Moisture Sorption Characteristics of Starchy Products: Oat Flour and Rice Flour

Moisture sorption isotherms for oat flour and rice flour were determined at 5, 23, and 45 °C using a gravimetric technique in an a _w range of 0.08–0.98. The results obtained showed that, for a _w values lower than around 0.75, in both flours, the sorption capacity decreased with increasing temperature, while the opposite behavior was observed at a _w greater than this value. It was found that the experimental data in the water activity range considered were better represented by the four-parameter Peleg equation. The monolayer water contents for both materials were determined by the BET and GAB models. The net isosteric heats of sorption were estimated using the Clausius–Clapeyron equation. For both materials, the monolayer water content and the isosteric heat of sorption were found to decrease with increasing temperature and increasing moisture content, respectively.     

Modeling the Effect of Glucose Syrup on the Moisture Sorption Isotherm of Figs

Moisture sorption isotherms of figs with and without glucose syrup (at 20% and 40%, w/w) were determined at 5 °C, 25 °C, and 40 °C. A static gravimetric method was used under 0.11–0.84 water activity ranges for the determination of sorption isotherms that were found to be typical type ΙΙΙ for control sample. The inclusion of glucose syrup had significant effects on the sorption isotherms, and the moisture content of samples at each a _w decreased with increasing temperature. The experimental data were fitted well with two-parameter Brunauer–Emmet–Teller, three-parameter Guggenheim–Anderson–de Boer, and four-parameter Peleg models that all had R ² of greater than 0.99. The net isosteric heats of sorption were estimated using the Clausius–Clapeyron equation from the equilibrium data at different temperatures. It was found that the addition of glucose syrup significantly increased the amount of monolayer water and the isosteric heat of sorption. Both water activity and isosteric heat of sorption increased with glucose syrup level and the shape and status of sorption isotherms tend to change toward the typical sigmoid shape of most food systems.     

Thermodynamics of water–biopolymer interactions: Irreversible sorption by a single,uniform sorbent phase

Sorption isotherms of water vapor by solid biopolymers are necessary for the determination of thermodynamic quantities for water–biopolymer interactions. Such isotherms are generally irreversible, so equilibrium thermodynamics may not be applicable. General relationships are derived for thermodynamic quantities of sorption when the sorbent is a single uniform phase. In general, use of the Clausius–Clapeyron equation allows correct determination of differential entropies of sorption. However, calorimetric data are also necessary for the correct determination of other thermodynamic quantities. The single uniform phase model appears more useful than a domain model in explaining the hysteresis seen in water–biopolymer sorption isotherms.     

Water desorption properties of separated manure solids

Separated manure solids were collected from three dairy farms with different solid-liquid manure separators. Desorption isotherms were obtained for water desorption equilibria at five temperature levels. Three isotherm models were fitted to the data. Equations for estimating the isosteric and integral heats of desorption were also developed.     

Thermodynamic functions of biopolymer hydration. I. Their determination by vapor pressure studies,discussed in an analysis of the primary hydration process

The primary hydration process of native biopolymers is analyzed in a brief review of the literature, pertaining to various aspects of biopolymer–water systems. Based on this analysis, a hydration model is proposed that implies that the solution conformation of native biopolymers is stable at and above a critical degree of hydration (h_p′ = 0.06–0.1 g H₂O/g polymer). This water content corresponds to the fraction of strongly bound water, and amounts to ～20% of the primary hydration sphere. In order to test this model, detailed sorption–desorption scanning experiments were performed on a globular protein (α-chymotrypsin). The results obtained are consistent with the proposed hydration model. They show that under certain experimental conditions, sorption isotherms can be obtained that do not exhibit hysteresis. These data represent equilibrium conditions and are thus accessible to thermodynamic treatment. Valid thermodynamic functions, pertinent to the interaction of water with biopolymers in their solution state, can be obtained from these sorption experiments.     

Thermodynamic of Water Sorption of Grape Seed: Temperature Effect of Sorption Isotherms and Thermodynamic Characteristics

After determination of sorption isotherms of grape seeds using gravimetric method, five models with temperature effect were used to fit water sorption isotherms of grape seeds to investigate temperature effect on sorption isotherms and its thermodynamic characteristics. Halsey model had minimum mean relative percentage error (M _e ) and all other models used were good in fitting experimental data (with M _e of less than 10 %). Differential parameters such as net isosteric heat, isosteric heat, differential entropy and integral function such as equilibrium heat, net equilibrium heat, integral entropy and surface potential have been calculated. The net isosteric heat, isosteric heat and differential entropy decreased with moisture content. The net equilibrium enthalpy, equilibrium enthalpy and integral entropy decreased with moisture content. The surface potential at four temperatures (35, 45, 55 and 65 °C) was estimated, and low temperature effect was reported.     

Excess enthalpies of aqueous solutions of mono- and oligo-saccharide at 25°

The heats of dilution in water of d-xylose, d-fructose, d-galactose, d-mannose, lactose, and raffinose have been determined calorimetrically at 25°. The calorimetric data, expressed in terms of excess enthalpy, lead to an evaluation of pair- and triplet-interaction coefficients. Osmotic data, where known, permit the analogous coefficients of the excess free energy to be obtained and thence those of the excess entropy. Analysis of the excess functions and comparison with spectroscopic properties permits some qualitative hypotheses to be formulated on the molecular interactions occurring in these solutions.     

Water sorption-desorption in conifer cuticles: The role of lignin

Current information on the type and amount of biopolymers present in the epidermis of conifer species is still insufficient. This work presents the detailed morphology and chemical composition of Araucaria bidwillii cuticle after selective treatments to remove the different types of biopolymers. After removal of the waxes, cutin and polar hydrolyzable components, a lignin-like fraction, which makes up 25% of the initial cuticle weight, was identified by GC-MS and infrared spectroscopy. The isolated lignin is of G type, mainly formed by guaiacyl units. This composition indicates that the conifer cuticle investigated here has similar composition to other conifer-isolated cuticles. Water sorption and desorption by the isolated cuticle and the different cuticle fractions, including lignin, were studied. The analysis of the isotherms, following distinct physicochemical models, gave useful information on the structural and physiological role of the different biopolymers present in the cuticle. Lignin fraction showed both a high water sorption and capability of retaining it in comparision to other cuticle components. Hysteresis effect on water sorption–desorption cycle and water cluster formations has also been studied, and their physiological role discussed.     

Prediction of adsorption equilibria of water–methanol mixtures in zeolite NaA by molecular simulation

Predictions for the adsorption of mixtures of water and methanol in zeolite NaA are reported. The pressure dependence of the adsorption properties such as equilibrium amounts of adsorption and isosteric heats of adsorption are calculated at 378 K by molecular simulations using effective pair potential models. These data are also determined for the adsorption from liquid mixtures. The models predict selectivity inversion in the investigated range of pressure. The change in adsorption ratios can partly be explained by the structural characteristics of the system.     

Moisture Sorption Isotherms of Broccoli Interpreted with the Flory-Huggins Free Volume Theory

In this work, the Flory Huggins Free Volume theory is used to interpret the sorption isotherms of broccoli from its composition and using physical properties of the components. This theory considers the mixing properties of water, biopolymers and solutes and has the potential to describe the sorption isotherms for varying product moisture content, composition and temperature. The required physical properties of the pure components in food became available in recent years and allow now the prediction of the sorption isotherms with this theory. Sorption isotherm experiments have been performed for broccoli florets and stalks, at two temperatures. Experimental data shows that the Flory Huggins Free Volume (FHFV) theory represents the sorption isotherm of fresh and blanched broccoli samples accurately. The results also show that blanching affects the sorption isotherm due to the change of composition via leaching solutes and the change of interaction parameter due to protein denaturation.     

Atomic simulation of Xe and Kr separation in silica-templated amorphous mesoporous carbons CMK-3 and CMK-5

We perform a molecular simulation study on adsorption and separation of the noble gases Xe and Kr in silica-templated amorphous mesoporous carbons (CMK) materials. We generate the atomic models of CMK-3 and CMK-5 materials by adsorbing carbon in a model MCM-41 pore. Our carbon structures can capture the surface roughness and the disordered nature of the carbon rods and carbon pipes as reported in the experiment. The adsorption isotherms and isosteric heats of pure gases have been examined further. We find that the existence of the carbon interconnections between nanorods for CMK-3 and between nanopipes for CMK-5 will reduce the excess uptakes of the noble gases, whereas the isosteric heats are favoured in the materials with interconnections. The carbon interconnections are not advantageous to the adsorption storage of pure gases, but they can improve the separation ability of Xe for gas-mixture adsorption. The effects of temperature and concentration on the Xe separation are investigated and it is shown that the selectivities of Xe in the CMK-5 materials are insensitive to the two factors. We also find that both gas storage and separation of CMK materials are comparable to IRMOF-1 and UMCM-1 metal-organic frameworks.     

Zinc consumption from the nutrient medium of Trichosporon capitatum and Aspergillus niger]

The sorption capacity of the cultures Trichosporon capitatum and Aspergillus niger towards zinc dissolved in the culture liquid was studied by radio active labelling. The curves of sorption kinetics and the so-called sorption quasi-isotherms showing the dependence of zinc sorption by the microbial biomass upon zinc concentration in the liquid medium were derived. For the Aspergillus niger culture at zinc concentrations of 0.5 to 52 mug/ml the sorption quasi-isotherm was linear. The zinc extraction by microorganisms was related not only to the physico-chemical sorption but also to the zinc accumulation in the cell biopolymers. The paper presents calculations of the microbiological purification of sewage waters from zinc by means of the Aspergillus niger culture.     

Effect of glycerol on behaviour of amylose and amylopectin films

The effect of water and glycerol on sorption and calorimetric T_gs of amylose and amylopectin films were examined. The mechanical properties of the films were also analysed under varying glycerol content at constant RH and temperature. Based on changes observed in sorption and tensile failure behaviour glycerol was strongly interacted with both starch polymers. Even though water was observed to be more efficient plasticiser than glycerol, glycerol also affected the T_g. But in spite of the observed decrease in T_g under low glycerol contents brittleness of the films increased based on changes in elongation. The increase in brittleness of both polymers was also in agreement with their actual behaviour. At around 20% glycerol great change in the rheological properties occurred. Above 20% glycerol amylose film showed much larger elongation than the low glycerol content films and was still strong but the amylopectin produced a very week and non-flexible film.     

Water sorption isotherms and enthalpies of water sorption by lysozyme using the quartz crystal microbalance/heat conduction calorimeter

The water sorption isotherm and the water vapor activity dependence of the enthalpy of water sorption Delta(sorp)Hdegrees of lysozyme have been measured at 25 degrees C. A thin film of lysozyme of mass 250 microg was exposed to H2O/N2 mixtures in a quartz crystal microbalance/heat conduction calorimeter (QCM/HCC). The QCM/HCC is a new gravimetric/calorimetric method that measures simultaneously and with high precision the mass change and the corresponding heat flow in a thin film exposed to a gas. Delta(sorp)Hdegrees for lysozyme agrees with previous determinations, although hysteresis effects are evident in the data. No van't Hoff analysis is necessary because sorption enthalpies are measured calorimetrically. The water vapor activity dependence of Delta(sorp)Hdegrees agrees with that measured previously by Bone. As the water content of the lysozyme film drops below 10 mass%, Delta(sorp)Hdegrees becomes more exothermic, indicating that water is being bound to the charged or highly polar groups of the solvent-accessible surface of lysozyme. The dynamics of water uptake and release from lysozyme thin films are much slower than in polymer films of comparable thickness. Because the QCM/HCC operates with sub-milligram samples, any protein is now amenable to study by this technique.     

Removal of selenium and arsenic by animal biopolymers

The animal biopolymers prepared from hen eggshell membrane and broiler chicken feathers, which are byproducts of the poultry-processing industry, were evaluated for the removal of the oxyanions selenium [Se(IV) and Se(VI)] and arsenic [As(III) and As(V)] from aqueous solutions. The biopolymers were found to be effective at removing Se(VI) from solution. Optimal Se(IV) and Se(VI) removal was achieved at pH 2.5–3.5. At an initial Se concentration of 100 mg/L (1.3 m M), the eggshell membrane removed approx 90% Se(VI) from the solution. Arsenic was removed less effectively than Se, but the chemical modification of biopolymer carboxyl groups dramatically enhanced the As(V) sorption capacity. Se(VI) and As(V) sorption isotherms were developed at optimal conditions and sorption equilibrium data fitted the Langmuir isotherm model. The maximum uptakes by the Langmuir model were about 37.0 mg/g and 20.7 mg/g of Se(VI) and 24.2 mg/g and 21.7 mg/g of As(V) for eggshell membrane and chicken feathers, respectively.     

Effect of dioxane molecules on the hydration shell of polypeptides

Our interest in the modifying influence of low-molecular-weight organic compounds on the hydration shell of biopolymers is due to a well-known fact that the former can act as regulators of the enzymatic activity changing the hydration shell of the latter. Dioxane was chosen because of its wide application in non-aqueous biocatalysis. In the present study, we investigate the mechanisms of dioxane influence on water of the first hydration layer of the model polypeptides by FTIR-spectroscopy during simultaneous sorption of water-dioxane vapors into the polypeptide films at low water activity. It was found that modification of the hydration shell of the polypeptides studied was mainly due to the indirect ordering of polypeptide secondary structure with the penetration of dioxane molecules under these conditions.     

NMR spin-echo study of the effect of hydration on the mobility and conformation of linear polyethyleneimine]

It has been shown that mobility of protons in different groups of linear polyethylenimine (LPEI) is sensitive to the formation of H-bonds between amino groups of a polymer. Upon hydration of LPEI most of direct bonds between amino groups are substituted by the bonds via water molecules. This results in a conformational change of the polymer. Similar process may also occur in biopolymers.     

Deuteration and solvent composition effects in the helix–coil transition of poly-γ-beiizyl-L-glutamate

The effects of deuteration and of changes in solvent composition on the thermo dynamics of the helix–coil transition have been studied by calorimetric and optical measurements in the poly-γ-benzyl-L -glutamate–dichloroacetic acid–1,2-dichloro-ethanc system. For a given solvent composition, deuteration of the polypeptide and of the acid lowers the transition temperature T_c, while an increase in the volume fraction of acid in the solvent raises T_c. A rise in T_c is accompanied by a decrease in both the van't Hoff and the calorimetric heats of transition, but at different rates. The result is a temperature dependency in the Zimm-Bragg cooperation parameter σ. Possible causes of this result and its implications are discussed.     

Effect of inhibitor complex formation on the hydration properties of alpha-chymotrypsin. Changes induced in protein hydration by toxylation of the native enzyme

The effect of enzyme-inhibitor complex formation on the hydration properties of the macromolecular moiety was investigated on the model system of α-chymotrypsin and its Ser-195 tosyl derivative. The primary (A-shell) hydration of the native and modified enzyme was compared by sorption measurements. The secondary (B-shell) hydration water was investigated by differential scanning calorimetry. Tosylation is known to induce pronounced conformational changes in the chymotrypsin molecule. These structural modifications have the following effects on the hydration of the native enzyme. The water binding capacity of the protein surface is significantly increased, as shown by both the calorimetric and the sorption results. The amount of unfreezable water of primary hydration is increased by 50 mol H₂O/mol chymotrypsin. The heats (ΔH ) and entropies (ΔS ) of the interaction of water with chymotrypsin are strongly reduced in the modified enzyme. This effect is interpretable by a reduction of the H bonding potential of the protein surface. Parallel to this decrease in δH , the heats of fusion of the secondary hydration water (Q_fus) are significantly increased by tosylation (Q_fus = 256.2 ± 7.8 and 294.2 ± 4.8 J g^?1 H₂O for the native and the tosylated enzyme, respectively). This increase in Q_fus reflects an increase in the extent of H bonding in the B-shell hydration sphere. These changes in the hydration of the native enzyme, associated with the reaction: native chymotrypsin → tosylchymotrypsin, are interpreted by cooperative phase transitions of water molecules in the primary and secondary hydration water. One of these transitions was found to exhibit a significant, linear enthalpy–entropy compensation effect. The compensation temperature \documentclass{article}\pagestyle{empty}\begin{document}$ \hat{\beta} $\end{document} is 290.7 ± 2.8°K. This \documentclass{article}\pagestyle{empty}\begin{document}$ \hat{\beta} $\end{document} value agrees well with compensation temperatures reported in the literature for a series of biochemical reactions in aqueous solution (250–320° K). This agreement in \documentclass{article}\pagestyle{empty}\begin{document}$ \hat{\beta} $\end{document} may point to a common source of both compensation phenomena.     

Energies of freezing and frost desiccation

A stable cellulose paper system was studied to relate water distribution data, as obtained previously from plant tissues, to the analysis of freezing energy. Water distribution data for the cellulose system were obtained by several techniques and were coordinated with calorimetric data. The effect of the cellulose system on the latent heat of freezing was evaluated to estimate activation energies as functions of the amount of associated liquid water. Similar activation energies of water phase transitions in critical plant tissue systems may be heritable characteristics that affect freezing stress. Adhesion energy, that develops between ice and hydrophilic polymer systems as they compete for liquid water in a complex interface, was suggested as one possible source of freezing stress. This does not occur in frost desiccation.