be used to integrate the drying and polymer-science approaches is then presented.
The objective of this study is the formulation of a finite element model that could be used to analyze the stress crack formation in a viscoelastic sphere resulting from temperature and moisture gradients during the drying process. Numerical solutions to the simultaneous moisture and heat diffusion equations describing moisture removal and heat intake process for the sphere are obtained. The distribution and gradients of temperature and moisture developed inside the sphere during drying are established. The calculated temperature and moisture gradients are used in a finite element analysis of the thermo-hydro viscoelastic boundary value problem to simulate the stresses in the body.The model is used to solve a sample problem of drying a soybean kernel. The simulated drying curve for the soybean model is obtained and compared favorably with the experimental results reported in the literature. Tangential stress, as a criteria for failure, is shown to change from compressive to tensile stress as it approaches the surface. It reaches its peak value at the surface in one hour and then decays slowly. The effect of different drying conditions is studied and the results are discussed.
The aim of this work was to study the changes in volume, density, porosity and shape factors of pumpkin tissue during osmotic dehydration (OD) and air drying (AD). Pumpkin cylinders with length/diameter ratio of 5/3 were used. OD experiments were carried out with solutions of sucrose, sodium chloride and mixtures of both solutes at different temperatures. AD experiments were conducted at 70°C. Volume of samples decreased linearly with weight reduction (WR). Bulk density varied in a restricted range (5–13%) during dehydration and for all the methods maximum values were found. Particle density increased during both processes. Porosity increased at advanced degrees of dehydration, showing a minimum value at the beginning of OD and AD. The proposed models to evaluate shrinkage, bulk and particle densities and porosity from WR were satisfactorily applied. Image analysis showed that shrinkage of samples during OD was isotropic. Pumpkin cylinders increased elongation and decreased roundness and compactness during osmotic dehydration.
The soil gas and solute diffusion coefficients and their dependency on soil total porosity (Phi), fluid-phase (air or water) contents, and pore-size distribution largely control chemical release, transport, and fate in soil. The diffusion coefficients hereby play a key role in both local and global environmental issues including spreading, biodegradation and volatilization of hazardous chemicals at polluted soil sites, and soil uptake, production, and emission of greenhouse gases. In a series of papers, we present new advances in describing and predicting the gas and solute diffusion coefficients in variably saturated porous media, carefully distinguishing between repacked and undisturbed media. Also, we establish direct links between gas and solute diffusivity and pore-size distribution, with further links to pore continuity and tortuosity. In this first paper, a porosity correction term is added to a recently presented model for predicting gas diffusivity in repacked soil. The obtained POrosity-Enhanced (POE) model assumes that increased Phi creates additional interconnectivity between air-filled pores. The POE model is tested against data for 18 repacked soils ranging from 0 to 54% clay, including new data measured in this study for both noncompacted and, compacted, high-porosity soils. The POE model accurately predicts gas diffusivity across a wide Phi range up to 0.75 m(3) m(-3), whereas the original model is accurate only for Phi up to 0.55 m(3) m(-3). A unifying, two-parameter function for gaseous phase pore continuity (f(g)) is suggested. The fg function illustrates developments in gas diffusivity models during the last century, including assumptions behind the increasingly precise prediction models for repacked soil. Last, the POE model is coupled with the widely used van Genuchten (vG) soil-water characteristic model, hereby establishing an accurate and predictive link between soil gas diffusivity and pore-size distribution. The closed-form POE-vG gas diffusivity model is highly useful to evaluate effects of pore-size distribution and soil type on gas diffusivity and gas transport in repacked soil systems.
Fractional conversion technique was used on firmness change kinetics of sardine sheets during vacuum pulse osmotically dehydration at temperatures between 30 and 38°C, and brine concentrations between 0.15 and 0.27gNaCl/g. The equilibrium firmness of sardine sheets for different brine concentration and temperature were determined. The equilibrium firmness increased with increasing brine concentration as well as temperature (p0.90). The rate constant increased with increasing concentration as well as temperature of the osmotic solution (p0.90). The activation energies varied from 21.78 to 93.42kJ/mol when brine concentration increasing from 0.15 to 0.27gNaCl/g. Higher activation energy (93.42kJ/mol) indicated the greatest temperature sensitivity of firmness at 0.15gNaCl/g.
Numerical and experimental results of moisture transfer in drying process for apple and potato slices are compared in this study. Experimental results are obtained using a cyclone type dryer. Two-dimensional analysis of heat and moisture transfer during drying of objects is carried out solving heat and mass equations using finite-volume approach. Thus, moisture distributions inside the moist objects are obtained at different time steps. Comparison of results showed that there is a considerably high agreement between experimentally measured data and predicted values. Moist distribution also presented inside the products at different time periods.