Moisture Adsorption Isotherms Research Articles

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.

Exploring moisture adsorption on cobalt-doped ZnFe2O4 for applications in atmospheric water harvesting.

Sorption-based atmospheric water harvesting (SBAWH) is a highly promising approach for extracting water from the atmosphere thanks to its sustainability, exceptional energy efficiency, and affordability. In this work, ZnFe2O4 and Zn0.4Co0.6Fe2O4 were evaluated for moisture adsorption. The desired materials were synthesized by a surfactant-assisted sol-gel method. Synthesized samples were characterized using X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, vibrating sample magnetometry (VSM), and point of zero charge (PZC). Crystallinity and phase composition were evaluated by XRD analysis. Several parameters were determined using XRD analysis: lattice parameter, unit cell volume, crystallite size, and bulk density. The morphology of synthesized materials was assessed via SEM, and unveiled the acquisition of consistent, homogeneous, and uniform crystals. Elemental composition was determined through EDX spectroscopy. Water adsorption on the surface was evaluated by FTIR spectroscopy. The magnetic properties of synthesized ZnFe2O4 and cobalt-doped ZnFe2O4 ferrites were investigated using VSM. The negative charge on the Zn0.4Co0.6Fe2O4 surface was explored using PZC. Adsorption studies on synthesized materials were conducted with the help of an atmospheric water harvesting (AWH) plant created by our team. Moisture adsorption isotherms of synthesized materials were determined using a gravimetric method under varying temperature and relative humidity (45-95%) conditions. The moisture content (Mc) of Zn0.4Co0.6Fe2O4 and ZnFe2O4 was 597 mg g-1 and 104 mg g-1, respectively. Key thermodynamic properties, including isosteric heat of adsorption (Qst), change in Gibbs free energy (ΔG), and change in sorption entropy (ΔS), were evaluated. Qst was negative, which confirmed the sorption of water vapors on the material surface. ΔG and ΔS indicated that water-vapor adsorption was spontaneous and exothermic. A second-order kinetics study was carried out on synthesized materials, demonstrating their chemisorption behavior. The latter was due to the oxygen defects created by replacement of Co2+ and Fe3+ at tetrahedral and octahedral sites. Water vapors in the atmosphere became attached to the surface and deprotonation occurred, and the hydroxyl ions were formed. Water vapor attached to these hydroxyl ions. A second-order kinetics study was carried out to confirm the chemisorption behavior of synthesized materials.

Sorption Isotherms and Thermodynamic Characteristics of Gelatin Powder Extracted from Whitefish Skin: Mathematical Modeling Approach.

Moisture adsorption and desorption isotherms of gelatin extracted from whitefish skin powder (FSGP) at different temperatures across a wide range of water activity were determined along with their thermodynamic properties. Nine mathematical models were utilized for fitting the experimental data and simulating the adsorption and desorption behavior. The thermodynamic properties were determined and fitted to the experimental data. The results showed that Peleg and GAB models were the best fit for FSGP. The energies involved in the adsorption and desorption process of FSGP indicated a stronger dependence on equilibrium moisture content (Xe). When Xe decreased, there was a consistent trend of increasing thermodynamic properties. Both the moisture adsorption and desorption behaviors of FSGP were, therefore, non-spontaneous processes. Linear correlations between the changes in enthalpy and entropy for adsorption and desorption were observed, indicating the presence of enthalpy-entropy compensation for FSGP. For preserving FSGP quality, it should be stored with Xw ≤ 8 (gw/gdm, d.b.) at temperatures below 53 °C and an RH of 50% to avoid it becoming rubbery. These findings are crucial for providing insight into the optimal drying and storage conditions.

A 3D multi-scale hygro-mechanical model of oak wood

A multi-scale framework is proposed for the prediction of the macroscopic hygro-elastic properties of oak wood. The distinctive features of the current multi-scale approach are that: (i) Four different scales of observation are considered, which enables the inclusion of heterogeneous effects from the nano-, micro-, and meso-scales in the effective constitutive behavior of oak at the macro-scale, (ii) the model relies on three-dimensional material descriptions at each considered length scale, and (iii) a moisture-dependent constitutive assumption is adopted at the nano-scale, which allows for recovering the moisture dependency of the material response at higher scales of observation. In the modeling approach, oak wood is assumed as homogeneous at the macro-scale. The meso-scale description considers the cellular structure of individual growth rings with three different densities. At the micro-scale, the heterogeneous nature of cell walls is described by the characteristics of the primary and secondary cell wall layers. Finally, the nano-scale response is determined by cellulose micro-fibrils embedded in a matrix of hemicellulose and lignin. The oak properties at the four length scales are connected via a three-level homogenization procedure, for which, depending on the geometry of the fine-scale configuration, an asymptotic homogenization procedure or Voigt averaging procedure is applied at each level to determine the effective hygro-elastic properties at the corresponding coarse scale. In addition, the moisture adsorption isotherms at each scale are constructed from a volume-weighted averaging of the moisture adsorption characteristics at the scale below. The computational results demonstrate that the macro-scale moisture-dependent, hygro-elastic behavior of oak wood is predicted realistically, thereby revealing the influence of the material density, the micro-fibril orientation, and the hygro-elastic properties from the underlying scales. The computed macro-scale properties of oak are in good agreement with experimental data reported in the literature.

Impact of Treatment with Superheated Steam on the Structural, Thermal, and Functional Characteristics of Quinoa Starch

AbstractThe objective of the study is to evaluate the impact of treatment with superheated steam on the structural, thermal, and functional characteristics of quinoa starch. The superheated steam treatment is applied to the starch at 130 and 170 °C for 1 and 4 min, then dried at 50 °C and stored. Moisture adsorption isotherms are performed at 25 °C, and data are fitted to the Oswin, GAB, and Peleg models. Structural characterization is done using XRD and FTIR, thermal analysis using DSC, and functional characterization include water absorption capacity (WAC), oil absorption capacity (OAC), and syneresis. The QS170/4 treatment shows a reduction in crystallinity index of up to 48.24%, with the appearance of the amylose‐lipid complex, an increase in initial and final gelatinization temperatures, and a decrease in enthalpy of up to 39.53%. For modified starches, WAC and OAC increase by 9% and 7%, respectively, and syneresis decreases significantly by 17.4%. The results demonstrate the feasibility of modifying quinoa starch with superheated steam treatment, which, unlike other methods, has the advantage of altering the amylose and amylopectin chains in just a few minutes. Thus, the results show a new perspective for the use of superheated steam in starch modification.

Water adsorption isotherms and phase transitions of spray-dried chickpea beverage

Chickpea hydrolysate powders were obtained by spray-drying (70 and 60 °C as outlet and 180 °C inlet air temperatures), using inulin and maltodextrin as adjuvants (12 or 25 g/100 g solids). No effects of the variables studied were observed on solubility (88–93 g/100 g solids) and final moisture (3.50–6.15 g/100 g db). Yields were 49.44–61.24 and 44.53–51.55% at 70° and 60 °C respectively. Moisture adsorption isotherms (25°, 35° and 45 °C) were obtained by dynamic dew point method and modeled with GAB and BET equations. BET monolayer moisture values (5.53–9.66 g/100 g db), were slightly different and higher than those obtained for the GAB model. Critical values of water activity (awc) and critical moisture (Mc), related with phase transitions, were determined using the second derived from moisture change with respect to water activity (Sovitsky-Golay 2nd derivate). At 25 °C the highest awc and Mc values, 0.515 and 0.535, and 8.5 and 9.35 g/100 g db occur for products dried at 60 °C and with the lowest level of both adjuvants, while the product without adjuvant has an awc and Mc f 0.466 and 7.46 g/100 g db. The increase in awc and Mc, due to the presence of the inulin and maltodextrin reflects their protective effect. According to these results spray-drying (Tout = 60 °C) could be used to generate a stable dehydrated hydrolysate chickpea beverage basis using 12.5 g/100 g db of the adjuvants evaluated.

Hermetic storage of okra seed maintains seed longevity under changing environment.

Okra seed is vulnerable to loss of germination and vigor in variable storage conditions. High seed moisture contents (SMC) accelerate seed deterioration during storage thus keeping low seed moisture contents by storing seed in hermetic bags may help to retain seed longevity. Okra seed was equilibrated to four initial moisture levels including 8,10, 12 and 14% SMC. Seed was then packed and stored in traditional storage bags (Paper, cloth, polypropylene and jute bag) and hermetic Super Bag for 12 months under ambient conditions. Seed stored in hermetic Super Bag at 8 and 10% moisture contents maintained higher germination due to low seed moisture contents. Moreover, activities of α-amylases and total soluble sugars were higher while electrical conductivity of seed leachates, malondialdehyde (MDA) and reducing sugar contents were less in the seeds stored in hermetic Super Bag at 8 and 10% SMC as compared to seed stored in traditional storage bags. Hermetic storage at 14% moisture negatively influenced the seed quality. Moisture adsorption isotherms of okra seeds were developed at constant temperature of 25°C and varying levels of relative humidity from 60 to 90%. Moisture isotherms indicated no significant increase in seed moisture contents at 60 and 70% relative humidity (RH) in hermetic bags whereas a minor increase in seed moisture at 80 and 90% RH has been observed for the seeds incubated in hermetic bags. SMC significantly increased in traditional storage bags particularly in jute bag at high RH. In conclusion, storage in hermetic bags, maintain low seed moisture and high seed quality. Okra seed storage in hermetic bags at 8 and 10% SMC maintains seed longevity under ambient storage conditions.

Contrasting seed moisture sorption behaviour between two species and the implication for seed longevity

AbstractUnderstanding seed moisture desorption and adsorption isotherms is important for seed quality maintenance and better predicting seed storage lifespan. Freshly harvested oilseed rape and barley seeds were dried and then rehydrated twice. Seed equilibrium relative humidity (eRH) and moisture content (MC) were determined at different humidity levels so that two cycles of desorption and adsorption could be constructed. In addition, seeds were dried to 30% RH and then rehydrated to 50% RH for five cycles to determine whether they shift to the adsorption isotherm. Monolayer MC was determined using the Gugenheim-Anderson-de Boer model. Storage experiments were conducted for seeds equilibrated at 30, 40, 50, 60 and 70% RH for two cycles of desorption and adsorption at 45°C. Isotherm curves’ shapes were similar for oilseed rape and barley, although spanning a greater MC range in barley. The hysteresis effect was observed for oilseed rape and barley seeds when dried over silica gel at <10% RH. However, this effect was only observed for barley seeds when dried to 30% RH, but not for oilseed rape seeds. Longevity was greater for adsorbing seeds than desorbing seeds at a given eRH, however, there was no significant difference in σ (the standard deviation of the normal distribution of seed deaths over time)–MC log–log relationship. The relationship shifted for seeds on the second cycle. In conclusion, if seed lots are stored at a specific RH, reaching equilibrium by desorption or adsorption can strongly influence their longevity. Also, when seeds of different species are dried to low RH, they will respond differently to a subsequent increase in RH, which could profoundly affect their longevity.

Moisture adsorption isotherms properties of dried overripe barlin fruit (Musa acuminata AA.) powder

Moisture sorption of dried overripe barlin banana powder using the static gravimetric method. The materials were conditioned at 5, 10, and 25 oC with a water activity range of 0.16 to 0.86. Five mathematical models to describe the suitability of the phenomenon of adsorption experimental data using non-linear regression. The thermodynamic properties such as isosteric heat and Gibbs free energy are evaluated in this paper. The experimental results indicated that the equilibrium moisture content of dried overripe barlin banana powder increased with increasing water activity and decreasing temperature. The results of the model are based on the goodness of fit, and the Peleg model is the most suitable for describing the adsorption phenomenon with the type II sigmoidal shape. Monolayer moisture content and adsorption surface area using the GAB model are in the range of 6.18-7.81%d.b and 219.09-246.39 m2/g d.b, respectively, which increases with increasing temperature. Moreover, isosteric heat decreases with an increase in equilibrium moisture content and is opposite to the value of Gibbs free energy. In addition, the hygroscopicity of the dried overripe barlin banana powder increased with temperature and water activity.

Water adsorption properties of microalgae powders: Thermodynamic analysis and structural characteristics

Moisture adsorption isotherms and thermodynamic properties of dried Chlorella pyrenoidesa and Spirulina platensis powders were investigated by using a static gravimetric at temperatures of 20, 30, and 40 °C and within aw range of 0.112–0.976. Structural characteristics involving morphology, functional group, surface element composition, pore size distribution, and surface area were analyzed to explore the water adsorption mechanism. FTIR and XPS analysis indicated that spirulina powder had a higher proportion of hydrophilic sites to bind water molecules in comparison with chlorella powder. BET surface area for chlorella and spirulina powders were 25.10 and 25.19 m2/g, respectively. Water adsorption data were adjusted using a variety of sorption models, and the GAB equation was the most appropriate for representing the experimental data in the studied aw and temperature range. The monolayer moisture content (Xm) values at 20, 30 and 40 °C were 0.0526, 0.0483, and 0.0456 g/g dry basis for chlorella powders, and 0.0581, 0.0553, and 0.0420 g/g dry basis for spirulina powders, respectively. The net isosteric heat (Qst) and differential entropy (δSdif) for both microalgae powders decreased with an increase in water content. Using the compensation theory, we determined that the processes were governed by the enthalpy and that they were non-spontaneous (δG>0) for the samples. Both microalgae powers were classified as micro and mesoporous materials, and the pore radius (Rp) varied from 1.481 to 23.694 nm for chlorella powders and from 1.193 to 39.392 nm for spirulina powders, respectively.

Comparison of critical storage parameters of the powders containing soy protein isolate and inulin, based on the concepts: Water activity and Temperature of glass transition

In this study water activity and glass transition concepts were used to evaluate stability of the two component powder systems containing inulin and soy protein isolate. Moisture adsorption isotherms of soy protein powder with 25, 50 and 75 g of inulin on 100 g powders additions at 25 °C were determined by static gravimetric method. The experimental data obtained were fitted to three mathematical models. All curves exhibit sigmoidal shape corresponding to type II isotherms. The monolayer moisture content for GAB (Guggenheim–Anderson–Boer) model obtained for powder systems varied between 0.0647 and 0.0739 g water/g dry solids. Thermal transitions of equilibrated powders were analyzed using differential scanning calorimetry and glass transition curves were plotted by Gordon–Taylor equation. The highest value of glass transition temperature of anhydrous solid was calculated for soy protein without inulin addition. In order to investigate optimum storage conditions diagrams including water activity, equilibrium moisture content and glass transition relationship were constructed by using Khalloufi–El-Maslouhi–Ratti equation. Critical moisture content values of the powders estimated based on both, water activity and glass transition concepts, were significant higher than corresponding them monolayer capacity values.

An Equilibrium State Diagram for Storage Stability and Conservation of Active Ingredients in a Functional Food Based on Polysaccharides Blends.

A functional food as a matrix based on a blend of carbohydrate polymers (25% maltodextrin and 75% inulin) with quercetin and Bacillus claussi to supply antioxidant and probiotic properties was prepared by spray drying. The powders were characterized physiochemically, including by moisture adsorption isotherms, X-ray diffraction (XRD), scanning electron microscopy (SEM), and modulated differential scanning calorimetry (MDSC). The type III adsorption isotherm developed at 35 °C presented a monolayer content of 2.79 g of water for every 100 g of dry sample. The microstructure determined by XRD presented three regions identified as amorphous, semicrystalline, and crystalline-rubbery states. SEM micrographs showed variations in the morphology according to the microstructural regions as (i) spherical particles with smooth surfaces, (ii) a mixture of spherical particles and irregular particles with heterogeneous surfaces, and (iii) agglomerated irregular-shape particles. The blend's functional performance demonstrated antioxidant activities of approximately 50% of DPPH scavenging capacity and viability values of 6.5 Log10 CFU/g. These results demonstrated that the blend displayed functional food behavior over the complete interval of water activities. The equilibrium state diagram was significant for identifying the storage conditions that promote the preservation of functional food properties and those where the collapse of the microstructure occurs.

Physicochemical, Rheological and Moisture Adsorption Characteristics of Two Basmati Rice (<em>Oryza sativa</em> L.) Varieties Differing in Amylose Content

Purpose: The purpose of this study was to determine the physicochemical, viscosity and moisture sorption properties of high-amylose (At-306) and low-amylose (At-405) basmati varieties. Research Method: The viscometer method was used to measure the apparent viscosity of the flour samples at 65 and 75°C. Moisture adsorption isotherms were determined by the gravimetric method at 28, 35 and 45°C. Findings: The bulk-density, grain-hardness, gelatinization temperature, protein and amylose contents of the At-306 and At-405 varieties were in the range of 794-780 kg m-3, 55.5-49.7 N, 70.34-66.14°C and 8.80-8.00% and 26.70-15.37%, respectively. At-405 samples showed significantly higher viscosity (8-13.5 Pa s) at 65°C and lower viscosity (1.4-5.3 Pa s) at 75°C but the opposite trend was observed for the At- 306. The flow behavior index, varied with temperature between 0.55-0.54 and 0.75-45, respectively, for At-306 and At-405. At-306 showed a higher equilibrium moisture content (EMC) value compared to At- 405 when aw>0.70. The GAB isothermal model best described the experimental EMC data (R2adj>0.98 and MRD<3.8). At-306 has a higher specific surface area (≈115.5 m2 g-1 d.b) and higher monolayer moisture content (≈3.3 g/100 g) than At-405. The effective pore size of At-306 and At-405 varied between 1.04-12.82 and 0.73-9.18 nm, respectively. The isosteric-heat of adsorption was significantly higher for At-405 than At-306. Research Limitations: Further studies with medium amylose basmati are needed to confirm the applicability of these findings. Originality/ Value: This result provides some information of the physicochemical, rheological and storability characteristics of low and high basmati flours for the food industry application.

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%.

A long-acting hygroscopic and antibacterial composite filler: A new approach to phytoextraction solid residues from Citrus aurantium L.

A promising new composite filler with hygroscopic and antibacterial properties was developed based on the Fructus Aurantii Immaturus solid residues (FAIR) from Citrus aurantium L. , a typical bulk forest industrial crops. FAIR@AM-APTAC composite filler was established using FAIR as substrate, allyl glycidyl ether (AGE) as the cross-linker, while functional monomers of acrylamide (AM) and (3-acrylamidopropyl) trimethyl ammonium chloride (APTAC) were introduced. The structure of FAIR@AM-APTAC was characterized by FTIR , SEM, BET and TG–DSC analysis. The results confirmed that the FAIR@AM-APTAC composite filler was successfully prepared, which exhibited a three-dimensional(3D) network structure with a specific surface area of 0.1758 m²/g and exhibited excellent thermal stability. The equilibrium percent moisture absorption of FAIR@AM-APTAC (63.0%) was higher than that of FAIR (15.7%) under RH= 80% at 25 ℃ for 48 h, and much better moisture adsorption was achieved. The moisture adsorption process of FAIR@AM-APTAC followed a type III moisture adsorption isotherm and conformed to GAB, Peleg and pseudo-second order kinetics model. The moisture adsorption process of FAIR@AM-APTAC was a multi-layer adsorption process with enthalpy driven non-spontaneous and endothermic, which was dominated by chemical adsorption simultaneous existing physical adsorption, and the adsorption force was the synergy of both hydrogen bond and van der Waals force. The inhibition ratio of FAIR@AM-APTAC was 97.1% for E. coli and 95.4% for S. aureus . The antimicrobial efficacy of FAIR@AM-APTAC was enormously improved compared with that of FAIR due to the introduction of quaternary ammonium groups. The antibacterial mechanism of FAIR@AM-APTAC may be that the surface contact between bacterial and FAIR@AM-APTAC leads to inactivation. Significantly, FAIR@AM-APTAC showed long-acting hygroscopic and antibacterial properties, with little weakness even after 120 times cycle of wetting-drying. It is expected to be applied to an indoor air purifier or filter. • A new approach to phytoextraction solid residues from Citrus aurantium L. • Establishment of 3D structure long-acting hygroscopic and antibacterial composite. • Superior hygroscopic properties. Percent moisture absorption: 63.0% (25 ℃，RH=80%). • Superb antibacterial properties. Inhibition ratio: 97.1% ( E. coli ) and 95.4% ( S. aureus ). • A promising new filler: expected to be applied to indoor air purifier or filter.

Effect of 60Co γ-rays on dried figs adsorption isotherms and thermodynamic properties.

Irradiation is one of the promising food preservation techniques, but few are known about its impact on foods' water vapor change. In this research, the impact of gamma irradiation on moisture adsorption isotherms of dried figs, one of the most emblematic foods of the Mediterranean diet, at increasing doses (0, 1, 1.5, and 2 kGy) was investigated. The isotherms data of equilibrium points displayed a sigmoid-shaped curve of the type II pattern for both controlled and irradiated dried figs, with a notable effect of irradiation on equilibrium moisture content, which revealed a decreasing pattern as irradiation dose and temperature increase. This effect was also seen in data fitting, where GAB model showed the best prediction statistics for control samples, while Peleg model displayed the most suitable samples irradiated at 1 and 1.5 kGy, then the Enderby model for those treated with 2 kGy. Results of Net isosteric heat of adsorption suggested that high irradiation dose increases the spontaneity of moisture adsorption. Hence, gamma irradiation exhibited a significant effect on the water-specific surface area of which the magnitude was proportional to the increasingly applied doses. This effect was also visibly significant on the optimum water activity [aw (op)] for proper dried fig storage. Indeed, aw was about 0.4243 for control samples, which is much higher compared to irradiated ones (aw = 0.2). Information from this research suggests that gamma irradiation at a dose up to 2 kGy extended the dried figs' shelf life. Since many aspects related to the impact of gamma irradiation on the moisture adsorption isotherms and thermodynamic properties of dried figs as well as in other foods have yet to be further investigated, this study provides interesting results that may be a useful reference for future research direction.

Effects of gliadin and glutenin on the hygroscopicity of freeze-dried apple powders.

Wheat gluten addition in freeze-dried apple powders can effectively prevent their undesirable moisture adsorption and caking during long-term storage, but the working mechanism of wheat gluten had not been expounded. Therefore, such anti-hygroscopicity effects were systematically investigated from the perspective of wheat gluten major components: gliadin and glutenin. Herein, moisture adsorption curve/isotherm, morphology, and moisture migration law of the protein-added apple powders were analyzed at varied storage humidities. Results showed that Peleg, GAB, and Ferro-Fontan models could describe the moisture adsorption process of gliadin-added and glutenin-added freeze-dried apple powder. By comparing the model fitting results, it was found that the fitting degree of moisture adsorption isotherm of the sample increased with the increase of water activity, and the imitative effect of the Ferro-Fontan model was the best. According to the result of the fitting prediction, the equilibrium moisture content of glutenin-added apple powder was 4.7% lower than that of gliadin-added apple powder at 25°C and 75% relative humidity (RH). Type III moisture adsorption isotherms were observed for gliadin-added apple powder, while that of glutenin-added apple powder was type II. In addition, the gliadin-added apple powder demonstrated better fluidity and lower water migration when the relative humidity (RH) of the environment was lower than 58%. Once above this RH value, the protecting effect of glutenin was more obvious. These findings not only elucidate the anti-hygroscopic mechanism of wheat gluten in the processing of apple powder, but also provide a new idea for improving the quality of apple powder and the development of new anti-hygroscopic agents.

Evaluation of physicochemical and functional attributes of whey powder incorporated with pomegranate peel extract

A study has been conducted to evaluate the effect of pomegranate peel extract (PPE) (1, 2 and 3%) on physico-chemical and functional attributes of whey powder such as total phenolic content (TPC), flavonoid, proanthocyanidin, alkaloid, antioxidant activity, colour profile, protein-polyphenol interaction, rheology, differential scanning calorimetry (DSC), moisture adsorption isotherm (MAI) and microstructure. The TPC (1.02–27.80 mg/g), flavonoid (1.08–10.93 mg/g), proanthocyanidin (0.62–5.82 mg/g), alkaloid (0.63–2.28%), antioxidant activity (ABTS, 16.61–88.01%; DPPH, 17.02–49.34%), redness (2.33–8.05) and yellowness (27.77–32.24) were increased significantly (P < 0.05) with the increase in PPE. Protein-polyphenol interaction was confirmed with fluorescence spectra, FTIR and SDS-PAGE assays. The protein-polyphenol interaction brought significant changes in exothermic events (103.97–109.61 ºC) and viscosity (0.02–0.11 Pa.s) of the reconstituted whey samples. The DSC (glass transition temperature 77.15–71.37 ºC) and MAI (Equilibrium moisture content 38.75–70.45%) studies revealed that hygroscopic nature of whey powder increased with increase in the PPE. The microstructure analysis revealed that particles combined to form large aggregates upon addition of PPE. The PPE significantly increased the hygroscopicity of the powder and viscosity after reconstitution. These results are useful during drying of PPE added powders as well as polyphenol rich powders.

Moisture sorption isotherms and thermodynamic properties of tiger nuts: An oil-rich tuber

The moisture adsorption isotherms of tiger nuts were determined by a gravimetric static method at 15, 25, 35 °C within the water activity varying from 0.113 to 0.979. Ten mathematical models were selected to fit the adsorption data using non-linear regression technique. Thermodynamic properties such as isosteric heat, sorption entropy and Gibbs free energy were evaluated. The results indicated that equilibrium moisture content of tiger nuts tended to increase with increasing water activity and decreasing temperature. The isotherm curves of tiger nuts exhibited a Type Ⅱ sigmoidal shape. Peleg model was the most suitable for describing the experimental sorption behavior, followed by the Smith and GAB models. The adsorption surface area and monolayer moisture content of tiger nuts obtained from GAB model were 166.37–149.74 m2/g solid and 4.71–4.24 H2O/100 g solid, respectively, which decreased with increasing temperature. Moreover, the isosteric heat of adsorption decreased exponentially with the increase of equilibrium moisture content, while the Gibbs free energy was opposite. Adsorption entropy was negative in value and it decreased sharply and then rose slowly as the moisture content increased, having a minimum value (6.43 J/mol K) at a moisture content of 11 g/100 g d.b.

Adsorption Isotherms and Thermodynamic Properties of Dried Tomato Slices

Moisture adsorption isotherms and thermodynamic properties of dried tomato slices obtained from four tomato varieties were investigated. Freshly harvested tomatoes were pretreated with potassium metabisulphite solution (0.2%, weight/volume) before drying in a cabinet dryer at 60± 2° C. Moisture adsorption behavior of the dried tomato slices was determined using the static gravimetric method at 25, 30 and 40o C. The data fitted to GAB, M.BET, DLP, Smith and Oswin sorption models. The isosteric heat of sorption was also determined. Moisture adsorption isotherm of dried tomato slices from UC82B, Roma, Eva-F1 and Kerewa varieties exhibited a sigmoid isotherm curve typical of type II BET classification. Increase in temperature resulted into a decrease in the equilibrium moisture content. The GAB, DLP and modified BET model adequately modeled the isotherms of dried tomato slices. The relationship between isosteric heat of sorption and the equilibrium moisture of dried tomato slices were accurately described by exponential model.