Guggenheim Anderson De Boer Equation Research Articles

Assessment of the performance of Cromarty's equation to predict seed equilibrium moisture content during drying

For conventional seed (gene)banking of orthodox seeds, it is essential to effectively dry the seeds and maintain a low moisture content (MC). Cromarty's equation describes the MC and relative humidity (RH) relationship of drying seeds, based on their oil content, and can be used to predict the MC seeds would reach when dried to equilibrium in a controlled environment (RH, temperature). However, the equilibrium MC-RH relationship ('isotherm') varies not only between seeds of different species and depending on temperature, but also on whether seeds are losing (desorbing) or gaining (adsorbing) moisture. The reliability of Cromarty's equation in predicting the equilibrium MC for drying different seed species was examined and compared with the Guggenheim-Anderson-De Boer (GAB) equation, to model both desorption and adsorption data. Cromarty's equation provided a good fit to the desorption data for oilseed rape and barley (R 2 = 0.98). For yellow mustard, seed MC was overestimated and for lupin, wheat, buckwheat and pea, the MC equilibria predicted by Cromarty's equation were closer to the adsorption data. Overall, the GAB equation provided a better fit of the data. While Cromarty's equation is a useful tool for estimating the MC of seeds under a given environment, it should be used with caution in critical situations.

Physical origin of adsorption heat and its significance in the isotherm equation

Adsorption heat is a cornerstone concept underpinning almost all the existing theoretical isotherms for porous media. Yet, it remains elusive what this concept stands for and what are the physical sources for it. Here, a rigorous thermodynamic formulation is derived for the adsorption process with the aid of the law of mass action, leading to an expression of adsorption heat as the external chemical potential difference between two adjacent adsorbate layers. The interaction between adsorbent and adsorbates like van der Waals is theoretically identified as the intermolecular source for the change of adsorption heat. Thereby, adsorption heat is formulated as a spatially varied function of the distance to adsorbent surfaces. This adsorption heat function facilitates the establishment of a two-parameter sorption isotherm equation. The equation can be theoretically converted to two widely used adsorption isotherm equations, namely Brunauer–Emmet–Teller (BET) and Guggenheim-Anderson-de Boer (GAB) equations, and shows excellent performance in capturing experimental isotherm data of a wide array of materials. The comparative analysis demonstrates that the derived two-parameter isotherm equation outperforms the two-parameter BET equation and the three-parameter GAB equation in most cases. Such performance verifies the generality of the derived isotherm equation, thus further confirming the validity of the derived formulation of adsorption heat.

Study on water absorption and dielectric response of epoxy resin impregnated paper bushing

AbstractEpoxy‐impregnated paper transformer bushings are prone to water absorption due to the presence of water‐attracting moieties in the cellulose chemical structure and epoxy resin, leading to moisture‐induced insulation defects. To understand the mechanism of moisture's impact on epoxy‐impregnated paper, this study developed a testing platform that integrated moisture diffusion, adsorption, and dielectric properties of insulating materials. Insulation specimens made of epoxy resin and epoxy‐impregnated paper were prepared and their water diffusion characteristics were investigated using the Fick diffusion model and the Langmuir model, respectively. The Guggenheim–Anderson–de Boer equation was used to examine the vacuum vapour adsorption characteristics of the materials, providing a theoretical foundation for examining the form of water present within them. The dielectric response of materials with varying moisture levels was then tested to study the effect of water on the dielectric spectrum curve. Using the Extended Derivative Method, the characteristic frequency reflecting the water content of the epoxy‐impregnated paper was extracted. The results demonstrate that 0.01‐Hz characteristic frequency provides superior accuracy for moisture assessment in epoxy resins compared to 50 Hz, and extracting and fitting the relaxation peak characteristic frequency in epoxy‐impregnated paper moisture evaluation yields higher accuracy than using tan δ at the power frequency.

The role of natural hybrid nanobentonite/nanocellulose in enhancing the water resistance properties of the biodegradable thermoplastic starch

Abstract This study focuses on investigating the effect of hybrid nanofillers on the hydration characteristics and soil biodegradability of the thermoplastic corn starch (TPCS) hybrid nanofiller biocomposite (TPCS-HB) films. The data were benchmarked with that of the pure TPCS and TPCS single nanofiller biocomposite (TPCS-SB) as control films. The water absorption properties of TPCS, TPCS-SB, and TPCS-HB films were analyzed and fitted with the standard Guggenheim–Anderson–de Boer equation to study the water activity of the films. Besides, the water permeability test, water vapor permeability, and soil biodegradability of the films were also studied and correlated with the films’ surface morphology. The results indicated that the TPCS-HB films possess excellent hydration resistance and comparable biodegradable rate with the TPCS-SB films. The optimal water resistance properties were achieved when the optimal ratio of nanobentonite/nanocellulose (4:1) was incorporated into the TPCS matrix. The outcomes of this study provide an innovative idea and new insights that, by using natural and hybrid nanofillers, the hydrophobicity of the TPCS films could be enhanced. TPCS-HB films show great potential to be developed into a fully green biodegradable TPCS biocomposite film, especially for single-use plastic applications.

Sorption and thermal characteristics of ancient grain pasta of various compositions

The effect of ancient grain pasta composition on its sorption properties and phase transitions was evaluated. Three pasta samples were prepared from ancient grain flours: spelt wheat, einkorn wheat, emmer wheat and quinoa, and for comparison purposes one pasta sample from durum wheat flour. Water adsorption and desorption isotherms of pasta were determined and they were fitted by the Guggenheim–Anderson–de Boer equation. The state diagrams of pasta samples were developed by measuring their freezing points, glass transition temperatures, and the maximum-freeze-concentration conditions by Differential Scanning Calorimetry. All the pasta samples exhibited sorption hysteresis with higher equilibrium water content determined for desorption. Substitution of spelt wheat flour with other ancient grain flours in pasta samples resulted in decreased glass transition temperature, freezing temperature and the end point of freezing. The amount of un-freezable water in ancient wheat flour-based pasta was significantly higher than in durum wheat pasta. The results showed that the modification of chemical composition of pasta as a result of replacing semolina with flours from ancient grains is accompanied by a change in their sorption and thermal properties.

Soil water content–water activity relations of structured kaolinitic specimens from GAB equation

The GAB (Guggenheim–Anderson–de Boer) equation is explored to describe the relation between equilibrium soil water content (wequil) and water activity (relative humidity) of structured kaolinitic soils along the drying path. The equation is chosen as it has the advantage of a theoretical basis and can describe sorption behaviour of soils over a wide range of water activities. The GAB parameters evaluated from desorption experiments with de-structured specimens were successful in predicting the equilibrium water contents of structured kaolinitic specimens along the drying path. Insight into the influence of water activity on moisture desorption from structured soil specimens is obtained from energy requirements to desorb water molecules and by estimating the relative affinity (distribution constant) of water molecules for retention in soil pores or to undergo desorption.

Kinetic study of vitamin D2 degradation in mushroom powder to improve its applications in fortified foods

The aim of this study was to develop a value chain approach to address the need for sustainable vitamin D2 food sources. A combined process of UV-irradiation and air-drying was used to produce a Pleurotus ostreatus powder with a target amount of vitamin D2 as an ingredient for functional foods. The kinetics of vitamin D2 degradation was studied as a function of water activity (aw) in the range 0.11–0.75 at 30 °C, and temperature in the range 20–40 °C, at aw 0.32. The Guggenheim–Anderson–de Boer equation was applied to model experimental data of moisture content as a function of aw at 30 °C, and the resulting monolayer water activity was found to correspond to the aw level of 0.45. During storage under different environmental conditions, vitamin D2 degradation followed first-order kinetics. The rate constants ranged from 0.00308 to 0.0121 d−1 at aw 0.11 and 0.75 at 30 °C, respectively. The Arrhenius equation was applied to calculate the activation energy for vitamin D2 degradation at aw 0.32, which resulted 37.6 kJ/mol. The kinetics data obtained can be used as a basis to design the best formulation strategy to deliver this vitamin with functional foods.

Water retention of a bentonite for deep geological radioactive waste repositories: High-temperature experiments and thermodynamic modeling

Thermo-hydro-mechanical coupling is relevant in various natural processes and engineering applications involving clay soils. It can affect slope deformations and stability, as well as the functioning of clay barriers and energy piles. Temperature changes can alter the water retention capacity of expansive clays and, in turn, produce pressure, strength, and volume changes. In deep geological repositories, for instance, the design of bentonite buffers and the study of their interaction with the host formation must account for the heat released by radioactive decay. Here, to investigate how temperature controls the water retention capacity, vapor transfer experiments under adsorption/desorption (wetting/drying) paths were performed on the Czech B75 bentonite. The tests were conducted in a wide range of temperatures (20–80°C) and initial dry densities (0.6–1.9 g/cm3), at high total suction (4–400 MPa), without mechanical loads. The results showed a systematic loss of water retention capacity at high temperature, particularly at low suction, irrespective of the initial compaction. To predict the behavior at any temperature, a model was constructed from the Clausius–Clapeyron and the Guggenheim–Anderson–de Boer equations. It was calibrated and validated at various temperatures, also on a different bentonite (without further tuning), showing good performance. Dry density-specific calibrations did not affect the model predictions significantly, consistently with results that exclude an effect of initial compaction on water retention at high suction. The proposed model seems suitable for inclusion into thermo-hydraulic descriptions in comprehensive constitutive frameworks for expansive clays, potentially improving the understanding of some behaviors related to thermo-hydro-mechanical coupling.

Sorption equilibrium moisture and isosteric heat of cold plasma treated milled rice

Abstract To promote industrial adoption of cold plasma as a sustainable and safe processing technology for rice, data on equilibrium moisture content (EMC) for cold plasma treated milled rice of five Chinese varieties were collected by a gravimetric method at 11–96% equilibrium relative humidity (ERH) and a temperature range of 15–35 °C. Nine models were fitted well to the sorption data, with the modified Guggenheim–Anderson–deBoer equation (3-MGAB), modified Henderson equation (MHE), and a polynomial equation being the best fits. At a constant ERH, the EMC was negatively correlated with temperature, whereas there was a strong effect of temperature on the sorption isotherms of the milled rice. Initially, the isosteric heats of sorption for the cold plasma treated rice decreased rapidly with increasing sample moisture content (MC); however, when MC was higher than 15% of the wet basis (w.b.), further increases in MC caused a slight decrease in heat sorption values. The heat of vaporization of the milled rice approached the latent heat of pure water at a moisture content of ~17.5% w.b., which was ~2500 kJ/kg. The isosteric heat of sorption values of the milled rice predicted by the modified Chung-Pfost equation (MCPE) and MHE models negatively correlated with temperature. At 70% ERH, the safe-storage MC of the cold plasma treated rice were ≤14.5% w.b. at 25 °C. In comparison to the untreated milled rice, the cold plasma treated rice with 120 W for 20 s and 60 s significantly decreased the water contact angle and increased kernel broken index, without significantly changing the appearance quality of milled rice. The cold plasma treated rice with 120 W-20 s had insignificantly higher EMC than that of 120 W-60 s at the studied temperature range. This study demonstrates that helium cold plasma treatment insignificantly changed hygroscopic property of milled rice whilst maintaining the appearance quality.

ADSORPTION ISOTHERMS OF KIWIFRUIT DRIED BY DIFFERENT DRYING METHODS

The aim of this study was to determine the moisture adsorption isotherms of kiwifruit dried by hot air, vacuum and freeze drying methods. Equilibrium moisture contents (EMC) of dried kiwifruits were obtained by using the standard gravimetric method at two different temperatures (25 and 45°C) within a range of water activities from 0.112 to 0.936. The adsorption isotherms of dried kiwifruits decreased with increasing temperature and exhibited type III behavior. Six different isotherm equations (GAB (Guggenheim-Anderson-de Boer), BET (Brunauer-Emmett-Teller), Oswin, Henderson, Halsey and Peleg) were employed to describe the experimental adsorption isotherm data. Adsorption data obtained at both 25 and 45°C for vacuum dried samples and data obtained at 45°C for hot air and freeze dried samples were best represented by Peleg equation. For the samples dried by hot air and freeze drying, GAB equation gave the best description of the experimental data obtained at 25°C.

Water sorption isotherms of molecularly imprinted polymers. Relation between water binding and iprodione binding capacity

Molecularly imprinted polymers are often used in aqueous medium in order to recognize specifically a target molecule. The molecular recognition is usually based on hydrogen bonding. In this case, water molecule presents a serious competition towards the target molecule. In this study, the water sorption by molecularly imprinted polymers was studied in aqueous medium. The molecularly imprinted polymers were specific for iprodione fungicide and were prepared using a 24 full factorial experimental design. They were synthesized using EGDMA or TRIM as crosslinker, methacrylamide or styrene as functional monomer and using bulk or precipitation polymerization. The water sorption isotherms were established in a range of water activities 0.05–0.90 at 25°C. The kinetics of water sorption by the polymers were modeled using Peleg's equation. This model shows that polymers having the highest water sorption capacities have high values of imprinting factor. The Guggenheim–Anderson–de Boer isotherm equations were used to fit the equilibrium data and the corresponding parameters were calculated. This model shows that polymers synthesized with EGDMA have higher water sorption capacities than those synthesized with TRIM due to the higher hydrophobicity of the latter. Peleg and Guggenheim–Anderson–de Boer equations satisfactorily modeled the water sorption on the imprinted and non-imprinted polymers. The results obtained from both equations were practically coincident. Principal component analysis was used as a chemometric tool in order to demonstrate that a polymer having a low adsorption energy and a high capacity of water retention could be applied to extract a target molecule from aqueous media.

Modified GAB model for correlating multilayer adsorption equilibrium data

Abstract A new multilayer gas adsorption model is built based on the GAB (Guggenheim–Anderson–de Boer) model and L–F isotherm (Langmuir–Freundlich isotherm). Accounting for the heterogeneity of the adsorption system, the adsorption rate is assumed to be α th power of the surface area as demonstrated in L–F isotherm; the modified GAB model has the same form as that of the GAB equation with the difference lying on the relative pressure form; the nominal relative pressure is the α th power of the relative pressure. Different adsorption isotherm models are applied to correlate the adsorption data of microporous materials. The modified GAB model has the best conformity with the experimental data and can get almost the same so called “BET monolayer capacity” with that of the original BET equation using consistence criteria. The parameters in the modified GAB model were calculated as well; the non-unity of α indicated that the heterogeneity of the adsorption system is un-negligible even on the highly homogeneous surface.

피속 잡초 종자의 등온흡습곡선 특성

The equilibrium moisture contents (EMC) in seeds of four Echinochloa (E. crus-galli var. crus-galli, E. crus-galli var, echinata, E. crus-galli var. praticola, E. esculenta) were measured at 20oC with equilibration over a series of lithium chloride solutions with relative humidities ranging from 0.11 to 0.8 to determine sorption isotherms and safe storage relative humidity. Standard seed sorption isotherm models i.e. modified Henderson, modified Chung-Pfost, modified Halsey, modified Oswin and Guggenheim-Anderson-deBoer (GAB) equations were adopted to evaluate the goodness of fit to sorption isotherms. This study indicated that EMC of seeds was significantly different in four Echinochloa species at various relative humidity. The modified Oswin equations for E. crus-galli var. crou-galli, E. crus-galli var, echinata, E. esculenta and GAB equation for E. crus-galli var. praticola were adequate models for the EMC data. Seeds of four Echinochloa species have monolayer moisture contents when stored at RH < 0.1. These results show that seed moisture isotherm model should be selected according to genetic variation.

Water vapor transport properties of regenerated cellulose and nanofibrillated cellulose films

In this study, water vapor transport properties of nano-fibrillated cellulose (NFC) and regenerated cellulose films, derived from different sources, were investigated and compared with the transport properties of unmodified paper. Gravimetric-IGA experimental system was used to measure the kinetics and water vapor permeabilities (WVPs) of the samples. Water vapor adsorption–desorption isotherms were measured for different cellulose films using Belsorp instrument. Monolayer moisture content was determined by fitting the adsorption isotherm with the Guggenheim–Anderson–De Boer equation (GAB model). The monolayer moisture content of the regenerated cellulose and NFC films were found to be more than two times larger than the monolayer moisture content obtained for unmodified paper sample (made from bleached Kraft pulp ~4.12wt%), at saturation. This indicates a large number of hydrophilic sites available on the surface of regenerated cellulose and NFC films. The water transmission rates (WVTR’s) of regenerated cellulose and NFC films were similar, but lower compared to the unmodified paper measured at a wide range of relative humidities. Furthermore, water vapor permeabilities (WVP’s) of NFC and regenerated cellulose films were found to be concentration dependent exhibiting lower values up to RH=25%, but then showing a rapidly increasing trends above RH=25%. WVP’s of the cellulose films revealed an Arrhenius type of dependency with temperature, indicating an activated process.Water vapor diffusivities were also measured from the uptake rate measurements for a wide range of relative humidities. The diffusivities generally showed dependency on the moisture content of the sample. The effective diffusion coefficients (Deff) of NFC and regenerated cellulose films are 1–2 orders of magnitude lower in comparison with the unmodified paper, depending on the moisture content. The mechanisms of water vapor transport through the cellulose films were also evaluated from the uptake rate experiments. The results showed that the external surface resistance was a more dominant mechanism to mass transfer in the NFC and regenerated cellulose films. On the other hand, water vapor uptakes on unmodified paper seem to be consistent with internal diffusion control mechanism, except at the high moisture contents. At the high relative humidity or moisture contents of the films, both the external surface resistance and diffusion control the transport in transparent cellulose films and paper samples.

Water relationships in Haematoccoccus pluvialis and their effect in high-pressure agglomeration for supercritical CO2 extraction

Stickiness and caking of fine powders such as in dry disrupted microalgae should be avoided in supercritical (sc) CO2 extraction, because they negatively impact extraction rate and yield. To establish limits in water content of H. pluvialis cysts and extraction temperature, this work studied water-state diagrams of the powder. The powder’s squeeze flow behavior as a function of water content was useful to characterize the transition between glassy and rubbery states as water content increased. Water sorption (W versus aw) at 20°C was represented using the Guggenheim–Anderson–de Boer equation, with a monolayer water content of 3.67% (d.b.). The glass transition diagram (Tg versus Ww) was represented using the Gordon–Taylor equation, with Tgs=88.3°C (glass transition temperature of the anhydrous solids) and k=3.49. The compression pressure necessary for squeeze flow behavior decreased 2.5–3 times at ambient temperature (ca. 23°C) as a result of an increase in water content from 3.8% (d.b.) to 10–15% (d.b.) at which level glass–rubber transitions manifested, and then kept relatively constant when the water content increased even further. Alternatives to prevent caking of H. pluvialis during scCO2 extract include reducing the initial water content of the powder, increasing particle size by high-pressure agglomeration, and/or reducing the extraction temperature so as to prevent the glass–rubber transition that is responsible for sample stickiness. Taking into account that the scCO2 extractions are carried out above ambient temperature (40⩽T⩽60°C), we recommend reducing the water content of H. pluvialis powder to W⩽5% (d.b.).

Vacuum-Belt Drying of Rabbiteye Blueberry (Vaccinium ashei) Slurries: Influence of Drying Conditions on Physical and Quality Properties of Blueberry Powder

Continuous vacuum-belt drying was studied as a means to produce high-quality powders from blueberry slurries, with limited degradation of anthocyanins. Drying was performed at three different temperatures (80, 95, 110 °C) and the resulting dried material (a w ∼ 0.2) ground into powders. Drying times ranged from 70 min at 80 °C to 50 min at 110 °C. Maltodextrin (MD) was used as a drying agent at three levels (0.3, 0.45, and 0.6 kg/kg dry blueberry solid). Powders were purple, with no signs of browning, and similar in appearance to those produced by freeze-drying. Increasing MD level and drying temperature decreased the hygroscopicity of the powders. Moisture isotherms showed type 3 behavior and were well-fit with the Guggenheim–Anderson–de Boer equation. Higher levels of MD improved flowability of the powders, with >93 % of the powders with MD flowing from the test fixture after 30 s, compared to only 62.1 % emerging for powders without MD. Powders dried at 80 °C were slightly darker (L* = 25.73–28.4) than those produced 110 °C (L* = 27.10–28.53), presumably due to less degradation of anthocyanins. Total monomeric anthocyanins (TMA) for MD dried at 80 °C (13.1 mg C3G/g) were not different than for freeze-dried blueberries. Higher drying temperatures caused some loss of TMA. Higher levels of MD result in lower TMA by increasing the amount of dry matter in the powders. Vacuum-belt drying at 80 °C with 0.3 kg MD/kg dry solids produced non-sticky powders with anthocyanin content similar to freeze-dried powders.

Analysis of water adsorption by wood using the Guggenheim-Anderson-de Boer equation

The Guggenheim-Anderson-de Boer (GAB) three-parameter sorption equation has been used to interpret the adsorption and desorption isotherms of water vapour measured for 21 important cultural heritage wood species used in the past for panel paintings and woodcarving. The equation is capable of describing the full shape of the isotherms and yields meaningful physical parameters, especially the monolayer capacity from which the water accessible specific surface area can be obtained. It is demonstrated that average sorption isotherms can be derived using the GAB equation for the sorption data available for sets of specimens and that moisture properties of various wood specimens or chemically modified wood can be more easily compared.

FOAM‐MAT FREEZE‐DRYING OF APPLE JUICE PART 2: STABILITY OF DRY PRODUCTS DURING STORAGE

ABSTRACT Sorption isotherms at 5, 20 and 35C and glass transition temperature as a function of water content were evaluated for foamed (3% egg white and 1% methylcellulose) and nonfoamed freeze‐dried apple juice by using the static gravimetric method and differential scanning calorimetry, respectively. Equilibrium isotherms were fitted to the Guggenheim–Anderson–de Boer equation, whereas glass transition temperature to the Gordon–Taylor model. After freeze‐drying at 20C during 48 h, the dry products were stored at different temperatures (5 and 20C) under ambient conditions or vacuum. The nutritional, physical and structural properties were assessed before and at the end of the freeze‐drying process and after storage by determining vitamin C content, solubility, color and microstructure. Freeze‐dried nonfoamed juice retained more vitamin C and was more soluble than foamed products after freeze‐drying. However, foam‐mat juice powders presented higher stability during storage at 20C, which agreed with their higher values of glass transition temperature. Freeze‐dried juice stored at this temperature collapsed showing a decrease in solubility and a marked color change. PRACTICAL APPLICATIONSQuality of dry products depends largely on how they are stored (relative humidity, temperature, presence of light and vacuum). Degradation of flavor, color and texture occur under adverse storage conditions. Nutritional compounds such as vitamins or unsaturated fats could also be negatively affected because of oxidation reactions, which could be a function of the dehydration method or the pretreatment used to manufacture the dry product. The determination stability and quality degradation of foamed and nonfoamed apple juice products during freeze‐drying and storage of the dry products will complete the evaluation of foaming as a potential pretreatment for freeze‐drying.

SHELF‐LIFE SIMULATION OF PACKAGED RICE CRACKERS

ABSTRACT Two varieties of rice crackers (RC‐1 and RC‐2) were packaged in two types of packaging materials, polyethylene and polypropylene pouches, and stored at 30C/75% RH and 30C/85% RH to simulate actual storage conditions and determine shelf‐life. The main composition differences in the samples were in their fat content (1.87% for RC‐1 and 21.09% for RC‐2) and initial moisture content (4.12% for RC‐1 and 2.28% for RC‐2). The shelf‐life of this product is mainly affected by moisture adsorption as evidenced by sensory evaluation. Guggenheim‐Anderson‐de Boer (GAB) model was used to fit the moisture sorption isotherm. Good precision of fit was found as measured by a determination coefficient (R2) close to 1. The shelf‐life was then predicted based on the relationship between permeability coefficient of the packaging materials and moisture adsorbed by the rice crackers determined by the GAB equation. The validation of the simulations against the experimental shelf‐life gave R2 of 0.90 and 0.51, and root mean square error of 2.93 and 5.20 for RC‐1 and RC‐2, respectively. The simulation model was found to be applicable for a rapid and accurate shelf‐life prediction of RC‐1. However, a large difference between experimental and simulated shelf‐life of RC‐2 was probably because the moisture content may not be the only parameter influencing the shelf‐life of the RC‐2 samples. Other factors may also significantly affect the shelf‐life characteristics of the packaged rice crackers. PRACTICAL APPLICATIONSFor a low‐moisture food product, actual storage testing by a long‐term stability study involves storing a packaged product under typical storage conditions and examining the product at regular time intervals. The testing is costly and time consuming, since most low‐moisture food products have a shelf‐life of several weeks or even months. This paper describes the shelf‐life prediction of two varieties of rice crackers having different compositions using a simulation model based on the relationship between barrier property of the packaging materials and moisture adsorbed by the rice crackers determined by the Guggenheim‐Anderson‐de Boer (GAB) model. The shelf‐life simulation provides a powerful support tool for shelf‐life estimation and packaging development.

Determination of Moisture Sorption Isotherms of Jasmine Rice Crackers Using BET and GAB Models

Moisture sorption isotherms of Thai Jasmine rice crackers were determined at 30, 45 and 60°C over a water activity range of 0.10 to 0.95 using a static gravimetric technique. Moisture sorption isotherms of rice crackers exhibited the sigmoid (Type II) shape. The moisture content of rice crackers decreased as temperature increased at a given water activity of the storage environment. The Brunauer, Emmett and Teller (BET) and Guggenheim-Anderson-de Boer (GAB) models were applied to fit the experimental data. The isosteric heat of sorption at different moisture levels was also determined using the Clausius–Clapeyron thermodynamic equation. A nonlinear regression analysis method was determined to evaluate the parameters of sorption equations. The criteria used to evaluate the goodness of fit of each model were the mean relative percentage deviation modulus (E) and the percentage root mean square error (RMSE). The more extended range of application of the GAB equation over the BET equation was evident. The GAB model gave the best fit to the experimental sorption data for a wide range of water activity (0.10–0.95) while the BET model gave the best fit for a water activity range of less than 0.60. The GAB model is considered suitable to predict the moisture sorption isotherm of rice crackers since it gave low E and RMSE values. The heat of sorption values of rice crackers were found to be large at low moisture content and decreased with an increase in food moisture content.