De Boer Model Research Articles

Physical and Thermal Stability of Spray-Dried Swiss Cheese Bioaroma Powder

The effect of water content on the glass transition temperature of Swiss cheese bioaroma microencapsulated with a spray dryer was determined using differential scanning calorimetry (DSC) while mass loss was determined by thermogravimetric analysis (TGA). The sorption isotherm behavior was assessed at 15–45°C. Data were fitted with different sorption models. The bioaroma microparticles were produced via spray drying in a matrix with a 1:1 ratio (w/w) of maltodextrin 20DE and modified corn starch (Capsul). The isotherms displayed Type II behavior, and the best fit was obtained by the Guggenheim–Anderson–de Boer (GAB) model (coefficient of determination R² ≥ 0.98). The DSC analysis showed that the increased equilibrium moisture content caused a significant reduction in the Tg of the microparticles. The samples stored at intermediate humidity showed thermal stability and the samples with equilibrium moisture content of 17.92% showed a lower mass loss.

Experimental and Mathematical Investigations of Dicalcium Phosphate:Moisture Sorption Isotherms

The aim of this work was to determine desorption isotherms of Tunisian dicalcium phosphate. The equilibrium moisture contents of dicalcium phosphate were measured using the gravimetric method at four temperatures (50, 60, 70 and 80°C) and in wide range water activity (0.021-0.989). Desorption data of dicalcium phosphate were best fitted by the Guggenhein, Anderson and de Boer model at four temperatures.

Kinetic model of water vapour adsorption by gluten-free starch

Abstract This study evaluated the kinetics of water vapour adsorption on the surface of starch molecules derived from wheat. The aim of the study was to determine an equation that would allow estimation of water content in tested material in any timepoint of the adsorption process aimed at settling a balance with the environment. An adsorption isotherm of water vapour on starch granules was drawn. The parameters of the Guggenheim, Anderson, and De Boer equation were determined by characterizing the tested product and adsorption process. The equation of kinetics of water vapour adsorption on the surface of starch was determined based on the Guggenheim, Anderson, and De Boer model describing the state of equilibrium and on the model of a first-order linear inert element describing the changes in water content over time.

Thermodynamic properties, kinetics and adsorption mechanisms of Swiss cheese bioaroma powder

Water adsorption kinetics of Swiss cheese bioaroma microparticles were determined by a static method at 15°C, 25°C, 35°C and 45°C. This work used the Guggenheim–Anderson–de Boer (GAB) model to calculate thermodynamic properties of water adsorption. Additionally, this work predicted conditions for the stable storage of microparticles obtained through a spray drying encapsulation process with maltodextrin and modified corn starch (Capsul®) at a 1:1 (w/w) ratio. We evaluated the mechanisms that direct water vapor adsorption by studying enthalpy–entropy compensation. The product reached equilibrium phases after 120h of storage. The observed minimum values for the net integral entropy were indicative of maximized stability conditions of the product. At these conditions, water activity values ranged from 0.391 to 0.537, and the temperature ranged from 15°C to 35°C. An isokinetic compensation was confirmed for the adsorption phenomenon. This approach resulted in two zones, low and intermediate-high water activities. Under low moisture, the process was controlled by entropy; under intermediate-high moisture, it was driven by enthalpy.

Physical and Thermal Properties of Oregano (Origanum vulgare L.) Essential Oil Microparticles

AbstractIn this study, the physical and thermal properties of essential oil microparticles of oregano (Origanum vulgare L.) dried via spray drying were examined. The product was characterized by morphology, mean diameter, particle size distribution, moisture sorption curve, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The process promoted the formation of spherical capsules with high polydispersity. The isotherm exhibited type II behavior (sigmoidal curve), and the best fit was obtained by the Guggenheim–Anderson–de Boer (GAB) model (E = 6.748%). The DSC analysis showed that the increase equilibrium moisture content reduced the Tg value of the microparticles (164.47–91.29C). The samples stored at low humidity resulted in more thermally stable particles, and the samples with equilibrium moisture content of 4.74% showed higher thermal stability.Practical ApplicationsThe applications of essential oils with relevant antioxidant activities, such as oregano essential oil, as a food additive is limited in the conventional form, due to their fast degradation triggered by temperature, light, presence of oxygen and humidity, among others. The encapsulation technique by spray drying has been successfully used to overcome this drawback. However, the spray‐dried products may present some technological problems, such as high hygroscopicity and low resistance when subjected to high temperatures. The evaluation of microparticle stability is a relevant and important issue when desiring to ensure their quality and application. Studies of the functional properties such as hygroscopicity, sorption behavior and thermal resistance determine the ideal conditions for the storage of this type of product.

Analysis of gas sorption in glassy polymers with the GAB model: An alternative to the dual mode sorption model

The suitability of the Guggenheim–Anderson–De Boer (GAB) model for the parameterization of gas sorption isotherms and their dependences on temperature is explored. The GAB model implies that molecules adsorb on inner surfaces of the polymer in multilayers, which contrasts with the assumptions of the classical Dual Mode Sorption (DMS) model which implies the simultaneous occurrence of Henry-like dissolution and Langmuir's case I adsorption. The GAB model shows similar efficacy of the parameterization of the gas sorption isotherms in polymers as the DMS model. The isosteric heat of adsorption shows clear dependence on relative surface coverage for carbon dioxide sorption in cellulose acetate, polyethylene terephthalate, and the first polymer of intrinsic microporosity (PIM-1), thus allowing for the occurrence of adsorption multilayers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 1490–1495

Sweetpotato (SP-30) Flakes: Process Optimization and Moisture Adsorption Isotherm Studies

Sweetpotato is one of the predominant crops grown by local farmers in the marginal uplands of Brgy. Linao, Sitio Batuan, Inopacan, Leyte. The need to produce quality food products from sweetpotato is a continuing challenge to open new opportunities for farmers and entrepreneurs alike. This study aimed to determine the potential of sweetpotato var.SP30 for flake production and conduct moisture adsorption isotherm studies. Two screening processes were made using the 7-variable 8-run Plackett-Burman design while a face centered Central Composite Design (CCD) was employed during optimization. Sensory evaluation results were subjected to response surface regression (RSREG) analyses to generate optimum processing condition(s). Moisture adsorption studies were carried out to determine the nature of the product isotherm based on Brunauer-Deming-Deming-Teller (BDDT) classifications. Fitting of data was done using the Bruanauer-Emmettand Teller(BET) and Guggenheim-Anderson de Boer (GAB) models to determine the amount of adsorbed moisture in the product during storage at different temperature levels. Screening results identified Drying time (Dt), Drying Temperature (DT) and Oven Toasting time (OTt) as the critical processing variables. A set of combinations of Dt (min.), DT (°C), and OTt (min.) were generated as a result of the optimization. These combinations were 75-50-20, 80-50-20, 80-50-18, 85-50-20 and 90-50-20. Calculated values for the mass fraction of adsorbed water in the monolayer (WmB and WmG) at 30°C, 40°C and 50°C are 0.0971, 0.1311, 0.0591 and 0.1046, 0.2447 and 0.2224 respectively (expresseding/100gH2O) Sweetpotato (var. SP30) was found suitable for flake production. Moisture adsorption isotherm of sweetpotato flakes was sigmoid in shape and classified as type II in the BDDT classification. Wm values for both BET and GAB were found to follow the relationship WmB < WmG (Timmerman,2003).

Humidity-sensing properties of ZnO QDs coated QCM: Optimization, modeling and kinetic investigations

Uncapped 8nm average diameter ZnO QDs were successfully prepared by the sol–gel method and studied for moisture detection application by QCM technique. The developed humidity sensors were built by a quartz crystal microbalance (QCM) as the transducer and ZnO thin layer as a humidity sensing element. The synthesized ZnO QDs were characterized by powder X-ray diffraction (PXRD) and UV–visible. The experimental investigation indicates that the sensitivity as well as the response and recovery times of the sensors were greatly influenced by the thickness of the deposited layer. The optimized thickness of 370nm shows a good sensitivity, a good long-term stability and reproducibility, a short response and recovery time and a small hysteresis. To elucidate the effect of the thickness on the response of the sensors, the thermodynamic and the kinetics adsorption–desorption processes were investigated in real time by the multi-layer Guggenheim–Anderson–deBoer model (GAB model) and bimodal exponential kinetic model, respectively. The constructed adsorption isotherms coincide and show a sigmoidal shape (S-shaped, type II) for all sensors. The estimated characteristic times, deduced from the time-dependent frequency shift, were correlated to different kinetic steps involved during sorption processes.

Thermal, textural, and physicochemical analysis of corn extrudates enriched with broccoli or olive paste

The growing consumers’ demand for healthier snacks is of high importance and is driving research and industry towards developing novel ready to-eat expanded products. Thus, it would be interesting to enrich these products with additives that possibly lead to highly nutrient products. In the present study, extruded snacks based on corn flour enriched with broccoli or olive paste were developed and studied. Although the addition of broccoli or olive paste in extruded snacks can improve their nutritional properties, the final properties of these products must also be considered. Textural analysis (compression tests), thermal analysis (glass transition temperature), and moisture sorption measurements (sorption isotherms) were performed. A Guggenheim–Anderson–de Boer model has been applied to describe moisture sorption isotherms. Moreover, simple mathematical models were developed in order to correlate textural properties (maximum stress, maximum strain, elasticity parameter, number of cracks) with the process conditions during the extrusion (screw speed, temperature) and the raw materials’ characteristics (moisture content, concentration of broccoli or olive paste). Regression analysis was used to estimate mathematical models’ parameters. The influence of process conditions and raw materials’ characteristics on the measured properties of corn-based snacks enriched with broccoli or olive paste was presented based on the alterations of the estimated parameters.

Influence of Microwave Heating on Moisture Sorption Isotherm and Drying Characteristics of Green Gram (V igna radiata ) Seeds

The study describes the the moisture sorption isotherms of untreated and microwave-treated green gram (Vigna radita) seeds using optimum condition, i.e., at 808 W and 80 s. Different models were compared using the coefficient of determination (R2), reduced chi-square (χ2) values, and on the basis of residual plots. In untreated green gram seed, the Guggenheim Andersen de Boer was found suitable for predicting the equilibrium moisture content (EMC)–aw relationship for both the adsorption and desorption. For the microwave-treated seed, modified Chung–Pfost and Guggenheim Andersen de Boer models were found to give the best fit for describing the adsorption and desorption, respectively. Practical Applications Adsorption sorption isotherm having the significant effect of temperature on EMC was observed for microwave-treated seed as compared to untreated seeds. These isotherms were found to be type II sigmoid. The EMC of green gram seed increased above 0.6 aw. The isosteric heat of sorption was high in the case of desorption for both untreated and treated seeds. Untreated green gram has the highest rate of water absorption.

Moisture Sorption Characteristics of Pineapple Processing Waste: Shell and Central Cylinder

AbstractThe moisture adsorption isotherms of pineapple processing waste – shell and central cylinder – were determined at 40, 50, 60 and 70C using a gravimetric method. The sorption data were fitted to six well‐known sorption isotherm models. The Guggenheim–Anderson–de Boer model was found to be the most satisfactory to represent the equilibrium moisture content data for the pineapple shells and central cylinders. The thermodynamic properties – differential enthalpy and entropy – were estimated by the Clausius–Clapeyron method. The differential enthalpy of the pineapple shells and central cylinders ranged between 11.486 to 1.671 kJ/mol and 23.655 to −0.945 kJ/mol, respectively. The differential entropy had minimum values at 0.04 and 0.005 kgwater/kgdry solids for the pineapple shells and central cylinders, respectively. The pineapple shells presented two lines of compensation, one controlled by entropy and the other controlled by enthalpy and the pineapple central cylinders showed only one zone controlled by enthalpy mechanisms.Practical ApplicationsThis work presents information about the moisture sorption characteristics of pineapple processing waste. This kind of information is important for designing the unit operations necessary in the waste process use. In addition, knowledge of the moisture sorption characteristics is useful with respect to selection of packaging materials and storage stability. In general, this work gives relationship between water activity, entropy, enthalpy and moisture content of pineapple processing waste.

Experimental Analysis of Shale for Evaluating Shale Drilling Fluid Interaction in Agbada Formation

Aims: To characterize the shale samples from Agbada formation and to develop an inhibitive water-based mud for the shale types. Study Design: Experimental. Place and Duration of Study: Department of Petroleum, University of Port Harcourt Rivers State, Agbada Formation Niger-Delta Region, between March 2011 and August 2012. Methodology: This study includes the determination of shale properties such as mineralogy, cation exchange capacity, native moisture content and total organic carbon content of the shale samples collected from two wells in Agbada Field. It also involves the establishment of an adsorption isotherm for the shale and the modeling of these isotherms using the Guggenheim, Anderson and Deboer model. Results: Based on the results of the dispersion and swelling tests, 3% Bentonite + 1% Potassium Chloride (KCl) were selected as the promising fluid. Well A exhibited the Type II isotherm which is common to most shale while Well B showed the Type V isotherm. Adsorption isotherm model predictions were in agreement with experimental observations. The samples from the wells exhibited dispersion after testing with deionized water. For Well A and B, 3% Bentonite + 1% Potassium Chloride (KCl) inhibits and yielded higher shale percent recovery values from dispersion tests. Conclusion: It was observed from adsorption isotherm models that the total organic carbon content is not a significant factor in the adsorptive and dispersive behaviors exhibited by the shale samples.

Moisture Sorption Isotherms and Thermodynamic Properties of Whey Protein Concentrate Powder from Buffalo Skim Milk

Adsorption and desorption isotherms of whey protein concentrate powder prepared from buffalo skim milk were determined at 25, 35 and 45C, over a water activity range of 0.11–0.97, using static moisture gain/loss from test samples. Both the adsorption and the desorption isotherms exhibited sigmoid shape corresponding to type II, typical to many foods. There was generally a negative temperature effect on equilibrium moisture content. The Guggenheim–Anderson–de Boer model gave the best fit for the sorption data throughout the entire water activity range and at all three temperatures. The monolayer moisture content values were higher in desorption than in adsorption and deceased with an increase in temperature. Isosteric heat of sorption and the entropy data displayed a strong dependence on moisture content. The adsorption data gave lower values than the corresponding desorption data. Temperature of sorption had profound influence on the properties of bound water and surface area of adsorbent. Practical Applications Dried milk products are the important segments of dairy industry. Whey is a by-product of cheese, paneer or casein production, and is a source of best-quality proteins. Indian subcontinent is the largest producer of buffalo milk in the world, and the indigenously available whey is mostly obtained from buffalo milk products. The results of the present study would have practical applications in exploiting the competitive advantages of buffalo milk and in developing high-protein multicomponent functional foods using buffalo skim milk whey protein concentrate powder. The analysis of moisture sorption characteristics and thermodynamic properties of bound water would provide information regarding process energy requirements, shelf life appraisal and design of suitable packaging systems for the product.

Stability of whey protein hydrolysate powders: Effects of relative humidity and temperature

Whey protein hydrolysate (WPH) is now considered as an important and special dairy protein ingredient for its nutritional and functional properties. The objectives of the present study were to investigate the effect of environmental relative humidity (RH) and storage temperature on the physicochemical stability of three WPH powders with hydrolysis degrees (DH) of 5.2%, 8.8% and 14.9%, respectively. The water sorption isotherms of the three WPH powders fitted the Guggenheim–Andersson–DeBoer model well. An increase in water content leaded to a decrease in glass transition temperature (Tg), following a linear Tg vs log water content relationship. Moreover, an increase in DH caused the decrease in Tg at the same water content. Changes in microstructure and colour occurred significantly when the WPH powders were stored at high environmental RH or temperature, especially for those with high DH.

Influence of alternative drying aids on water sorption of spray dried mango mix powders: A thermodynamic approach

Mango pulp mixed with drying aids (maltodextrin and skimmed milk) was spray dried to obtain three powder formulations. The water sorption behavior of these mango mix formulations was determined at temperatures of 20, 30, 40 and 50°C in water activity ranging between 0.059 and 0.907. The Guggenheim, Anderson and De Boer (GAB) model was applied to modeling the adsorption isotherms of mango mix powders, resulting in statistical values of mean relative error (MRE≤5.14%). Differential and integral thermodynamic properties related to water sorption for the mango powders were determined by the analytical derivation of the water activity with respect to temperature based on the GAB model fitting. The differential thermodynamic properties indicated a decrease in the water sorption energy with increasing water content and the negative values of the Gibbs free energy revealed that the sorption process was spontaneous for the three powder formulations. In spite of the formulation containing skimmed milk have shown the higher monolayer water contents, the minimal integral entropy zone observed at similar values of water activity for the three mango mix powders indicated that all of them could be safely stored at the same relative humidity condition.

Modeling water vapor adsorption/desorption cycles

This modeling work deals with the adsorption of water vapor on different porous materials where it undergoes capillary condensation and its adsorption/desorption isotherms exhibit hysteresis. The focus is on the description of the so called scanning curves, i.e. the adsorption/desorption isotherms observed when such an adsorbent is repeatedly loaded and unloaded in a range of conditions where hysteresis is observed, and on the simulation of fixed bed adsorption/desorption cycles. We use an approach originally developed by Štěpánek et al. (Chem Eng Sci 55(2):431–440, 2000), and expand it so as to include more general isotherms (not only the Dubinin–Radushkevich and Dubinin–Astakhov model, but also the Guggenheim–Anderson–de Boer model and the Do and Do model) and to allow for less than infinitely fast heat transfer, so as to consider non-isothermal situations. From a modeling point of view the results are satisfactory and highlight the need for better experimental data on water vapor adsorption, which need to be measured in enhanced experimental set-ups, capable to tightly control the relative humidity of the gas phase.

Study of adsorption isotherms of green coconut pulp

Brazil is considered one of the largest producers and consumers of tropical fruits. Green coconut (Cocos nucifera L.) stands out not only for its production and consumption, but also for the high amount of waste produced by coconut water industry and in natura consumption. Therefore, there is a need for utilization of this by-product. This study aims to study the adsorption isotherms of green coconut pulp and determine its isosteric heat of sorption. The adsorption isotherms at temperatures of 30, 40, 50, 60, and 70 °C were analyzed, and they exhibit type III behavior, typical of sugar rich foods. The experimental results of equilibrium moisture content were correlated by models present in the literature. The Guggenheim, Anderson and De Boer (GAB) model proved particularly good overall agreement with the experimental data. The heat of sorption determined from the adsorption isotherms increased with the decrease in moisture content. The heat of sorption is considered as indicative of intermolecular attractive forces between the sorption sites and water vapor, which is an important factor to predict the shelf life of dried products.

Chemical Composition, Water Sorption Isotherm, and Phenolic Contents in Fresh and Dried Pomegranate Peels

Pomegranate peels were dried by freeze drying at 20°C; air and vacuum drying at 40, 60, and 90°C; and sun drying. The moisture sorption isotherm was measured and modeled using the Brunauer–Emmett–Teller (BET) and Guggenheim–Anderson–De Boer (GAB) models. Two solvents (methanol and ethanol) and water were used to extract the phenolic compounds in pomegranate fruit peel. Fresh peels contained 5,990, 4,530, and 8,460 mg gallic acid equivalent (GAE)/100 g dry-peel solids for methanol, ethanol, and water extracts, respectively. The total phenolic content of ethanol extracts of freeze-dried peels was comparable to that of fresh peels (4,900 mg GAE/100 g dry-peel solids), whereas air- and vacuum-dried peels had significantly lower phenolic contents. Peels air dried at 60°C had the highest phenolic content (2,320–4,650 mg/100 g dry-peel solids) compared to samples air dried at 40 or 90°C (1,160–4,480 mg/100 g dry-peel solids), whereas vacuum-dried peels did not show any trends with temperature. In general, methanol had a higher capacity for extracting phenolic compounds from dried pomegranate peels than water, and ethanol showed a low extraction capacity. In all cases, phenolic compounds were significantly lower in ethanol extracts compared to methanol or water extracts (p < 0.05). In addition, phenolic compounds soluble in water and ethanol were more sensitive to all drying methods except freeze drying.

Fabrication and physicochemical characterization of HPMC films with commercial plant extract: Influence of light and film composition

Betacyanins used as natural red color (NRC) are known as antioxidants. The present paper was focused on their effect on physicochemical properties of hydroxypropyl methylcellulose (HPMC) films. All the films were evaluated for their photo-aging stability on optical, mechanical, barrier, thermal and structural properties. Both, tensile strength and Young's modules of NRC composite films decreased, while elongation significantly increased compared to control films. Dynamic vapor sorption data fitted by Guggenheim–Anderson–de Boer (GAB) model showed lower values of sorption energy for NRC composite films. NRC films showed an initial decrease in oxygen permeability that was more decreased after 20 days of photo-aging. Inversely, a significant increase in water vapor permeability of films by increasing NRC was observed. The films composed of 4% NRC (v/v) showed the highest WVP and lowest oxygen permeability. HPMC films transparency decreased with NRC contents.

Water Adsorption and Glass Transition of Spray-Dried Soy Sauce Powders Using Maltodextrins as Carrier

Moisture adsorption isotherm and glass transition temperature of various spray-dried soy sauce powders containing different types and concentrations of maltodextrins were studied and compared. Maltodextrins of dextrose equivalent (DE) = 5, DE = 10 and DE = 15, respectively, with concentrations of 20 or 40 % (w/v) were used as carrier agents. The equilibrium moisture content was reduced with increased maltodextrin concentration, whereas it was not apparently influenced by the value of maltodextrin DE. Both the Brunauer–Emmett–Teller (BET) and Guggenheim–Anderson–de Boer (GAB) models could be applied to simulate the moisture adsorption behaviour of the soy sauce powders. The monolayer moisture content of the powders was determined by fitting experimental data to the BET/GAB models with a w up to 0.53, although both models could fit satisfactorily with the experimental data to a higher water activity level. The glass transition temperatures (T g) of the powders equilibrated under various water activities were determined using a differential scanning calorimeter. Increasing moisture adsorption of the soy sauce powders resulted in a T g reduction, and the experimental T g values fitted the Gordon–Taylor model well. The BET and Gordon–Taylor models were applied together to predict the critical moisture contents (i.e. 0.0464–0.0777 g water/g dry matter) and water activities (i.e. 0.032–0.241), above which the soy sauce powders become vulnerable to degradation and changes in their physicochemical properties.