GAB Equation Research Articles

Sorption Isotherm and Effect of Packaging Materials on Proximate, Organoleptic and Lipid Oxidation Quality of Chicken Nuggets Stored at Two Different Temperatures

The study Investigated sorption isotherm features and the effects of packaging materials of both high-density and low-density polyethylene on sensory properties, proximate composition and lipid oxidation of chicken nuggets in storage. Boneless chicken breast was procured from a reputable source and cut into sizeable weight of 50g each to produce the chicken nuggets used for the studies. The experimental setup for sorption isotherm analysis in this study involved using a gravimetric method to equilibrate the product at various relative humidity levels. Five (5g) grams of oven-dried chicken nugget samples of known moisture content were placed in a controlled humidity chamber, and the weight changes of the samples were monitored until equilibrium was reached. GAB equation was used to evaluate the product ware activity and monolayer moisture. Sensory assessment was evaluated using a 9- point hedonic scale while proximate composition of the chicken nuggets samples was determined according to the methods of the Association of Official Analytical Chemists. Thiobarbituric acid reactive substances (TBARS) assay was used to measure malondialdehyde (MDA) levels as a marker of lipid oxidation. The investigation showed that sensory qualities, proximate composition and lipid oxidation of chicken nuggets were markedly affected by the variance in temperature settings, with distinct disparities seen among different materials for packaging. Chicken nuggets stored at 25 0C caused a significant loss in organoleptic properties and some nutritional composition such as protein and fat. Storage of chicken nugget at 25 0C and 40 C showed a varied values in malondialdehyde as content ranged from 0.52 to 0.81 for chicken nugget stored at 250 C and 0.17 to 0.43 for the product stored at 40 C across the packaging materials investigated. The water activity and monolayer moisture results of sorption analysis revealed that good packaging materials of very low water vapour transmission rate should be used for storage of chicken nuggets as high-density polyethylene offered a promising alternative than low density polyethylene.

SORPTION ISOTHERM, PROXIMATE COMPOSITION AND SENSORY EVALUATIONS OF OVEN DRIED AND FRIED CHEESE PRODUCTS FROM LOCAL SOFT CHEESE

In this study, the sorption isotherm, proximate composition and sensory characteristics of oven dried and fried cheese were investigated. The understanding of the moisture sorption properties, nutrient composition and sensory properties of the oven dried and fried cheese can help quality, shelf-life prediction and overall acceptance. The experimental methodology for this study followed a standard procedure to determine the sorption isotherm of oven-dried and fried cheese samples. First, the raw milk samples were obtained from white Fulani cows at the Teaching and Research Farm, Ekiti State, University, Ado-Ekiti, Nigeria and processed into cheese. The cheese was divided into two portions: one group was oven-dried at 50 0C for 16 hours, while the other group was fried in pre-heated edible canola to internal temperature of 68oC. Sorption parameters, proximate and sensory characteristics were carried out according to standard methods. This study revealed that the monolayer moisture was higher in fried cheese than oven dried cheese. Oven-dried cheese had 0.299 water activity and 21.26 monolayer moisture while fried cheese had higher water activity of 0.32 and monolayer moisture of 29.67. Fitness of curve (R2) of 0.731 0.903 were computed for oven-dried and fried cheese. The results of proximate composition and sensory characteristics showed that processing methods influenced the sensorial properties and nutritional composition of oven-dried and fried cheese. In conclusion, oven-dried cheese can be predicted to be more stable than fried cheese. KEYWORDS: Adsorption, Equilibrium, GAB Equation, Monolayer, Salts.

Desorption and Sorption Isotherms of Different Varieties of Hemp Seeds with Different Percentages of Dockage under Different Temperatures and Different Relative Humidities

Hemp cultivation faces challenges due to the adoption of dioecious cultivars, which suffer from biomass loss and fibre heterogeneity. In contrast, monoecious cultivars offer simultaneous fibre and seed production, albeit with lower fibre quality. Understanding the drying characteristics and storage requirements of hemp seeds is crucial for effective post-harvest management. This study explored the moisture sorption and desorption isotherms of two common Canadian hemp seed varieties, Altair (dioecious) and CanMa (monoecious), by using both saturated salt solution (SSS) and thin-layer drying methods. Their isotherms were also compared with the published isotherm of Finola—a common dioecious variety in Europe. The thin-layer drying method yielded higher EMC values than the SSS method due to incomplete equilibrium attainment. Larger EMC differences existed between different seed types (dioecious vs. monoecious), and this difference was small between the same seed types (dioecious vs. dioecious). The GAB equation provided the most accurate prediction of equilibrium moisture contents for both varieties.

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.

Water adsorption properties of microalgae powders: Thermodynamic analysis and structural characteristics

Moisture adsorption isotherms and thermodynamic properties of dried Chlorella pyrenoidesa and Spirulina platensis powders were investigated by using a static gravimetric at temperatures of 20, 30, and 40 °C and within aw range of 0.112–0.976. Structural characteristics involving morphology, functional group, surface element composition, pore size distribution, and surface area were analyzed to explore the water adsorption mechanism. FTIR and XPS analysis indicated that spirulina powder had a higher proportion of hydrophilic sites to bind water molecules in comparison with chlorella powder. BET surface area for chlorella and spirulina powders were 25.10 and 25.19 m2/g, respectively. Water adsorption data were adjusted using a variety of sorption models, and the GAB equation was the most appropriate for representing the experimental data in the studied aw and temperature range. The monolayer moisture content (Xm) values at 20, 30 and 40 °C were 0.0526, 0.0483, and 0.0456 g/g dry basis for chlorella powders, and 0.0581, 0.0553, and 0.0420 g/g dry basis for spirulina powders, respectively. The net isosteric heat (Qst) and differential entropy (δSdif) for both microalgae powders decreased with an increase in water content. Using the compensation theory, we determined that the processes were governed by the enthalpy and that they were non-spontaneous (δG>0) for the samples. Both microalgae powers were classified as micro and mesoporous materials, and the pore radius (Rp) varied from 1.481 to 23.694 nm for chlorella powders and from 1.193 to 39.392 nm for spirulina powders, respectively.

Static Water Vapor Sorption Properties of Honey

Abstract Static sorption properties of pine honey (PH) and citrus honey (CH) were studied at 20, 30 and 40°C. Yeast formation was observed on the surface of honeys at water activity (aw)>0.7 at all temperatures. Visible yeast formation (YF) took place earlier in PH than in CH under the same conditions due to its characteristic higher pH and lower monosacchride content. The temperature was insignificantly effective on YF (p>0.05). The honeys exhibited a sorption isotherm (SI) in the shape of a “J”. Their SIs exhibited desorption and adsorption at aw<0.7 and aw>0.7, respectively and the desorption part was almost linear. Aw=0.7 emerged as a border between the absence and presence of YF and between the desorption and adsorption. The SIs of honeys were insignificantly affected by temperature (p>0.05). PH had a significantly lower SI than that of CH (p≤0.05) due to its characteristic lower monosacchride content. GAB equation exhibited a good fit to the honeys' SIs. Sorption heat vs equilibrium moisture content (EMC) revealed monolayer, multilayer and loosely bound free water regions in the SIs of PH and CH.

Impact of temperature and relative humidity on physicochemical properties of the spray dried red flesh pitaya powder during storage

This study was carried out to evaluate the changes in physicochemical properties of pitaya powder produced by spray-drying under the different temperature storage at 5-7 , room temperature, and 50 for 40 days, The results showed that delta E of color increased but the content of betacyanin and total phenolic decreased following temperature increase. The degradation of betacyanin and total phenolic content in all samples during storage fitted the first-order reaction. Moreover, the behavior of moisture content in pitaya powder under different relative humidity was investigated. The isotherm curve of pitaya powder was built (y = 3,2655e0,0106x). The result also showed the GAB equation can be used to calculate the M0 of the sample better than the BET equation.

Sorption isotherm study on vacuum and freeze-dried jamun pulp

Fruits play the most important role in nutrition. In India many underutilized medicinal fruits are available, and the most important fruit is jamun which is otherwise called black plum. Drying of underutilized jamun fruits helps in minimizing their post-harvest loss which occurs during harvesting season. The freeze-dried powder results with polar sites in molecular structure material which is occupied with water in wet conditions. During drying the molecules which were holding the water particles are attracted closely to each other. The study on sorption isotherms was carried out on the dried powder. These results gave a suitable model to fit sorption behaviour. The empirical equations frequently used to model drying kinetics are Newton, Henderson–Pabis, Page, Modified Page, Wang– Singh, Logarithmic, Two-Terms, Modified Henderson–Pabis and many mathematical models to describe the water sorption behaviour of foods. The GAB equation was fitted as the best fit for vacuum-dried jamun pulp powder stored at 27°C and 37°C.

Shelf‐life estimation of packaged dried foods as affected by choice of moisture sorption isotherm models

The moisture sorption isotherms (MSIs) of Oswin, Halsey, GAB, and linear models were compared for their ability to predict the shelf life of typical permeable packages of four dried foods (onion flakes, rice crackers, cassava-flour-based baked product, and dried tea) whose isotherm data are given in the literature. Parameters of MSI equations were used to mathematically simulate aw change of the packaged foods. The simulation model was applied to predict the times to reach the critical aw values under storage at 30 or 37°C and 65% or 85% RH. The GAB equation was best able to fit the moisture sorption data with the highest coefficient of determination (>.99) and the lowest root mean square error (≤0.01). The linear model consistently estimated the shelf life in close agreement with the GAB equation. The Oswin and Halsey equations differed with each food in their ability to estimate the shelf life accurately. Practical applications Shelf-life determination is a critical issue for packaged dried foods where the moisture sorption isotherm selected may influence its accuracy. While a convenient and simple way of estimating shelf life is required, the validity and limitations of the applied method should be examined and determined. The general versatility of the GAB equation and the tolerable validity of the linear sorption model over the low aw range were confirmed, which is useful for practical shelf-life determination of packaged dried foods.

Efecto de la adición de subproductos agroindustriales en las propiedades físicas de un biopolímero almidón-gelatina

En este trabajo se reporta el efecto de la adición de subproductos de mango, jamaica y café a una formulación de almidón-gelatina para elaborar una bioplástico en forma de cuchara. Se encontró que la adición de los subproductos mejoró las propiedades mecánicas del bioplástico debido a la compatibilidad de sus componentes observados a nivel microscópico (la dureza aumento de 190 hasta 290 N). Asimismo, las propiedades físicas de los bioplásticos como el ángulo matiz (63-89), y los índices de solubilidad y absorción en agua se modificaron por la adición de subproductos. Se observó que las condiciones de máxima estabilidad de los bioplásticos obtenidas a partir del modelado de las isotermas de adsorción a 35 °C con la ecuación de GAB y el cálculo el volumen de microporo correspondieron a una actividad de agua cercana a 0.40, independientemente del subproducto agregado. Las distintas formulaciones exhibieron un evento endotérmico a una temperatura de 180ºC, asociado a un proceso de fusión, así como una elevada tasa de degradación en suelo después de 120 h. Los subproductos probaron ser un refuerzo en la formulación de bioplásticos. El uso de subproductos de mango, café y jamaica representan una alternativa interesante para incrementar su potencial tecnológico.

Application of Dynamic Temperature-Humidity Chamber for Measuring Moisture Sorption Isotherms of Biomaterials as Compared to the Conventional Isopiestic Method

Measurement of water activity and moisture sorption isotherms of foods and biomaterials are important to determine the state of water. In this work, a dynamic temperature-humidity (DTH) controlled chamber was used to measure water sorption isotherm and compared with the conventional isopiestic method. Temperature and relative humidity of DTH chamber can be controlled in the range of -15 to 100°C and 0 to 98%, respectively; thus, measurement of water activity at any point can be measured within the above ranges. The DTH chamber method showed high reproducibility as compared with the conventional isopiestic method when measured isotherms of cellulose, lignin, and hemicellulase were compared at 30°C. Finally, isotherm data of cellulose, lignin, and hemicellulase were generated in the temperature range of 10-90°C using DTH chamber, and these were modelled by BET and GAB equations. The model parameters were correlated with the temperature.

Sorption properties, glass transition and state diagrams for pumpkin powders containing maltodextrins

The state diagrams of freeze-dried pumpkin powders with different maltodextrin additions were developed using glass transition line, freezing curve and maximal-freeze-concentrations conditions. The freezing curve was plotted employing Clausius – Clapeyron equation and glass transition lines were developed using Gordon – Taylor model. The ultimate maximum-freeze-concentration conditions of the powders were observed in range from 0.685 to 0.745 g solids/g sample. Characteristic glass transition temperature of maximum-freeze-concentration (Tg’) of the pumpkin was equal to - 83.7 °C and was increase with increasing maltodextrin addition. Adsorption isotherms of pumpkin – maltodextrin powders were determined at 25 °C by static - gravimetric method and the experimental data was modelled with BET and GAB equations. Monolayer moisture content of the pumpkin powder decreased with increasing maltodextrin additions. The state diagram and water adsorption isotherms of the pumpkin – maltodextrin powders are useful for predicting suitable storage and processing conditions.

Effect of drying temperature on color and desorption characteristics of oyster mushroom

Oyster mushroom (Pleurotus ostreatus) slices were dried in a hot air dryer at three temperatures (45, 55 and 65 °C). The sorption isotherm of dried samples in the water activity (aw) range of 0.556-0.970 was also determined at three temperature levels. Moisture desorption isotherms were obtained from changes in water activities of oyster mushroom slices during drying, and the fitness of GAB, BET, Oswin, Henderson and Halsey isotherm equations to sorption data was calculated. The effect of temperature on color change kinetics of oyster mushroom slices was also investigated during drying. GAB model was the best equation for the prediction of the desorption moisture content of samples. Mathematical modeling of color change kinetics indicated that both zero and first order kinetic models were adequate to describe the browning index (BI) value; however, total color change (ΔE) followed zero-order kinetics. The values of the reaction rate constant, found after the drying at 45, 55 and 65 °C, of the ΔE value were respectively 0.058, 0.065 and 0.089.

Application of the Guggenheim, Anderson, de Boer (GAB) equation to sealing treatments on pine wood

Surface treatments can modify the materials behavior toward water sorption phenomena and the GAB equation is here proposed to study pine wood samples treated with difference sealing materials limiting in different ways the access and release of water moisture. Particularly, the modification of the kGAB, CGAB, Vads and SGAB parameters as a function of the applied coating is studied here in order to explore the usefulness of such variables as indicator of the presence of chemical treatments on wood at high RH values.

Moisture sorption isotherm, isosteric heat and adsorption surface area of whole chia seeds

This study aimed to evaluate moisture sorption isotherm of whole chia seed. The equilibrium moisture content (EMC) of seeds were detected by saturated salt solutions which have the water activity (aw) range of 0.2–0.9. The isosteric sorption heat was calculated by the Clausius-Clapeyron equation using three different sorption temperatures (15 °C, 25 °C and 35 °C). The adsorption surface area of seeds was also calculated by monolayer moisture content obtained from BET and GAB equation. The EMC content of seeds had an increasing trend and determined as 18–20 g H2O/100 g solid at the highest aw level. The whole chia seeds became less hygroscopic with the rising sorption temperatures at constant aw. The moisture sorption isotherm was determined as Type II. The monolayer moisture content was determined as 2.39–2.91 g H2O/100 g solid. BET and Peleg were the best-fitted models. The isosteric and net isosteric heat were 77.74 and 34.74 kJ/mol at lowest moisture content, respectively. Additionally, the adsorption surface area changed between 95.31 and 102.72 m2/g.

Models of Sigmoid Equilibrium Moisture Sorption Isotherms With and Without the Monolayer Hypothesis

Among the numerous moisture sorption models, the GAB, an expanded version of the BET equation originally derived for inert gases adsorption on solid surfaces, is the most prominent. Both models are based on distinction between the adsorbate molecules settling on the bare surface in a monolayer (Langmuir adsorption) and those settling on already absorbed molecules forming multilayers. The BET theory has been successfully used to determine porous catalysts’ and fine powders’ specific surface area to this day. In contrast, applying the BET and GAB equations to water vapor sorption by solid foods (and non-foods) has at least three major problems: The calculated food powders’ specific surface area is independent of their particle size; the expected shoulder in foods’ enthalpy vs. moisture plot is absent; and there is a huge discrepancy between the specific surface areas calculated from moisture sorption isotherms and those of nitrogen. An alternative modeling approach posits the non-existence of a water monolayer, and suggests that moisture sorption is governed by at least two simultaneous mechanisms having different scaling exponents. Mathematical analysis and comparison of the resulting sorption models with the GAB equation show that they produce practically indistinguishable moisture sorption isotherms even with the same number of adjustable parameters. They also demonstrate that the sigmoid shape of a moisture sorption isotherm does not contain enough information to identify and quantify the underlying sorption mechanisms, and that a model’s good fit by statistical criteria in itself does not validate mechanistic assumptions.

Optical, mechanical, and moisture sorption properties of whey protein edible films

AbstractThe impact of protein and glycerol concentration on the optical, mechanical, and moisture sorption properties of whey protein isolate edible films was determined. The increasing of protein concentration leads to decreasing opacity and moisture adsorption of films but improving its tensile strength and elongation at break. Color parameters for all films remain constant and were not dependent on the film composition. Films with increasing glycerol concentration showed weakened mechanical resistance and higher moisture adsorption rates. Moisture sorption isotherms data were well described by GAB, Peleg, and Lewicki equations. These findings can be used to better design applications of whey protein films containing plasticizers, in order to optimize film formulation in a rational manner considering their practical use as protective coatings or edible packaging.Practical applicationsThe increased interest in the development of edible films for food packaging applications has been raised to minimize the use of synthetic petroleum‐based polymers. Moisture sensitivity of films showed the capacity of such materials to modify their physical properties which are influenced by different relative humidity or temperature conditions. The results presented in this study, concerning optical, mechanical, and sorption properties of whey protein‐based edible films, would provide the scientific basis for developing functional protein films and their application for food products including nuts, seeds, fruits, or vegetables.

FREEZE DRYING AND MOISTURE ADSORPTION KINETICS OF KEFIR POWDER

Freeze drying and moisture adsorption behaviour of kefir powder were investigated by fitting the experimental drying data to ten thin layer drying and sorption isotherm models. Moisture adsorption isotherms of kefir powder were determined at 5-35°C and within the range of 0.11–0.88 water activity. By statistical comparison of the values, Midilli et al. was found to be the best model describing the freeze drying behaviour. The GAB and Oswin equations gave the closest fit to the adsorption data over the tested range of temperatures and water activities. Additionally, adsorption isotherms data were used to determine the thermodynamic properties such as isosteric heat, sorption entropy and Gibbs free energy. The enthalpy entropy compensation was valid for the adsorption process and showed that the process was controlled by the enthalpy. Gibbs free energy was negative at all of the tested temperatures, which indicates that moisture adsorption of kefir powder was a spontaneous process.

Drying kinetics and sorption behavior of two varieties banana (sagor and sabri) of Bangladesh

The study was concerned with determining the drying kinetics and sorption behavior of two varieties ripe banana of Bangladesh namely, Sagor and Sabri. The fresh ripe banana collected from the local market were sliced into three different thicknesses (4 mm, 6 mm and 8 mm) and dried at 45°C, 55°C and 65°C in a cabinet dryer. The result showed that the drying rate increases with the increase in temperature and decreases with the increase in slice thickness. The sorption properties of dried banana were studied over a wide range of water activity (0.11-0.93). The BET and GAB models were fitted to the sorption data. It was found that both varieties gave sigmoid (type II) shape isotherm and GAB equation gave the much higher value of monolayer moisture content compared to BET equation. The chemical compositions of fresh and dried banana were determined. The dried products gave substantially higher solid content as well as protein, ash and carbohydrate.
 SAARC J. Agri., 16(2): 181-193 (2018)

Equilibrium Moisture Content of Hazelnut Husks, Shells, and Kernels

Abstract. Hybrid hazelnuts that are predominately a cross between the American hazelnut () and the European hazelnut () are being grown and evaluated as part of an effort to develop a thriving hazelnut industry for the Upper Midwest of the U.S. Along with this plant development effort, researchers are investigating and assessing various harvesting and processing methods and equipment in an effort to create a robust and food-safe production industry. One harvesting alternative is to pick hazelnut clusters off plants before the nuts fully ripen and fall to the ground, an approach that requires greater attention to drying. Whether entire clusters are dried or the nuts are separated from the husks prior to drying is a decision that will be influenced by the drying requirements and potential uses for these hazelnut fractions. To this end, a study was undertaken to establish desorption isotherms for the husks, shells, and kernels of hybrid hazelnuts grown in the Upper Midwest. Clusters were hand-picked from shrubs in Wisconsin and immediately placed in 18 different controlled environments (six different relative humidity levels at three different temperatures). Actual moisture conditioning took place over saturated salt solutions in specially fabricated biomaterial moisture conditioning units. After a six-week period during which the clusters reached equilibrium with their environment via desorption, they were separated into husk, shell, and kernel fractions and returned to their respective conditioning units. After another six weeks in the conditioning units, the moisture content (MC) of each fraction was determined by oven-drying at 103°C for 48 h. Under equilibrium conditions, the kernel MC was found to be only 37% of that for shells, whereas the equilibrium moisture content (EMC) values for husks were on average 14% greater than those for shells. On a dry basis, the average cluster mass was 32.9% husk, 43.9% shell, and 23.2% kernel. Likewise, on a dry basis, the average whole nut mass was 65.5% shell and 34.5% kernel. The desorption data were fit to the Modified Henderson, Modified Chung-Pfost, Modified Halsey, Modified Oswin, and Modified GAB equations. Overall, the best fit to the experimental data was provided by the Modified Chung-Pfost equation with parameters determined using equilibrium relative humidity (ERH) as the dependent variable in regression analyses. For ERH values above 0.70, the temperature-modified form of the GAB equation is recommended for predicting desorption EMC values for hazelnut fractions. Keywords: Desorption, Equilibrium moisture content, Equilibrium relative humidity, Hazelnuts, Kernels, Nuts, Shells, Water activity.