Advances on the antioxidant peptides from edible plant sources

The potential applications of food-derived antioxidant peptides as additives, nutraceuticals and therapeutic agents have fueled current interests to discover them from diverse plant sources. A growing number of antioxidant peptides have been identified from edible plant sources, as well as plant-based agricultural and food-processing by-products. We summarized recent progress in the research of plant-derived antioxidant peptides, particularly their biological effects, mechanisms, and structure-activity relationship. Many studies assessed the potency of antioxidant peptides by using chemical assays. However, the outcome of chemical methods may not reflect the biological significance. Thus, this review focusses on antioxidant peptides whose effectiveness was demonstrated by using cellular and/or animal models. This review pays particular attention to studies which successfully determined the sequences of antioxidant peptides under investigation. Due to the scarcity of the assessment of pure antioxidant peptides in animal models, in vivo evidence from well-characterized peptide fractions or hydrolysates will also be discussed. Plant-derived antioxidant peptides diminished reactive oxygen species production, besides activating endogenous antioxidant defenses in cellular models. Some such peptides exerted protection by modulating pro- and anti-apoptotic proteins as well as gene and protein expression of antioxidant enzymes. By using cellular models, the intestinal absorption and metabolism of such peptides were elucidated. Plant protein hydrolysates enhanced antioxidant protection in animal models, often by upregulating antioxidant enzyme activities in various body tissues. The structure-activity relationship of plant-derived antioxidant peptides is not well-understood. Nevertheless, information connecting peptide secondary structure to cellular antioxidant effects has emerged.