Searching the most optimal model of water sorption on foodstuffs in the whole range of relative humidity

Physical, chemical, sorption and microbiological characteristics of fennel fruits

Fennel (Foeniculum officinale Mill. var. dulce Mill) is an annual aromatic plant of the Lamiaceae family. Its fruits are processed to obtain essential oil for use in the food industry and cosmetics. The physical parameters of the fruits, i.e. length (5.50-8.00 mm), width (1.50-2.00 mm), volume of 100 fruits (1.36 × 10-6 m3), density of 100 fruits (935.82 kg/m3), average volume of one fruit (1.36 × 10-8 m3), average equivalent diameter of one fruit (2.96 mm), angle of repose, stainless steel (from 16 to 22°), angle of repose, black steel (from 19 to 28°), angle of repose, plywood (from 18 to 24°), and their chemical parameters, i.e. moisture (13.49%), ash (6.49%), protein (18.25%), essential oil (8.38%), vegetable oil (10.52%), and total carbohydrates (51.04%) were determined for the fruits. The adsorption and desorption isotherms of the fennel fruits were obtained using the static gravimetric method at two temperatures, 20 and 40 °C. The Halsey model provided a good description of the sorption isotherms, which were of type II according to Brunauer's classification. The increase in the temperature led to a significant decrease in the monolayer moisture. The contamination on the fruit surface at three relative humidities (0.43, 0.59, and 0.76) at 20 °C was determined.

Analysis of molecular mobility in corn and quinoa flours through 1H NMR and its relationship with water distribution, glass transition and enthalpy relaxation

Solids-water interactions of corn and quinoa flours were evaluated through ¹H NMR, DSC, and water sorption isotherms. Glass transition temperature (T_g), observed by DSC, was better distinguished through FID signals, and correlated to water content through the Gordon and Taylor model. Enthalpy relaxations, identified by thermal analysis at 50-70 °C were studied through transverse relaxation times (T₂) measured after Hahn spin-echo sequence, which revealed a rearrangement of the biopolymers structures that cause immobilization of polymer chains and reduced mobility of water molecules with weak interactions with solids (lower T₂₂). The higher lipid content of quinoa flour was manifested after the CPMG sequence (T₂ ≈ 100 ms) and caused reduced hygroscopicity and T_g values compared with corn flour systems. ¹H NMR resulted efficient for assigning proton populations and understanding the changes in their distribution with temperature, analyzing glass transition and interpreting the implications of enthalpy relaxations processes in corn and quinoa flours.

Exploration on self-equilibrium rule and adsorption-desorption model between pine nut (Pinus koraiensis) peptide molecules and environmental moisture molecules

The storage of pine nut (Pinus koraiensis) peptide (PNP) powder involves hygroscopic phenomena. To investigate the adsorption and self-equilibrium rules between these peptides and the environmental moisture molecules, several studies such as low-field nuclear magnetic resonance (LF-NMR), dynamic vapor sorption (DVS) and adsorption-desorption models were done. The results showed that the outward moisture migration occurred during storage as 7.80% and 16.68% moisture were respectively constrained by the original sample and 90 days after lyophilization, by chemical bonding. Additionally, 1.79% moisture was lost in PNP powder at day 90. The optimized adsorption model for PNP powder was changed from Henderson's to Oswin's model during the 90 days' storage whereas the optimized desorption model was changed from Halsey's to GAB's model. The PNP powder at day 90 presented smaller particles with an average diameter and height of 15.645 nm and 50 nm, respectively, and it contained more molecular moisture which cannot be removed. The free thiol of the PNP powder at day 0 and day 90 was 1.75 ± 0.16 μM SH/g and 1.95 ± 0.16 μM SH/g, respectively, and the total sulfhydryl was 101.46 ± 1.06 μM SH/g and 118.44 ± 1.27 μM SH/g. The registered increased sulfhydryl content contributed to the generation of off-flavor.

Moisture sorption properties and glass transition temperature of a non-conventional exudate gum (Prosopis alba) from northeast Argentine

Water-solid interactions were explored in purified and freeze-dried Prosopis alba exudate gum as approach to get a deeper insight of structural and functional aspects of this novel biomaterial. Particularly, the study of water-binding properties combined with glass transition temperatures allowed obtaining interesting theoretical data for practical applications. The Guggenheim-Anderson-de Boer (GAB) and Generalized D'Arcy and Watt (GDW) models were applied to describe the sorption behavior and thermodynamic properties of the studied gum. The study of the relationship between relative humidity, water content and thermal transitions allowed to characterize the material in terms of water plasticizing susceptibility as well as define the suitable storage conditions that guarantee the quality, safety and physical stability of P. alba gum. Obtained results contribute to the characterization of a non-conventional exudate gum with great potential for its use in different food industry applications.

Inactivation of Lipase and Lipoxygenase of Wheat Germ with Temperature-Controlled Short Wave Infrared Radiation and Its Effect on Storage Stability and Quality of Wheat Germ Oil

Wheat germ (WG) is quite susceptible to deterioration due to the presence of lipase (LA) and lipoxygenase (LOX). Therefore it is indispensable to adopt a stabilization step to decrease the activity of LA and LOX while retaining a maximum level of nutrients. But over-drying can make foodstuffs more susceptible to autoxidation. So a stabilization protocol for inactivating LA and LOX of WG with a temperature- controlled short wave infrared (SIR) radiation system was adopted to retard its rancidity and retain a maximum level of fat-soluble nutrients. Meanwhile, the critical storage water activity (Aw) of WG for inhibiting both hydrolytic and oxidative rancidity was appraised. Results indicate that WG irradiated at 90°C for 20 min acquired the optimal stabilization effect, and its residual LA and LOX activity were 18.02% and 19.21%, respectively. At this condition, the free fatty acids (FFA) content and peroxide value (PV) increment of WG oil at 40°C remained below 5% and 2.24 meq O2/kg for 60 days, respectively. The residual Aw of this WG sample was 0.13, and it is near the Aw corresponding to its monolayer. No significant decrease of fatty acids was observed during SIR processing, while about 96.42% of its original tocopherols still retained in WG treated at 90°C for 20 min.

Influence of activated carbon porosity and surface oxygen functionalities' presence on adsorption of acetonitrile as a simple polar volatile organic compound

Based on series of porous carbon models, systematic Monte Carlo studies on the adsorption of acetonitrile (as a simple representative of polar volatile organic compounds) were performed. The influence of porosity and chemical composition of the carbon surface on CH3CN adsorption was studied and it was shown that both the factors influenced the adsorption mechanism. A decrease in the pore size and the introduction of oxygen surface groups led to a rise in adsorption energy and to an increase in the filling of accessible volume in the low-pressure part of the isotherm. However, from a practical point of view, it is easier to increase the adsorption by introducing polar groups on the carbon surface than by modifying the porosity.

Applicability of molecular simulations for modelling the adsorption of the greenhouse gas CF4 on carbons

Tetrafluoromethane, CF(4), is a powerful greenhouse gas, and the possibility of storing it in microporous carbon has been widely studied. In this paper we show, for the first time, that the results of molecular simulations can be very helpful in the study of CF(4) adsorption. Moreover, experimental data fit to the results collected from simulations. We explain the meaning of the empirical parameters of the supercritical Dubinin-Astakhov model proposed by Ozawa and finally the meaning of the parameter k of the empirical relation proposed by Amankwah and Schwarz.

Heterogeneity of the state and functionality of water molecules sorbed in an amorphous sugar matrix

An amorphous matrix, comprised of sugar molecules, is frequently used in the pharmaceutical industry. An amorphous sugar matrix exhibits high hygroscopicity, and it has been established that the sorbed water lowers the glass transition temperature T(g) of the amorphous sugar matrix. It is naturally expected that the random allocation and configuration of sugar molecules would result in heterogeneity of states for sorbed water. However, most analyses of the behavior of water, when sorbed to an amorphous sugar matrix, have implicitly assumed that all of the sorbed water molecules are in a single state. In this study, the states of water molecules sorbed in an amorphous sugar matrix were analyzed by Fourier-transform IR spectroscopy and a Fourier self-deconvolution technique. When sorbed water molecules were classified into five states, according to the extent to which they are restricted, three of the states resulted in a lowering of T(g) of an amorphous sugar matrix, while the other two were independent of the plasticization of the matrix. This finding provides an explanation for the paradoxical fact that compression at several hundreds of MPa significantly decreases the equilibrium water content at a given RH, while the T(g) remains unchanged.

The influence of the carbon surface chemical composition on Dubinin-Astakhov equation parameters calculated from SF6 adsorption data-grand canonical Monte Carlo simulation

Using grand canonical Monte Carlo simulation we show, for the first time, the influence of the carbon porosity and surface oxidation on the parameters of the Dubinin-Astakhov (DA) adsorption isotherm equation. We conclude that upon carbon surface oxidation, the adsorption decreases for all carbons studied. Moreover, the parameters of the DA model depend on the number of surface oxygen groups. That is why in the case of carbons containing surface polar groups, SF(6) adsorption isotherm data cannot be used for characterization of the porosity.

The system of carbon tetrachloride and closed carbon nanotubes analyzed by a combination of molecular simulations, analytical modeling, and adsorption calorimetry

Using the combined techniques of molecular simulation, simple analytical modeling, and adsorption calorimetry, we propose new models describing adsorption onto closed carbon nanotubes. The models are capable of describing the adsorption isotherms and calorimetric enthalpy of carbon tetrachloride adsorption measured on three different closed carbon nanotubes. It is shown that the assumption of the presence of two types of surface centers (high- and low-energy centers) on external tube surfaces is sufficient to describe experimental adsorption and calorimetric enthalpy data.