Soy protein-phlorizin conjugate prepared by tyrosinase catalysis: Identification of covalent binding sites and alterations in protein structure and functionality.

Tyrosinase-catalyzed synthesis of soy 7S/11S-phlorizin conjugates was performed, and the reaction sites, conformation alterations and functional properties of complexes were evaluated using proteomic, in combination with multispectral technologies. Phlorizin was conjugated to 7S/11S primarily via residues of Lys, Cys, His and Arg residues. The phlorizin binding equivalents and decreased contents of free and total sulfhydryl groups and free amino groups confirmed the covalent interaction in the 7S/11S-phlorizin complexes. Conjugation with phlorizin promoted the conversion of α-helix to ß-sheet and ß-turn, with simultaneous transformation of the microenvironments around Trp and Tyr residues to hydrophilic and hydrophobic microenvironments, respectively, and lowering of the surface hydrophobicity of 7S/11S. The DPPH and ABTS radical scavenging abilities and α-glucosidase inhibitory activities of 7S/11S were increased by three-, two- and three-fold after the covalent binding of phlorizin. The study provided an ideal tyrosinase-catalyzed approach to fabricate custom-tailored nutritional soy protein-polyphenol products.

Dynamic monitoring of the protein-lipid co-oxidation of algae oil-enriched emulsions coated with soybean protein-rutin covalent conjugates.

The stabilities and levels of protein-lipid co-oxidation of algae oil-in water (O/W) emulsions coated with the soybean protein 7S/11S or their rutin covalent conjugates were studied during storage. After 96 h of storage, the emulsions stabilized with the covalent conjugates exhibited decreased droplets sizes and ζ-potentials and increased concentrations of adsorbed proteins. Therefore, the covalent binding of rutin in different mixing ratios (at 7S/11S:rutin molar ratios of 1:10 and 1:20) improved the physical stabilities of the emulsions compared with those of the emulsions stabilized by native 7S/11S. The 7S/11S-rutin covalent conjugates, which formed interfacial barriers and exhibited good free radical scavenging properties, inhibited protein oxidation (with lower contents of protein carbonyls, N'-formyl-L-kynurenine, and Schiff bases, and decreased intensities of intrinsic tryptophan fluorescence) and lipid oxidation (with lower contents of lipid hydroperoxide and malondialdehyde) as storage time increased. The electronic nose test distinguished the flavor characteristics of the emulsions coated with different protein-based stabilizers. These results reveal the viability of utilizing soybean protein-rutin conjugates in protein-stabilized algae oil-fortified emulsions with enhanced storability.

Effects of Salinity Stress at Reproductive Growth Stage on Rice (Oryza sativa L.) Composition, Starch Structure, and Physicochemical Properties.

This study aimed to investigate the changes in polished rice composition, starch structure, and physicochemical properties from three rice cultivars treated with medium and high salinity stress at the reproductive growth stage. The results showed that salt stress led to poor milling and appearance quality, higher total starch content, protein content, higher proportion of the medium, and long chains of amylopectin, as well as gelatinization temperature (GT) but lower amylose content and lower proportion of the short chain of amylopectin. Compared with salt-sensitive cultivars, the salt-tolerant cultivars exhibited lower GT and gelatinization enthalpy, better pasting properties, and more stable crystal structure; therefore, their eating and cooking quality (ECQ) was less affected. The above results imply that salt stress at the reproductive growth stage can degrade ECQ and can slightly increase the pasting property of starch from salt-tolerant rice cultivar.

Effects of Cd uptake, translocation and redistribution in different hybrid rice varieties on grain Cd concentration.

In order to identify the key transport process that determines the Cd concentration in brown rice, this study used 21 hybrid rice varieties as experimental materials and conducted field experiments in Qiyang (cadmium-contaminated site) and Yongding (low-cadmium site). Cd concentrations in 8 organs were measured, and bioconcentration factors and transfer factor were further calculated. The results showed that the Cd concentrations of the organs related to the xylem transport were as follows: root > node > stem > leaf sheath > leaf. In the phloem, the Cd concentrations were as follows: rachis > brown rice > rice husk. And the results of the correlation analysis found that Cd concentration between brown rice and root showed a significant positive correlation in Cd-contaminated site, but no significant correlation in low-cadmium site. Meanwhile, at both experimental sites, the Cd concentration of brown rice showed the most significant correlation with the phloem transfer factor from leaf and leaf sheath to brown rice. Principal Component Analysis (PCA) and stepwise regression analysis likewise found that Cd concentration in leaf and leaf sheath and their phloem transport of Cd to brown rice were significantly and positively correlated with Cd concentration in brown rice. The above results showed that the transport of leaf and leaf sheath to brown rice was a key process, and played a more important role in the accumulation of cadmium in brown rice than in root.