Structural and functional properties of rice bran protein oxidized by peroxyl radicals

Abstract

The structure and functionalities of rice bran protein (RBP) oxidized by peroxyl radicals were analyzed in this study. The thermal decomposition of 2,2′-azobis [2-amidinopropane] dihydrochloride (AAPH) was used to generate peroxyl radicals. Increased oxidation of RBP by AAPH gradually generated more carbonyl (COOH) groups, which resulted in a loss of protein sulfhydryl groups. Low oxidization (≤0.2 mmol/L AAPH) could cause structural unfolding with an increase in surface hydrophobicity and emulsion properties but reducing the solubility and disulfide bonding. Moderate and high oxidization (>0.2 mmol/L AAPH) could result in soluble aggregates formed by subunits with molecular weights of 53, 49, and 36 kDa, attributed to globulin, albumin, and glutelin, increasing the solubility and disulfide bonding but decreasing the surface hydrophobicity and emulsion stability. Oxidization by low concentration AAPH induced a more unordered structure and transformation from β-turn to β-sheets, while a more ordered structure increased with aggregation.

Angiotensin‐I‐converting enzyme (ACE)‐inhibitory peptides from Thai jasmine rice bran protein hydrolysates

“…KDML105). Rice bran, a co‐product from the rice milling industry contains ~10–15% highly nutritional proteins (Chandi & Sogi, ; Zhou et al , ), which have been recognised as being superior to some alternative protein sources due to their hypoallergenic property and they are also contain highly digestible properties which provide effective functional food ingredients and nutritional supplements (Sharif et al , ). Moreover, the essential amino acids such as lysine (a limiting amino acid in cereal grains) are abundantly present in rice bran proteins (Sohail et al , ).…”

Effect of peroxyl radicals on the structure and gel properties of isolated rabbit meat myofibrillar proteins

“…() on egg white protein. This increase in surface hydrophobicity is attributed to the exposure of hydrophobic groups, reflecting the structural changes in MPs during oxidation (Zhou et al ., ). In general, hydrophobic amino acid residues, particularly nonpolar aromatic amino acids, appear obscured deep inside the folded structure of native MPs (Qiu et al ., ).…”

“…Zhou et al . () argued that protein aggregation is associated with the decreased fluorescence intensity. Sun et al .…”

“…Therefore, the interaction between lipid and protein oxidations in rabbit meat should be fully understood. Peroxyl radicals (ROO·) serve as key species during lipid oxidation, and are ROS for protein oxidation (Zhou et al ., ). As a kind of electrophilic radical, ROO· is the first to attack the sites that enrich electrons in proteins, and the abstraction of a hydrogen atom from C–H (or S–H) bonds is a major oxidative mechanism (Davies, ).…”

“…As a kind of electrophilic radical, ROO· is the first to attack the sites that enrich electrons in proteins, and the abstraction of a hydrogen atom from C–H (or S–H) bonds is a major oxidative mechanism (Davies, ). Previous studies have evidenced that ROO· can affect the protein structures and functional properties of pork MPs (Zhou et al ., ), rice bran protein (Zhou et al ., ), ovalbumin (Bao et al ., ) and egg white protein (Duan et al ., ). To our knowledge, studies have yet to determine how ROO· affects the structure and functional properties of MPs of rabbit meat.…”