Investigation of nutritional and functional effects of rice bran protein hydrolysates by using Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines: A review

Rice bran protein hydrolysates (RBPHs) are peptides hydrolysed by different enzymes on rice bran protein (RBP). Protein hydrolysis cleaves storage proteins at either C-terminal or N-terminal of peptide bonds producing unique peptide sequences with various nutritional and functional properties as well as amino acids with aromatic, hydrophobic and charged ends. The Web of Science database was searched for studies published between 2014 and 2019 using Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines in order to investigate the relationship between RBPHs and functional/health outcomes. The aim of this review is to reinforce and summarise the protective role of RBPHs as an antioxidant, an antidiabetic agent and an Angiotensin-converting enzyme (ACE) inhibitor with other nutritional properties and functional properties. RBP cleaved by different enzymes produces low molecular weight (MW) antioxidant peptides with radical scavenging activity and metal chelation power. These peptides restrain ACE activity and significantly reduce the intracellular ACE levels in rodent models. These peptides are also antidiabetic as they inhibit amylase, α- and β-glucosidase and dipeptidyl peptidase-IV (DPP-IV). They also suppress intracellular glutathione (GSH) levels by down-regulating the expression of a variety of inflammatory factors including 2(Nrf2), quinone oxidoreductase1 (NQO1) and hemeoxygenase 1 (HO-1). The health promoting effects of anti-melanogenesis, antimicrobial, and iron availability enhancement are described. Plus, RBPHs fortified food shows better preservation against lipid oxidation. Nowadays, turning rice mill wastes into the more manageable and sustainable applications has received attentions for their nutritional and functional properties rather than only animal feeds and a source of the biomass fuel. But the application of the rice bran for nutritional purposes is still limited. The high cost of the enzymes and the sensitive nature of peptides are the major industrial concerns. It is expected that the number of rice bran products and their acceptance will increase in the future market.