GAB Model Research Articles

Water adsorption isotherms and phase transitions of spray-dried chickpea beverage

Chickpea hydrolysate powders were obtained by spray-drying (70 and 60 °C as outlet and 180 °C inlet air temperatures), using inulin and maltodextrin as adjuvants (12 or 25 g/100 g solids). No effects of the variables studied were observed on solubility (88–93 g/100 g solids) and final moisture (3.50–6.15 g/100 g db). Yields were 49.44–61.24 and 44.53–51.55% at 70° and 60 °C respectively. Moisture adsorption isotherms (25°, 35° and 45 °C) were obtained by dynamic dew point method and modeled with GAB and BET equations. BET monolayer moisture values (5.53–9.66 g/100 g db), were slightly different and higher than those obtained for the GAB model. Critical values of water activity (awc) and critical moisture (Mc), related with phase transitions, were determined using the second derived from moisture change with respect to water activity (Sovitsky-Golay 2nd derivate). At 25 °C the highest awc and Mc values, 0.515 and 0.535, and 8.5 and 9.35 g/100 g db occur for products dried at 60 °C and with the lowest level of both adjuvants, while the product without adjuvant has an awc and Mc f 0.466 and 7.46 g/100 g db. The increase in awc and Mc, due to the presence of the inulin and maltodextrin reflects their protective effect. According to these results spray-drying (Tout = 60 °C) could be used to generate a stable dehydrated hydrolysate chickpea beverage basis using 12.5 g/100 g db of the adjuvants evaluated.

Effect of ultrasound-assisted osmotic dehydration on the drying kinetics, water state, and physicochemical properties of microwave vacuum-dried potato slices

The effects of pre-treatments on the drying characteristics, water state, thermal properties, and bulk shrinkage of potato slices during microwave vacuum drying (MVD) were investigated. The pre-treatment included ultrasound in distilled water (USOD-0%), and ultrasound-assisted osmotic dehydration in a 60% sucrose solution (USOD-60%). Results showed that the drying time of potato slices was reduced and the drying rate was increased when USOD-0% was used as a pretreatment, whereas USOD-60% had a negative effect on the drying rate of the samples. The Weibull model was effective in predicting the water changes in potato slices during the drying process. NMR analysis revealed that the relative content of immovable water (M22) increased initially, then decreased for drying, while the transverse relaxation time (T2) and the relative content of free water (M23) decreased consistently. The DSC results indicated that the glass transition temperature (Tg) had an inverse relationship with the water content of the samples, yet had virtually no influence on the volume shrinkage. The sample volumes decreased linearly with the decrease in water content during the initial drying stages. USOD pre-treatment lessened the volume shrinkage of MVD potato slices. Static gravimetry was used to determine the moisture sorption isotherms of MVD potato slices at 30 °C within the aw range of 0.113–0.923. The GAB model accurately fitted the experimental sorption data, which showed sigmoid shape curves for the MVD samples. When aw values exceeded 0.7, the USOD-60% treatment significantly reduce the water sorption capacity of MVD potato slices, while USOD-0% treatment was observed to increase the hygroscopic properties of MVD samples. Compared with the control, USOD-0% pretreatment significantly increased the monolayer water content (X0), sorption surface area (S0), the thickness of sorbed water multilayer (tm), and density of sorbed water (Ds) values of MVD potato slices, while USOD-60% decreased these values.

Sorption properties of paper treated with silane-modified starch

Sorption properties of paper products are important when applying paper as the packaging material. Hydrophobicity, i.e. reduced affinity of paper surface to liquid water, is of particular importance from the point of view of the direct impact on packed goods. However, hygroscopicity of the material is significant during storage of goods. The analysis of changes in the hygroscopic properties of paper products induced by the treatment with silane modified starch was presented. The results on the hygroscopicity of treated paper were related to the previously published results on the hydrophobicity. The discrete values of equilibrium moisture content allowed constructing adsorption and desorption isotherms. The three-parameter Guggenheim, Anderson, and De Boer (GAB) model, the four-parameter Generalized D’Arcy and Watt (GDW), and Yanniotis and Blahovec (Y-B) sorption isotherm models were used to quantify the hygroscopic properties for all options of untreated and modified paper samples. The effectiveness of silanes for improving hygroscopic properties was determined and compared to their impact on hydrophobicity of the studied materials. It was found that 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane was the only silane improving hydrophobic and hygroscopic properties. The analysis of the applied models of sorption isotherms depicted that the GAB model was not valid for describing water sorption isotherms in the case of the tested materials, while the GDW and Y-B models provided a much more realistic description of water sorption mechanisms. The evaluation of the results of fitting the GDW model indicated that water molecules bonding to the primary sites was the dominating mechanism of sorption.

Effect of Temperature on Moisture Migration in Earth and Fiber Mixtures for Cob Materials

This paper highlights the impact of environmental conditions on cob buildings. Different factors such as wall thickness, material permeability and interactions between moisture and heat fluxes can all have significant effects on the performance and durability of cob buildings. An experimental and modeling-based study was conducted on the hygrothermal characterization of cob building materials, which were obtained by mixing earth and fibers. Two types of cob materials that can be used as insulation and to form structural materials in buildings were tested. The effect of outside temperature on adsorption isotherms was investigated for both materials. The experimental data were fitted using the GAB model, after which a new correlation of water content correlation was proposed. Three specific configurations were investigated in which cob material was subjected to moisture transfer and a zero, positive or negative temperature gradient. Based on the resulting measurements, a high coupling effect between heat and moisture transfer inside the structural material was analyzed. A comparison of the experimental and modeling results demonstrated the satisfactory correlation and reliability of the developed model. Simulations were carried out for various wall thicknesses, in order to assess the effect of heat and moisture transfer on water content. The three scenarios were simulated and distributions of water content inside the walls were determined. The results show that the wall thickness of cob buildings and the direction of heat and moisture fluxes affect water content distribution in the structure. A greater thickness of the cob wall leads to higher water content, but this relationship reverses when the heat and moisture fluxes move in the same direction.

Antioxidant Potential of Spray- and Freeze-Dried Extract from Oregano Processing Wastes, Using an Optimized Ultrasound-Assisted Method.

Origanum vulgare is recognized worldwide for its numerous applications, in the food industry and beyond. However, the extraction of its essential oils generates a significant amount of waste. The aim of this research was to achieve the valorization of solid waste from oregano hydro-distillation, by (i) optimizing the ultrasound extraction of antioxidants, (ii) evaluating the effect of spray and freeze drying on the extract's physicochemical properties, and (iii) characterizing the obtained powder by its antioxidant capacity. A central composite design of experiments was used to optimize the sample/solvent ratio, ethanol/water ratio, and extraction time. The extract was analyzed for its antioxidant potential by determining the percentage of DPPH inhibition, FRAP, and total phenolic content (TPC). The GAB model best fit the data for the moisture sorption isotherm of the resulting powder. The antioxidant activity of the powders was tested in a ground-beef food system. The TPC was maximized at times longer than 58 min, a sample/solvent ratio between 0.058 and 0.078, and a ratio of ethanol/water around 1. Neither drying method significantly affected the antioxidant properties of the extract, even though the resulting powders from each showed a different morphology (determined using SEM). Encapsulation with maltodextrin protected the spray-dried extract during a 6-month storage period. Powders from both drying methods equally retarded lipid oxidation, and were comparable to the synthetic antioxidant BHT. It is concluded that oregano processing waste is a potent source of antioxidants, and that its dried extract, via an ultrasound-assisted process, can potentially be used as a natural alternative to synthetic antioxidants.

Sorption of Polar Sorbates NH3, H2O, SO2 and CO2 on Selected Inorganic Materials.

In this paper, the sorption of NH3, H2O, SO2 and CO2 was tested for several selected inorganic materials. The tests were performed on samples belonging to two topologies of materials, faujasite (FAU) and framework-type MFI, the structures of which differ in pore size and connectivity. All sorbates are important in terms of reducing their emissions to the environment. They have different chemical nature: basic, alkaline, and acidic. They are all polar in structure and composition and two of them (ammonia and water vapor) can form hydrogen bonds. These differences result in different interactions with the surface of the adsorbents. This paper presents experimental data and proposes a mathematical description of the sorption process. The best fit of the experimental data was obtained for the Toth and GAB models. The studies showed that among the selected samples, faujasite has the best sorption capacity for ammonia and water vapor, while the best sorbent for sulfur dioxide is the MFI framework type. These materials behave like molecular sieves and can be used for quite selective adsorption of relevant gases. In addition, modification of the faujasite with organic silane resulted in a drastic reduction in the surface area of the sorbent, resulting in significantly lower sorption capacities for gases.

Moisture adsorption isotherms properties of dried overripe barlin fruit (Musa acuminata AA.) powder

Moisture sorption of dried overripe barlin banana powder using the static gravimetric method. The materials were conditioned at 5, 10, and 25 oC with a water activity range of 0.16 to 0.86. Five mathematical models to describe the suitability of the phenomenon of adsorption experimental data using non-linear regression. The thermodynamic properties such as isosteric heat and Gibbs free energy are evaluated in this paper. The experimental results indicated that the equilibrium moisture content of dried overripe barlin banana powder increased with increasing water activity and decreasing temperature. The results of the model are based on the goodness of fit, and the Peleg model is the most suitable for describing the adsorption phenomenon with the type II sigmoidal shape. Monolayer moisture content and adsorption surface area using the GAB model are in the range of 6.18-7.81%d.b and 219.09-246.39 m2/g d.b, respectively, which increases with increasing temperature. Moreover, isosteric heat decreases with an increase in equilibrium moisture content and is opposite to the value of Gibbs free energy. In addition, the hygroscopicity of the dried overripe barlin banana powder increased with temperature and water activity.

Measurement and modeling of water vapor sorption on nano-sized coal particulates and its implication on its transport and deposition in the environment

One major cyclical environmental parameter within the underground mine space is the fluctuation of relative humidity, which varies daily and seasonally. Therefore, moisture and dust particle interactions are inevitable and indirectly control dust transport and fate. After being released into the environment, the coal dust particles stay there for a long period depending upon several parameters such as particle size, specific gravity, ventilation etc. Due to their smaller size, nano-sized coal dust particles could remain in the mine environment indefinitely while interacting with it. Correspondingly the primary characteristic of nano-sized coal dust particles could get modified. The nano-sized coal dust samples were prepared in the lab and characterized using different techniques. The prepared samples were allowed to interact with moisture using the dynamic vapor sorption technique. It was found that the lignite coal dust particles could adsorb up to 10 times more water vapor than the bituminous coal dusts. Oxygen content is one of the primary factors in deciding the total effective moisture adsorption in the nano-sized coal dust, with moisture adsorption proportional to the oxygen content of the coal. This means that lignite coal dust is more hygroscopic when compared to bituminous coal dust. GAB and Freundlich's models perform well for water uptake modeling. Because of interaction with atmospheric moisture, particularly swelling, adsorption, moisture retention, and particle size changes, such interactions will significantly change the physical characteristics of nano-sized coal dust. This will affect the transport and deposition behavior of coal dust in the mine atmosphere.

Equilibrium Moisture Sorption Isotherms of Aspirin

Equilibrium Moisture sorption isotherms are very important in drying and storage analysis. Experimental moisture equilibrium data (adsorption and desorption) of Aspirin were determined using the static method of saturated salt solutions and that by exposing the material to different conditions of temperatures and water activities. Three different temperatures (25, 30, 40Cº) and water activities in the range of (6.3- 83.6%) were used. The results showed that the equilibrium moisture content increased with the increase in water activity at any temperature and decreased with temperature increase at constant water activity. The water activity increases with increasing in temperature when moisture content was kept constant. The sorption isotherm curves are of type II according to Brunauer`s classification. The hysteresis effect was not distinctly expressed only for equilibrium sorption values of Aspirin at 25ºC. The experimental results were fitted to two sorption models (GAB and Henderson).The average relative deviation between the experimental and calculated data were obtained to select the best model. The GAB and Henderson models, obtaining values of 3.54 and 1.42 % average relative deviation and coefficient of regression of 0.98 and 0.977 respectively. The Henderson model was found to be the best fit out of the two models to predict the sorption behavior of Aspirin.

The Effect of Drying Temperature and Thickness on the Drying Kinetic, Antioxidant Activity, Phenolic Compounds, and Color Values of Apple Slices

Dried fruit slices are important, healthy, and popular snacks and gain importance day by day due to their high nutritional content. In this context, this study mainly focused on the production of healthy apple chips snacks and the determination of degradation kinetics of antioxidant activity, total phenolic compounds, and color values of apple chip snacks during convective hot air drying at three different temperatures (45, 55, and 65°C) and sample thicknesses (1.5 and 5 ± 0.5 mm). The drying kinetics, desorption isotherms, activation energy, and half-life of the apple chip snack were also calculated. The Page and GAB models are the best models for the determination of the drying (>0.992) and desorption (>0.9979) behavior of apple snacks with the highest R2 values. The drying of all samples took place in the falling rate period. The Deff values increased depending on the increasing air temperature and slice thickness. The antioxidant activity, total phenolic compounds, and total color change of the 5 mm thick samples were degraded following the first-order reaction kinetics. The higher antioxidant activity, phenolic compounds, L∗ values, and lower half-life values were observed in conditions where the thickness (1.5 mm) and temperature (45°C) are low. The activation energy values calculated for the total phenolic compounds are higher than those calculated for the antioxidant activity. As a result, it can be concluded that apple chip snacks with high nutritional value can be produced by choosing low temperatures and slice thickness.

Effects of thermodynamic properties of rice and ambient conditions on moisture migration during storage at naturally ventilated warehouses

The current study dealt with characterizing the effect of external variables on the moisture migration phenomenon in two naturally ventilated rice warehouses. Secondly, the thermodynamic properties of rice during the rehydration cycle were illustrated as numerical models to predict their behavior. Thai rice was stored at Shiraz city and Abadeh town for a total of 9 months in two identical warehouses. The effect of outside temperature and relative humidity on ambient conditions inside the warehouses as well as rice moisture content was evaluated. The dehydration rate of rice stored at Shiraz facility was higher than those stored at Abadeh warehouse by an average of 166% resulting in lower rice moister content. The 60-day latency in reaching minimum rice bulk moisture content at Abadeh warehouse was due to its cooler climate and less intense boundary area temperature gradient. The type II sigmoid-shaped sorption isotherm (fitted with the GAB model) indicated moisture content elevation above 11% sharply increased with the water activity beyond 0.7. The isosteric heat of sorption was linearly correlated with the entropy of sorption indicating adsorption was governed by compensation theory, was enthalpy driven and non-spontaneous. The most suitable conditions to store rice were determined by relating the grain’s moisture content and its thermodynamic properties during the sorption process. Therefore, storage of rice for prolonged durations was possible by maintaining the ambient temperature and relative humidity between 20.0 °C and 28.5 °C and 15.0% to 25%, respectively.

Farklı Kurutma Ajanları Eklenmesinin Dondurarak Kurutulmuş Hünnabın Fizikokimyasal Özellikleri ve Sorpsiyon Davranışı Üzerine Etkisi

The physical properties (bulk, tapped and particle density, flowability, porosity, particle size, hygroscopicity, degree of caging and reconstitution properties), chemical properties (moisture content, color, glass transition temperature, total phenolic content, and antioxidant activity) properties and sorption isotherms of freeze-dried jujube powder prepared with and without carrier agents (inulin, gum arabic, and whey) were studied. The moisture content, hygroscopicity, Carr index, Hausner ratio, and degree of caking of the powder with a carrier agent, especially whey, were lower than jujube powder without carrier agent (control). In contrast, the glass transition temperature, bulk, and tapped density were higher. Jujube powder with inulin (74.07) and whey (72.07) retained more brightness compared to gum arabic (66.56) and control (65.85). The sorption isotherms of all jujube powders depend on the temperature and the type of carrier agent. The equilibrium moisture content decreased with increasing temperature. The monolayer moisture content of the powder containing whey was lower than other samples (M0=0.072 g/g dry solids for 25°C and M0=0.062 g/g dry solids for 40°C according to GAB model), followed by inulin added powder, gum arabic added powder, and control

Processing of encapsulated flaxseed oil‐rich banana‐based (Dwarf cavendish) functional fruit leather

AbstractBanana fruit leather enriched with flaxseed oil in the form of encapsulates was prepared. Initially, the optimized conditions of 836 W power for 4 min for blanching of banana using microwave were obtained by Response Surface Methodology with residual polyphenol oxidase activity and vitamin C retention taken as responses. The addition of maltodextrin, citric acid, and pectin for blending with banana puree to obtain a non sticky puree having low pH was also optimized, while keeping the quantity of sugar constant. The blend was added with 5% encapsulates of flaxseed oil (FSO) in alginate used as wall material. The blend was dried in a tray drier at 40, 50, and 60°C and the drying behavior of the leather was studied. Henderson and Pabis model satisfactorily described the drying kinetics of banana leather. GAB model described well the sorption behavior of the leather. Fat content in the optimized leather increased to 3.27% due to addition of FSO. The ash content in the enriched leather was 5.56 ± 0.03%. Phenolic content increased from 91.84 ± 0.06 mg GAE/100 g to 100.90 ± 0.05 mg GAE/100 g for the enriched leather as compared to the control. The study revealed that the banana leather can be considered as a functional snack food due to the availability of flaxseed oil (rich in ω‐3 fatty) and high phenolic acid content.Practical ApplicationsBanana can be processed into functional fruit leather with the addition of flaxseed oil encapsulated beads to complement the fast moving consumer goods market. Developing the banana leather by drying enhances its shelf life while encapsulation increases the stability of flaxseed oil for a prolonged storage of the product. Flaxseed oil is rich in ω‐3 fatty acid, an important bioactive compound required for good human health. Moreover, modeling of the drying behavior allows optimization of the process, which is necessary for designing of energy efficient industrial flow dryers. Therefore, this study on development of a novel functional product and drying kinetics will give a new edge to the industrial processing of similar snack products with a potential alternative to reduce the waste of banana as a raw material.

Experimental Analysis of Drying Conditions’ Effect on the Drying Kinetics and Moisture Desorption Isotherms at Several Temperatures on Food Materials: Corn Case Study

This work studied the effect of external conditions on the drying kinetics of a thin layer of corn during convective drying. The density and the specific volume of the corn grain were reported and the desorption isotherms of the corn were determined at three temperatures and for a water activity from 0.1 to 0.9 using the static gravimetric method. Initially, a thin layer of corn about 7 mm thick with an initial moisture content of 45% (d.b) was investigated, and the external conditions were tested. Afterwards, a comparison between the experimental convective drying of a packed bed and a thin layer was performed under the same conditions. Finally, the values of equilibrium moisture contents, water activities and temperatures obtained were fitted using seven sorption models. It was found that the experimental desorption data exhibited type II behavior, according to Brunauer’s classification. The GAB model was found as the most suitable semi-empirical model which was well suited to represent the desorption equilibrium moisture content of corn kernels in the suggested ranges of temperature and water activity. It can be concluded from the entropy–enthalpy compensation theory that the desorption process of the corn kernels is controlled by the enthalpy mechanism.

Water sorption isotherms on lyophilized jabuticaba (Myrciaria cauliflora) peel: potential byproduct for the production of dehydrated foods.

In this work, water sorption profiles on lyophilized jabuticaba peel were evaluated using the BET, GAB, Halsey, Henderson, Oswin and Smith isotherm models. All water sorption studies were conducted using the static gravimetric method and saturated CH3COOK, K2CO3, NaBr, SnCl2, KCl and BaCl2 solutions at 20, 30 and 35°C. The best water sorption isotherm fits were determined with the GAB model at 20°C, Oswin model at 30°C and Halsey model at 35°C. The curve profiles of the isotherm models employed were classified as type III. The results revealed that lyophilized jabuticaba peel can be safely stored at 20, 30 or 35°C with the monitoring and control of relative humidity, equilibrium humidity and water activity. However, microbial action and undesirable enzymatic reactions may occur at 35°C when the relative humidity is above 22%. The present results are useful for defining suitable storage and production conditions of a novel jabuticaba peel-based process for the production of dehydrated foods.

Hemp protein isolate – gum Arabic complex coacervates as a means for oregano essential oil encapsulation. Comparison with whey protein isolate – gum Arabic system

The potential of hemp protein isolate-gum Arabic complex (HPI-GA) coacervates to encapsulate Origanum vulgare L. subsp. hirtum essential oil (OEO) was evaluated in comparison to the well-studied whey protein isolate-GA encapsulating system. Different biopolymer (1 or 2% w/w) and OEO (0.5 or 1%) concentrations were tested and the formed OEO microcapsules were characterized in terms of encapsulation yield and efficiency, as well as structural, morphological, moisture sorption, antioxidant, and antimicrobial properties. Gas chromatography was applied to determine possible ensuing changes to oil's composition. OEO was successfully encapsulated in both protein-polysaccharide systems as demonstrated by encapsulation yield and efficiency results and confirmed by FTIR spectroscopy, while its major volatile constituents (carvacrol and thymol) were highly preserved. Biopolymer concentration increase and low OEO's addition levels positively affected the encapsulation parameters (e.g., ∼90% encapsulation efficiency for the HPI-GA) due to the more complete droplets' surface coverage and enhancement of proteins-GA interactions at the interface. SEM analysis showed the typical, uneven, irregular morphology of freeze-dried powders, being denser and more aggregated upon OEO content increase. The sorption characteristics of coacervates exhibited the type II isotherm and the GAB model accurately described the obtained curves revealing lower monolayer moisture content in the case of HPI. The implementation of disc diffusion method showed that encapsulation acted protectively on OEO's antimicrobial activity, while DPPH and CUPRAC assays revealed the preservation of EO's antioxidant activity. These features provide evidence that HPI-GA can be used as alternative wall materials to encapsulate EOs by the complex coacervation method.

A long-acting hygroscopic and antibacterial composite filler: A new approach to phytoextraction solid residues from Citrus aurantium L.

A promising new composite filler with hygroscopic and antibacterial properties was developed based on the Fructus Aurantii Immaturus solid residues (FAIR) from Citrus aurantium L. , a typical bulk forest industrial crops. FAIR@AM-APTAC composite filler was established using FAIR as substrate, allyl glycidyl ether (AGE) as the cross-linker, while functional monomers of acrylamide (AM) and (3-acrylamidopropyl) trimethyl ammonium chloride (APTAC) were introduced. The structure of FAIR@AM-APTAC was characterized by FTIR , SEM, BET and TG–DSC analysis. The results confirmed that the FAIR@AM-APTAC composite filler was successfully prepared, which exhibited a three-dimensional(3D) network structure with a specific surface area of 0.1758 m²/g and exhibited excellent thermal stability. The equilibrium percent moisture absorption of FAIR@AM-APTAC (63.0%) was higher than that of FAIR (15.7%) under RH= 80% at 25 ℃ for 48 h, and much better moisture adsorption was achieved. The moisture adsorption process of FAIR@AM-APTAC followed a type III moisture adsorption isotherm and conformed to GAB, Peleg and pseudo-second order kinetics model. The moisture adsorption process of FAIR@AM-APTAC was a multi-layer adsorption process with enthalpy driven non-spontaneous and endothermic, which was dominated by chemical adsorption simultaneous existing physical adsorption, and the adsorption force was the synergy of both hydrogen bond and van der Waals force. The inhibition ratio of FAIR@AM-APTAC was 97.1% for E. coli and 95.4% for S. aureus . The antimicrobial efficacy of FAIR@AM-APTAC was enormously improved compared with that of FAIR due to the introduction of quaternary ammonium groups. The antibacterial mechanism of FAIR@AM-APTAC may be that the surface contact between bacterial and FAIR@AM-APTAC leads to inactivation. Significantly, FAIR@AM-APTAC showed long-acting hygroscopic and antibacterial properties, with little weakness even after 120 times cycle of wetting-drying. It is expected to be applied to an indoor air purifier or filter. • A new approach to phytoextraction solid residues from Citrus aurantium L. • Establishment of 3D structure long-acting hygroscopic and antibacterial composite. • Superior hygroscopic properties. Percent moisture absorption: 63.0% (25 ℃，RH=80%). • Superb antibacterial properties. Inhibition ratio: 97.1% ( E. coli ) and 95.4% ( S. aureus ). • A promising new filler: expected to be applied to indoor air purifier or filter.

Evaluación de las isotermas de sorción en snacks con mandioca pregelatinizada

Sorption characteristics are studied for their influence on the storage stability of dehydrated products and their effect on water vapour diffusion. In the present work, the adsorption curves of snacks with and without substitution of wheat flour by dehydrated cassava puree (PDM) were analysed using saturated salt solutions at 10, 30 and 50 ºC. Type III curves were obtained for the samples with PDM and type II for the control sample. Mathematical modelling was then performed using 8 different equations, obtaining the best fits for the Peleg (R2adjust =0.999-0.988), Ferro Fontan (R2adjust =0.998-0.970) and GAB (R2adjust =0.999-0.955) models. The values of the model constants in some cases turned out to be formulation and temperature dependent, and in general do not show a definite trend. This can be seen graphically as crossovers between the curves. This crossover of curves has been attributed to the increased exposure of hydrophilic groups due to increased molecular mobility at high humidity and occurrence of the glass transition in the system and/or endothermic dissolution of sugars.

The sorption properties, structure and shrinkage of freeze-dried multi-vegetable snack bars in the aspect of the environmental water activity

The aim of the research was to determine the water condition in freeze-dried multi-vegetable snacks, using a method based on the determination of sorption isotherms, with particular attention to the influence of storage conditions in the variable water activity of the environment on the structure and shrinkage of the snacks tested.Models to describe the course of sorption processes were well suited to the experimental data. Due to the observed differences during sorption properties, most likely resulting from the raw material (vegetable) composition of the tested freeze-dried multi-vegetable snack bars in the form of bars, the water level was analyzed based on the description of the experimental data using BET and GAB models.Due to the observed differences in the course of sorption processes, most likely resulting from the raw material composition of the tested freeze-dried multi-vegetable snacks in the form of bars, the water level was analyzed on the basis of the description of experimental data using BET and GAB models. The samples of bars with the addition of a mixture of locust bean flour and xanthan were characterized by the most porous structure typical for freeze-dried food, regardless of the vegetable ingredients used in the recipe.

Moisture Sorption Isotherms of Sweet Cherry (Prunus Avium L.): Comparative Study of Kinetics and Thermodynamic Modeling of Five Varieties

Moisture sorption isotherms of five sweet cherry cultivars (Prunus avium L.) at three temperatures of 30°C, 40°C, and 50°C, and water activity range of 0.057-0.898 were determined using the static gravimetric method. The sorption isotherms of all cultivars decreased with increasing temperature, and they all exhibited type II behavior according to the classification of IUPAC (International Union of Pure and Applied Chemistry). The isosteric heat of sorption, differential entropy, spreading pressure, and water surface area were determined, and the energy associated with the sorption processes was defined. The curves were fitted to GAB, PELEG, and ENDERBY models, and the GAB model gave the best fit for the whole set of data. The enthalpy-entropy compensation proved that the process occurs spontaneously and is fully controlled the enthalpy. The spreading pressure value varied with temperature in all sweet cherry cultivars in both the desorption and adsorption processes. The average surface area varied from 78.05 to 214.02 m2/g for desorption and from 49.0 to 204.4 m2/g for adsorption from 30 to 50°C.