Water Activity Range Research Articles

Microstructures containing nanocapsules of unsaturated fatty acids with biopolymers: Characterization and thermodynamic properties

Unsaturated fatty acid concentrates (UFAC) were nanoencapsulated by emulsification/lyophilization using chitosan:gelatin matrices as wall material. Nanoemulsions presented droplets size between 40 and 280 nm. There was a decrease in droplets size due to gelatin addition, resulting in a decrease of encapsulation efficiency and an increase in porosity and pores volume. UFAC oxidation in chitosan capsules was slower than in free oil. Sorption isotherms were performed at 4 and 25 °C, and GAB model showed the best fit to experimental data. Differential enthalpy and entropy increased with the moisture content decrease, and the adsorption process was spontaneous. Pores radius increased with the increase of gelatin in the microstructures. The critical storage conditions of the microstructures were calculated. The range of water activity, which represents the maximum stability zone, was of 0.65–0.75 at 4 °C and of 0.73–0.85 at 25 °C. This zone hinders the oxygen diffusion through the pores, retarding oxidation.

Modeling of Moisture Adsorption Isotherm of Selected Commercial flours of Bangladesh

The moisture adsorption behavior is a fundamental knowledge in the processing and storage of food materials. In this paper, the experimental adsorption behavior of wheat, rice and corn flours were compared with five widely recommended adsorption models (BET, GAB, Oswin, Smith and Halsey) in the literature. From the sorption data, monolayer moisture content of wheat, rice and corn flours were estimated as per BET and GAB models. For all flours, GAB model gave higher monolayer moisture content compare to the BET model. Linear regression analysis was done to determine the model constants where all models were compared using regression coefficient and standard error of the estimate. It was observed that there is no single model that could describe accurately the sorption isotherm over the whole range of water activity (aw) and for all types of flours. BET model was found as the best model for the prediction of equilibrium moisture content (EMC) of the most stable region (i.e. EMC corresponding to aw range below 0.52) but it was not suitable at aw above 0.52. The GAB model was found to be the most suitable to predict the EMC for wide range of water activity (0.11 to 0.93).
 The Agriculturists 2018; 16(2) 35-42

Moisture Sorption Characteristics of Selected Commercial Flours (Wheat, Rice and Corn) of Bangladesh

Moisture sorption isotherms of commercial wheat flour, rice flour and corn flour were determined within the water activity range of 0.11-0.93 at different temperatures (5°C, 30°C and 55°C) using the static gravimetric method. The moisture sorption isotherm of all flours exhibited type II characteristics according to BET classification. It was found that corn flour had a higher sorption capacity than wheat and rice flour. Temperature influence on sorption behavior was found that, for wheat and corn flour, the sorption capacity decreased with the increase of temperature, while for the rice flour an opposite behavior was observed at water activity value higher than 0.75. The Clausius–Clapeyron equation was used to calculate the net isosteric heat of sorptions. For all flours, the heat of sorption decreased with the increase of EMC.

MOISTURE SORPTION ISOTHERMS OF QUINOA SEEDS: THERMODYNAMIC ANALYSIS

The present work aimed to study the water sorption behavior of quinoa seeds analyzing the hysteresis phenomenon and determining thermodynamic properties. Static gravimetric technique was used to obtain the equilibrium moisture content of quinoa seeds in different temperature conditions (15, 25, 35 e 50 °C) and relative humidity (between 11 and 96%). Equilibrium moisture content data were adjusted by eight mathematical models and the Modified Halsey model was the best one to describe the water sorption phenomena of quinoa seeds. Hygroscopic equilibrium moisture content of quinoa seeds is directly proportional to the water activity and decreases with increasing temperature. The hysteresis phenomena were observed throughout the range of water activity, showing more evident at low temperatures. Integral isosteric heat and differential entropy decreased with the increase of equilibrium moisture content. Gibbs free energy decreased with the increase of temperature and equilibrium moisture content. Compensation enthalpy-entropy theory was confirmed and the sorption mechanism is controlled by enthalpy.

Sorption isotherms and isosteric heat estimation of purple cactus pear (Opuntia stricta) juice embedded in gelatin–maltodextrin matrix

AbstractMoisture sorption isotherms of microencapsulated juice from purple cactus pear were determined at different temperatures (15, 20, and 30 °C) in water activity (aw) range from 0.112 to 0.976. The experimental data were correlated to GAB, BET, Caurie, Smith, Henderson, Bradley, Kuhn, and Oswin models. The obtained isotherms present a sigmoid shape Type IV. The models of Smith, Kuhn, and Oswin were found as the most suitable (EMR < 10%). The isosteric heat (Qst) decreased with the increase in moisture content obtaining the maximum and minimum values of 14.84 and 5.60 kJ/mol, respectively, for moistures between 10 and 70%.Practical applicationsToday, the food industry is looking for new storage procedures for the preservation of bioactive compounds contained in fruits. Until now, many native Mexican fruits have not been processed in agro‐food industry, for example, purple cactus pear (Opuntia stricta) fruit, which is one of the natural products not widely processed. There is strong evidence that such fruit contains antioxidants, natural pigments, and phenolic compounds. The conservation of the bioactive compounds can be carried out by embedding the juice into a biodegradable matrix. We first propose the encapsulation of the juice through using the gelatin–maltodextrin composite as wall material. Then, the characterization of the dried product by determining the sorption isotherms can be useful to predict the optimum storage conditions, life prediction, and packaging design of this type of products.

Moisture sorption isotherms and thermodynamic properties of sorbed water of chironji (Buchanania lanzan Spreng.) kernels at different storage conditions

Moisture sorption isotherms of chironji kernels were determined at 25, 35 and 45 °C over a water activity range of 0.11–0.93. Three sorption models i.e., Guggenheim–Anderson–de Boer (GAB), Brunauer–Emmett–Teller (BET) and Caurie were evaluated to find out their fitness to the sorption data. Thermodynamic properties of sorbed water were analyzed over the selected range of water activity and temperature. The result showed that the sorption isotherms reflected Type II BET sorption characteristics with a clear hysteresis at the temperatures. Of the three models, GAB and Caurie models were found superior predicting the sorption of chironji kernels over the entire range of water activity values. The monolayer moisture content values calculated by the best-fitted GAB and Caurie model for adsorption were 9.86 and 6.31%, 8.023 and 6.18%, 6.90 and 5.97% (db) and for desorption were 6.53 and 6.01%, 5.85 and 5.68%, 4.21 and 5.60% (db), respectively at 25, 35 and 45 °C. The value of isosteric heat decreased with increasing moisture content and approached the latent heat of pure water. Sorption entropy increased with increasing moisture content and decreased gradually with increase in moisture content. The spreading pressures, for both adsorption and desorption, increased with increasing water activity at the three selected temperatures.

Thermodynamic Study of Adsorption Properties of Rocoto Pepper (<em>Capsicum pubescens</em>) Obtained by Freeze-Drying

The aim of this study was to establish a study of the thermodynamic adsorption to rocoto pepper obtained by freeze-drying at temperatures of 15, 25 and 35°C, by the gravimetric method in the range of water activity between 0.131 and 0.847. Rocoto pepper (<em>Capsicum pubescens</em>) is a natural source of capsaicinoids which gives the level of pungency or hotness attractive gastronomy. Actually, dehydrated and powered food matrices are a good option to ensure stability and techno-functional properties for later uses and applications. A mathematical modeling of the respective isotherms was obtained using different models reported in the literature. The BET model (Brunauer-Emmett-Teller), GAB (Guggenheim-Anderson-de Boer), Herdenson, Smith, Oswin, Peleg and Caurie, based on the moisture content in equilibrium reached freezer-dried samples pepper. The statistical results indicated that the model GAB was the most appropriate to describe the respective sorption curves, whose behavior was completely sigmoidal type II. From these results, the net isosteric heat of adsorption was determined using the Clausius-Clapeyron, ranging from 52.5 to 46.6 (kJ/mol) a moisture content from 2 to 38% dry basis. Also, Gibb's energy (∆G<0) showed that the process will proceed spontaneously (exothermic process) which increased to higher moisture content (X_w). The differential entropy (ΔS) was less at 15°C, making the adsorption process thermodynamically favorable at low temperatures.

Thermodynamic properties of Buriti (Mauritia flexuosa) tree gum

Abstract Moisture adsorption and desorption isotherms from buriti tree gum (BG) were obtained at different temperatures (25 to 55 °C) in a water activity range of 0.1 to 0.9. The isotherms were classified as type II. The hysteresis loop and moisture of the monolayer decreased as temperature increased and Halsey’s equation proved able to predict with good precision the product’s sorption isotherms in the conditions studied. BG’s isosteric heats of moisture adsorption and desorption were close to the latent heat of vaporization of pure water for moisture levels above 30 g/100 g db and exponentially increased below that level. The enthalpy-entropy compensation theory and the isokinetic relationship were applied and indicated that BG’s moisture adsorption and desorption processes are spontaneous. The integral sorption properties indicated that the increase in surface tension at BG’s moisture sorption sites was more representative for the desorption process.

Modelling of moisture sorption isotherms and glass transition temperature of spray-dried honey powder

This work intended to evaluate sorption isotherms and glass transition temperature (Tg) of spray dried honey powders produced by using three carrier agents viz. maltodextrin (MD), gum Arabic (GA) and whey protein concentrate (WPC) at different water activities. Experimental data were fitted to five mathematical models [Guggenheim, Anderson, and de Boe (GAB), Brunauer–Emmett–Teller (BET), Halsey, Oswin and Smith] among which the GAB model was found to be the best fit. The monolayer moisture content of honey powders developed with MD, GA and WPC were determined 0.066 (g water/g solids), 0.071 (g water/g solids) and 0.079 (g water/g solids), respectively. The best retention of total phenolic content, vitamin C content and antioxidant activity was observed for honey powder developed with WPC in the water activity range of 0.113–0.529. Water displayed a strong plasticizing effect on Tg with a large reduction in Tg for all honey powders, as the water activity increased.

Immobilized lipase-catalyzed esterification for synthesis of trimethylolpropane triester as a biolubricant

Abstract Synthetic oleochemical esters of polyols and fatty acids are biodegradable and possess desirable technical and ecological properties. Trimethylolpropane (TMP) triester has been widely applied as a hydraulic fluid. TMP triester was effectively synthesized by lipase-catalyzed esterification from TMP and high oleic fatty acid from palm oil using an immobilized lipase. The immobilized lipase was prepared with liquid Lipozyme TL 100 L from Thermomyces lanuginosus with Duolite A568 as a carrier. The effects of temperature, enzyme loading, vacuum level, and water activity of the enzyme on the synthesis of TMP triester were investigated. The optimum temperature, enzyme loading, and vacuum level were 60 °C, 15% (based on total substrate), and 6.7 kPa, respectively. The optimum water activity range of the enzyme was 0.5–0.9. Under the optimum conditions, the maximum conversion reached up to 95% after 9 h. No significant differences in physical properties were observed between TMP triester from this study and a commercial TMP triester prepared by chemical catalyst.

Thermodynamic analysis for assessing the physical stability of core materials microencapsulated in taro starch spherical aggregates

Taro starch has the ability of producing spherical aggregates under spray-drying without the addition of binding agents. This property makes taro starch suitable for microencapsulation of dietary compounds. This study addressed the physical stability of hydrophilic and hydrophobic core materials microencapsulated by spray-drying into taro starch spherical aggregates determined from a thermodynamic standpoint via vapor adsorption isotherms. Ascorbic acid and almond oil were used as compound models. Encapsulation efficiency, GAB sorption parameters, differential and integral thermodynamic properties, Gibb’s free energy, entropy-enthalpy compensation, spreading pressure, effective diffusion rate, activation energy and critical water activity were determined. The encapsulation efficiency of ascorbic acid and almond oil was 99% and 56%, respectively. Monolayer moisture content was relatively low for ascorbic acid microcapsules. The adsorption process was driven by entropic mechanisms. The physical stability of taro starch spherical aggregates microcapsules with different core material was guaranteed for a range of water activities and temperatures.

Preparation and characterization of octenyl succinylated normal and waxy starches of maize as encapsulating agents for anthocyanins by spray-drying.

The encapsulation by spray drying of maize anthocyanins was evaluated using two types of wall materials, consisting of normal and waxy maize starch, which were esterified with octenyl succinic anhydride. The X-ray diffraction analysis revealed that SWMS possessed a completely amorphous, while SNMS had a crystalline structure. SNMS showed peaks at 2θ = 13.1°, 19.8° and 22.4°. The results revealed that SNMS and SWMS had almost the same encapsulation productivity (EP); SNMS showed the best performance because its EP was higher (95%) than in SWMS (90%). The stability of microcapsules produced with SNMS showed the highest anthocyanin retention after storage in the water activity (aw) range of 0.11-0.94 at 40°C.

The prediction of moisture adsorption isotherm for sucrose powder in Côte d’Ivoire

Moisture sorption isotherms play an essential role in preservation and storage of dehydrated food. To study the behavior of sucrose, it’s moisture adsorption isotherm was investigated using the static gravimetrique method at laboratory temperature (29 ±1°C) in a water activity range (aw) of 0.07-0.97. The results showed that the equilibrium moisture content of sucrose increase substantially above aw = 0.6. The moisture adsorption isotherm was sigmoid in shap, showing a type III BET isotherm. The data obtained were fitted to several models including two-parameter (BET, Hasley, Kuhn and Oswin), three parameter (GAB). A non-linear least square regression analysis was used to evaluate the models constants. The GAB model best fitted the experimental data in the wide range of water activity. The best fitted equation provide a sound basis for futur work on the drying and storage of sucrose. The accurate moisture content and the stability profile of sucrose were determined. The results of determination show that sucrose powder was stable below 7.7% RH at 29°C. The content of water adsorbed in the monomolecular layer was calculated (GAB Xm=0.950 g H2O/100 g solids; BET Xm= 1.072 g H2O/100 g solids).

Moisture adsorption properties and shelf-life estimation of dried and pulverised edible house cricket Acheta domesticus (L.) and black soldier fly larvae Hermetia illucens (L.)

Edible insects are part of the diets of a significant proportion of rural populations in the tropics especially Africa and Asia, and their use as source of key nutrients for better nutrition is re-emerging. Indigenously, elemental methods are used to process the insects before they are consumed or sold in retail outlets. In recent years, better knowledge of processing, packaging and storage has become necessary because of commercialisation needs. A common processing approach involves drying after a brief heat-treatment step, and then milling into a powdered product which is sold to manufacturers or consumers as ingredient for processing final products. The hydration properties of dried powders of edible house cricket and black soldier fly larvae (BSFL) were studied with the aim of predicting shelf-life stability under typical packaging and storage temperatures experienced in the tropics. Moisture adsorption isotherms were determined gravimetrically at 25, 30 and 35 °C, over 0.11–0.97 water activity (aW) range, and the data fitted to various models. Sorption isotherms were of type II according to Brunauer classification indicating monolayer-multilayer sorption behaviour. Cricket powder exhibited higher hydration capacity, and aW of this product was less sensitive to temperature variation as compared to BSFL powder. In the two products, water exhibited transitions from bound- to free- state at ~5 g/100 g moisture content. Based on Heiss-Eichner model, a shelf-life of 7 months at 25 °C can be achieved if the cricket and BSFL powders are dried to ca. 5 g/100 g moisture content and packaged in 80 μm thick polyethylene films. At 35 °C the shelf-life of the cricket product is shortened three- to four-fold whereas the BSFL powder is unable to store.

Bazni pristup verifikaciji i validaciji modela izoterme sorpcije

In this paper, a procedure for the statistical verification and validation of a newly generated sorption isotherm M01 model is defined. A basic approach to the evaluation of a model for approximating experimental sorption data is presented. Based on the accuracy within an acceptable range, a model is considered valid for a set of experimental conditions conducive to its intended purpose. The matching of experimental data to the data obtained in the calculations was examined. Several statistical criteria, proposed in the literature, and indicators (the coefficient of determination (R2), the root mean squared error (RMSE) and the mean relative deviation (MRD)) were used for the quantitative verification of the newly generated sorption isotherm model. A qualitative statistical analysis was performed by the validation of statistical assumptions relative to the residuals obtained from the regression analysis. This was achieved by creating a normal quantile-quantile diagram with a normal residual distribution, and a Scatter plot diagram with a random residual distribution. Fitted with the newly generated three-parameter sorption isotherm model, the validation of the experimental data on the sorption isotherms of pear flesh tissue (determined at four temperatures 15˚C, 30˚C, 45˚C and 60˚C, and over a range of water activity from 0.110 to 0.920) was performed relative to the results of the Guggenheim, Anderson and De Boer (GAB) model. The success of the newly generated model was confirmed in relation to this reference model.

Microbiology in the sugar industries

The environment of a sugar factory is conducive to the propagation of microbes that are introduced with the harvested crop. Further introductions are made from the machinery surfaces and water during processing. Each microbe type has a preferred range of temperature and water activity, so a factory may have different populations in different areas. It is important to detect microbial presence so appropriate control measures can be taken, and to conserve expenses when treatment is not needed. The most ideal detection methods in a factory will yield accurate results quickly and inexpensively. A mannitol detection method has been developed for the sugarcane industry, and subsequently applied to sweet sorghum and sugar beet. Conversion of sugar crop byproducts, such as bagasse, are a potential new value stream. An analysis was conducted to determine whether environmental conditions and the presence of microbes in bagasse affects the chemical composition, and subsequent application for novel uses. Fuel value was found to be negatively affected when bagasse was left uncovered and exposed to sun and rain. The fuel characteristics were maintained. Bagasse was also successfully pelletized and converted to biochar for stable storage and transport.

Evaporation, diffusion and self-assembly at drying interfaces.

Water evaporation from complex aqueous solutions leads to the build-up of structure and composition gradients at their interface with air. We recently introduced an experimental setup for quantitatively studying such gradients and discussed how structure formation can lead to a self-regulation mechanism for controlling water evaporation through self-assembly. Here, we provide a detailed theoretical analysis using an advection/diffusion transport equation that takes into account thermodynamically non-ideal conditions and we directly relate the theoretical description to quantitative experimental data. We derive that the concentration profile develops according to a general square root of time scaling law, which fully agrees with experimental observations. The evaporation rate notably decreases with time as t-1/2, which shows that diffusion in the liquid phase is the rate limiting step for this system, in contrast to pure water evaporation. For the particular binary system that was investigated experimentally, which is composed of water and a sugar-based surfactant (α-dodecylmaltoside), the interfacial layer consists in a sequence of liquid crystalline phases of different mesostructures. We extract values for mutual diffusion coefficients of lamellar, hexagonal and micellar cubic phases, which are consistent with previously reported values and simple models. We thus provide a method to estimate the transport properties of oriented mesophases. The macroscopic humidity-independence of the evaporation rate up to 85% relative humidities is shown to result from both an extremely low mutual diffusion coefficient and the large range of water activities corresponding to relative humidities below 85%, at which the lamellar phase exists. Such a humidity self-regulation mechanism is expected for a large variety of complex system.

Applicability of the Guggenheim–Anderson–Boer water vapour sorption model for estimation of soil specific surface area

SummarySoil specific surface area (SA) controls fundamental soil processes such as retention of water, ion exchange, and adsorption and release of plant nutrients and contaminants. Conventional methods for determining SA include adsorption of polar or non‐polar fluid molecules with associated advantages and limitations. The Guggenheim–Anderson–Boer (GAB) sorption model accurately characterizes soil water vapour sorption isotherms and is posited as an alternate approach for the determination of SA from water vapour sorption. The present study investigates the GAB model as an alternative to other water sorption‐based modelling approaches to determine SA. Measured water vapour adsorption and desorption isotherms for 321 soil samples were used to parameterize the GAB model, the Brunauer–Emmet–Teller (BET) equation and a film adsorption Tuller–Or (TO) model to estimate SA. For adsorption isotherms, the values of the GAB parameters varied depending on the water activity or relative humidity range of measured data (0.03–0.93 compared with 0.10–0.80), whereas the variation for desorption was minimal. For desorption isotherms, the average water activity value at which the GAB monolayer parameter was obtained was 0.24 for kaolinite‐rich samples, 0.31 for illite‐rich or mixed clay samples, 0.34 for smectitic samples and 0.30 for organic matter‐rich samples, respectively. The GAB model provided reasonable estimates of SA (root mean squared error from 11.6 to 36.4 m2 g−1), in particular for smectite‐rich soil samples, when compared with SA measured by the ethylene glycol monoethyl ether (EGME) method. For kaolinitic samples, however, the BET equation provided the best estimate of EGME‐SA. The SA estimates of the GAB model were comparable to those obtained by the TO adsorption model. Thus, the GAB model provides a good alternative to the TO model (applicable only to adsorption data) or the BET model, which fails when the fraction of swelling clay minerals increases.HighlightsGAB, BET and film adsorption models were parameterized with water vapour sorption data.Water activity at GAB monolayer coverage depended on clay mineralogy.Soil organic matter did not affect water activity at monolayer coverage.Estimates of SA from GAB were in accord with EGME‐measured SA.

Predicting Storage Conditions for Rice Seed with Thermodynamic Analysis

Abstract The desorption isotherms of japonica and indica rice seeds were determined at 15, 25, 35, 45 °C within the water activity range from 0.12 to 0.92 and it was observed that GAB model could accurately describe the desorption behaviors with low values of mean relative error (MRE). The thermodynamic properties of rice seeds were obtained by water desorption isotherms. The moisture content with the minimum integral entropy was considered as the best storage condition where the strongest energetic interaction between water molecular and solid occurred and the optimum seed moisture for storage at 35 °C occurred at 6.02 g water per 100 g of dry matter (ɑw of 0.12) for japonica rice seed and 5.28 g water per 100 g of dry matter (ɑw of 0.08) for indica rice seed, respectively. The mechanisms of desorption process were determined with integral enthalpy–entropy compensation theory and it was observed that the at low moisture content the desorption process of rice seed was controlled by changes of entropy, whereas the desorption process was considered to be controlled by enthalpy mechanism at high moisture content. It was found that the indica rice seed exhibited a wider water activity range in the minimum integral entropy zone, indicating that indica rice seed was more stable to withstand the different storage conditions compared with japonica rice seed.

Improved survival of Lactobacillus zeae LB1 in a spray dried alginate-protein matrix

The objective of the current research was to investigate the in vitro gastrointestinal digestion and storage properties of probiotic bacteria encapsulated in microparticles containing sodium alginate (AG) and sodium caseinate (NaCas) or soy protein isolate (SPI) through spray drying technology. A probiotic isolate Lactobacillus zeae LB1 was spray dried in AG solution combined with either SPI or NaCas at different ratios. High survival rate (>80%) was obtained for all the encapsulation formula tested. Combination of SPI or NaCas with AG showed a positive effect on both the in vitro gastric resistance and storage stability of L. zeae LB1. Among the formulas tested, microparticles made from a blend of NaCas and AG showed the highest glass transition temperature (Tg), corresponding to the best survival of L. zeae LB1 during storage under the water activity range of 0.11–0.76. The presence of two Tgs in the NaCas-AG particle suggested that phase separation occurred, which proved to have a positive effect on the viability of encapsulated probiotic bacteria during storage and gastric transition. In conclusion, the current study demonstrated that AG combined with NaCas may provide best protection to probiotic bacterial cells during storage, whereas AG combined with SPI proved to have the best gastric resistance property.