Moisture adsorption isotherms for mushroom

The moisture adsorption isotherms of Agaricus bisporus and Pleurotus florida mushrooms were determined at temperatures (30-70°C) typically found in drying and storage. The samples were equilibrated above saturated salt solutions. Equilibrium moisture content of mushroom decreased with an increase in temperature at constant water activity. The data was adjusted to 11 sorption models to ascertain the best fit. Comparisons were based on mean relative error, standard deviation and coefficient of determination. Of the models tested, the Chung and Pfost model showed the best fit. The net isosteric heat of sorption was determined using the Clausius-Clapeyron equation. The net isosteric heat of sorption decreased from 13 to about 1 kJ/mol when the moisture content increased from 5 to 50 g /100 g dry matter.     

Sorption isotherms and thermodynamics of water sorption of ready-to-use Basundi mix

Basundi mix representing powdered Basundi (an Indian traditional milk product somewhat similar to sweetened condensed milk) is a convenience product developed for enhanced shelf life at ambient temperature. Water sorption isotherms were obtained for this ready-to-use mix over the temperature range of 5-45 °C. There was definite inversion of the temperature effect at high water activity (>0.7). GAB model gave excellent agreement between experimental and predicted values. Other properties of sorbed water viz., monolayer water, number of adsorbed monolayers, density and amount of bound water and surface area of adsorption were also obtained. The net isosteric heat of sorption had strong dependence on moisture content. The enthalpy-entropy compensation suggested that the sorption mechanism involved is enthalpy driven over the entire range of moisture content studied.     

Moisture sorption characteristics of dried acid casein from buffalo skim milk

Adsorption and desorption isotherms of dried acid casein prepared from buffalo skim milk were determined at 25°, 35° and 45 °C over a water activity range of 0.11-0.97 using static moisture gain/loss from test samples. Both the adsorption and desorption isotherms exhibited sigmoid shape corresponding to type II, typical to many foods. There was generally a negative temperature effect on equilibrium moisture content. The effect of temperature was, however, statistically not significant over the temperature range of 25-45 °C. Of the seven sorption models tested for fitting the sorption data, the GAB model gave the best fit at all the three temperatures. The temperature dependence of GAB parameters has been determined in the form of Clausius-Clapeyron equation. The calculated values of monolayer moisture content from BET isotherm equation have been found to be lower than the corresponding values found by using GAB equation. However, in both cases the monolayer moisture was higher in desorption than the adsorption and deceased with increase in temperature. The net isosteric heat of sorption decreased exponentially with increasing moisture content and approached a constant value of 0.331 kJ/mol at moisture content 28 g/100 g (d.b.). The moisture sorption hysteresis observed at 25°, 35° and 45 C was statistically significant. The extent of hysteresis was negligible in monolayer moisture content region, occurred predominantly in the water activity range 0.35-0.60 and decreased at higher water activities. Total hysteresis energy was evaluated from the sorption data using Everett and Whitton plot. The effect of increase in temperature was to decrease the amount of hysteresis.     

Moisture adsorption isotherms of guar (Cyamposis tetragonoloba) grain and guar gum splits

Moisture adsorption isotherms of guar grain and guar gum splits were determined at 10, 20, 30 and 40 °C and 23-96% relative humidities using gravimetric method. The sorption data were fitted to six well-known sorption isotherm models (modified Chung-Pfost, modified Halsey, modified Henderson, modified Oswin, Chen-Clayton, and GAB models) using non-linear least square method. The GAB model was found the most satisfactory for representation of the equilibrium moisture content data for guar grain and guar gum splits. The equilibrium moisture content of guar gum splits was found to be significantly higher (p < 0.05) than that of guar grain. The isosteric heat of sorption was determined from the equilibrium moisture adsorption data using Clausius-Clapeyron type equation. Exponential relationship described well the dependence of isosteric heat of sorption on the equilibrium moisture content. The enthalpy-entropy compensation theory applied to sorption isotherms indicated enthalpy controlled sorption process.     

Glass transition and state diagram for freeze-dried Agaricus bisporus

Sorption isotherms and state diagram of freeze-dried Agaricus bisporus were developed to further investigate the connection between the two distinct criteria of food stability. Sorption isotherms of freeze-dried A. bisporus were determined by the gravimetric method and the data were modeled by GAB model. The GAB monolayer moisture content was calculated to be 6.2 g/100 g (d.b.). The glass transition temperature of freeze-dried A. bisporus was determined by differential scanning calorimetry. The state diagram was composed of the freezing curve and glass transition line, which were fitted according to Clausius–Clapeyron model and Gordon–Taylor model, respectively. The state diagram yielded maximally-freeze-concentrated solutes at 0.704 solids with the characteristic temperature of glass formation being −77.9 °C. The state diagram and sorption isotherms of freeze-dried A. bisporus are useful in evaluating the storage stability as a function of temperature and moisture content as well as optimizing drying and freezing conditions.     

Adsorption isotherms of pinhão (Araucaria angustifolia seeds) starch and thermodynamic analysis

The seeds of Araucaria angustifolia, commonly known as pinhão, are widely consumed in both Southern and Southeastern Brazil due to their high nutritious value comprised basically by starch. The literature on the technological aspects of this seed is still very scarce. Moisture adsorption isotherms of pinhão starch were determined at 10, 20, 30 and 40 °C using the gravimetric method. Results show that the Peleg model most appropriately represents the experimental data. Other models (Chung–Pfost, GAB, Henderson, BET and Chirife) also were found to adjust well. The isosteric heat of sorption (differential enthalpy) was calculated by using the moisture adsorption isotherm and decreased as moisture content increased. The enthalpy–entropy compensation theory was applied to adsorption isotherms and the isokinetic temperature for pinhão starch was calculated by plotting the differential enthalpy versus differential entropy. It was found that the adsorption process investigated was enthalpy-controlled and spontaneous.     

Moisture sorption isotherms of sorghum malt at 40 and 50 °C

The desorption and adsorption equilibrium moisture isotherms of sorghum malt at the temperatures of 40 and 50 °C, over the water activity range of 0.1-0.9, were determined using the static gravimetric method. A non-linear regression programme was used to fit five moisture sorption isotherm models [Modified Henderson, Modified Chung-Pfost, Modified Guggenheim-Anderson-de Boer (GAB), Modified Halsey and Modified Oswin] to the experimental data. The models were compared using the standard error of estimate, mean relative percentage deviation, fraction explained variation and residual plots.The Modified Chung-Pfost model was found to be the best for predicting the desorption equilibrium moisture content, while the adsorption equilibrium moisture content was best predicted by the Modified Oswin model. The desorption and adsorption water activities were found to be best fitted by the Modified Oswin model.The moisture sorption isotherms were sigmoidal in shape and showed a marked effect of temperature. The span of the moisture sorption hysteresis loop formed, decreased with increase in temperature, while the size increased with increase in temperature.     

Drying kinetics and quality changes during drying of red pepper

A mathematical model is proposed to simulate the process of drying of individual pieces of red pepper under constant external conditions and to predict changes in some nutritional and organoleptic attributes of the product. The model was solved numerically to obtain moisture content and temperature as well as ascorbic acid and carotenoids concentration in the product as a function of time. A good agreement between predictions and experimental data at different drying temperatures was obtained.Water sorption isotherms of red pepper were determined in the range 20-50 °C and represented by two different sorption equations. Drying kinetics were represented by a diffusive model, the effective moisture diffusivity ranging from 5.01 to 8.32×10⁻¹⁰ m²/s with an activation energy of 23.35 kJ/mol. Degradation kinetics for ascorbic acid and total carotenoids were measured in the range 50-70 °C and modelled as first-order reactions. The rate constants increased with temperature and product moisture content. Average activation energies for carotenoids and vitamin C degradation were 50.1 and 26.9 kJ/mol, respectively.     

Equilibrium moisture content and sorption isosteric heats of five wheat varieties in China

The moisture sorption isotherm data of five Chinese wheat varieties were investigated via the gravimetric static method at five different temperatures (10, 20, 25, 30, and 35 °C) and relative humidity ranging from 11.3 to 96.0%. The sorption data of wheat decreased with an increase in temperature at a constant relative humidity (r.h.). The hysteresis effect was observed between adsorption and desorption isotherms. The width and span of the hysteresis loop decreased with increased temperature, but was not influenced by the hardness of wheat varieties. Six models, namely the Chen-Clayton (CCE), Modified BET (BET), Modified-Chung-Pfost (MCPE), Modified-Henderson (MHE), Modified-Oswin (MOE) and Strohman-Yoerger (SYE), were employed to describe the experimental data. The BET, MCPE and MOE models were selected to best describe the sorption isotherms of wheat in the ranges of 11.3-49.9, 11.3-96.0 and 11.3-96.0% r.h., respectively. The hygroscopic property difference between hard wheat (cv. ‘Longyuan’ and ‘Nanduan’) and soft wheat (cv. ‘Zhaozhuang’ and ‘Lumai’) was very small. The sorption isosteric heat of wheat decreased with an increase in moisture content until the dry bulb moisture content (m.c.) of 20% was reached, and then decreased smoothly with increasing moisture content. A big difference was found between adsorption and desorption isosteric heats of wheat below 20% m.c., but the sorption isosteric heat difference between hard and soft wheat isotherms was small.     

The fitting of various models to water sorption isotherms of tea stored in a chamber under controlled temperature and humidity

The moisture sorption characteristics of tea stored in a chamber regulated by an atomizing humidification system were investigated at 25, 35 and 45 °C for water activity ranging from 0.1 to 0.9. The sorption isotherms of tea were typical type II sigmoidal curves according to BET classification. In both adsorption and desorption, an increase in temperature resulted in lower equilibrium moisture contents at corresponding values of water activity. The sorption isotherms exhibited hysteresis over the whole water activity range. GAB, BET, Henderson, Iglesias and Chirife, Oswin, Peleg, Smith and Caurie models were applied for analysing the experimental data. Nonlinear regression analysis was used for the determination of the parameters in the equations. Estimated parameters and fitting ability for sorption models were evaluated. The Peleg model was found to be the most suitable for describing the relationship between equilibrium moisture content and water activity for the whole range of temperatures and relative humidities studied. The surface area of monolayer was calculated. The BET equation was solved for the monolayer moisture content and the corresponding a_w values at which monolayer forms were presented. Sorption isotherm data were used to determine the thermodynamic functions such as isosteric heat of sorption, sorption entropy, spreading pressure, net integral enthalpy and entropy. The Clausius-Clapeyron equation was used to evaluate the isosteric heats of sorption. The isosteric heats of sorption and sorption entropy decreased with increasing moisture content. The heat of desorption was little higher than that of adsorption at low moisture content. The enthalpy-entropy compensation theory could be successfully applied to water sorption by tea. This theory showed that the moisture sorption of tea was governed by enthalpy-controlled mechanisms. The spreading pressure increased with increase in water activity and decreased with increasing temperature. The net integral enthalpy decreased with moisture content while the net integral entropy increased.     

Water sorption isotherms for lemon peel at different temperatures and isosteric heats

Lemon peel constitutes a potential source of dietary fiber to formulate new and healthier products, as well as a source of essential oils. The relationship between moisture content and water activity provides useful information for lemon peel processing, especially for drying and storage. Water sorption isotherms of lemon peel were obtained using a standardized conductivity hygrometer at four different temperatures (20, 30, 40 and 50 °C) and wide ranges of moisture content (5.381-0.002 kg water/kg dry solid) and water activity (0.984-0.106). One theoretical (GAB) and four empirical equations (Oswin, Henderson, Halsey and Ratti) were used for modelling sorption isotherms. After evaluating the models according to several criteria, the GAB model appeared as the best option. Isosteric heats of sorption were assessed from experimental sorption isotherm data using different methods.     

Water adsorption isotherms of microcapsules with hydrolyzed pinhão (Araucaria angustifolia seeds) starch as wall material

Water adsorption isotherms of microcapsules that use pinhão starch as the wall material and β-carotene as the core material were evaluated. Pinhão was chosen as the raw material because it is primarily composed of starch, and in the literature there are few technological aspects with regard to this polymer. Moreover, this wall material has been previously studied and demonstrated good encapsulation properties. Moisture adsorption isotherms were determined at 10, 20 and 30 °C using the gravimetric method. The Peleg model was used to fit the experimental data. The differential enthalpy and entropy of sorption were calculated using moisture sorption data; both decreased as moisture content increased. The enthalpy–entropy compensation theory was applied to adsorption isotherms and the isokinetic temperature was calculated by plotting the differential enthalpy as a function of differential entropy. We found that the adsorption process was enthalpy-controlled, the T_β (352.61 K) was higher than the T_hm (292.77 K), and the process was spontaneous (ΔG = −470.17 J mol⁻¹).     

Desorption isotherms and isosteric heat of desorption of previously frozen raw pork meat

Some meat products involve drying previously frozen pork meat, which makes the knowledge of sorption characteristics very important for the design and management of meat dehydration processes. The sorption isotherms of raw pork meat from the Biceps femoris and Semimembranosus muscles were determined at four temperatures: 25, 30, 35 and 40 °C. The experimental results were modelled using the GAB (Guggenheim, Anderson and De Boer) model. The effect of temperature was also taken into account to model the experimental sorption isotherms using four models (GAB, Oswin, Halsey and Henderson). The best results were provided by the GAB model. From the experimental sorption isotherms the isosteric heats of sorption were determined. For a moisture content higher than 0.15 kg water/kg dm, the isosteric heat of meat was similar to the latent heat of vaporization for pure water. For a lower moisture content, an increase in the isosteric heat was observed when the moisture content decreased.     

Equilibrium moisture contents of a medicinal herb (Melissa officinalis) and a medicinal mushroom (Lentinula edodes) determined by dynamic vapour sorption

The measurement of moisture sorption isotherms is of great importance in the fields of food and agricultural engineering. Although the static gravimetric method is still commonly used, automated instruments for the determination of sorption isotherms have been designed to overcome some of the drawbacks associated with the standard method. The dynamic vapour sorption (DVS) is a modern technique which can produce sorption data with high accuracy under controlled conditions in a short period of time. The method was examined and validated by measuring the equilibrium moisture contents of lemon balm herb (Melissa officinalis L.) and Shiitake mushroom [Lentinula edodes (Berk.) Pegl.] at a temperature of 25 °C in the range of 0-95% relative humidity. The experiments were performed in triplicate for a total of fifteen target values of relative humidity. A parallel exponential kinetics model (PEK-model) was used to evaluate the change in mass during the adsorption process of each relative humidity step. Additionally, the GAB model was tested for its effectiveness to describe the equilibrium MC/RH data of both products. The PEK-model fitted adequately to the experimental sorption kinetic data over the entire range of relative humidity. Sigmoid characteristic curves, type II pattern were obtained, as indicated by the C and K values of the GAB model. Differences in the hygroscopic characteristics of the two products tested were ascribed to differences in nature of the material.     

Moisture sorption properties of smoked chicken sausages from spent hen meat

Moisture sorption characteristics of smoked chicken sausages from spent hen meat were investigated at 5, 25 and 50°C over a water activity (a_w) range of 0.11–0.87. Sigmoidal (type-II) desorption isotherms were observed for these samples. The sorption data were analysed using mathematical equations of Caurie, Halsey, GAB and Oswin. The Halsey equation gave the best fit over the entire temperature range. GAB model also described the isotherms fairly well. The GAB and BET monolayer moisture values were not significantly different (P>0.01) and decreased with increasing temperature. The number of adsorbed monolayers, density and amount of bound water and surface area of adsorption also decreased as the sorption temperature increased. The pores, in general, enlarged with rising temperature.     

Desorption isotherms for fresh beef: An experimental and modeling approach

Desorption isotherms for fresh beef were determined at 30, 40 and 50 °C by the static gravimetric method. The resulting isotherms exhibited a type II sigmoid shape. The BET, GAB and Halsey models were used to fit these experimental data. The GAB model was most accurate for all temperatures and all levels of water activity, followed by the BET and Halsey models. The temperature dependence of GAB constants was estimated. The isosteric heat of desorption and its evolution in relation to moisture content were calculated using Clausius–Clapeyron equations. The monolayer moisture content was determined using the GAB model: it decreased as the temperature increased. The density of bound water, the number of adsorption sites, the sorption surface area and the percentage of bound water were calculated using the Caurie equation: all these quantities decreased as the temperature increased. The Kelvin and Halsey equations were used for calculation of pore size, which increases with an increase in moisture levels and sorption temperature.     

Moisture sorption isotherms – Experimental and mathematical investigations of orange (Citrus sinensis) peel and leaves

The aims of this work were to determine chemical composition and sorption isotherms of Tunisian orange peel and leaves of the “Maltaise” variety. These by-products were found to be rich in fibre, soluble sugars, protein, minerals and phenols. The equilibrium moisture contents of “Maltaise” peel and leaves were measured using the static gravimetric method at three temperatures (40, 50 and 60 °C) and in wide range of water activity (0.109–0.891). Desorption and adsorption data of peel and leaves were best fitted by the Peleg model at 40, 50 and 60 °C. The net isosteric heats of desorption and adsorption were determined from sorption isotherms. For both peel and leaves, the net isosteric heat of desorption was higher than the net isosteric heat of adsorption and both decreased continuously with increasing of the equilibrium moisture content.     

The prediction of moisture sorption isotherms for dairy powders

Moisture sorption isotherms were measured for whey protein isolate, high micellar casein and a milk protein concentrate powder. No temperature dependence was observed over the temperature range of 4–37 °C. At 50 °C the powders absorbed less moisture than observed at the lower temperatures. These isotherms were used to predict the isotherms for freeze-dried amorphous lactose/casein/whey protein powders. An isotherm for micellar casein was predicted using a simple additive isotherm model and was used along with isotherms for whey protein and amorphous lactose to predict moisture sorption isotherms for commercial dairy powders. Predicted isotherms compared well with measured isotherms indicating that this simple additive isotherm model is suitable for predicting moisture sorption isotherms of dairy powders. Delayed lactose crystallisation was observed in lactose/whey protein powders when compared to lactose/casein powders over the same water activity range.     

Effect of Cooking on Moisture Sorption Isotherms of Sheanut (Vitellaria paradoxa Gaertn.) Kernels: Evidence from Light and Scanning Electron Microscopy

The standard static gravimetric method was used to determine moisture sorption isotherms of both raw and cooked sheanut kernels at 40, 50 and 60 °C in the water activity range 0.11–0.96 in order to evaluate the influence of cooking on the moisture sorption capacity of the kernels. Preliminary analysis showed that the kernels lost a significant quantity of its proteins and carbohydrate during the cooking process. Results of analysis of the moisture sorption isotherms revealed that cooked kernels generally had significantly (p?<?0.05) lower equilibrium moisture contents (EMC) than the raw ones for both desorption and adsorption processes. The effect of temperature on the sorption processes as portrayed by the desorption isotherms revealed that EMC decreased steadily with increase in temperature within the water activity range 0.10–0.8 a_w but increased rapidly with increase in temperature above 0.8 a_w resulting in the overlap of isotherms for all sorption processes. This crossing over of isotherms was attributed to the dissolution of sugars at higher water activities. The protein matrix in the kernel was observed using light microscopy and was found to have been disorientated after cooking. Studies using light and scanning electron microscopy revealed that the reduced ability of cooked kernels to sorb water could be linked to changes in the structure of the kernels brought about by the cooking of the kernels. It is concluded that cooking had a very significant effect on the amount of water sorbed by sheanut kernels.