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This work investigated changes in the chemical composition and structure of soybean straw (SS) treated with alkali (NaOH 5% and 17.5%) and bleached with hydrogen peroxide (HO) or sodium hypochlorite (NaOCl). Removal of the amorphous constituents increased the degree of crystallinity and the content of cellulose fibers particularly after reaction with high concentrations of alkali. Treatment with NaOH 17.5% contributed to the allomorph transition from cellulose I to II regardless of the bleaching agent, but HO as bleaching agent promoted more effective delignification. This work also evaluated the potential use of treated and non-treated SS as reinforcement filler in soy protein isolate film (SPI). Films added with treated SS presented higher mechanical resistance, lower elongation at break, and lower solubility in water. Addition of non-treated SS did not affect the properties of the SPI film significantly. The low solubility and the reasonable water vapor permeability of the composite films make them suitable packaging materials for fresh fruit and vegetables.

a b s t r a c tIn this work we studied the influence of the drying temperature and relative humidity on the solubility, mechanical properties, water vapor permeability (WVP), and drying time of amaranth flour films plasticized with glycerol or sorbitol. The effect of drying temperature and relative humidity on the mechanical properties of the film is a function of the plasticizer type. In the presence of glycerol, tougher flour films are obtained at a lower drying rate, but an inverse behavior is observed for the films plasticized with sorbitol. The drying conditions do not have a significant effect on WVP compared with sorbitol-plasticized samples, the water sorption isotherm shows that the glycerol-plasticized flour films are able to retain more water at equilibrium at all the studied temperatures. The lower moisture content, WVP and drying time achieved for these films in all the drying conditions indicate better interaction of sorbitol with the starch and protein macromolecules present in the amaranth flour. The optimized drying conditions are 50 C and 76.2% RH, and 35 C and 70.3% RH for the films plasticized with glycerol and sorbitol, respectively.

Amaranth protein-lipid (PL) and protein (P) films were elaborated and compared with amaranth flour films in order to determine the contribution of the interactions between the biopolymer (starch and protein) and the lipids to the film properties. The films were made by the casting method, using the same glycerol concentration (0.9 g glycerol/100 g solution). A separation of the lipid fraction in the PL films and a polymorphic transformation of the corresponding fatty acids were observed by differential scanning calorimetry (DSC) and verified by an analysis of the microstructure by scanning electron microscopy (SEM). The flour films showed no separation of the lipid fraction, evidence that the lipids were strongly associated with the proteins and homogenously distributed throughout the starch network, contributing to the good mechanical properties when compared to the PL films and to the excellent barrier properties when compared to both the PL and P films. The protein-protein interactions also contributed to the mechanical properties of the flour films. The presence of proteins and lipids in the flour films had an important effect on film solubility, and also on the color and opacity of the films. This study showed that the flour film properties depended on the interactions formed by their polymers (starches and proteins) and by the lipid, on the distribution of these interactions within the film matrix and on the concentrations of each component in the film.

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