Modification of the WLF model for characterization of the relaxation time-temperature relationship in trehalose-whey protein isolate systems

Investigating the Water Relations in Aqueous Extract Powders of Mango (Mangifera indica) Peel and Seed Waste for Their Use in Food Matrices as a Value-Added By-Product

This study investigated the potential uses of discarded mango peel and seed parts by analyzing their water sorption behavior, hydration kinetics, and stability when converted into extract powders at pH 3 and 10. The results revealed that peel extracts had a higher water adsorption capacity compared with seed extracts due to differences in their composition. Peel extracts were primarily composed of carbohydrates (approximately 75%) with a low protein content, while seed extracts contained fewer carbohydrates (less than 30%) but higher levels of proteins (more than 30%) and lipids. The critical water content for maintaining the glassy state of peel extract powders during storage was found to be 0.025 and 0.032 g of water/g for extracts obtained at pH 3 and 10, respectively. In contrast, the Tg values of seed extracts remained relatively unchanged across different water content levels, suggesting that proteins and lipids inhibited the water's plasticizing effect in the solid matrix. These findings indicate that both mango waste fractions exhibit distinct hygroscopic behaviors, necessitating different approaches to processing and utilization. These extracts hold potential applications for various food products such as beverages, gels, sauces, or emulsions, contributing to the reduction in waste and the creation of value-added products from mango residues.

Physicochemical properties and Strength analysis of vitreous encapsulated solids for the safe delivery of β-Carotene

β-Carotene (β-Car) is insoluble compounds in water and liable to degradation, which has health benefits for human beings. Although layer-by-layer (LBL) emulsions provide a better protection for β-Car towards environmental stresses, the handling and transportation of LBL emulsions still faces restrictions. In this paper, therefore, the LBL emulsions including β-Car were carefully prepared and encapsulated to obtain vitreous encapsulated solids (VES) using trehalose and maltodextrins (MD) as wall materials. Morphological results indicated that the LBL emulsions were formed a spheric shape, in where the polyelectrolyte shell was 30 nm. The MD exhibited the characteristics of not easy to absorb moisture, suitable carrier, and good stabilizer, which could improve the stability of VES systems at studied environmental stresses. Despite compositional effects from MD and environmental stresses, LBL emulsions changed the water sorption behavior of VES as oil dispersion in storage. Strength analysis indicated that LBL emulsions lubricated systems and increased the molecular mobility of wall materials. Structural collapse, rapid color changes, and β-Car loss were confirmed in VES systems at 0.56 a_w from 25 to 45 °C after 30 days of storage. Besides, a relationship between S and β-Car loss kinetics was established, where the β-Car degraded more rapidly in a sample with quicker molecular mobility of wall materials Therefore, the controlling of molecular mobility in wall materials can slow down the β -Car degradation and improve the quality and stability of lipophilic nutrients delivery systems with high total solids.

Glass Transition Behavior of Wet Polymers

We have performed a systematical investigation on the glass transition behavior of amorphous polymers with different solvent concentrations. Acrylate-based amorphous polymers are synthesized and treated by isopropyl alcohol to obtain specimens with a homogenous solvent distribution. The small strain dynamic mechanical tests are then performed to obtain the glass transition behaviors. The results show that the wet polymers even with a solvent concentration of more than 60 wt.% still exhibit a glass transition behavior, with the glass transition region shifting to lower temperatures with increasing solvent concentrations. A master curve of modulus as a function of frequency can be constructed for all the polymer-solvent systems via the time-temperature superposition principle. The relaxation time and the breadth of the relaxation spectrum are then obtained through fitting the master curve using a fractional Zener model. The results indicate that the breadth of the relaxation spectrum has been greatly expanded in the presence of solvents, which has been rarely reported in the literature. Thus, this work can potentially advance the fundamental understanding of the effects of solvent on the glass transition behaviors of amorphous polymers.

Rheology of carbohydrate blends close to the glass transition: Temperature and water content dependence of the viscosity in relation to fragility and strength

Several modifications of the Williams-Landel-Ferry (WLF) equation that incorporate the water-content dependence of the viscosity are introduced and applied to the fitting the zero-shear viscosity of a systematic series of maltopolymer-maltose blends for water contents w between 4% and 70% (M. Dupas-Langlet et al., Carbohydrate Polymers 213 (2019) 147-158). These models include a previously published model that addresses the water-content dependence of the viscosity via a Gordon-Taylor-type modification of the C₂ coefficient of the WLF equation. New models that are based on two simple assumptions are introduced: 1. The viscosity at the glass transition temperature T_g decreases exponentially with the water content and 2. The WLF coefficient C₂ depends linearly on the water content. The modified WLF models allow to extract the so-called isoviscosity lines, that connect points of varying temperature and water content that are characterized by the same viscosity. Based on data obtained between T = -15 °C and 70 °C using shear rheology (w = 30-70% w/w) and dynamic mechanical thermal analysis (w = 4-9% w/w), we conclude that the models provide a good fit of the experimental data, and that additional data, specifically very close to the glass transition line, is needed, to assess the hypotheses underlying the various modified WLF models. It is established that the viscosity at T_g is dependent on the composition and decreases with the content of maltose and water. The modified WLF models are used to determine Angell's fragility parameter m and Roos' strength parameter S. m and S are observed to increase, respectively decrease with increasing water and maltose content, signifying an increasing temperature dependence of the viscosity close to T_g with decreasing diluent content. The application of the isoviscosity concept to unit operations in the food and pharmaceutical industry is discussed. Specifically, we show how to analyze atomization, agglomeration, sintering and compaction using the isoviscosity concept.

Effects of lipids on the water sorption, glass transition and structural strength of carbohydrate-protein systems

Encapsulant systems are gaining wide practical interest due to their functional and nutritional properties. This paper was focusing on understanding structural relaxations in that systems near glass transition temperature. Freeze-dried trehalose-whey protein isolate-sunflower oil systems with various ratios of the last were used as a carbohydrate-protein-lipid food model. The Guggenheim-Anderson-de Boer (GAB) water sorption relationship was used as a tool to model water sorption isotherms. The glass transition temperature was obtained by differential scanning calorimetry (DSC). Structural α-relaxation temperatures were measured by dynamical mechanical analyses (DMA), dielectric analysis (DEA) and combined to cover a broad range for strength assessment. The microstructure was characterized by optical light microscopy, confocal laser scanning microscopy and scanning electron microscopy. The C₁ and C₂ constants for Williams-Landel-Ferry (WLF) equation and structural strength parameter were calculated for each system. The effect of sunflower oil and water contents on strength of carbohydrate-protein system was analyzed. Strength shows decreasing with increasing of lipid concentration in the mixtures and more complex dependence on the water content in a system.