Drying Of Food Materials Research Articles

Computational study of the performance of a solar dryer for improvement in the shelf life of the food materials.

In this study, the thermal and drying characteristics of a thin layer food sample were investigated. An indirect type, simple, efficient, and economically feasible solar dryer was fabricated and used for food preservation. However, a dynamic model of a fabricated solar dryer was also presented to gain a better insight into the drying and thermal actions. This model consists of thermal modeling of the drying chamber, solar collector, and solar-dried food sample. The law of conservation of energy was applied to evaluate the temperature at different sections of the solar dryer with respect to drying time. All listed model equations were solved in the MATLAB environment. This study helps to examine the influence of solar radiation on the collector plate temperature, drying chamber temperature, food sample temperature, and performance parameters such as thermal efficiency with respect to drying time. Model data was found in good agreement with experimental data within a 4% error. It is concluded that the drying of food material is affected by air temperature, the collector temperature, mode of heat transfer, and material characteristics such as dimension and mass of the food sample.

Modelling of convective drying of potatoes polyhedrons

Abstract This work aimed to develop numerical models to predict the moisture content and deformation of potato slices during convective drying (40–80 °C, 0.5 m·s−1). Three-dimensional slices were considered in cylindrical, cubic, parallelepiped, and prism geometries. The first classic model coupled the linear constant drying rate period with the analytical solution of Fick’s law in spherical coordinates, evaluating the mass diffusion coefficients (4.2–15.5·10−10 m2·s−1), critical drying time (1640–5085 s), and critical moisture content (1.8–2.4 kg·kg−1). The Finite Element Method (FEM) was a more robust model, that combined momentum and mass transfer to three-dimensional solid deformation of polyhedrons by ALE method, evaluating the mass diffusivity (1.4–6.5·10−10 m2·s−1). The FEM model could predict the shrinkage due to water molar flux removal on moving solid boundaries and explain the pseudo-constant drying rate detected in experimental data. The developed models accurately described the drying of food materials with a high shrinkage ratio.

Effects of carbon nanodots coating and airflow rate on the thermal efficiency of flat plate collector

ABSTRACT The application of nanoparticle coating in a collector could resolve the issues of lesser heat transfer rate and lower thermal efficiency associated with the flat plate collector (FPC). In this study, carbon nanodots (CNDs) synthesized from fish scales wwere coated over the black paint coating to enhance the thermal efficiency of FPC. The effect of various concentrations (0, 0.1, 0.2, and 0.5%w/v) of CND coatings and mass flow rates of air (0.011 kg/s (natural convection) and 0.015, 0.029, and 0.044 kg/s (forced convection)) on the collector outlet air temperature and efficiency of the FPC were evaluated with a control (black paint). Solar radiation ranged from 382 to 913 W/m2 on the experimental days, and the atmospheric temperature and relative humidity values varied from 26.2 to 34.8°C and 50–72%, respectively. Fourier transform infrared spectroscopic studies of absorber plate coating revealed that the CNDs interacted with the black paint surface through phenolic OH, C=O, and NH mainly by hydrogen bonding. It was observed that the exit air temperature of the collector varied from 55 to 65°C. The thermal efficiency of 59.97%, 62.72%, 71.87%, and 67.75% was obtained for control (black-paint), 0.1%, 0.2%, and 0.5% CNDs coating, respectively, at the airflow rate of 0.044 kg/s. The coating of 0.2% CNDs recorded a maximum thermal efficiency of 71.87% at 0.044 kg/s. Overall, the CNDs coating on the absorber surface enhanced the thermal efficiency of the collector by 19.84% over the black paint-coated surface (control). It can be concluded from the study that CNDs coating resulted in enhanced outlet air temperature and improved thermal efficiency, which can be utilized for low-temperature applications like the drying of food materials.

Effect of ultrasound and chemical pretreatment on drying characteristics and quality attributes of hot air dried pineapple slices.

Drying of food materials is a time consuming activity making the process cost and energy intensive and hence, several pretreatments are used to improve the drying rate. The present study aims to study the effect of potassium metabisulphite (KMS solution, 0.25% w/v) and ultrasound (20 and 30min) pretreatment on hot air drying characteristics and quality of pineapple slices. The results indicated that pretreated samples provided higher drying rate, enhanced moisture diffusivity, brighter color and lower hardness than that of untreated dried sample. It was observed that KMS and ultrasound pretreatment for 20 and 30min reduced the drying time by 23.8%, 19% and 14.3%, respectively. Further, ten thin layer drying models were applied to the experimental drying data and logarithmic model was best fitted to explain the drying behavior of pretreated and untreated samples. Additionally, the effect of shrinkage on moisture transfer mechanism was also studied. Results highlighted that instantaneous moisture diffusivity was increased during drying while shrinkage was not accounted. However, shrinkage consideration reduced the average moisture diffusivity values by 72-83%. Overall color change (13.95 ± 0.92) and browning index (36.02 ± 2.45) were found to be lowest in ultrasound (30min) pretreated dried sample, highlighting better color stability. Scanning electron microscopy presented noticeable effects of pretreatment on alterations of microstructure of pineapple slices. It can be interpreted that KMS pretreatment was found to be more effective for improvement of drying characteristics of pineapple slices as compared to ultrasound pretreatment.

Effect of novel atmospheric-pressure jet pretreatment on the drying kinetics and quality of white grapes.

Raisin is a popular snack and a common constituent of many foods owing to its good flavor and nutritional value. Conventional drying of grapes can be a slow and energy-consuming process as their waxy surface hinders efficient moisture migration. A drying pretreatment that disrupts the waxy cuticle is usually applied to increase the drying rate. The application of an atmospheric-pressure air plasma jet to the grape surface could effectively enhance the drying kinetics and decrease the drying time by more than 20%. Through etching of the waxy cuticle, the air plasma jet optimally improves the quality of the final product. Although the surface hydrophilicity was increased by 40%, the physical appearance, color, and texture of plasma-treated raisins were similar to the product from untreated control and chemical-treated groups. A more than twofold increase in the total phenolic content and antioxidant capacity was observed when compared to other experimental groups. The results indicate that atmospheric plasma could be a better option than using chemicals to pretreat grapes before drying since it leaves no toxic residue, while successfully preserving the product quality. This work shows the great potential for the application of atmospheric air plasma in the drying of food materials. © 2019 Society of Chemical Industry.

Development of a porosity prediction model based on shrinkage velocity and glass transition temperature

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.

Study on osmo-convective dehydration of papaya (Carica papaya L.) slices and evaluation of quality during storag

Osmotic dehydration (OD) is one of most important complementary treatment and food preservation technique in the processing of dehydrated foods, since it presents some benefits such as reducing the damage of heat to the flavor, color, inhibiting the browning of enzymes and decrease the energy costs. Osmotic dehydration results in increased shelf-life, little bit loss of aroma in dried and semidried food stuffs, lessening the load offreezing and to freeze the food without causing unnecessary changes in texture. Drying is a technique of conservation that consists of the elimination of large amount of water present in a food by the application of heat under controlled conditions, with the objective to diminish the chemical, enzymatic and microbiological activities that are responsible for the deterioration of foods. Hot air drying often degrades the product quality, provides low energy efficiency and lengthy drying time during the falling rate period. It has been reported that hot-air drying of food materials, involving their prolonged exposure to elevated drying temperatures, results in substantial deterioration of such quality attributes as color, nutrient concentration, flavor and texture. Papaya (Carica papay L.) is an important fruit crop grown widely in tropical and subtropical low land regions. Excellent in vitamin C, pro-vitamin A, minerals as well as rich in dietary fiber, papaya is emerging as a popular fresh fruit which offers health benefiting properties. The desire to eliminate this problem, prevent significant quality loss and achieve fast and effective thermal processing, has resulted in the increasing use of microwaves for food drying.

Study on OSMO-Convective dehydration of papaya (Carica papaya L.) slices and evaluation of quality during storage-A review

Osmotic dehydration (OD) is one of most important complementary treatment and food preservation technique in the processing of dehydrated foods, since it presents some benefits such as reducing the damage of heat to the flavor, color, inhibiting the browning of enzymes and decrease the energy costs. Osmotic dehydration results in increased shelf-life, little bit loss of aroma in dried and semidried food stuffs, lessening the load of freezing and to freeze the food without causing unnecessary changes in texture. Drying is a technique of conservation that consists of the elimination of large amount of water present in a food by the application of heat under controlled conditions, with the objective to diminish the chemical, enzymatic and microbiological activities that are responsible for the deterioration of foods. Hot air drying often degrades the product quality, provides low energy efficiency and lengthy drying time during the falling rate period. It has been reported that hot-air drying of food materials, involving their prolonged exposure to elevated drying temperatures, results in substantial deterioration of such quality attributes as color, nutrient concentration, flavor and texture. Papaya (Carica papay L.) is an important fruit crop grown widely in tropical and subtropical low land regions. Excellent in vitamin C, pro-vitamin A, minerals as well as rich in dietary fiber, papaya is emerging as a popular fresh fruit which offers health benefiting properties. The desire to eliminate this problem, prevent significant quality loss and achieve fast and effective thermal processing, has resulted in the increasing use of microwaves for food drying.

Performance Comparison Between Batch and Continuous Thawing of Food Products Assisted by Radio Frequency Heating

Radio frequency (RF) assisted heating of foods is an established technique used in food processing such as postharvest treatment of in-shell fruits, drying of food materials and products. More recently, it has been proposed as industrial solution for continuous tempering of frozen meat blocks. In the last years, scientific literature has shown interest on using RF heating to enhance food thawing prior to further processing or consumption, due to the possibility to reduce processing time, raise the power efficiency of the thawing process, and eventually provide better quality and safety of the thawed product. The purpose of this study was to evaluate the performance between batch and continuous thawing of food products assisted by RF heating. A pilot scale RF system with 27.12 MHz and 6 kW used to thaw 1.2 kg block of minced lean beef meat and to evaluate the performance under different conditions. The results showed that continuous RF thawing slightly improved the heating uniformity and relatively uniform heating rate compared to batch system under the same process conditions. End point temperatures of -0.2°C ± 1.5 and -0.4°C ± 0.7 were achieved at the center of the sample in 17 min thawing time using batch and continuous conditions, respectively. These comparison results may provide detailed performance information to optimize and design processing parameters and, to promote further practical applications of RF heating in food processing industry.

Multiphase porous media model for intermittent microwave convective drying (IMCD) of food

Intermittent microwave convective (IMCD) drying is an advanced drying technology that improves both energy efficiency and food quality during the drying of food materials. Despite numerous experimental studies available for IMCD, there is no complete multiphase porous media model available to describe the process. A multiphase porous media model considering liquid water, gases and the solid matrix inside the food during drying can provide in depth understanding of IMCD. In this article, firstly a multiphase porous media model was developed for IMCD. Then the model is validated against experimental data by comparing moisture content and temperature distributions after each heating and tempering periods. The profile of vapour pressures and evaporation during IMCD are presented and discussed. The relative contribution of water and vapour fluxes due to gas pressure and diffusion demonstrated that the fluxes due are relatively higher in IMCD compared to convection drying and this makes the IMCD faster.

Mechanistic understanding of case-hardening and texture development during drying of food materials

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.

A Paradigm Shift in Drying of Food Materials via Free-Volume Concepts

We give an overview of the prediction of thermodynamics of food materials, and the kinetics of water transport in them using universal theories based on free volume concepts. These material properties are highly relevant to the prediction of food drying. These presented theories are shown to hold for a large class of polysaccharides and proteins. These different food materials apparently follow the soft matter paradigm that materials’ behavior at length scales larger than the molecular scale are dominantly determined by physical characteristics rather than their chemical details. We pose that for food and other bio-materials hydrogen-bonding is largely determining their physical behavior, as in drying. [Supplementary materials are available for this article. Go to the publisher's online edition of Drying Technology for the following free supplemental resource(s): Data sets.]

Determination of porosity change from shrinkage curves during drying of food material

Based on a very simple model of mass conservation, three experimental properties (solid density, liquid density and initial bulk density) and the simultaneous acquisition of the reduced moisture content and the volume shrinkage during drying, a simple method is proposed to calculate the bulk porosity of a material during drying. This model allows a graphical interpretation to visualize the porosity change by comparing the experimental shrinkage curve with an ideal shrinkage curve. In the present work, several examples were taken from the literature to illustrate the application of this method to foodstuffs (apple, banana, carrot, garlic, pear, potato and sweet potato) with two different processes (convective drying, freeze-drying) and different drying conditions. Porosity calculations including error estimations showed a good agreement with experimental values reported in the literature.

Experimental and Theoretical Studies on Drying of Food Materials.

A mathematical model was developed to predict heat and moisture transfer, drying-induced stresses and the material shrinkage of viscoelastic food materials during drying. Potato starch was selected as the model food material and physical and material properties such as moisture diffusivity, thermal conductivity, and viscoelastic properties were measured as a function of temperature and moisture concentration. To verify the numerical model, results of the drying experiments were compared with the numerically ohtained results and were found to be in good agreement with each other.

Book reviews

Book Reviewed in this Article:Micro‐algal Biotechnology. Edited by Michael A. Borowitzka and Lesley J. Borowitzka. Advances in Cereal Science and Technology, Volume IX. Edited by Yeshajaha Pomeranz. Sucrose. Edited by Gaston Vettorazzi & Ian Macdonald. Preconcentration and Drying of Food Materials. By S. Bruin. Low‐calorie Products. Edited by G. G. Birch & M. G. Lindley. Food Preservation by Moisture Control. Edited by C. C. Seow. Nutrient Interactions. IFT Basic Symposium Series. Edited by C. E. Bodwell & J. W. Erdman Jr. Marcel Dekker Inc. Meat Science, Milk Science & Technology. (World Animal Science, B3). Edited by H. R. Cross and A. J. Overby. Single Cell Oil. Edited by R.S. Moreton. Progress in Industrial Microbiology 25: Computers in fermentation technology. Edited by M. E. Bushell. Trace Minerals in Foods (Food Science & Technology Series/28). Edited by Kenneth T. Smith. Adulteration of Fruit Juice Beverages. Edited by Steven Nagy, John A. Attaway and Martha E. Rhodes.