Drying is a crucial unit operation within the functional foods and biopharmaceutical industries, acting as a fundamental preservation technique and a mechanism to maintain these products' bioactive components and nutritional values. The heat-sensitive bioactive components, which carry critical quality attributes, necessitate a meticulous selection of drying methods and conditions backed by robust research. In this review, we investigate challenges associated with drying these heat-sensitive materials and examine the impact of various drying methods. Our thorough research extensively covers ten notable drying methods: heat pump drying, freeze-drying, spray drying, vacuum drying, fluidized bed drying, superheated steam drying, infrared drying, microwave drying, osmotic drying, vacuum drying, and supercritical fluid drying. Each method is tailored to address the requirements of specific functional foods and biopharmaceuticals and provides a comprehensive account of each technique's inherent advantages and potential limitations. Further, the review ventures into the exploration of combined hybrid drying techniques and smart drying technologies with industry 4.0 tools such as automation, AI, machine learning, IoT, and cyber-physical systems. These innovative methods are designed to enhance product performance and elevate the quality of the final product in the drying of functional foods and biopharmaceuticals. Through a thorough survey of the drying landscape, this review illuminates the intricacies of these operations and underscores their pivotal role in functional foods and biopharmaceutical production.

The effect of processing temperature of hot air (HA) and superheated steam (SS) on functional and nutritional properties of yellow pea (Pisum sativum L.) kernels such as moisture content, hydration capacity, cooking characteristics, dehulling efficiency, microstructure, starch gelatinization, and protein content were studied. Three processing temperatures (120, 135, and 150 °C) for both HA and SS were used, while keeping the velocity of air and steam at 1 m/s. Both processing methods (HA and SS) exhibited a significant effect (p < 0.05) on the selected functional properties. Dehulling efficiency of HA-processed peas ranged from 83.5 to 88.2%, whereas for SS-processed peas, it ranged between 85.4 and 89.9%, within the processing temperature range. An increase of 19.1, 20.0, and 35.0% in porosity was observed in SS-processed yellow pea when compared to those processed with HA, at 120, 135, and 150 °C, respectively. At 150 °C, peas processed with HA demonstrated a greater reduction in protein content by 2.38%, whereas a protein reduction of 0.75% with SS was achieved. The study also explored optimization of initial moisture content (26, 40, and 54%) of yellow peas for selected SS temperatures (120, 135, and 150 °C) in order to minimize soaking time prior to cooking. Results showed a pronounced reduction in the peak extrusion force of cooked peas with an initial moisture content of (54%) and processed in SS, for 5 and 10 min cooking times, ensuring a cooked texture (force ratio < 0.5) Based on these results, it is inferred that SS has potential to minimize the overall cooking time of yellow peas without compromising functional and nutritional properties.

Abstract. This study focuses on the modeling of sorption characteristics of three varieties of soybeans (Akras R2, Lono R2, and Podaga R2). Three pretreatments related to post-harvest conditions were tested on the soybean varieties: (1) freshly harvested soybeans, (2) soybeans subjected to three drying and wetting cycles, and (3) soybeans subjected to three freezing and thawing cycles. The adsorption and desorption experiments were conducted at 5°C, 10°C, 15°C, 20°C, 25°C, and 30°C using a dynamic equilibrium relative humidity (ERH) apparatus. Equilibrium moisture content (EMC) and the corresponding ERH were measured. The parameters calculated for the modified Halsey equation are applicable for storage temperatures above 10°C in the relative humidity (RH) ranges of 10% to 80% for desorption and 30% to 80% for adsorption. No significant differences were found in sorption isotherms among the soybean varieties. However, the soybean varieties responded differently to the different pretreatments (i.e., drying/wetting and freezing/thawing cycles). The adsorption isotherms of Akras and Lono soybeans showed significant differences at 10°C to 30°C when subjected to drying and wetting cycles, while Akras and Podaga soybeans showed significant differences in the same temperature range when subjected to freezing and thawing cycles. The effect of drying and wetting cycles on the desorption isotherms was found only for Akras soybeans at 10°C and 15°C below 63% and 71% RH, respectively, and for Lono soybeans at 25°C and 30°C above 69% RH for both temperatures. In general, the effect of both pretreatments on the sorption isotherms of soybeans was a reduction in EMC of up to 20%, when compared to fresh samples at selected storage temperatures. The findings of this study serve as a primary tool for developing a lookup table for safe storage guidelines for soybeans. Keywords: Equilibrium moisture content, Equilibrium relative humidity, Halsey equation, Oswin equation, Soybeans.

Kraft lignin, acidic (LA) and alkaline (LB) types, byproducts of pulp manufacturing were mixed with crude glycerol, a by-product of biodiesel production, and humic acid to produce a mulch tackifier for soil erosion control. Lignin was dried at 70°C for 24 h before use. The study was a full factorial with lignin levels of 20, 50, and 80% and humic acid levels of 1, 2, and 5% (w/w). The remaining portion consisted of crude glycerol. The samples were homogenized using water to facilitate the homogenization process. After homogenization, the samples were left to settle for 36 h and then separated into solid and liquid portions. Both portions were dried at 70°C for 24 h and tested for tack after wetting with water. Dried lignin, as a standalone ingredient, was also tested for tack. The values for the strength of tack were compared to those obtained from a commercial tackifier. Acidic lignin could be used with lignin content ≥50%. Acidic lignin was comparable to the commercial tackifier, whereas alkaline lignin was found to have significantly more tack but was found to be unsuitable for soil erosion use.

Highlights Thermo-physical characterization of two types of Kraft lignin mixed with three bio-plasticizer. Crude glycerol showed the greater depression in melting point with its increasing proportion. The acidic lignin has more tensile strength and density than the alkaline lignin. Micro-pores of the lignin pellet were minimized by adding bio-plasticizer. Abstract. Kraft lignin, a by-product of the paper industry, is well known for its binding properties, enabling its use in the production of pellets and briquettes from biomass. Different bio-plasticizers, by-products from the vegetable oil processing industry, could serve as plasticizers for biomass briquettes. The properties of three bio-plasticizers (glycerol, fatty acid, and biodiesel), when mixed with isolated Kraft lignin, were studied to identify their potential application as efficient binders for biomass briquettes. The phase transition characteristics (glass transition, pre-melting crystallization, and melting) of two types of isolated lignin samples (acidic and alkaline) and lignin-plasticizer mixtures were determined using a differential scanning calorimeter. The mechanical (tensile strength) and physical (density) characteristics of the compacted cylindrical lignin pellets were tested. The spatial distribution of micropores in the lignin pellets was studied using x-ray tomography. Even though an overlap was observed in the glass transition temperatures of the mixtures, a significant depression in the pre-melting crystallization and melting temperatures was observed for both lignin samples containing elevated concentrations of the bio-plasticizers, and the highest tensile strength was obtained for pellets with 10% bio-plasticizer. Among the three bio-plasticizers, crude glycerol showed the greatest depression in melting point with increasing proportions of both acidic lignin (60.7°C ±2°C) and alkaline lignin (85.1°C ±2°C). In general, alkaline lignin showed some limitations over acidic lignin in the tensile strength of the pellets as well as their fusion temperature, even though the addition of a bio-plasticizer improved the strength and depressed the melting point in both lignin-based samples. Keywords: Bio-plasticizer, Lignin, Mechanical properties, Microstructure, Phase transition.

Background and objectives Bulgur, an ancient and traditional food extensively consumed in Turkey and the Middle East, has been gaining popularity elsewhere as a nutritious and convenient cereal product with prolonged shelf life. The cooking, drying, and comminution methods used for bulgur production may affect the color, yield, chemical composition, nutritive quality, and physical properties of bulgur. The objectives of this study were to produce bulgur from high-amylose and waxy hull-less barley (Hordeum vulgare L.) varieties and to investigate the effects of different drying methods: hot air, microwave, and superheated steam on the physicochemical and nutritional properties of barley bulgur. Findings Different drying methods applied in this study for the preparation of barley bulgur had significant effects on the physicochemical and nutritious properties of the final products. Bulgur products from high-amylose barley (cv. CDC Hilose) contained lower amounts of proteins, but higher amounts of ash, arabinoxylans, resistant starch, total dietary fiber, and vitamin E than bulgur products from waxy barley (cv. CDC Marlina). However, bulgur products from CDC Marlina exhibited significantly higher solubility of beta-glucans compared with bulgur from CDC Hilose. Conclusions Overall, the optimal quality characteristics in terms of high bulgur yield, short cooking time, low cooking losses, high beta-glucan solubility, and high retention of vitamin E were achieved for bulgur prepared from grain dried with superheated steam at 110 degrees C. The second best results were obtained for bulgur prepared from the microwave-dried grain. Some differences in composition and properties of bulgur prepared from waxy and high-amylose barley were related to genetic variations and differences in starch composition. The higher content of total dietary fiber in bulgur products from CDC Hilose was partly attributed to a higher content of resistant starch formed during the processing of this high-amylose barley. Significance and novelty Barley has been long considered a wholesome and nutritious grain, and the results of this study clearly showed that it can be used for the preparation of bulgur, a convenient and functional food product. The use of superheated steam as a drying method for the preparation of barley bulgur proved to generate product with superior properties, especially when compared to conventional hot air drying.

The effect of 105°C steam or hot air on adult mortality of three species of stored-product insect pests outside wheat kernels of 12.5, 14.5 and 16.5% moisture content was investigated. The species were Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae), and Sitophilus oryzae (L.) (Coleoptera: Curculionidae). In the case of S. oryzae, young adults and immature stages inside wheat kernels were also tested. The mortality of insects inside kernels was higher at lower moisture contents of wheat treated with hot air, whereas moisture content did not significantly affect mortality of insects treated with steam. In the hot air treatment, all adults of the three species outside kernels had 100% mortality when the treatment time was 75 s for wheat with 16.5% moisture content, and 60 s for 12.5 and 14.5% wheat. In the steam treatment, the time to reach 100% mortality of adults outside kernels was 1 s at any moisture content and without significantly affecting germination. The young adults and immature stages of S. oryzae inside kernels required 90 s to reach 100% mortality in hot air, whereas 3 s was needed in steam. The treatment to reach 100% mortality of insects inside kernels caused a 20% drop in germination in steam and 81% drop in hot air.

Superheated steam (SS) could be a more effective medium than hot air for drying slurry-like materials such as distillers spent grain. As large scale drying of spent grain slurry has many challenges related to handling and transportation, a multilayered/coated product drying approach, where wet material is dried over a relatively dry core, could provide a potential solution for effective drying. The present study focuses on 3D modelling of SS drying of compacted distillers' spent grain coated with solubles. The drying experiments were conducted with cylindrical spent grain pellets with 25% moisture content coated with a thin layer of solubles (79 +/- 2% moisture) at different SS temperatures (120, 150, 180 degrees C) and velocities (0.5, 1.0, 1.5 m/s). The effective moisture diffusivity and the thermo-physical properties of wet distillers' grain pellets with or without solubles (0, 10, 30%, 100% w/w) were determined by experimentation. A coupling model was developed by combining the Reynolds-Average Navier-Stokes and energy equations for the SS flow and the diffusion models for the coated pellet using computational fluid dynamics approach. The prediction model showed appreciable accuracy with maximum percentage error values for moisture and temperature curves of coated pellet as 9.1 and 8.0%, respectively. Sensitivity analysis for the SS operating conditions showed that the effect of SS temperatures is more prominent than that of SS velocities on drying time. Such models, capable of predicting heat and mass transfer phenomena of SS drying of multilayered products, can provide valuable information for the design or optimization of industrial-scale SS drying units. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

The spatially correlated microstructure of a material during any processing operation such as drying is very important as it influences the thermo-physical properties of the material. The heterogeneity of the distillers' spent grain (DSG) pellets' microstructure was evaluated using the X-ray micro-computed tomography. The effect of two drying methods, i.e. hot air and superheated steam (SS) drying on the microstructure of this porous material was compared. The DSG pellets were prepared by mixing different amounts of distillers' solubles (10, 30, and 50% w/w) with the coarse grain fraction of the spent grains. The effect of solubles on the microstructure (total porosity, open porosity, closed porosity, and connectivity) and stability (dimensional/volumetric changes and change in density) of the pellet prior to and post drying (hot air and SS drying) was analyzed statistically. The results showed that SS drying caused an overall expansion of the pellet in the range of 90–133%. The increase in the open porosity of the pellet during SS drying enhanced the drying process resulting in a decrease in the drying time by about 81% when compared to hot air drying. Also, by increasing the concentration of solubles above 30% w/w, the dimensional stability of pellets improved by 50% for both drying methods thereby improving the mechanical strength of pellets. These results are crucial in optimizing the composition of pellets from the point of view of the pellet's dimensional stability and drying efficiency.

Drying is an essential unit operation needed for safe storage and handling of the wet Distillers' spent grain (DSG), a major by-product of the ethanol industry. For the simulation and modeling of the drying process, a detailed study on different pre-requisite parameters such as the thermo-physical properties and effective moisture diffusivity of the material to be dried is required. The present study reports the effective moisture diffusivity and activation energy of the DSG pellets during superheated steam (SS) drying. Cylindrical DSG pellets at two moisture mass fractions (25 and 35%) and three mass fractions of distillers' solubles (0,10, and 30%) were dried at three SS temperatures (120, 135, 150, 165, and 180 degrees C) and three SS velocities (0.5, 1.0, and 1.5 m/s), respectively. The experiment-based moisture diffusivity of the DSG pellet with and without solubles was determined by using the drying characteristic and the analytical solution of Fick's law of diffusion. The results showed that the effective diffusivity increased with an increase in SS temperature and velocity and its value was in the range of 2.49 x 10(-9) to 17.9 x 10(-9)m(2)/s. The dependency of the moisture diffusivity on temperature and moisture mass fraction was established by using Arrhenius equation and Levenberg-Marquardt optimization algorithm. The model coefficient and constants were compared with the calculated values of instantaneous effective moisture diffusivity with the mean relative percentage deviation <= 10%. These findings could serve as a fundamental input for the numerical modeling of SS drying of DSG.

The classic method of modelling drying processes using the transfer coefficients can be replaced by a method of solving Reynolds-Averaged Navier-Stokes equations applicable to the drying medium. This specifically applies to superheated steam (SS) as the drying medium, where the mass transfer coefficient cannot be defined by heat transfer analogy. In this study, the heat and mass transfer phenomena of SS drying of distillers’ spent grain (DSG) pellets were numerically studied using a commercial Computational Fluid Dynamics (CFD) package by combining the drying models related to the moist cylinder with the model describing the external flow of SS. A three-dimensional (3D) model of the DSG pellet and the drying chamber was created. The governing differential equations for mass and energy balance of the pellet and steam-flow around it were solved using the finite volume method and SIMPLEC algorithm within the CFD package (ANSYS CFX). The validation of the numerical model with experimental observations showed a good agreement with a mean relative percentage error less than or equal to 10%. The obtained mathematical model could serve as a basic tool for optimization and design of large-scale SS dryers for DSG.

Powerful computational tools such as computational fluid dynamics (CFD) have now replaced the classic method of numerical analysis of drying processes based on experimental models. Its capabilities include the adaptability to model different flow processes such as drying, with high spatial and temporal resolution facilitates and an in-depth understanding of the heat, as well as mass and momentum transfer. CFD complements the experimental and analytical approaches by simulating a range of complex flow problems. Although CFD has immense industrial applications in fluid dynamics, its use in different drying simulations is still in early stages of development. This paper presents a thorough review of the computational power of CFD packages and their application in the drying process simulation. The review also covers different mathematical approaches used in drying models, the commonly available commercial CFD codes, and the turbulence models used in simulations of drying problems. The factors contributing to the complexity and computational load of such CFD-based models are discussed. The later sections of the paper discuss various bottlenecks in the application of CFD in drying, such as the complexity of the models for convoluted geometries, and the limited description regarding the turbulent interaction between different phases.

The thermo-physical properties of distillers’ spent grain (DSG) pellets are the key input parameters for the heat and mass transfer modeling of the drying process and for the design of the suitable drying and storage systems. The main thermo-physical properties like particle density, thermal conductivity, and specific heat capacity of DSG pellets were determined using standard laboratory methods. The effects of moisture content, percentage of condensed distillers’ solubles (also called solubles), and temperature on these selected properties were determined. The average particle density of the DSG pellets with 0, 10, 30, and 50 % solubles was found to be in the range of 898.8–1136.7 kg/m3. It was observed that the particle density of DSG pellets increased with an increase in condensed distillers’ soluble concentration and decreased with an increase in moisture content. Thermal conductivity (0.17–0.42 W/(mK)) and specific heat (1.76–3.47 kJ/(kgK)) of the DSG pellets increase linearly with an increase in moisture content, soluble concentration of the sample, and temperature of the drying medium. Three multiple linear regression equations were developed for predicting these properties as a function of moisture content, soluble concentration, and temperature with R 2 value ≥0.86.

In recent history, fears of climate change and a possible looming energy crisis due to depleting fossil fuel reserves have stimulated research into the use of lignocellulosic biomass as an alternative energy source. Political and social will has promoted the use of biomass for both heat and electric energy generation. Legislation, particularly European, has been a driving force in promoting the use of biomass. Tax incentives, feed in tariffs (FIT), quota systems, and subsidies have assisted in making the use of biomass economically feasible. A simplified mathematical model to determine the market value of biomass is examined and some of its limitations are discussed. The difference in higher heating value (HHV) and lower heating value (LHV), criteria for rating biomass, is demonstrated using mathematical relationships. Significant differences in composition, quality, and energy values of densified biomass products depend on factors including chemical composition, physical characteristics, the use of binders, and storage and handling conditions. Improper storage conditions increase the risk of life and property loss. Ash contributes to premature equipment failure and lowers the biomass energy value. Biomass sources with high ash content may fail to meet standards for compacted biomass.

Initial condensation on the sample surface during superheated steam (SS) drying leads to increased sample moisture affecting its mechanical and thermal properties. A study was conducted to understand the effect of temperature and velocity of SS on the amount of initial condensation on distillers' spent grain pellets with an initial moisture content of 25% (wet basis). These pellets were dried using SS at 120, 150, and 180 degrees C with velocities 0.5, 1.0, 1.2, and 1.4m/s. Separate experiments were conducted for recording mass and surface temperature of the pellets during SS drying. Mass recorded over the drying period was then compared with the predicted mass obtained by solving the standard heat balance and film condensation equations. The predicted values of mass flux due to initial condensation were in close agreement with directly measured values with a maximum mean square error of 0.20. There was a 60-64% decrease in the amount of initial condensation as the temperature of SS was increased from 120 to 180 degrees C. The results indicate that the initial condensation can be minimal when the temperature of SS is equal or above 180 degrees C with SS velocity equal or above 1m/s using a preheated drying chamber.

Biomass recalcitrance to bioconversion for microbial production of fuels and co-products is directly related to the structure and composition of lignocellulosic biomass. The effect of superheated steam (SS) pre-treatment on biomass fermentation by Clostridium thermocellum was investigated. Wheat straw was ground to < 355 μm and exposed to three methods of pretreatment of various severities: i) soaking in 119 °C boiling water (BW) under absolute pressure of 193 kPa for 15 minutes, which corresponded to a severity factor of 1.73; ii) processing with SS at atmospheric pressure for 15 minutes; and at 180, 200 and 220° C, which corresponded to a severity factor ranging from 3.53 to 4.70 and iii) soaking in 119°C BW under absolute pressure of 193 kPa for 15 minutes, followed by processing with SS at atmospheric pressure at 180, 200, and 220 °C, with a corresponding severity factor of 5.26 to 6.44. Processing with SS was conducted at three temperatures: 180, 200, and 220 °C. The intensity of pre-treatment was expressed through a ‘treatment severity factor’. Wheat straw samples were then used as substrates in fermentation reactions with C. thermocellum. The most pronounced effects were observed at the highest severity of 6.44, corresponding to treatment in BW followed by SS at 220°C. This resulted in structural changes in the material reflected in an increased ‘contribution of amorphous cellulose’ (CAC) of 22%, an increase of hydrogen production of 94.2%, an increase of carbon dioxide production of 221.5% and a 160% increase in ethanol production. The combinatorial effect of BW and SS pre-treatment was more effective in improving substrate conversion than either BW or SS pre-treatment alone.

Integration of renewable energy into industrial process streams is becoming increasingly important as concerns arise surrounding reliance on fossil fuels for electricity generation. Superheated steam (SS) is a valuable process medium, both for its capacity to carry energy and to remove moisture from biological materials, which stands to benefit from integration of solar energy since the only input required is high-quality heat. Though solar energy represents an abundant resource, its exploitation is currently very limited. Evacuated tube solar collectors (ETSC) are capable of delivering energy at temperatures in excess of 200 C, and were evaluated for their feasibility for integration into a SS process stream. Experimental results showed that SS could be generated using ETSC at temperatures up to 178 C at an efficiency of 8.95%, with efficiency shown to decrease with increasing temperature differential. Further investigation indicated that operation of the ETSC at such high temperature differentials may have a detrimental effect on the materials used in their construction. After 28 loading cycles, component failure began to occur at temperatures of 178 C. Conclusions drawn from this study were that while ETSC are capable of producing high-quality SS, they are not feasible for independent integration into an industrial process stream due to low efficiency and component failure.

Particle size distribution (PSD) in distiller's spent grain compacts was varied and their effect on the disintegration characteristics of compacts while drying in superheated steam (SS) was monitored. Volumetric change and stress-relaxation characteristics, in terms of hardness and asymptotic modulus (EA) for a 40% deformation, were analysed during the warm-up period (5 s) and after reaching the moisture levels of 40, 30 and 20% (w.b.) in SS. Results showed that particle size was inversely correlated with the expansion or the increase in volume of the compact during SS drying, and the hardness as well as the EA of the compact increased with a decrease in particle size of the compact. A stepwise regression method was used to determine appropriate variables for developing a multiple linear regression model for predicting the EA of the compact. (c) 2015 IAgrE. Published by Elsevier Ltd. All rights reserved.

Adsorption and desorption characteristics of three varieties of red lentils in commercial production (Robin, Blaze, and Redberry) were measured in a dynamic set-up where: (i) freshly harvested lentils of different initial moisture content, (ii) lentils that were exposed to successive rewetting and drying cycles, and (iii) lentils exposed to successive freeze/thaw cycles were placed on a set of stacked trays in air tight systems. The experiments were conducted for the air temperature range between 5 and 30°C (with a step of 5°C) and five relative humidity (RH) values to represent a typical storage range. The Modified Halsey equation was found most suitable for the description of lentil moisture relationships and a non-linear regression procedure was performed on both the adsorption and desorption data collected for each variety and treatment combination. The coefficient of determination for non-linear regression (R2) ranged between 0.952 and 0.982, while the standard error of the estimated relative humidity value was within 2.8 to 4.2%. Successive wetting and drying of lentils had little or no effect on the EMC-ERH (equilibrium moisture content - equilibrium relative humidity) characteristics of CDC Robin varieties and a significant change in EMC-ERH was observed for CDC Redberry and CDC Blaze above 60% RH. There was a significant difference between the fresh and freeze/thaw EMC samples for all three red lentil varieties studied. For each lentil variety, the predicted EMC value for the freeze/thaw treated lentils was lower than the predicted EMC value for freshly harvested lentils at a given ERH. The difference in EMC values between the two treatments was most significant at high RH levels.