ABSTRACT
Lipid-protein co-oxidation often causes nutrition loss, texture changes, and shortened shelf-life of emulsions. In this study, resveratrol significantly prevented lipid-protein co-oxidation in sodium caseinate (NaCas)-walnut oil emulsions, and the underlying mechanisms were explored in physical and chemical aspects. NaCas-walnut oil emulsions stabilized by resveratrol exhibited excellent physical stability at 55 °C for 12 days or at room temperature for 10 months due to forming a stable interfacial layer composed of resveratrol-modified NaCas. Furthermore, resveratrol binding caused NaCas structure's partial unfolding and a â¼ 8% increase in hydrophobicity, in turn enhancing NaCas' emulsification properties and electrostatic repulsion. Besides, more than 90% of resveratrol was loaded at the interface and enhanced NaCas' Fe2+ chelating, DPPH scavenging abilities, and O2 quenching by â¼ 22.6%, 5.26 times, and 31.84%, respectively. Simultaneously, resveratrol significantly improved NaCas' oxidative stability, as reflected by the decrease in adsorbed NaCas' intrinsic fluorescence loss and protein carbonyls gain by â¼ 30% and 37%, respectively. Simultaneously, lipid hydroperoxides and TBARS were reduced by â¼ 30% and 20% in the NaCas-walnut oil emulsions containing 6 mM resveratrol than the control. Our findings contribute to further understanding of the possible interaction among lipid, protein, polyphenols, and their oxidative products at the oil-water interface, minimizing lipid-protein co-oxidation and extending functional oils' shelf life. Finally, walnut oil emulsions with high physical and oxidative stabilities using resveratrol were prepared, further broadening resveratrol's application in the food industry.
Subject(s)
Caseins , Juglans , Caseins/chemistry , Emulsions/chemistry , Plant Oils , Resveratrol , Water/chemistryABSTRACT
ß-Carotene is a precursor of vitamin A and a dietary supplement for its antioxidant property. Producing ß-carotene by microbial fermentation has attracted much attention owing to consumers' preference for the natural product. In this study, an engineered photosynthetic Rhodobacter sphaeroides producing ß-carotene was constructed by the following strategies: (1) five promoters of different strengths were used to investigate the effect of the expression level of crtY on ß-carotene content. It was found that PrrnB increased the ß-carotene content by 109%. (2) blocking of the branched pentose phosphate pathway by zwf deletion, and (3) overexpressing dxs could restore the transcriptional levels of crtE and crtB. Finally, the engineered RS-C3 has the highest ß-carotene content of 14.93 mg/g dry cell weight (DCW) among all of the reported photosynthetic bacteria and the ß-carotene content reached 3.34 mg/g DCW under light conditions. Our results will be available for industrial use to supply a large quantity of natural ß-carotene.