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Equilibrium Moisture Content and Heat of Desorption of Some Vegetables
Abstract
The equilibrium moisture content of potato, carrot, tomato, green pepper and onion was determined within the range of 10 to 90% water activity at three different temperatures (30, 45 and 60°C), using the standard static gravimetric method developed by the European Cooperation Project COST 90. The GAB equation was fitted to the experimental data, using the direct nonlinear regression analysis method and the agreement between experimental and calculated values was satisfactory. The net isosteric heat of desorption of water was determined from the equilibrium desorption data, using the Clausius-Clapeyron equation. An empirical exponential relationship between the net isosteric heat of sorption and the moisture content was proposed and validated.
... The Clausius-Clapeyron equation, grounded in solid theoretical principles, is commonly employed to calculate the total heat of sorption (Qst) in agricultural products (Iglesias and Chirife, 1976;Kiranoudis and al., 1993). It serves to estimate the heat necessary for the evaporation of both free and bound water within a product. ...
... In this equation, represents the net isosteric heat of desorption for the initial water molecules in the product (measured in kJ/mol), while indicates the characteristic water content at which this heat is determined, specifically at 63% ( Kiranoudis and al., 1993). ...
... The q0 parameter is particularly significant, as it provides valuable insight into the physicochemical interactions between water and the product's major constituents, as well as the water's state within the product. This information is crucial for estimating energy requirements during the drying process (Kiranoudis et al., 1993). ...
The analysis of sorption isotherms is a favored method for gaining insights into the distribution and strength of water bonds, along with their functional availability in biochemical and biological food products. In drying, we are particularly interested in the phenomenon of desorption. This study aims to model desorption isotherms and estimate the thermodynamic parameters of Peulh cheese produced in Benin for solar drying. For this, we experimentally determined the desorption isotherms of the cheese produced at ∘ C, ∘ C , ∘ C and ∘ C, by the static gravimetric method, using saturated saline solutions. The desorption curves obtained from the study were compared to theoretical models, including those proposed by Smith, Harking and Jura, Iglesias and Chirife, and the GAB model. Optimization of these theoretical models was performed using the least squares method. Additionally, the net isosteric heat of sorption was calculated via the Clausius-Clapeyron equation. An empirical exponential correlation was established to illustrate the relationship between sorption heat and equilibrium water content. The findings indicated that equilibrium water content decreases with rising temperature across a range of water activity from. % to %. The desorption isotherms were classified as type II, characterized by multimolecular adsorption. Notably, the GAB model provided the best fit for the experimentally obtained desorption curves at 50°C. Furthermore, enthalpy-entropy compensation and isokinetic theory were effectively applied to analyze the desorption process of Peulh cheese.
... Researchers have developed various mathematical, theoretical, and empirical equations to characterize the sorption isotherms of different food products. Numerous models have been proposed to explore the relationship between relative humidity (RH) and equilibrium moisture content (EMC) (Chung and Pfost, 1967;Dhingra, 2003;Kiranoudis et al., 1993;Hossain and Bala, 2000;Soysalan and Oztekin, 2001). Additionally, some studies have incorporated the effect of temperature on EMC (Attkan et al., 2016). ...
... The experimental data obtained were analyzed using IBM SPSS 20.0 (Statistical Package for the Social Sciences). The sorption data were then validated against six equilibrium moisture content (EMC) models (Table 2), which are commonly used to describe the sorption behavior of various agricultural products (Kiranoudis et al., 1993;Tsami et al., 1990). ...
... [Alam and Singh, 2011; Kiranoudis et al., 1993;Madamba et al., 1993] 6 ...
... The Clausius-Clapeyron equation, due to its theoretical basis, is often used in the determination of the total heat of sorption (Q st ) of agricultural products [22] [23] [24]. This equation is applied to estimate the quantity of heat useful for the evaporation of water (free + bound) in a product. ...
... Enthalpy-Entropy compensation theory applied to the isosteric heat of desorption The differential entropy is calculated from the Gibbs-Helmholtz equation, Equation (24) where the Gibbs free energy is obtained by the equation Equation (25), [11] [24]. Substituting Equation (25) into Equation (26) and arranging the result, we get: ...
... Enthalpy-Entropy compensation theory applied to the isosteric heat of desorption The differential entropy is calculated from the Gibbs-Helmholtz equation, Equation (24) where the Gibbs free energy is obtained by the equation Equation (25), [11] [24]. Substituting Equation (25) into Equation (26) and arranging the result, we get: ...
... The parameters of GAB, DLP, modified BET, Oswin and Smith equations along with coefficient of determination (r2), mean relative percentage error (E%), root mean square error (RMSE) and residual sum of squares (RSS) for each of the models are summarized in [16,51]. A decrease in GAB monolayer moisture content with corresponding rise in temperature depicts that the absorbed water molecules gained kinetic energy making the attractive forces to be loosened and this permitted some water molecules to dissociate from their sorption sites thereby decreasing the equilibrium moisture values [26,49]. ...
... This is in agreement with previous reports for similar products such as by Mariem Generally, a model with a P value of less than 10% is considered suitable [64]. From the parameters presented in [51,[64][65][66]. These findings is in agreement with that obtained by previous authors, who had studied the sorption isotherms of many fruits and vegetables. ...
... Kiranoudis et al inves-tigated the equilibrium moisture content of the potato, carrot, tomato, green pepper and onion in the range of 10 to 90% relative humidity and at three different temperatures (30° C, 45° C and 60° C) and concluded that GAB model is the best for predicting the experimental sorption data. Mc Laughlin and Magee determined the sorption isotherms of potatoes at temperatures from 30 to 60° C, and among the models tested, the GAB model gave the best adjustment with the experimental data [51,52]. According to Noumi et al, the GAB model adequately represents the sorption isotherms of Canarium schweinfurthii fruit, while Akanbi et al concluded that the equilibrium moisture content of tomato slices follows closely the GAB equation [17,67]. ...
Moisture adsorption isotherms and thermodynamic properties of dried tomato slices obtained from four tomato varieties were investigated. Freshly harvested tomatoes were pretreated with potassium metabisulphite solution (0.2%, weight/volume) before drying in a cabinet dryer at 60± 2° C. Moisture adsorption behavior of the dried tomato slices was determined using the static gravimetric method at 25, 30 and 40o C. The data fitted to GAB, M.BET, DLP, Smith and Oswin sorption models. The isosteric heat of sorption was also determined. Moisture adsorption isotherm of dried tomato slices from UC82B, Roma, Eva-F1 and Kerewa varieties exhibited a sigmoid isotherm curve typical of type II BET classification. Increase in temperature resulted into a decrease in the equilibrium moisture content. The GAB, DLP and modified BET model adequately modeled the isotherms of dried tomato slices. The relationship between isosteric heat of sorption and the equilibrium moisture of dried tomato slices were accurately described by exponential model. Volume 7 | Issue 3 | 249 www.opastonline.com
... In addition, one replicate for each experimental condition was used and a total of 32 model food systems were prepared. Equation (3): GAB model parameters Equilibration of Model Food Systems at Different Storage Water Activity For moisture conditioning in the samples, about 6 g of powder for each one of the sugar mixtures proposed in Table 1 were placed at 30 °C in hermetic glass jar containing different saturated salt solutions (P 2 O 5 , CaCl 2 *2H 2 O, K 2 CO 3 , SrCl 2 *6H 2 O) which produced water activity values between 0 and 0.70 (Kiranoudis et al., 1993). The samples were equilibrated for at least 6 months in order to promote moisture change in crystalline samples. ...
... If the values of x i are fixed, then equation (1) can be expressed in the form: represents the regression coefficient of the model. The sorption isotherm of crystalline sugars was modeled using the non-linear regression with the Guggenheim-Anderson-DeBoer (GAB) equation (Kiranoudis et al., 1993;Syamaladevi et al., 2009). The GAB equation is usually presented in the form: ...
... where X is the water content (dry basis), X m is the GAB monolayer water content (dry basis), w a is the water activity and C and K are constants related to the temperature effect (Kiranoudis et al., 1993). ...
Recently, the concepts of water activity (aw) coupled with glass transition temperature (Tg)
have been used in literature to evaluate the storage stability of fruit powder, since a product
is most stable at its monolayer moisture content or at below the corresponding Tg. Low
molecular weight sugars such as fructose, glucose, and sucrose constitute over 90% of the
solids of juice and the technical difficulties of storage of fruit powders are generally
associated with the basic physical characteristics of the mixtures of these sugars. However,
there are limited data of Tg regarding sugar mixtures of dehydrated fruit model systems in
the literature. Therefore, the glass transition temperature of model food systems including
mixtures of fructose, glucose and sucrose was studied using differential scanning
calorimetry (DSC). A distance-based experimental design for mixtures of three components
was used to establish the proportion of sugars of the model food systems. Thermograms
showing the complete process of heating-cooling-reheating were used to determine the
precise Tg values in amorphous sugars. Samples were conditioned by absorption at several
aw (0-0.7) and a new expression obtained from the adapted Scheffe’s cubic polynomial
equation was obtained to adequately describe the relationship between Tg and aw
(R2
=0.993, model significance <0.0001). It was observed that independent of the aw value,
the maximum and minimum glass transition temperatures were exhibited at the point which
correspond to pure sucrose and for samples containing pure fructose, respectively.
Additionally, it was noted that when aw was increased, the glass transition temperature of
model food systems decreased.
... Once a w of the samples at which the sample could be stable is known. From moisture sorption isotherm data it is possible to predict the corresponding optimum residual moisture content of the drying sample to decide the end-point of drying process [4]. Whereas the glass transition temperature can be taken as a reference parameter to characteristic properties of safety, stability, and quality [5]. ...
... Foods can be considered as stable at the glassy state, since in the state compounds involved in the deterioration reactions take times to diffuse IJSER over molecular distances and approach each other to react [14]. Sablani, [4] pointed out that certain physicochemical and structural processes such as stickiness, crispness, collapse, amorphous-to-crystalline transformations and the rates of non-enzymatic browning are better correlated to the glass transition temperature through plasticization by water or temperature than water activity. Differential scanning calorimeter (DSC) is by far the most commonly used method for determination of Tg in almost all cases, However, DSC said to be not sensitive enough to detect glass transition in materials such as starch containing products [15]. ...
... More than fifteen samples are dried with different salt solutions (relative humidity) at 65°C and 1000 mbar (LiCl, MgCl 2 , K 2 CO 3 , Mg(NO 3 ) 2 , SrCl, NH 4 Cl, NaCl, KI, NaNO 3 and KCl). These salts permit to cover a wide range of relative humidity from 20 to 95% as reported by many authors [23]. Drying is stopped when sludge reaches equilibrium moisture content X e and the change in weight is lower than 0.01 g during hours. ...
... They provide precision on the water transport and its removal during drying [40]. As reported in the literature [23,41,42], water sorption isotherm can be determined using static or dynamic methods. In both methods, the equilibrium phase has to be reached to determine the water content of the sample at equilibrium with a relative humidity, and finally to access at the sorption isotherm [43]. ...
In this study the thermo-physical and mechanical properties of an industrial sludge like shrinkage coefficient, density, water activity, apparent moisture diffusivity, effective thermal conductivity and heat capacity are determined experimentally. These properties constitute a major part of the required input data to model the sludge drying. The sludge shrinks linearly until reaching a critical water content Xcr = 23 % and then maintains a constant volume until the end of drying. Therefore, the density increases with decreasing the water content until the critical value (Xcr = 23 %) then it decreases until the end of drying. The Henderson equation seems to be the most appropriate statistical model to describe the water sorption isotherm of the sludge. The apparent moisture diffusivity is determined from the numerical solution of Richard’s law of diffusion with shrinkage. The results show that the effective thermal conductivity and the heat capacity decrease with the reduction of the water content from 2.60 W m⁻¹ K⁻¹ and 2.52 J g⁻¹ K⁻¹ for a wet sludge to 1.71 W m⁻¹ K⁻¹ and 0.78 J g⁻¹ K⁻¹ for a dry sludge respectively. The relationships between thermo-physical / mechanical properties and the water content / temperature of the sludge are established to be introduced in the created numerical drying model.
... En la misma se observa curvas con forma sigmoidea, que corresponden al tipo II de las cinco establecidas por Van der Waals, las cuales son las más frecuentes en la mayoría de los alimentos como frutas y verduras (Martínez et al., 1998). Diferentes autores que han trabajado con otros tipos de alimentos observaron un comportamiento similar (Kiranoudis et al., 1993;Timmermann et al., 2001;Kaymak-Ertekin and Gedik, 2004). Las isotermas tipo II, aparecen cuando la energía de enlace entre el agua y la capa primaria o monocapa es menor que las que se producen entre las moléculas de agua entre sí dentro de los tejidos del alimento. ...
... El comportamiento de los datos de humedad de equilibrio X we mostrados en la tabla 4., son similares a los observados por otros autores para diferentes frutas y vegetales deshidratados a 30-60 °C tales como uvas, higos, ciruela cebollas, tomates. (Kiranoudis et al., 1993); en pimientos rojos y verdes secados en un intervalo de temperatura de 30-60 °C (Kaymak-Ertrkin and Sultanoglu, 2001). Asimismo, un aumento en la temperatura de secado disminuye el tiempo de proceso y reduce el consumo de energía necesario para remover el agua de la superficie del mismo hasta una obtener una actividad acuosa en el producto final que garantice la estabilidad microbiológica del mismo. ...
... Sorption and thermodynamic data are the basis for calculation of the driving force in mass transfer operations [3]. Knowledge of the seeds hygroscopic behavior enables the development of drying mechanisms and storage conditions customized to the specific needs of the malting process. ...
... In the majority of cases in the literature, X m is considered to be constant with temperature [3]. However, for better accuracy and physical consistency with the other parameters, X m should not be considered constant, and independent fits elucidate that the parameter decreases with temperature [14]. ...
... However, in this study, the Guggenheim-Anderson-de Boer (GAB) model was selected to describe the absorption curve of the material, as the GAB equation is regarded as one of the most versatile models. It can be applied across a broad range of water activities (0.1 < aw < 0.9) and to a variety of materials [21,22]. ...
An upscaling methodology for designing convective drying systems is presented, specifically focusing on tray and belt dryers of sliced food. Based on the convective drying history of a single food slice, a semi-empirical model, named the Reaction Engineering Approach (REA) model, is developed to describe the heat and mass interaction between the food and drying agent. The model is integrated into the belt dryer's energy and mass conservation equations for co-current and counter-current configurations. The results indicate a remarkable maldistribution of air temperature and relative humidity along the belt and tray length, leading to a significant variation of the drying rate. The drying time and the moisture content uniformity are strongly dependent on the airflow and product flow configurations. The methodology proposed in this work can help design and operate the drying system accurately by knowing the single sample drying kinetics.
... According to the standard static gravimetric method standardized in the European COST project [23], the sorption isotherm of ordinary and artificially cured onion was carried out gravimetrically. The sample preparation was followed according to Kiranoudis et al. [24] and Gazor and Eyvani [25]. Onion slices of 1 mm thickness were air dried under ambient conditions (30-35 °C) and a varying relative humidity of 32-40%), to a moisture content of 15% d.b. for a period of 15 days. ...
Small onion or multiplier or aggregatum onion (Allium cepa L. var. aggregatum) is widely grown in southern regions of India. The enormous post-harvest losses are the main cause of concern in cultivating small onions, especially during the monsoon period. Curing is an important practice followed after onion harvest to minimize storage loss. In this context, a curing cum storage structure was designed and fabricated. Based on the physiological and physicochemical properties, a comparative analysis between the conventionally cured onions under the sun and those cured artificially by blowing hot air at 38–40 °C. The Physiological Loss in Weight (PLW), Total Soluble Solids (TSS), and Pyruvic acid content increased significantly (p < 0.01) whereas the firmness and moisture content decreased significantly (p < 0.01) with increasing curing time. The sorption isotherms of both conventional and artificially cured onions at ambient and 40 °C followed the characteristic sigmoid shape exhibiting a type II sorption behaviour. The curing time for conventional and artificial curing of onion was found to be 192 and 72 h, respectively. Based on the parameters analyzed it could be concluded that artificial curing would be the best curing method compared to the conventional practice.
... An EMC test was performed for solid fuels, such as coal, to evaluate the stability in the transport and storage stages [25,26]. Herein, the EMC was assessed according to the reaction temperature of the hydrochar generated during the HTC of EFB. ...
This study explores the effects of hydrothermal carbonization (HTC) on the fuel properties of empty fruit bunches (EFB) by varying the reaction temperatures between the range of 180–300 °C. The improved properties of hydrochars following HTC were achieved by analyzing the changes in the physical and chemical properties of EFB. Moreover, it can save energy during treatment processes, in addition to evaluating the improvement of the biofuel stability based on the equilibrium moisture content and agglomeration. The results showed that the chemical structure of EFB decomposed owing to dehydration and decarboxylation reactions, leading to increased carbon and fixed carbon concentrations in the obtained hydrochar; and thus, an increased calorific value. Hydrochar generated during HTC exhibited chemical properties similar to those of conventional coal fuel. The optimal HTC reaction temperature range was ~230–250 °C. Based on the X-ray fluorescence results, hydrochar produced during HTC had smaller K and Cl contents and a smaller degree of agglomeration than the original sample, indicating that clinker production can be reduced by the HTC of EFB. The results of this study have significance in the utilization of unused waste biomass as an energy source that can replace fossil fuels.
... The model becomes extremely complicated as the number of variables increases, making it more difficult to interpret and apply. Kiranoudis [38] reported that the GAB equation variables for onion and other vegetables are estimated, including physical properties such as: ...
A transient mathematical model has been evaluated to determine the principle of a solar crop dryer for drying vegetables (onion). Considering the meteorological conditions of Freetown (Latitude 8.4840 N, Longitude -13.2300 W), the model was developed to determine air temperatures and other operational parameters of the drying system for a day of March 21st. However, the investigated system had effectively reduced the drying process of onion. The developed double-pass solar air collector system showed a low-temperature output in the morning hours and displayed high-temperature results in the afternoon hours. From 8:00 to 16:00, the solar collector generates fluid output temperatures above 50 0C, with a peak value of 96 0C occurred at 12:00. The influence of the mass flow rate on the system's thermal efficiency was investigated. It was noticed that for a certain solar radiation value, an increased in the mass flow rate caused an exponential increased in the solar air collector thermal efficiency. Findings also revealed that an increased in the solar collector length led to a slightly decreased in the outlet air temperatures at a mass flow rate of 0.02 kg/s. The influence of increasing drying air temperatures and air velocity within the drying chamber reduces drying time significantly. The drying time for products dried in the first tray is lesser than for products dried in the subsequent trays, owing to temperature variations. The computation findings were verified to previous studies in the literature and observed to be strongly comparable.
... According to the literature, at an a w lower than 0.75, bacterial growth is inhibited [59]. Finally, the heat-dried byproduct had a w values comparable to those obtained with the prototype, thus supporting possible inhibition of bacterial activity despite the higher moisture content observed for this treatment compared to the two other drying methods; these results are similar to those found in the literature for comparable products [60]. Table 1. ...
The extraction of molecules with high added value plays an important role in the recovery of food waste. This work aimed to valorize tomato pomace, a by-product composed of skin and seeds, through extraction of carotenoids, especially lycopene and β-carotene. The tomato pomace was dried using three different methods (freeze-drying, heat drying, and non-thermal air-drying) to reduce its weight, volume, and water activity and to concentrate the carotenoid fraction. These drying approaches were compared considering the extractive potential. Three solvent mixtures were compared, a traditional one (n-hexane:acetone) and two green deep eutectic solvent mixtures (ethyl acetate:ethyl lactate and menthol:lactic acid) in combination with different drying procedures. The extract obtained using ethyl acetate:ethyl lactate with non-thermal air-drying showed the highest contents of lycopene and β-carotene (75.86 and 3950.08 µg/g of dried sample, respectively) compared with the other procedures.
... The mass of the dry matter was evaluated by drying in an oven at (105 ± 2) °C for 24 hours. Desorption isotherms were modeled with the GAB (Guggenheim-Anderson-de Boer) model (Van den Berg, 1984) since this model has been applied successfully to various foods (Kiranoudis et al., 1993 and. The equation for the GAB model is as follows: ...
La désertification est un problème mondial qui touche 40% de la planète et au moins deux millions de personnes. Ce phénomène est le résultat de combinaison des facteurs directs et indirects; certains liés au climat et d’autres liés aux activités anthropiques. En Algérie, ce phénomène touche l’écosystème steppique (dont la région d’étude fait partie) caractérisé par une longue période de sécheresse avec une dégradation de la végétation. Cette étude a été réalisée dans le but de la connaissance du degré de conscience de la population de la région de Boussaâda sur ce grave phénomène ainsi que sur leurs connaissances des moyens de lutte. Il s’agit d’une série d’enquêtes portées sur 151 sujets au niveau des sites de Maader, Maiter, El Hamel et Oultem par un échantillonnage aléatoire. Les résultats ont montré que les populations interrogées ont participé positivement aux enquêtes due à l’importance du phénomène et le phénomène de désertification est vaincu dans l’âme et l’esprit des populations vivant à proximité des sites relativement sensible à la désertification.
Mots clés: Algérie, Boussaâda, désertification, population.
... The water vapour sorption isotherms of selected films were determined by a gravimetric method, using desiccators containing saturated salt solutions: LiCl, CH 3 COOK, CaCl 2 , K 2 CO 3 , Mg(NO 3 ) 2 .6H 2 O, NaNO 2 , NaCl, KCl, BaCl 2 with a water activity at 20 • C of 0.122, 0.231, 0.323, 0.438, 0.547, 0.660, 0.757, 0.854, 0.91, respectively [23]. Film samples (25 × 25 mm) were dried at 40 • C for 48 h and weighed to determine their dry weight. ...
This study aimed to develop edible monolayer emulsion-based barriers with polysaccharides as film-forming components (chitosan and sodium alginate), soy lecithin as a surfactant and olive oil as a hydrophobic barrier. Monolayer barriers in the form of films were prepared by casting filmogenic emulsions composed of 2% w/v chitosan (dissolved in lactic acid 1% v/v) or 1% w/v sodium alginate, with different lipid contents (25, 50 and 100% w/w biopolymer basis) and different surfactant concentrations (5, 10 and 25% w/w, lipid basis). Glycerol was used as a plasticizer (25 % w/w, biopolymer basis). After the emulsion drying process, the obtained stand-alone films were sprayed with a crosslinking solution, achieving an optimized crosslinker content of 3.2 mgCa²⁺/cm² alginate film and 4 mg tripolyphosphate/cm² chitosan film. The effect of oil and lecithin contents, as well the presence of crosslinking agents, on the film’s water vapour permeability (WVP), water vapour sorption capacity, mechanical properties and colour parameters, was evaluated. The results have shown that the lowest WVP values were obtained with formulations containing 25% lipid and 25% surfactant for chitosan films, and 100% lipid and 25% surfactant for alginate films. The application of the crosslinking agents decreased even further the WVP, especially for chitosan films (by 30%). Crosslinking also increased films’ resistance to deformation under tensile tests. Overall, the films developed present a good potential as polysaccharide-based barriers with increased resistance to water, which envisages the use of the designed formulations to produce either edible/biodegradable films or edible coatings.
... Cette figure représente la chaleur isostérique nette de sorption de la figue en fonction de la teneur en eau entre 15 et 60°C et les courbes de corrélation correspondantes. La courbe de la chaleur isostérique nette de désorption est supérieure à celle d'adsorption (Fig. 4), ceci indique que l'énergie nécessaire dans le processus de désorption est supérieure à celle d'adsorption, [53][54][55][56]. On observe également une augmentation de la chaleur nette de sorption, au fur et à mesure que le degré de déshydratation augmente. ...
In this study, the hygroscopicity and thermodynamic properties of figs were studied to simulate their hygroscopic behavior during storage and drying. The experimental results were analyzed by the nine models of sorption isotherms. The Peleg model was considered the most appropriate to describe the relationship between the equilibrium moisture content and water activity. The thermodynamic functions such as net isosteric heat sorption, the entropy of sorption, spreading pressure, net integral enthalpy, and entropy were determined. Net isosteric heat of sorption and sorption entropy decreased with increasing moisture content. The heat of desorption is slightly greater than that of adsorption with low moisture content. The integral net enthalpy decreases with the moisture content while the entropy integral net increased. The theory of enthalpy-entropy compensation can be successfully applied to water sorption by fig.
... Considering the physical meaning of the X m parameter [11], we can observe its decrease when the temperature is increased. The literature often shows the values of X m as constant [16]. However for better accuracy and physical consistency of the values of the other GAB model parameters, X m should not be considered constant for different temperatures [11]. ...
Purple Ipê (Handroanthus impetiginosus Mart. ex DC. Mattos) is a tree of South America, known for reforestation use, medicinal use and as hardwood. Its seeds are very sensitive and need to be processed and stored under strict conditions to ensure their germination capacity. Analysis of their hygroscopic behaviour serves as a basis for studies on drying processes and storage conditions. The aim of this paper is to determine the desorption isotherms of Purple Ipê whole seeds, husk and endosperm at 20°C, 30°C and 40°C with subsequent analysis of the multilayer Guggenheim, Anderson and de Boer sorption model (GAB) parameters, as well as liquid isosteric heat and desorption entropy calculations. To determine the isotherms, the static gravimetric method using saturated solutions of known water activity was used. The isotherms presented good reproducibility, although the influence of temperature is slight in the range of values studied. The GAB model fitted well to the experimental data obtained for the desorption isotherms for whole seeds, but presented incoherent values for the husk and endosperm due to the experimental deviations resulting from the nature of the samples. The isosteric heat and desorption entropy calculations showed deviations from those predicted by the GAB model for monolayer moisture, but were considered adequate within the order of magnitude.
... The GAB equation is based on the Brunauer-Emmett-Teller (BET) adsorption theory, which gives a physical explanation for the parameters of the equation (Kiranoudis et al. 1993). The monolayer moisture content (Xm) for the GAB and BET models is related to food stability and indicates that the primary adsorption locations (ionic and polar groups) in the macromolecular surface (polysaccharides and proteins) are saturated by a monomolecular hydrating layer (Vega et al. 2007). ...
Chicken "isaw," which is common street food in the Philippines, is prepared by conventional frying and is observed to have poor shelf-life and keeping qualities. Hence, a new product was developed employing vacuum frying technology to minimize undesirable changes and provide longer shelf-life as the conditions under vacuum frying involves the use of low temperature and minimal exposure to oxygen. However, data on its quality is not yet available since the product is new. Thus, the development of sorption isotherm and understanding of isosteric heat of sorption to the newly developed product is essential for the quantitative approach to predicting stability and quality changes during packaging and storage. Isotherms of vacuum fried chicken "isaw" were measured at 20 °C, 30 °C, and 40 °C by the static gravimetric method over a range of relative humidity (RH) from 7-75%. BET (up to 43% Aw), Smith, Kuhn, Oswin, Karel, and Peleg were the mathematical models used in fitting the experimental sorption data. Corresponding to BET, the monolayer moisture content (Xm) revealed that the vacuum fried chicken "isaw" must have a moisture content of 3.79%, 1.98%, and 1.96% at 20 °C, 30 °C, and 40 °C, respectively to prevent auto-oxidation and to enhance product stability of vacuum fried chicken "isaw" during storage. The net isosteric heat was calculated using the Clausius-Clapeyron equation and was observed that as moisture content is decreased, the isosteric heat of sorption increases. With these data gathered, generating and understanding the product's sorption isotherm, energy constants, and general equation at 20 °C, 30 °C, and 40 °C would provide valuable information for predicting quality changes during storage and packaging and for convenience in its future processing in an attempt to improve its quality, safety, and profitability.
... The material was not able to bind the water due to the limited amount of solid matrix in freeze-dried cucumber soup. The sorption isotherms of many vegetable and vegetable powders followed type II according to Brunauer's classification [40,82,83]. The procedure and Equation (12) described by Blahovec and Yanniotis [61] was applied to classify the isotherm sorption of freeze-dried soups. ...
The aim of this study was to investigate selected physical and biochemical properties of four vegetable freeze-dried soups. The water content, water activity, pH, color parameters, antioxidant activity (EC50), total polyphenolic content of fresh tomato, pumpkin, beetroot, and cucumber, and freeze-dried soups were measured. Sensory analysis was applied to compare sensory attributes of fresh and rehydrated soups. The sorption isotherms of freeze-dried soups were obtained with the application of the static and dynamic vapor sorption (DVS) method. The application of the freeze-drying method enabled the obtaining of dry soups with a low water content of 2–3%. The drying caused a significant change of color of all soups. The redness of soups decreased after drying for the beetroot soups from +39.64 to +21.91. The lower chroma value of 25.98 and the highest total color change ΔE*ab = 36.74 were noted for freeze-dried beetroot soup. The antioxidation activity and total polyphenolic content were reduced after drying, especially for the cucumber and tomato soups. The Peleg model was selected to describe the sorption isotherms of dried soups. The sorption isotherm of freeze-dried cucumber and beetroot soups had a sigmoidal shape of type II. The shape of the moisture sorption isotherm for freeze-dried tomato and pumpkin soups corresponded more with type III isotherms. The DVS method can be used to characterize the moisture sorption isotherms of freeze-dried products.
... Ghodbanan et al. (2017) used a non-linear programming optimisation method to optimise total steam and air consumption in the dryer section of multi-cylinder fluting paper machine, achieving a reduction of 11% in the total steam use. Also, several mathematical models may be used to describe the drying process and help in its optimisation, and assist in the effective design of dryers (Kiranoudis et al. 1993). Most of these models derive from the diffusion model of Fick's equation. ...
Citation: Carrera-Escobedo J., Cruz-Domínguez O., Guzmán-Valdivia C., Carrera-Escobedo V., García-Ruíz M., Durán-Mu-ñoz H. (2020): Cost analysis of drying process by studying its kinetic parameters: A new study in Mexican chillies. Czech J. Food Sci., 38: 375-387. Abstract: The drying process of vegetables is a widely used technique for food conservation. However, this process can be expensive, and the cost highly depends on the ventilation, drying temperature and drying characteristics of the chillies. The contribution of this new study was to obtain the drying kinetics parameters of two different types of Mexican Capsicum annuum (Puya and Mulato) and model it at different temperatures with two different ventilation levels. The aim of this study is to provide a method to analyse the cost of the drying process by studying its drying kinetics parameters. The experimental results were fitted to Weibull distribution and Newton's model, obtaining an adequate numerical fit at different drying temperatures. The Weibull distribution demonstrates to be a better fit than Newton's model. Drying kinetics parameters were also studied by a diffusive model with effective diffusivity. The effect of temperature on the diffusivity was described by the Arrhenius equation with activation energy of 49.7 kJ mol −1 for Puya and 24.1 kJ mol −1 for Mulato. The ventilation effect on chilli drying kinetics parameters was qualitatively assessed. As expected, the ventilation effect improved the drying rate and reduced the drying time, and consequently the cost of the drying process was reduced. In addition, a new method is presented to evaluate the cost of the drying process considering the kinetic parameters obtained. This new method allows evaluating the cost of the drying process in a simple way and with little experimental work. Consequently, it is possible to greatly reduce the cost of the drying process.
... Duplicate samples of spray dried powders were placed in pre-weighed aluminum dishes, dried in a vacuum chamber at 70 • C overnight (WTB-BINDER, Tuttlinge, Germany) and afterwards stored in a desiccator for 24 h. After this time, the samples were weighed and placed in desiccators with five saturated salt solutions: LiCl, Mg(NO 3 ) 2 .6H 2 O, NaCl, KCl, and BaCl 2 with a water activity at 20 • C of 0.122, 0.547, 0.757, 0.854, and 0.91, respectively [33]. The desiccators were maintained at room temperature and the samples were weighted until constant mass. ...
A pineapple peel hydroalcoholic extract rich in phenolic compounds, was stabilized by microencapsulation using spray drying technology, with maltodextrin, inulin, and arabic gum as wall materials. The influence of the type of wall material and drying temperature (150 and 190 °C) on the particles properties was studied. The particles presented a spherical shape with a diameter ranging from approximately 1.3 to 18.2 µm, the exception being the ones with inulin that showed a large degree of agglomeration. All powders produced presented an intermediate cohesiveness and a fair to good flowability according to Carr index and Hausner ratio, which envisages suitable handling properties at an industrial scale. The microencapsulation processes using maltodextrin and arabic gum at 150 °C were the ones that showed higher maintenance of the antioxidant activity of compounds present in the extract before encapsulation during spray drying. In addition, the microparticles obtained were quite efficient in stabilizing the encapsulated phenolic compounds, as their antioxidant activity did not change significantly during six months of storage at 5 °C.
... In other words, the net isosteric heats of desorption are inversely proportional to the equilibrium water contents because the lines slopes are always negative (Equation 4). Similar results have been reported by other authors [3,8,9,30]. ...
In this paper, a new unpublished study on the watermelon fruit is presented. It concerns the experimental determination of the water desorption isotherms at three different temperatures, using the dynamic method requiring the Dynamic Vapor System device (DVS). In order to select the appropriate desorption curve equation, 11 different models available in the literature were applied to the experimental data. The models were compared using the correlation coefficient, the standard error, the reduced chi-squared, the mean bias error and the root mean square error; they were predicted by a non-linear regression analysis using the Curve Expert software. The effect of the temperature on the constants of the found equation is also examined. Finally, the desorption isosteric heat of watermelon is determined using the Clausius-Clapeyron relation. Contrary to long times taken in the static method, the results show that 4.5 days are widely sufficient to reach the equilibrium via the DVS device. In addition, the obtained curves are of the type III and the Henderson model is the most appropriate model representing them. In the interval 0.05-0.45 kg of water/kg d.m of equilibrium moisture, the values of the isosteric heat vary from 65.02 to 113.25 kJ/mol. Finally, the equation giving the isosteric heat of desorption v.s. the equilibrium moisture content is obtained.
... For measuring the equilibrium moisture content and equilibrium Young's modulus, a sample of the previously specified dimensions (14 � 14 � 2 mm) was weighed and then dried in a forced convection oven for 24 h by passing dry air at 120 � C with a velocity of 1 m s 1 and near-zero relative humidity. Then the sample was brought out of the oven and cooled until the temperature decreased to that of the ambient (Kiranoudis et al., 1993) and then weighed again. Equilibrium moisture content was calculated on the basis of mass difference and initial moisture content. ...
Young's modulus is one measure of texture, an important quality parameter in processed food materials. During thermal drying, the Young's modulus undergoes significant variation due to moisture loss and rubbery-glassy state transitions, and physics-based models help in understanding trade-offs involved in dryer designs. However, studies that establish the relationship among drying kinetics, state transition and Young's modulus changes are lacking in the literature. In this paper, the role of various stages of drying and rubbery–glassy states on Young's modulus variation is presented. A modelling framework is developed to capture the effect of moisture loss on local and effective Young's modulus. Experiments are conducted for measuring local and effective Young's modulus variation with time and moisture content. The model is validated with experiments conducted in this work as well as with those reported earlier in the literature, and the agreement is within 10% on average. The importance of a two-stage model for predicting Young's modulus variation during different drying stages and in case of state transition is discussed. The present work could serve as an initial step towards improved understanding and model development for Young's modulus variations during thermal drying.
... Birçok gıdanın adsorpsiyon izoterminin GAB eşitliğine uyduğu pek çok araştırmacı tarafından belirlenmiştir. Bu durum; soğan, yeşil fasulye ve kayısılarda [33]; patates, havuç, domates, yeşilbiber ve soğanda [34] ortaya konulmuştur. ...
... Figures 5, 6 and 7 show that the desorption isotherm has a sigmoidal appearance. This is consistent with the behavior of other agri-food products [23][24][25][26][27][28][29][30]. ...
The equilibrium water content of a product to be dried is essential during a forced convection solar drying and storage operation. These values are often taken from the so-called isothermal sorption curves. The isotherms determination is an essential step to know the distribution and the intensity of the water connections in the products. They make it possible to determine the products final water content to be reached in order to optimize the drying conditions and give valuable information on the hygroscopic equilibrium. As a result, this experimental study aims to determine the physicochemical components' and the desorption isotherms curves for deferent date type L'hmira, Bamakhlouf and Tegazza from the Touat region, in SouthWest Algeria, using the saturated salt solution method. The experiment is carried out for three temperature values 40 ° C, 50 ° C and 60 ° C, to study the influence of the temperature on the equilibrium curves of the product and finally to describe the isothermal moisture desorption for deferent date types for three temperatures using known models of GAB, SMITH, LANGMUIR and OSWIN.
... This information relates to the optimum moisture content to be achieved during drying, which is close to steady state. studies on sorption isotherms are carried out by mathematical modeling, eight mathematical models (in the literature) empirical and semi-empirical based on more or less physical bases [10], describing the correlation of water content with balance with the water activity of the products. among these models: GAB [11], modified BET [12], Henderson-Thompson [13], modified Halsey [14], modified Oswin [15], Peleg [16]. ...
Mastering the process of drying the palm heart (Jomare) requires knowing their isothermal sorption. The purpose of this work is the experimental determination of the palm heart sorption isotherms. the gravemitric method of saturated saline solutions is used at three different temperatures (40, 50 and 60 ° C) with a water activity extending from 0.067 to 0.85. The equilibrium was obtained after about 10 days. Four mathematical models have been used (LANGMUIR, GAB, modified BET and Peleg) to model and predict hygroscopic behavior during drying and storage. After smoothing and optimization of these models on the basis of the statistical processing of the obtained data, the results shows that the GAB and modified BET models best match the sorption isotherms. The isosteric desorption heats for the heart of palm are calculated using the Clausius-Clapeyron equation. Through this study, an expression has been proposed that allow the prediction of the thermodynamic properties of the palm heart. The results of this research can be used to determine characteristic drying curves and to have optimal storage conditions.
... Balaban and Pigott 9 provided a statistical model in which moisture diffusivity is a function of temperature. Kiranoudis et al 39 suggested that the effective moisture diffusivity will be treated as a function of material moisture content and temperature, as follows. ...
In this paper, we studied a single‐phase‐lag model of heat and moisture transfer in a finite slab, cylinder or sphere, undergoing industrial drying of foods. The present model is a boundary value problem of a system of two nonlinear second‐order hyperbolic partial differential equations. The solution of the present is model obtained by using finite difference Legendre wavelet collocation (FDLWCM) and Galerkin methods. In case of constant moisture diffusivity, we observe that the finite difference Legendre wavelet Galerkin and collocation solutions are exactly the same. Laplace transform and FDLWCM solutions are approximately the same. The L 2 norm error decreases as Legendre wavelet basis functions increases and strip size decreases. The L 2 norm relative error increases as Luikov number increases. L 2 norm relative error is highest in cylindrical shape and lowest in slab shape while in between spherical shape. The effects of the dimensionless parameters of heat and mass transfer are discussed in detail.
... It could be due to the instability and degradation of the color pigment when dried at a higher temperature (Chong et al., 2008;Lee et al., 2012). In addition, acceleration of Maillard and enzymatic reactions could be the reason of brown pigment formation (Adam et al., 2000;Kiranoudis et al., 1993) or caramelization process occurred during the increment of drying temperature (Dıáz et al., 2003;Ghanem et al., 2012). A similar trend has been discovered by dried lemon slices using pulsed vacuum drying process during elevated different drying temperature (60, 65, 70 and 75°C) (Wang et al., 2018). ...
... It could be due to the instability and degradation of the color pigment when dried at a higher temperature (Chong et al., 2008;Lee et al., 2012). In addition, acceleration of Maillard and enzymatic reactions could be the reason of brown pigment formation (Adam et al., 2000;Kiranoudis et al., 1993) or caramelization process occurred during the increment of drying temperature (Dıáz et al., 2003;Ghanem et al., 2012). A similar trend has been discovered by dried lemon slices using pulsed vacuum drying process during elevated different drying temperature (60, 65, 70 and 75°C) (Wang et al., 2018). ...
Moisture sorption properties of whole date-pits (WDP) and three fractionated date-pits; defatted date-pits (DDP), residue (REP) and supernatant (SUP) fractions were studied. Sorption isotherms were measured using Differential Thermal and Humidity chamber at different temperatures (10, 30, 50, 70 and 90 °C) and relative humidity ranged from 0.05 to 0.9. Crossovers of isotherm curves were observed for all fractions between different temperatures. At 30 °C, BET-monolayers of WDP, DDP, REP and SUP were 4.9, 4.2, 3.8 and 3.2 g/100 g ds, respectively. The complete isotherms (i.e. 0.05–0.90 water activity) were modelled by GAB with high coefficient of determination (i.e. 0.944 to 0.999). In the cases of WDP and DDP, the isosteric heat plots showed increasing trends with the decreased moisture and peaks at moisture 0.025 and 0.040 g/100 g ds. Unlike all fractions, DDP isokinetic temperatures Tis (i.e. 97.4 °C) was lower than isobound temperatures Tib (i.e. 145.0 °C) indicating complete removal of bound water occurred at higher temperature as compared to the temperature when all reactions reached at the same. The moisture sorption isotherm characteristics could be used in determining the end point of drying and storage stability as well as packaging design of the date-pits and their fractions.
The application of hydrothermal carbonization to improve biomass-derived energy sources is crucial because of insufficient supplies of fossil fuels and concerns associated with the impact of fossil fuels on the environment. Hydrothermal carbonization technology has been developed to circumvent the energy-intensive drying step required for the thermal conversion of high-moisture organic feedstocks into fuel. In this study, the quality of livestock manure was upgraded, and its energy density was increased through hydrothermal carbonization at various temperatures. The evolution of waste biomass under hydrothermal carbonization was chemically analyzed. The increased carbon content of the resulting biochar upgraded its fuel properties, leading to energy savings in the treatment process. After hydrothermal carbonization, the H/C and O/C ratios were lower owing to chemical conversion. The optimal temperature for hydrothermal carbonization was approximately 220 °C. The inorganic content resulted in a lowered degree of agglomeration and reduced the likelihood of fouling during combustion. The thermogravimatric analysis also provided the changing combustion characteristics due to the increased fixed carbon content. Fourier transform infrared spectra revealed that hydrothermal carbonization reaction reduced the numbers of C-O and C-H functional groups and increased the number of aromatic C-H functional groups. The equilibrium moisture content decreased rapidly when hydrothermal carbonization was conducted at temperatures higher than 200 °C, and the initial moisture content was reduced by 75% after hydrothermal carbonization at 300 °C.
Two mathematical models were used to determine the moisture adsorption isotherm curves of dry pet foods. Ten extruded commercial diets for dogs (n = 6) and cats (n = 4) were tested within 7 days of manufacture. The equilibrium moisture content of each food at 30 and 40 °C was determined by gravimetry. Six saturated saline solutions (lithium chloride, potassium acetate, sodium nitrite, magnesium chloride, sodium chloride, and potassium chloride) were prepared and used to obtain pet food samples at different water activities. Solutions were placed in airtight flasks containing food samples (without direct contact) and oven-dried to constant weight. The relationship between water activity and equilibrium moisture content was modeled by the exponential Peleg and Guggenheim–Anderson–de Boer (GAB) models. All pet foods exhibited a type II isotherm. Akaike information criterion, R², and standard deviation values were −29.79, 0.914, and 3.89, respectively, at 30 °C by the Peleg model; −28.86, 0.876, and 6.36 at 40 °C by the Peleg model; −31.17, 0.937, and 4.34 at 30 °C by the GAB model; and −29.63, 0.888, and 7.71 at 40 °C by the GAB model. At 0.60 water activity, equilibrium moisture contents by the Peleg and GAB models were 12.04 ± 0.84 and 11.67 ± 0.78 g H2O/g dry matter, respectively, at 30 °C and 7.83 ± 1.31 and 8.09 ± 0.81 g H2O/g dry matter at 40 °C. The GAB model also allowed estimating monolayer moisture content (5.81 ± 0.81%). Both models provided similar results and may be useful for determining quality parameters for pet foods. Adsorption isotherm studies can provide practical information about the moisture ranges of pet foods, contributing to the optimization of food safety, palatability, and processing conditions.
In this study, adsorption isotherms of freeze‐dried mahaleb powder were obtained using gravimetric method at four different temperatures (5, 25, 35, and 60°C). Experimental adsorption data were modeled using empirical models and artificial neural network. The GAB model gave the best fit among the empirical models with high R² (0.9908–0.9982) and low P% (4.71–8.40%) values. However, artificial neural network (ANN) model having 10 hidden neurons optimized using Lavenberg‐Marquardth training algorithm was superior to the empirical models with the highest R² (0.9965–0.9999) and lowest P% (0.74–8.52%) values. The ANN model explained the adsorption behavior of mahaleb powder ideally at all temperatures. In addition to the adsorption kinetics of mahaleb powder, thermodynamic properties such as isosteric heat of sorption, differential entropy and Gibbs free energy were also determined. Isosteric heat of sorption values were high when moisture contents of the powders were low. Also, differential entropy values followed the same trend which indicated that the adsorption process was driven by enthalpy. Gibbs free energy at the isokinetic temperature of 458.48 K was determined as −306.7 J/mol. Gibbs free energy values were below zero at all different temperatures. The results showed that ANN model can be suitable for predictive control systems in the food industry and the data obtained for thermodynamic properties can be useful for the storage of mahaleb powder in industrial scale.
Practical Applications
An intelligent model, which is artificial neural network was used for modeling of adsorption behavior of freeze‐dried mahaleb powder and it predicted the adsorption data better than empirical models. Thermodynamic properties which are mostly important for the prediction of energy consumption of a process were also determined. The data of the freeze‐dried mahaleb powder can be significant for the food industry in terms of prediction of shelf‐life and energy requirements.
Ce travail de thèse s’intéresse à l’étude expérimentale et à la modélisation des mécanismes du séchage de boues industrielles. Le partenaire industriel de cette thèse a proposé le procédé de séchage de boue in situ, qui vise le conditionnement de boues de co-précipitation issues du retraitement d’effluent radioactifs par séchage à l’intérieur d’un fût. Ce procédé permet d’éliminer l’eau de la boue par un traitement thermique sous vide. La finalité est d’obtenir une boue sèche et stable, avec la plus faible teneur en eau possible. L’objectif principal de ce travail est alors d’identifier les phénomènes qui se produisent au sein de la boue au cours du séchage, d’identifier les processus physiques et chimiques mis en jeu afin de modéliser le séchage. Les phénomènes présents peuvent se regrouper en phénomènes de transferts (chaleur et de matière) et en rétrécissement. De plus, lors du séchage les concentrations en sels solubles augmentent dû à l’évaporation. A l’atteinte des seuils de solubilités, des sels précipitent mettant en évidence le phénomène de cristallisation qui n’intervient qu’en fin du séchage de la boue. Ces phénomènes dépendent principalement des paramètres de transferts qui varient en fonction des conditions opératoires du séchage (température, pression et humidité relative), de la teneur en eau de la boue et du retrait. L’étude expérimentale de séchage comprend l’acquisition des caractéristiques intrinsèques de la boue en fonction de la teneur en eau, la température et la pression. Un modèle numérique qui simule le procédé de séchage de la boue à petite échelle est développé sous COMSOL-Multiphysics et prend en compte la géométrie déformable du matériau. Les mises en équations sont validées à partir des résultats expérimentaux. Un changement d’échelle est mis en œuvre avec la conception d’une maquette à l’échelle du laboratoire (1/23ème du fût industriel). Des expériences de séchage de boue réalisées à cette échelle sont dédiées à la validation du modèle. Une étude paramétrique et une étude de sensibilité sont également réalisées sur le modèle de séchage.
PurposeThe aim of this study was to determine the experimental moisture sorption isotherm of green pepper and okra, assess the performance of literature sorption models describing their behavior, and specify bound water properties.Methods
Isotherms were determined through the static gravimetric method at 30, 40, 50, and 60 °C. Twenty models were studied and fittings were done through nonlinear regression using MATLAB R2015b. GAB and Caurie models were used to determine energy constants and bound water properties respectively. Structural parameters were determined according to Kelvin and Halsey equations.ResultsAll the experimental isotherm were of sigmoid shape. For both samples, Peleg, Enderby, and Guggenheim Anderson de Boer (GAB) models gave the best validation statistic criteria. R-squared (R2) values were all greater than 0.926 and root-mean-square error (RMSE) values less than 0.04 for both substrates. The GAB energy constants varied with temperature between 6.00 to 51.75 and 34.23 to 176.78 for Cg constants, and 0.70–0.99 and 0.75–0.93 for Kg constants, respectively, for okra and green pepper. The Cg energy constant globally decreased with increasing temperature. The monolayer moisture content Wm, varied with temperature between (0.0740–0.1044) kg kg−1 and (0.0760–0.1522) kg kg−1 respectively for okra and green pepper. Green pepper bound water property values were globally higher than those of okra and both were successfully modeled according to the equilibrium moisture content and according to the temperature. Analysis based on the IUPAC classification revealed a macroporous structure of the two materials.Conclusions
The hygroscopic equilibriums, physicochemical and microbiological stability conditions of green pepper and okra, were determined, for given environmental temperature values. The results obtained from the present study would serve in understanding the water state and mechanism of water sorption, defining drying and storage conditions of the tested vegetables, as well as designing corresponding dryers and packaging.
There is currently no recognised equation, or set of equations, that can be used to adequately describe moisture dependant dielectrics. This study addresses this issue so that moisture dependant dielectric properties can be directly input into drying models, where the microwave or radio frequency source is always limited to a single frequency. This was achieved by adapting water activity equations to describe the moisture dependant behaviour of the loss factor and the dielectric constant of hygroscopic inhomogeneous materials at microwave and radio frequencies. These equations were fitted to thirty moisture dependant loss factor and dielectric constant data sets. The adapted water activity equations proved to be very effective at describing dielectric behaviour, with the best equation fits to the thirty moisture dependant dielectric data sets having an average Mean Relative Error of 2.99%. The suitability of the equations are discussed, and specific equations are recommended for fitting to different types of moisture dependant dielectric response.
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Lesser mealworm (Alphitobius diaperinus) is an insect species that can be reared on an industrial scale for human consumption. In this study, the hydration behaviour of processed lesser mealworm food ingredients (whole powder, protein concentrate, textured protein) was analysed in comparison to whey protein concentrate and tofu. Moisture adsorption isotherms were determined gravimetrically over 0.11-0.96 water activity range at 5 and 20°C, and seven sorption models were applied to fit the experimental data. The Guggenheim-Anderson-de Boer model performed best on the isotherms of all studied samples. The determined adsorption isotherms were type III according to Brunauer classification. Mealworm protein concentrate presented the strongest hydration capacity at 20°C, followed by whey protein concentrate and whole mealworm powder. Textured mealworm protein and tofu exhibited similar hydration behaviour at 5°C. Moreover, browning and agglomeration of mealworm protein concentrate powder were observed at water activities of 0.73 and higher, which can be explained by its composition and porous structure and were not typical for whey protein concentrate. The moisture adsorption results are important for the prediction of lesser mealworm ingredients shelf-life or prevention of undesirable quality changes during storage, but more research on microbial growth and sensory quality is needed.
The high water content in fresh onion bulb make it difficult to preserve. In order to remedy these situation, it can be converted into dried slices. The objective of this work was to optimize the phenolic compounds and antioxidant properties of dried onion slice. Box Behnken design was performed to determine the effect of drying temperature (25–45 °C), water activity (0.2–0.6) and drying time (12–24 h) on the moisture content, total phenolic, flavonoids content, DPPH free radical scavenging and total reducing power on dried onion slice. Desirability was fixed to obtain the best possible combination of factors to a maximum values of total phenolic and flavonoids content, DPPH free radical scavenging, total reducing power and a low level of moisture content. Data analysis showed that the factors significantly (p < 0.05) affected the responses variables. Desirability function showed that the optimal dry conditions were 20 h for drying time, drying temperature of 28 °C and water activity of 0.48. At this optimum point the moisture content, polyphenol and flavonoids content, DPPH free radical scavenging and total reducing power were respectively: 9.53%, 1060.45 mg gallic acid/100 g DM; 342.61 mg quercetin/100 g DM; 52.18 mg Trolox/100 g DM and 78.14 mg Vitamin C/100 g DM. In this overall optimum point desirability was 0.9. No significant difference (p < 0.05) was found between the experimental and predicted values of the response variables at optimum point.
The amount of water available in food for enzymatic and oxidative reactions as well as for microbiological proliferation is an important factor in the conservation, storage, and development of new food products. Adsorption and desorption steps at different temperatures act as important parameters used to further understand the behavior, response, and interference of moisture in the technological properties of food. This behavior can be observed using sorption isotherms. The use of by-products from maize processing has increased. Obtaining food from these materials depends on the technological analysis of these raw materials. The objective of this study was to show the benefits of a predictive experimental model of the sorption behavior of flours obtained from two different by-products of waxy corn wet-milling using the Dynamic Dewpoint Isotherm (DDI) method. The sorption profiles of flours at 20, 30, and 40 °C were estimated and mathematically fitted to different models. This study showed type III sorption curves (Thommes et al., 2015) behavior for both flours and the mathematical adequacy of different models. Numerical math methodology, with validated statistics, showed that the Peleg model is the best fit. The net isosteric heat of sorption estimated using the Clausius–Clapeyron equation, decreased in both flours when the moisture content of samples increased. Residual pattern analysis and linear graphical correlation of predicted models and experimental data showed that the scoring method using the interpolation of data obtained in the analyses of statistical factors and segregation using Sturges’ rule, is a viable way to determine the most suitable mathematical model to describe sorption curves.
Hybrid mixture theory-based multiscale fluid transport equations were solved for drying of strawberries and carrots to predict the moisture transport during the process. The fluid transport equation was coupled with the selected product quality and nutritional attributes to predict changes in stress distribution, shrinkage, color parameters, and ascorbic acid/β-carotene content. The fluid transport equation includes a non-Fickian term that incorporates the effect of glass transition on moisture transport. A transformation between Eulerian and Lagrangian coordinates was used to include the moving volume effects due to shrinkage. Good agreements between the experimental and the predicted values of moisture content (RMSE ≤ 0.095, RMSE ≤ 0.579), color parameters (R² ≥ 0.958, R² ≥ 0.934), and volume changes (R² ≥ 0.871, R² ≥ 0.865) were obtained for strawberries and carrots, respectively. Drying in the vicinity of glass transition regime led to sharper moisture profiles, indicating non-Fickian transport. However, drying at temperatures higher than glass transition temperature of strawberries and carrots resulted in Fickian characteristics-round and smooth drying profiles for drying at 70 °C. Drying at higher temperature caused higher loss of quality attributes; it resulted in samples with lower color parameters and ascorbic acid or β-carotene content. Higher drying temperature resulted in greater shrinkage and deformation throughout the structure, leading to cracks and openings and faster degradation in quality attributes. The developed model would allow improving quality attributes and finding optimum processing conditions of strawberries and carrots.
The latent heat coefficient of water vaporization is a necessary coefficient for evaluating the theoretical heat consumption of drying, which is of great significance for guiding engineering practice and evaluating energy consumption of the system. However, previous experimental models of latent heat coefficient of vaporization have their own defects, and the calculation results have large non-linear deviation. Based on the principle of non-equilibrium thermodynamics and quasi-equilibrium, according to the energy balance characteristics of grain dry state and water collection state, the mathematical solution of the latent heat coefficient of grain moisture vaporization was given by unifying free energy transfer and conversion into a scale. According to the internationally recognized saturated water and saturated steam state parameters, the expression of characteristic constant for water vaporization process was developed, which provides a theoretical basis for evaluating the energy consumption of the drying process and developing a scientific evaluation criteria of the drying process.
Sweetpotato is one of the predominant crops grown by local farmers in the marginal uplands of Brgy. Linao, Sitio Batuan, Inopacan, Leyte. The need to produce quality food products from sweetpotato is a continuing challenge to open new opportunities for farmers and entrepreneurs alike. This study aimed to determine the potential of sweetpotato var.SP30 for flake production and conduct moisture adsorption isotherm studies. Two screening processes were made using the 7-variable 8-run Plackett-Burman design while a face centered Central Composite Design (CCD) was employed during optimization. Sensory evaluation results were subjected to response surface regression (RSREG) analyses to generate optimum processing condition(s). Moisture adsorption studies were carried out to determine the nature of the product isotherm based on Brunauer-Deming-Deming-Teller (BDDT) classifications. Fitting of data was done using the Bruanauer-Emmettand Teller(BET) and Guggenheim-Anderson de Boer (GAB) models to determine the amount of adsorbed moisture in the product during storage at different temperature levels. Screening results identified Drying time (Dt), Drying Temperature (DT) and Oven Toasting time (OTt) as the critical processing variables. A set of combinations of Dt (min.), DT (°C), and OTt (min.) were generated as a result of the optimization. These combinations were 75-50-20, 80-50-20, 80-50-18, 85-50-20 and 90-50-20. Calculated values for the mass fraction of adsorbed water in the monolayer (WmB and WmG) at 30°C, 40°C and 50°C are 0.0971, 0.1311, 0.0591 and 0.1046, 0.2447 and 0.2224 respectively (expresseding/100gH2O) Sweetpotato (var. SP30) was found suitable for flake production. Moisture adsorption isotherm of sweetpotato flakes was sigmoid in shape and classified as type II in the BDDT classification. Wm values for both BET and GAB were found to follow the relationship WmB < WmG (Timmerman,2003).
Three two-parameter equations and one three-parameter equation were evaluated for goodness of fit of moisture content vs. water activity for 75 sorption isotherms representing fruit, vegetable and meat food products. It was found that the three-parameter Guggenheim-Anderson-de Boer (GAB) equation could represent more than 50% of the food isotherms with great accuracy. An equation having a mean relative deviation modulus of equal to or less than 5 was considered to represent a good fit to the sorption data. In all cases, the GAB equation described the fruit, vegetable and meat isotherms much better than the two paramèter equations. The mean relative deviation modulus and parameters for each of the equations are given in this paper.
Two equations derived from a modification of BET theory were evaluated for goodness of fit over 74 experimental food isotherms representing spices, fruits, vegetables, meats, proteins, starchy foods and milk products. About 77% of the isotherms represented principally by starchy foods, proteins meats and spices obeyed to Eqn [1]. Such isotherms when compared to BET equation showed lower sorption capacity than BET at high water activity. On the contrary, 23% of the products formed principally by high-sugar foods, i.e. fruits and some vegetables, whose sorption capacity resulted much higher than BET isotherm for water activities above 0.45 were adequately correlated by Eqn [2].
In recent years many efforts have been made to determine the sorption isotherms of foods at different temperatures. Ten years ago Wolf et al. (110) published a comprehensive collection of sorption isotherms measured by the authors or taken from literature. The same authors (111) measured several foods and spices in the temperature range from 5 to 60°C. Chirife et al. (23, 24, 26) and Iglesias and Chirife (52, 53, 55) frequently used these data in their important articles on the calculation of sorption isotherms and heat of sorption. Recently Iglesias and Chirife (56) published a book containing more than a thousand isotherms.
Water vapour sorption isotherms of various caseins, wheat flours and mixtures of both were determined at 25°C. The isotherm equation according to Guggenheim, Anderson and de Boer (G. A. B.) was applied to the data. The fit was better for the individual components. The estimated values of the G. A. B. constants were found to depend on the type of regression procedure used. The traditionally used polynomial regression, applied to the transformed data (aw/water content versus aw), was compared with direct non-linear regression analysis. The use of weighted non-linear regression analysis for the estimation of G. A. B. constants is recommended. Equations for estimating the error of the constants have been derived for the case of the transformed data.
Sorption isotherms of well-defined food materials presented in the pertinent literature by various authors differ in most cases considerably from each other.
As part of a more extensive study of the practical and theoretical aspects of water activity of foods in relation to drying and storage, a search was made for a suitable general equation which is able to describe food-water sorption isotherms and also supplies useful theoretical information. Such an equation is not accepted yet and it needs no further comment that present-day techniques which are in use for processing data in food engineering and research could greatly benefit from a relatively simple equation for the standardized description and interpretation of these important relations between water activity and water content. Until now the well-known isotherm equation of Brunauer, Enmett and Teller (B E T, 1938) is used in food science mainly for the estimation of monolayer water contents that are related to the longest storage life of dried products. But since the B E T - equation fits practical isotherms only up to about 0.35 water activity, empirical equations or numerical techniques are generally used for the practical isotherm description.
In a comprehensive collaborative study within the frame-work of COST (European Cooperation in the Field of Scientific and Technical Research) — the COST 90 project — the mean adsorption isotherms of MCC and a potato starch and the precision data, viz. the repeatability/reproducibility of the total sorption measurement procedures, were determined.Recommendations on the practical determination of sorption isotherms of foods based on this work are made.
A refinement of the Guggenheim-Anderson-de Boer (GAB) sorption model which allows for the existence of a third sorption stage, was used to analyze the behavior of adsorption isotherms of starches at very high water activity (aw). The results of experimental isotherm analysis with the new model revealed that above about aw=0·90 a change in the physical state of adsorbed water in starch occurred; i.e. the water molecules would be more ‘liquid-like’ than in the preceding layers. This transition corresponds with the unfreezable water content in starch, as determined by others.
The moisture sorption isotherms for dried onions, green beans and apricots were determined at 20, 30 and 40°C using the proximity equilibration cell method. Three regression methods were used to fit the GAB (Guggenheim-Anderson-de Boer) model to the experimental results. The direct nonlinear weighted regression analysis was shown to be the preferred procedure for estimating the six constants of the GAB model and predicting the moisture sorption isotherms of the dried products over the temperature range tested.
The moisture adsorption isotherms for dried raisins, figs, prunes, and apricots were determined at 15, 30, 45 and 60°C, using the gravimetric static equilibrium method. The applicability of the GAB (Guggenheim-Anderson-de Boer) model to the experimental results was found to depend on the regression method employed. So, using direct non-linear regression analysis, five constants of the GAB model were estimated which enables the equilibrium moisture content of each dried fruit in the temperature range 15–60°C to be predicted with reasonable accuracy. The indirect (successive) non-linear regression method is not recommended since the basic three constants of the GAB equation are interrelated.
Moisture content and temperature are of first importance in the storage of seeds. Seeds are usually stored in porous containers like sacks and paper bags, and their water content fluctuates with the humidity of the surrounding atmosphere. In sealed chambers, on the other hand, the humidity of the atmosphere will be determined by the water content of the seeds and, with different kinds of seeds in an enclosed space, an exchange of water will occur until equilibrium has been reached. This does not mean, however, that different kinds of seeds, or even different samples of the same kind will have exactly the same final water content, since the water content/humidity relations are affected by differences in structure, chemical composition and previous drying treatment; it is permissible, however, for practical purposes, to ignore the slight differences which occur between samples of the same kind of seed.
An evaluated compilation of equilibrium relative humidities in air vs. temperature from pure phase to approximately 10**5 pascal (1 atm) in pressure is presented for 28 binary saturated aqueous solutions. The relative humidities of the solutions range from about 3 to 98%. Using a data base from 21 separate investigations comprising 1106 individual measurements, fits were made by the method of least squares to regular polynomial equations with two through four coefficients. Equations and tables are presented along with the estimated uncertainties in the correlated results.
Amorphous (metastable) sucrose and glucose powders were exposed to relative humidities ranging from 4.6 to 33.6% at 25° C. At humidities lower than about 12% for sucrose and 5% for glucose, moisture equilibrium was attained and practically no crystallization occurred in nearly 3 years. A vapor pressure isotherm was evaluated for sucrose-water solutions from 0 to 100% sucrose at 25° C. At higher humidities the absorbed water initiated crystallization of the sugars with subsequent release of moisture to yield essentially anhydrous materials. The rate of crystallization of amorphous sucrose, evaluated from changes in the moisture content, followed an exponential law with respect to time, after an initial induction period. This period was interpreted to be the time for a build-up of sufficient nuclei to initiate an appreciable rate of crystallization.
Differential heat curves (obtained from adsorption and desorption isotherms) previously reported, were utilized for calculating ‘integral’ heats of water vapour sorption in dried foods. Foods examined amounted to almost thirty and included fruits, meats, vegetables and spices. ‘Integral’ heats were calculated by integrating the area under each differential heat curve in the moisture range of more practical interest. Calculated heats may be useful for estimating the heat requirements during dehydration. Average values of the heats of sorption were also reported which may be useful for the analysis of sorption rates.
An empirical equation was obtained for expressing with very high accuracy, the differential (isoteric) heats of desorption as a function of moisture content.
The water contents of some dehydrated plant products have been determined in atmospheres of known humidity within the range 0% to 80% saturation, usually at a temperature of 50° F. (10° C.) and also at 98–6° F. (37° C), 140° F. (60° C.) and 176° F. (80° C.) with dried potato and dried carrot.
The non-diffusible colloids and soluble constituents each play a definite part in affecting the water content at any humidity; the colloids have a relatively high water content at low humidities and the soluble constituents have a low water content.
The humidity/water relations of mechanical mixtures, such as soup powders, can be calculated from the proportions and properties of the constituents.
The equilibrium isotherms and the rates of adsorption and desorption of water vapor by selected freeze-dried food materials were studied between −20 and 50°C with a spring-balance sorption apparatus. In simple freeze-dried gels (starch, gelatin) the quantity of adsorbed water at equilibrium increased as the temperature was lowered from 50 to 0°C, and it remained almost constant below 0°C. In freeze-dried foods (potato, peach, and raw beef) and sugar-containing starch gel, adsorption was maximum at between 10 and 30°C. The equilibrium vapor pressure of simple gels followed the Clausius-Clapeyron equation throughout the temperature range studied, and the same relationship applied to the foods at the high and low temperature regions, with a change of slope at about 20°C. The rates of adsorption and desorption at a pressure of 0.1 mm Hg remained constant at temperatures below 0°C, and they increased linearly as the temperature was increased from 0 to 50°C. As the pressure was raised from 0.1 mm Hg to atmospheric, the rates of adsorption at 30°C decreased by a factor of about 100. The adsorption rates at atmospheric pressure increased exponentially with the temperature between 0 and 50°C. The results are discussed in relation to the freeze-drying operation.
Inverse gas chromatography was used to study moisture sorption properties of two bakery products as a function of temperature and food structure. Crackers (high in fat, low in sugar) were found to be more hygroscopic than sweet biscuits. Sorption isotherms at different temperatures were determined to obtain thermodynamic parameters of sorption. Enthalpy and entropy functions as weU as Zimm-Lundberg clustering analysis suggested different sorption mechanisms in the two systems. Active site binding mechanism was manifested in the cracker system by highly negative enthalpy and entropy changes at low moisture contents. Water-water interactions were more favored in the sweet biscuit system at the same free energy level. Addition of crystalline sucrose decreased hygroscopicity of the cracker system and increased formation of water-water interactions.
Water desorption isotherms were determined for New Zealand sweet potato at 25, 40 and 55°C, and for Philippines sweet potato at 28°C. The isotherms were sigmoid in shape and of type II according to the BET classification. The data were fitted to eight two-parameter equations reported in the literature. The effect of water activity, aw, and temperature, T°C, on the equilibrium moisture content, Me g water/100g dry solids, was best described for New Zealand sweet potato by: Me = 20.51 T-0.204 (aw/(1-aw)0.39 for aw= 0.06–0.81
The water adsorption isotherms of Sultana raisins were determined using the static method of saturated salt solutions at 20°, 25°, 30°, and 35°C. The equilibrium moisture content at water activities up to 0.70 decreased as the temperature was increased from 20° to 35°C. At higher water activities the moisture content increased sharply as the temperature was increased, resulting in crossing of the isotherm curves. This behavior is attributed to the increased solubility of fruit sugars at higher temperatures. The experimental data were fitted well with the 3-parameter GAB and Halsey equations, and best with the 5-parameter D'Arcy-Watt equation. The thermodynamic implications are discussed.
Moisture sorption isotherms (MSI) of dehydrated rice obtained at 10°, 20°, and 30° for two successive adsorption and desorption cycles were used to compute thermodynamic functions of water on rice. Uncompensated heats declined with increasing temperature, from 41 J/g dry matter at 10°C to 5.6 J/g dry matter at 30°C. No hysteresis was observed in cycle 2 isotherms at any temperature, indicating thermodynamic reversibility. The cycle 2 MSI were generally in between the adsorption and desorption branches of the cycle 1 MSI. Behavior of the thermodynamic quantities calculated from cycle 2 MSI was qualitatively similar to those calculated from the cycle 1 adsorption MSI, though their magnitudes differed. Some implications of these results are discussed.
Moisture equilibrium data for desorption of water from apples was determined at 20°, 30°, 40°, 50° and 60°C. The rehydration 40°C isotherm was also found. The experimental procedure was a gravimetric dynamic method. Sorptive capacity decreases as temperature increases. Rehydration of the dried material results in hysteresis. The data are interpreted in thermodynamic terms. Specific surface and monolayer concentrations are also found. Pore size distribution studies show that the most frequent pore radius at 20°C and 40°C are, respectively, 26 Å and 22 Å. Hysteresis data are compared with what would be expected from the cellulose wall, indicating that solubility and other effects increase sharply the sorptive capacity of the fruit. A comparison of desorption and adsorption characteristics shows that dehydration results in serious damage of the fruit structure.
The heats of moisture adsorption and desorption in four dried fruits (sultana raisins, figs, prunes and apricots) were estimated from equilibrium sorption data, using the Clausius-Clapeyron equation in the temperature range 15–60°C. The net isosteric heat of sorption (qst) decreased sharply from about 20 kJ mol−1 water to near zero when the moisture content was increased from 0.05 to 0.50kg water kg−1 dry matter. An exponential function was fitted to the experimental qst values at various moisture contents (X), yielding two characteristic constants (q0 and X0) for each fruit. Mean and total heats of sorption were calculated from the proposed empirical equation, which are useful for enthalpy prediction in food dehydration. The heats of desorption were higher than the heats of adsorption, indicating significant hysteresis in the sorption of water, especially in dried apricots.
Moisture sorption isotherms of dried fruits [Sultana raisins, Corinthian (black) currants, figs, prunes, and apricots] were determined at 15, 30, 45, and 60°C, using the standard static gravimetric method developed by the European Cooperation Project COST 90. Experimental curves showed an inverse effect of temperature at high moisture content due to high sugar content of dried fruits. The hysteresis between adsorption and desorption was verified experimentally. The GAB equation was used to predict experimental data for water activity range 0–0.95.
The hygroscopic behaviour of dried red pepper is characterized by means of water vapour adsorption isotherms at 5, 20 and 35°C; from the GAB equation, a monolayer water content of 0·0816 kg H2O per kg dry matter has been deduced. The effect of temperature on the drying rate of pepper is considered and yields are compared when the drying is carried out with ambient air and with different loading densities (10–40 kg m−2). The kinetics of paprika colour degradation during storage at different temperatures and with a moisture content corresponding to the monolayer have been studied. A sharp change in the rate of colour loss is observed at 15°C: the value Q10 (°C) changes from 1·62 to 2·82 when the temperature rises above 15°C.
Moisture equilibrium data of potatoes by desorption and adsorption were determined at 40, 50, 60 and 70°C. The experimental procedure was a gravimetric method. Isosteric heats of water desorption and adsorption were calculated by applying the Clausius-Clapeyron equation to the sorption isotherms at different temperatures. Seven mathematical models were used to fit the experimental data. A nonlinear least-squares regression program was used to evaluate the constants of the seven desorption and adsorption isotherm models.
Thermodynamics of foods in dehydration Heat of vaporization for shelled corn
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Ueber die wasserbindung durch eiweisstoffe und deren verthalten waehrend der trocknung
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Water sorption isotherms of raisins, currants, figs, prunes and apricots Development of B.E.T. like models for sorption of water on foods; theory and relevance Water activity and its estimation in food systems: theoretical aspects
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Badanie izoterm adsorpcji wody wybranych productow spozywczych
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Thermodynamics of foods in dehydration
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Metodo manometrico para medida de humedades de equilibrio
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