Guggenheim-Anderson-de Boer Model Research Articles

Water sorption modeling and monolayer of biological and food materials

Despite water molecules are strongly hydrogen bonding to hydrophilic solids, the Brunauer-Emmet-Teller (BET) and Guggenheim-Anderson-de Boer (GAB) surface adsorption models have been widely accepted to describe water sorption properties of biological and food materials. These mathematically quite similar models use parameters which include a theoretical ‘monolayer’ value and one or two other parameters which describe ‘surface affinity’ in thermodynamic terms as heat of sorption. A high surface affinity indicates a strong surface binding of water molecules and preferential monolayer adsorption prior to multilayer sorption. Conversely, biological materials are water plasticized and suffer physicochemical changes at various stages of water sorption. Dynamic water sorption measurements often show regions where time-dependent changes in material characteristics, such as viscous flow and crystallization, may occur as a result of the glass transition. The two or three parameters of the BET and GAB models, respectively, are useful in the analysis of water sorption characteristics of individual substances, although the existence of a monolayer particularly in multicomponent materials may not be justified. Fitting the models to experimental data may occur rather for empirical than theoretical reasons.

Osmotic Dehydration Model for Sweet Potato Varieties in Sugar Beet Molasses Using the Peleg Model and Fitting Absorption Data Using the Guggenheim-Anderson-de Boer Model.

This study investigates the applicability of the Peleg model to the osmotic dehydration of various sweet potato variety samples in sugar beet molasses, addressing a notable gap in the existing literature. The osmotic dehydration was performed using an 80% sugar beet molasses solution at temperatures of 20 °C, 35 °C, and 50 °C for periods of 1, 3, and 5 h. The sample-to-solution ratio was 1:5. The objectives encompassed evaluating the Peleg equation's suitability for modeling mass transfer during osmotic dehydration and determining equilibrium water and solid contents at various temperatures. With its modified equation, the Peleg model accurately described water loss and solid gain dynamics during osmotic treatment, as evidenced by a high coefficient of determination value (r2) ranging from 0.990 to 1.000. Analysis of Peleg constants revealed temperature and concentration dependencies, aligning with previous observations. The Guggenheim, Anderson, and de Boer (GAB) model was employed to characterize sorption isotherms, yielding coefficients comparable to prior studies. Effective moisture diffusivity and activation energy calculations further elucidated the drying kinetics, with effective moisture diffusivity values ranging from 1.85 × 10-8 to 4.83 × 10-8 m2/s and activation energy between 7.096 and 16.652 kJ/mol. These findings contribute to understanding the complex kinetics of osmotic dehydration and provide insights into the modeling and optimization of dehydration processes for sweet potato samples, with implications for food processing and preservation methodologies.

Hygroscopicity of nitrocellulose with different nitrogen content

AbstractResearch on the hygroscopic behavior of NC is essential because it affects the mechanical properties, combustion properties, and safe storage of NC‐based products. In this study, Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), and scanning electron microscopy (SEM) are used to characterize the chemical structure, crystal structure, and microscopic morphology of NC, respectively. The moisture adsorption isotherms of NC fibers with different nitrogen content are determined by dynamic vapor sorption (DVS) and fitted with Hailwood‐Horrobin (H−H) and Guggenheim‐Anderson‐de Boer (GAB) models. The specific surface area and surface energy of NC are also measured by inverse gas chromatography (IGC). The results show that as the nitrogen content of NC increases, the intensity of the −OH characteristic absorption peak is weakened, the crystallinity does not change much, the number of cracks and pores on the NC fiber surface increases, and the equilibrium moisture content (EMC) of the NC decreases in general. In addition, the fitting results based on the H−H and GAB models show that, under low humidity conditions, the EMC value of NC is determined by the adsorbed water content of the monolayer, which is mainly related to the −OH content in NC. However, with the increase of humidity, the EMC value of NC is gradually determined by the multilayer adsorbed water content, which is influenced by both the nitrogen content and the fiber cleavage structure. Meanwhile, the IGC results show that the surface energy of the NC consists mainly of the dispersive surface energy (values >46 mJ m−2), with the specific surface energy contributing approximately 25 mJ m−2. The total surface energy of NC and the bonding strength between NC molecules and water molecules decrease with increasing nitrogen content.

Model-based investigation of water adsorption in Achira (Canna edulis K.) biscuits

The water adsorption properties of Achira biscuits were investigated using a mathematical model-based strategy to understand the relationship between water activity and moisture content due to the fact that it is highly relevant for its storage. For this purpose, the water adsorption isotherms of commercial Achira biscuits were firstly experimentally determined by the dynamic dew point (DDI) method at 25, 35, and 45 °C and ATR–FTIR spectroscopy was used to detect the functional groups. Secondly, the Guggenheim-Anderson-de Boer (GAB) equation, 4 empirical models (Smith, Oswin, Peleg and DLP), and 5 machine-learning techniques (Regression trees, Random Forest, k-Nearest Neighbors, Artificial Neural Networks and Support Vector Machine) were used to model the isotherms. The fundamentals of water adsorption were analyzed via GAB model parameters, adsorption surface area, spreading pressure, effective pore size, and thermodynamic properties, such as enthalpy-entropy and Gibbs free energy. The experimental results reflected a type III water isotherm and a moderate temperature effect. The GAB model quantified the effect of temperature on the adsorption properties, which reflected a lower degree of hygroscopicity at high temperatures. The Support Vector Machine Learning model provided the best mathematical description of the water adsorption isotherms considering the temperature effect (MRE<3% and R2adj>99%).

Effect of Germinated Sorghum Extract on the Physical and Thermal Properties of Pre-Gelatinized Cereals, Sweet Potato and Beans Starches.

Starches from different botanical sources are affected in the presence of enzymes. This study investigated the impact of α-amylase on several properties of pre-gelatinized starches derived from chickpea (Cicer arietinum L.), wheat (Triticum aestivum L.), corn (Zea mays L.), white beans (Phaseolus vulgaris), and sweet potatoes (Ipomoea batatas L.). Specifically, the water holding capacity, freezable water content, sugar content, and water sorption isotherm (adsorption and desorption) properties were examined. The source of α-amylase utilized in this study was a germinated sorghum (Sorghum bicolor L. Moench) extract (GSE). The starch samples were subjected to annealing at temperatures of 40, 50, and 60 °C for durations of either 30 or 60 min prior to the process of gelatinization. A significant increase in the annealing temperature and GSE resulted in a notable enhancement in both the water-holding capacity and the sugar content of the starch. The ordering of starches in terms of their freezable water content is as follows: Chickpea starch (C.P.S) > white beans starch (W.B.S) > wheat starch (W.S) > chickpea starch (C.S) > sweet potato starch (S.P.S). The Guggenheim-Anderson-de Boer (GAB) model was only employed for fitting the data, as the Brunauer-Emmett-Teller (BET) model had a low root mean square error (RMSE). The application of annealing and GSE treatment resulted in a shift of the adsorption and desorption isotherms towards greater levels of moisture content. A strong hysteresis was found in the adsorption and desorption curves, notably within the water activity range of 0.6 to 0.8. The GSE treatment and longer annealing time had an impact on the monolayer water content (mo), as well as the C and K parameters of the GAB model, irrespective of the annealing temperature. These results can be used to evaluate the applicability of starch in the pharmaceutical and food sectors.

Evaluation of the BET and GAB models for interpretation of soil water isotherms: A molecular simulation study

Mathematical characterization of soil water isotherm (SWI) plays a significant role in modeling various processes in soils and estimating the soil properties, and the Brunauer-Emmet-Teller (BET) and Guggenheim-Anderson-de Boer (GAB) models are most widely used. Each model uses the amount of adsorbed gas in the monolayer on the surface for area estimates. Although these two models are widely used with soils, studies on the applicabilities of the SWIs estimated with the two models and the reliabilities of the derived monolayer contents are noticeably lacking. This work presents detailed evaluations of the two models and the resulting SWIs and determines whether these provide meaningful monolayer contents. The SWIs for four representative soils were generated with Grand Canonical Monte Carlo (GCMC) simulations, and the data were evaluated along with a wealth of information on the physical states of the adsorbed water molecules. The results showed that the GAB model was much superior to the BET model in terms of fitting the SWIs. A series of analyses validated the soundness of the monolayer contents determined, including analyses of the layer thickness, the area occupied by the water monolayer, and the orientations of the water molecules. The molecular simulation also revealed the very different effects of the surface hydroxyls and cations in adsorption by considering the densities, space locations, and orientations of the adsorbed water. This work provides crucial information for rational application of the BET and GAB models to SWIs.

Experimental investigation of thermodynamic and kinetic behaviors from water vapor adsorption on four typical clay minerals

Clay minerals within the shale reservoirs mainly exist in the water-bearing state in situ. The water adsorption behavior and behind mechanisms on the clay minerals are essential for the evaluation of shale gas reservoirs. In this work, combined experiments of water vapor adsorption (WVA) and nitrogen (N2) adsorption were conducted on four typical clay minerals, including montmorillonite (Mnt), illite (Ilt), chlorite (Chl), and kaolinite (Kln). Our results show that the various pore size distributions derived from the WVA and N2 adsorption data indicate that pores with a diameter smaller than 10 nm contribute 54%–82% to the total amount of water uptake. Fitting parameters obtained from five mathematical models, including the Guggenheim-Anderson-de Boer (GAB), Dent, Oswin, Freundlich, and Frenkel-Halsey-Hill (FHH), can illustrate physicochemical characteristics behind the WVA isotherm data. Compared to other models, the FHH model is more optimal to fit and predict the WVA isotherms on the four typical clay minerals. In addition, three kinetic models were utilized to evaluate the WVA kinetic behavior for the four typical clay minerals, including Pseudo-first-order (PFO), Pseudo-second-order (PSO), and Double-exponential (DE) model. Water adsorption process in the clay minerals is a two-stage process and is mainly controlled by the slow pore-diffusion process, as indicated by the best fitting results from DE model. Finally, the differences of the fitting parameters in the GAB model (the most versatile model on WVA experiments for shale rocks) and adsorption kinetics between clay minerals and shale in the WVA process were discussed, which can provide guidance for investigates of moisture distribution in the shale. Overall, the findings of this work are of great significance to determine the water distribution in the shale reservoirs and shale gas content evaluation in the actual moisture condition.

Utilization of industrial hemp by-product defatted seed flour: effect of its incorporation on the properties and quality characteristics of 'tsoureki', a rich-dough baked Greek product.

A rich-dough baked Greek product named 'tsoureki' was prepared using non-gluten hemp seed flour at ratios of 0:100, 10:90, 30:70, and 50:50. The effects of hemp flour addition on the properties of 'tsoureki', including physicochemical properties (moisture content, water activity, sorption phenomena), structural properties, textural properties, total phenolic content, antioxidant activity, and sensorial characteristics, as well as the macroscopic structure and morphological characteristics, were studied. Hemp flour addition affected dough rheology, showing tan δ values < 1, a decrease in both G' and G″ values, while both flow behavior and consistency indices were also significantly affected, which might have an influence on the final baked goods. The Guggenheim-Anderson-de Boer model satisfactorily described sorption data, while both hemp addition and temperature had a significant effect. A significantly higher hardness of 11.55 N, a lower specific volume of 2.65 cm3 g-1 , and a lower porosity of 0.676 were observed at high hemp additions. The hemp flour level influenced the color of the crumb and crust, and the total color difference (ΔE) increased significantly with the increase in hemp flour. Hemp flour additions were detectable by the naked eye, with an obvious color difference between control and hemp-containing samples. Moreover, the phenolic content and antioxidant capacity were increased, as were some organoleptic characteristics, such as the bitter aftertaste. Concurrently, overall acceptability decreased significantly. Overall, the incorporation of gluten-free defatted hemp seed flour in 'tsoureki' formulations seems to be a promising alternative for improving quality of such rich-dough baked products. © 2022 Society of Chemical Industry.

Investigating the moisture absorption behavior of bamboo fiber-reinforced epoxy composites by modelling

The aim of this research was to investigate the moisture absorption of bamboo fibers (BFs) and their composites manufactured using different methods. The hygroscopic properties of BFs, jute fibers (JFs), glass fibers (GFs), and epoxy (EP) were compared and analyzed using dynamic vapor sorption (DVS), as well as the hygroscopic properties of the BF-Naval Ordnance Laboratory (BF-NOL), JF-NOL, GF-NOL, and bamboo fiber-reinforced epoxy composites manufactured via filament winding (FW), hot pressing (HP), and resin transfer molding (RTM). The results were analyzed using the Guggenheim-Anderson-deBoer (GAB), parallel exponential kinetics (PEK), and DoseResp models. The results indicated that BFs conformed to type II. The moisture adsorption isotherms of BF-NOL, JF-NOL, GF-NOL, and BF composites prepared by different molding processes exhibited a typical V-shape. The GAB and DoseResp models provided good fits to the changes in adsorption and desorption processes. The final equilibrium moisture content (EMC) of BFs and BF-NOL were 27.1% and 3.95%, respectively, the final EMC of BF composites prepared by RTM was 2.34%.

Adsorption isotherm and thermodynamic properties of microwave vacuum dried tilapia fillets

The aim of the present study was to report the drying characteristics and adsorption isotherms of Tilapia Fillets. The static weighing method was used to measure the storage temperatures (25, 35, and 45 °C) and the moisture content (0.11–0.97) and determine microwave vacuum dried adsorption characteristics and thermodynamic properties of tilapia fillet. Eight classical adsorption models were used to evaluate the nonlinear fitting of the experimental data. The results showed that the dry tilapia products type adsorption isotherm belongs to the type III isotherm curve. At a given temperature, the equilibrium moisture content increased with an increase of water activity. The Guggenheim–Anderson–de Boer model was the optimal model for describing the adsorption kinetics of dry tilapia fillet products. The characteristic thermodynamic parameters showed that the enthalpy entropy compensation theory showed that the adsorption process of dry tilapia fillet products was non-spontaneous and enthalpy driven. This study provides a scientific reference for the processing and storage stability of tilapia and other aquatic products.

Enhanced removal of neonicotinoid pesticides present in the Decision 2018/840/EU by new sewage sludge-based carbon materials

Due to the increasingly strict legislation about the disposal of sewage sludge, it is necessary to find sustainable solutions to manage this waste at low-cost conditions. In addition, priority contaminants are now attracting much attention since they are usually detected in WWTP effluents. In this work, five sludge have been used as precursors for the synthesis of activated carbons subsequently tested in the removal by adsorption of three neonicotinoid pesticides listed in the EU Watch List: acetamiprid (ACT), thiamethoxam (THM), and imidacloprid (IMD). Generally, the activated carbons were prepared by chemical activation using ZnCl2 as an activating agent and then the resulting materials were pyrolyzed at 800 °C for 2 h. The synthesized activated carbons showed different textural properties; thus, the best adsorption results were found for AC-Industrial activated carbon, obtained from an industrial origin sewage sludge, with high equilibrium adsorption capacities (qe = 104.2, 137.0, and 119.9 mg g−1), for ACT, THM, and IMD, respectively. Furthermore, it was elucidated that the use of CO2 in the synthesis generated an opening, followed by widening, of the narrowest microporosity, increasing the specific surface area of the carbon materials. The kinetic and isotherm adsorption experimental data were obtained for each of the pesticide-activated carbon systems; thus, the kinetic curves were well-fitted to the pseudo-second-order kinetic model, as well as, Freundlich and Guggenheim-Anderson-de Boer (GAB) empirical models were used for the fitting of the equilibrium adsorption isotherms, finding that GAB model best fitted the experimental data. Additionally, the regeneration of the activated carbons using methanol as a regenerating agent and the single and simultaneous adsorption of a hospital wastewater effluent, fortified with the three studied pesticides have been explored.

PRELIMINARY EVALUATION OF COLOR STABILITY OF DATE FRUIT TABLETS

This paper reports on preliminary qualitative evaluation of relationship between color change and water activity (aw) of date (Phoenix dactylifera L., var. Mech-Degla) fruit tablets (DFTs) as natural supplement, in view to optimize their storage conditions. Eight types of DFTs were obtained, according to: i) mean particle size (225 and 282 μm) of the used fruit powder, and ii) compression pressure (5, 10, 15 and 20 kN) applied during the tableting process. The experimental adsorption curves, determined at 25°C using static-gravimetric method, were fitted to GAB (Guggenheim–Anderson–de Boer) and BET (Brunauer–Emmett–Teller) models. Results showed that the DFT color is significantly sensitive to aw since beyond the aw threshold value of 0.44, the DFT color changes from light grey to dark brown, independently of the particle size of fruit powder and compression pressure. Concerning the isotherm modeling, the both models tested seem especially suitable (R≈0,96 0.3≤MRE≤5 and SE≈0.03) for describing the experimental data for DFT obtained under a compression pressure of 5 kN from date fruit powder with mean particle size of 225 μm. The DFT color stability is considerably influenced by the environmental humidity. Considering the importance of color for consumer acceptance, the study deserves to be deepened concerning the quantitative analysis of the color (CIELab system), packaging of the tablets, etc.

A new theoretical model for moisture sorption isotherms and its application in deriving a hygroscopicity index for food products

In this paper, a new two-parameter moisture sorption isotherm (MSI) model was developed based on the non-random two-liquid (NRTL) theory. Compared to the most accepted theory of MSI, i.e., the layered adsorption theory, which includes only the effect of water clustering near food surfaces, the NRTL theory considers the effects of both water clustering and food swelling in the description of water adsorption on foods. This new model, referred to as the NRTL-solid-liquid-mixture (NRTL-SLM) model, revealed a rough linearity relationship between the reciprocal of the natural logarithm of water activity (1/ln a w ) and the equilibrium moisture content ( m 1 ). A new index, characterising the magnitude of the slope of the plot of 1/ln a w v. s. m 1 , was constructed for the hygroscopicity assessment of food products. This new index, referred to as the NHI index, was scaled between 0% and 100%, with the bigger value indicating higher hygroscopicity and 100% representing the hygroscopicity of glycerol. In order to evaluate the applicability and reliability of the NRTL-SLM model and NHI index, seven food samples, i.e., grapes, apples, pears, bananas, avocados, potatoes and beef, were selected. Glycerol was chosen as the hygroscopic reference material. The MSI data at 25 °C of all the eight materials, i.e., seven food products and glycerol, were subjected to model evaluation and index calculations. Our results showed that: (a) the NRTL-SLM model could satisfactorily fit the MSI curves of all the eight materials; (b) compared to the existing most successful MSI model, i.e., the Guggenheim-Anderson-deBoer (GAB) model, the NRTL-SLM model provides a slightly lower accuracy but is much simpler and requires fewer parameters; (c) the NHI index could correctly rank the hygroscopicity of the eight materials relative to each other; and (d) the existing most widely used and standardised physical parameter for MSI analyses, i.e., the monolayer moisture content ( M 0 ), which is typically calculated from the GAB model, could not be used as a measure of hygroscopicity for foods. • A new moisture sorption isotherm (MSI) model based on the NRTL theory reveals a linear relationship between 1/ln a w and m 1 . • A new hygroscopicity index was proposed based on the slope of 1/ln a w and m 1 . • MSI of seven food products were investigated by both the conventional and H 2 SO 4 methods. • The proposed model and hygroscopicity index were successfully validated against experimental data. • The monolayer moisture content ( M 0 ) does not correlate with the hygroscopicity level.

Influence of physical and chemical modifications on granule size frequency distribution, fourier transform infrared (FTIR) spectra and adsorption isotherms of starch from four yam (Dioscorea spp.) cultivars.

In this work, the effect of the modifications (annealing, acid hydrolysis and citric acid substitution) on starch granule size frequency distribution, Fourier Transform Infrared (FTIR) spectra, and adsorption isotherm of starches of four yam cultivars were studied. The native and modified white yam, water yam, and yellow yam starches had a normal distribution frequency profile for the granule sizes, which were similar among the cultivars. In contrast, the native and modified bitter yam starch granules were not normally distributed. The modifications resulted in a left shift in normal distribution frequency profiles for the granules sizes of the white, water and yellow yam starches due to broadening of the range of granule sizes. The FTIR spectra revealed that additional bands at 1726.95-1729.49cm-1 were introduced due to citric acid modification of the yam starches. The modifications also caused weakening of the FTIR band representing -CH2 and -OH stretching at 2927.85-2932.94cm-1 and 3259.42-3437.33cm-1, respectively. The native, annealed and acid hydrolyzed yam starches all had similar adsorption isotherms at 28°C. On the other hand, the citric acid-substituted yam starches showed a different adsorption isotherm, because they had significantly higher equilibrium moisture content at water activity (a w ) above 0.9. All the adsorption isotherms were type III, J-shaped isotherms. The adsorption isotherms data of the yam starches fitted best to the Guggenheim-Anderson-De Boer (GAB) model. The GAB model monomolecular moisture content ranged between 0.0165 and 0.0597g/g db. Native and modified yam starches' granules size were normally distributed except bitter yam starchFTIR revealed additional bands and molecular rearrangements were introduced due to modificationsAdsorption isotherms revealed type III, GAB-model isotherms with low monomolecular moisture. The online version contains supplementary material available at 10.1007/s13197-021-05200-7.

Determination and Modeling Desorption Isotherms of Okra (Abelmoschus esculentus L. Moench) and Sweet Green Pepper (Capsicum annum L. Moench)

The aim of this study was to determine the experimental moisture sorption isotherm of green pepper and okra, assess the performance of literature sorption models describing their behavior, and specify bound water properties. Isotherms were determined through the static gravimetric method at 30, 40, 50, and 60 °C. Twenty models were studied and fittings were done through nonlinear regression using MATLAB R2015b. GAB and Caurie models were used to determine energy constants and bound water properties respectively. Structural parameters were determined according to Kelvin and Halsey equations. All the experimental isotherm were of sigmoid shape. For both samples, Peleg, Enderby, and Guggenheim Anderson de Boer (GAB) models gave the best validation statistic criteria. R-squared (R2) values were all greater than 0.926 and root-mean-square error (RMSE) values less than 0.04 for both substrates. The GAB energy constants varied with temperature between 6.00 to 51.75 and 34.23 to 176.78 for Cg constants, and 0.70–0.99 and 0.75–0.93 for Kg constants, respectively, for okra and green pepper. The Cg energy constant globally decreased with increasing temperature. The monolayer moisture content Wm, varied with temperature between (0.0740–0.1044) kg kg−1 and (0.0760–0.1522) kg kg−1 respectively for okra and green pepper. Green pepper bound water property values were globally higher than those of okra and both were successfully modeled according to the equilibrium moisture content and according to the temperature. Analysis based on the IUPAC classification revealed a macroporous structure of the two materials. The hygroscopic equilibriums, physicochemical and microbiological stability conditions of green pepper and okra, were determined, for given environmental temperature values. The results obtained from the present study would serve in understanding the water state and mechanism of water sorption, defining drying and storage conditions of the tested vegetables, as well as designing corresponding dryers and packaging.

Isothermal adsorption modelling of pupuru flour

The amount of moisture adsorbed by stored food products usually varies with temperature and relative humidity at a constant pressure. This research was carried out to determine the sorption isotherm behaviour of pupuru flour in the temperature and water activity (aw) ranges of 10−50 oC and 0.10−0.93 using gravimetric method. The Guggenheim-Anderson-De Boer (GAB), Brunauer-Emmett-Teller (BET), Oswin and Smith sorption equations, formulated for the sorption characterization of starchy foods, were used to constitute the models. The results show that the sorption isotherm curve is similar to a Type II classification typical of starchy foods. Also, the sorption parameters (Mo, C and K) were generally higher for the products stored at 10 oC and 0.10 aw. The parameter K decreases with an increase in the temperature for the GAB and the Smith models, but remains inconsistent for the Oswin model. The Mo increases with an increase in the temperature for the GAB and Smith models. The GAB, Oswin and Smith models were generally adequate and valid with an MSE&amp;lt; 10% and a high degree of fitness (R2 and R2adj &amp;gt; 90%). This indicates their ability to predict the sorption isortherm characteristics of the pupuru flour within its range of the aw and the storage temperature.

Moisture sorption properties of two varieties of dehydrated mango slices as determined by gravimetric method using Guggenheim–Anderson–de Boer model

The moisture sorption isotherms for oven dried mango were constructed gravimetrically at three different temperatures of 25°C, 30°C, and 35°C, and relative humidity ranging 8.3%–97.0%. The Guggenheim–Anderson–de Boer model was used to fit sorption data and constant equations determined using nonlinear regression analysis. The isotherms had J-shaped curve that represents type III isotherms characterized by sugar-rich products. At increased temperatures, it was observed that equilibrium moisture content increased and crossing effect of isotherm curves was observed with a corresponding increase in water activity. A substantial increase in equilibrium moisture content was observed above water activity of 0.6. Monolayer moisture content of between 8 and 9.6% was predicted for dried slices where the lowest value indicated that moisture content should not be lower than 8.0% to avoid unnecessary energy consumption. For assured microbiological stability, the safe storage moisture content for dried mango should be maintained at approximately 15% or less that corresponded to 0.6 water activity. Practical applications Dehydration of fruits has been utilized as one of the most effective value addition procedures for extending their shelf-life. However, exposure to high drying temperature and significant loss of moisture in fruits cause irreversible stresses in the cellular structure of the fruits and may lead to robust textural changes especially during storage. This research finds practical application in shelf-life estimation and prediction of storage stability of the mango varieties. Additionally, the results can be used as a guide in product development and process design for dried mango slices.

Physicochemical Properties of Potato Starch Nanoparticles Produced by Anti‐Solvent Precipitation

AbstractThis work aims to understand the physicochemical properties of potato starch nanoparticles (SNPs) obtained by anti‐solvent precipitation. Moisture content, water activity, color, morphology, thermal behavior (differential scanning calorimetry), swelling factor, solubility in water, water sorption isotherms, rheological properties, and stability in water are analyzed and compared using native potato starch (PS) as control. The resulting SNPs after anti‐solvent precipitation have a particle size between 50 and 150 nm, smaller than those observed in PS (between 10 and 100 µm). SNPs behave as an amorphous material without gelatinization stage where the swelling factor is drastically reduced, while the solubility increased dramatically at low temperatures when compared with PS. The Guggenheim–Anderson–de Boer model from the isotherms data allows a calculation of the surface area, obtaining values of 105 and 211 m2 g−1 for PS and SNPs, respectively. The high surface area in SNPs is associated with an increase in the proportion of hydroxyl groups active for water adsorption throughout its structure. Both samples show Newtonian fluid behavior; however, SNPs solutions prove to be much more stable at room temperature than PS solution.

Mathematical modelling of moisture sorption isotherms by using BET and GAB models

Fish cracker is a popular local fish based snack in Malaysia. Besides the raw form which can be consumed directly, it is always eaten in the dried form. Thus study of moisture sorption isotherm of fish cracker is essential as to predict appropriate drying and storage conditions consecutively to enhance its nutrients, taste and aroma. In this study, the moisture sorption isotherms of fish crackers from two manufacturers M1 and M2 were developed by using a static gravimetric method at temperatures of 30, 40 and 50˚C and water activity (aw) range of 0.04 to 0.80. It is a relationship between equilibrium moisture content (EMC) and aw at a specified temperature. The isotherms exhibited a sigmoid shaped which classified as type II in Brunauer–Emmett–Teller (BET) classification. The increase of temperature decreased the EMC of fish crackers while increase of aw increased the EMC. There was no significant difference of EMC between manufacturers M1 and M2. The moisture sorption isotherms of fish cracker were fitted into predicted isotherms by Guggenheim-Anderson-de Boer (GAB) and BET models. GAB model was found to be the best fit model of fish crackers’ moisture sorption isotherms as compared to BET model.

Sorption behavior and storage stability of microencapsulated transglutaminase by ultrasonic spray–freeze–drying

Adsorption isotherms at 25 °C and 38 °C for microencapsulated microbial transglutaminase (mTG) powder produced by ultrasonic spray–freeze–drying (USFD), conventional spray drying (CSD), and conventional freeze–drying (CFD) methods and USFD–crude (without coating materials) were obtained using the standard static gravimetric method, and experimental data were fitted to the mathematical models. The sorption isotherms exhibited type III behavior, and the Ferro–Fontán model was selected as the best fit, having an R 2 of 0.920–0.995. The sorption isotherms of mTG powder depended on temperature and drying methods. The equilibrium moisture content decreased with increasing temperature, and the monolayer moisture content of the USFD sample was lower than other microencapsulated samples (M 0 = 0.133 kg/kg dry solids for 25 °C and M 0 = 0.080 kg/kg dry solids for 38 °C from Guggenheim–Anderson–deBoer model), followed by CFD and CSD. Furthermore, the storage stability of mTG powders produced by different methods in terms of quality parameters including enzyme activity, moisture content, water activity, color, density, porosity, flowability, and caking degree value was studied in aluminum-laminated polyethylene (ALPE) pouches under storage conditions of 25 °C, 50% relative humidity (RH) for 180 days and 38 °C, 90% RH for 90 days. Inactivation kinetics, the effect of drying methods, and application of the microencapsulation process were also examined on mTG powder during the storage period. The first-order kinetic reaction was successfully applied to the relative activity values of all samples for both storage conditions. Both the drying method and application of microencapsulation showed a significant effect on enzyme activity. When comparing the drying techniques, the USFD samples were the most stable, having 816 and 465 days of half-life times for both storage conditions, respectively. Storage at 25 °C, 50% RH increased the half-life twofold compared with that of the USFD samples kept at 38 °C, 90% RH. The physical properties of mTG powder obtained either USFD, USFD–crude, CFD, or CSD showed that moisture content and wettability values increased, while caking degree and enzyme activity values decreased during storage. USFD samples had the lowest moisture content (5.48%) and Hausner ratio (1.12) and the highest relative activity (86.2%) compared with other samples after 180 days storage at 25 °C, 50% RH. When all quality characteristics and enzyme stability were considered, the USFD method was superior to others, and it was determined to be the best method for the production of microencapsulated mTG powders. mTG powders stored at 25 °C, 50% RH exhibited a longer shelf life.