Antioxidant peptides extracted from natural foods have been studied for their potential use in the development of additives, nutraceuticals, and therapeutic agents. Nut proteins are considered an excellent source of plant-derived proteins for the human diet, due to their high protein content and digestibility of up to 86.22%. Furthermore, compared with grain and soybean proteins, nut proteins have a special amino acid composition, which makes their protein structure different, and promotes their disparate functional characteristics and great bioactivity potential. This review presents the most remarkable studies on antioxidant peptides from nuts, to gain insights into feasible production methods, different evaluation indexes within in vivo or in vitro systems, high bioavailability, and the complex structure-activity relationship resulting from the particularity of their protein structure and amino acid composition. Previously published studies mainly focused on the effects of the production methods/processes of nut-derived peptides on antioxidant activity, and proved that nut-extracted antioxidant peptides can resist the degradation of acid, alkali, and gastrointestinal enzymes, have high antioxidant activity in vitro and in vivo, and also have the potential to cross small intestinal epithelial cells in a stable and integral manner. However, the structure-activity relationship of antioxidant peptides from nuts has not been fully established, and the structure information of antioxidant peptides obtained from various nut protein sources is still unclear. The findings presented in this review can be used to provide the theoretical basis for the design and production of nut-derived antioxidant peptides.

Two doses (300 mg/kg bw and 600 mg/kg bw) of the Lactiplantibacillus plantarum JLAU103 exopolysaccharide (EPS103) were orally administered to a type 2 diabetic (T2DM) mouse model induced by streptozotocin and a high-fat diet. The hypoglycemic, hypolipidemic and neuroprotective effects of EPS103 on T2DM mice were evaluated. The results indicated that administration of EPS103 could alleviate insulin resistance, reduce the levels of fasting blood glucose, glycosylated hemoglobin A1c, leptin and fasting serum insulin, improve glucose tolerance, protect pancreas and liver, and modulate blood lipid disorders. EPS103 promoted hepatic glycogen synthesis by upregulating the phosphorylation of GSK3β. Meanwhile, it upregulated the phosphorylation of IRS-1, PI3K and Akt, as well as the expression of IRS-2 and GLUT4, and downregulated the expression of PEPCK, G6Pase and PGC-1α, indicating that EPS103 promotes the uptake and transport of glucose and inhibits gluconeogenesis, which might be related to the activation of the IRS-1/PI3K/Akt pathway. Additionally, EPS103 can protect against brain nerve damage through improving oxidative stress injury, restoring the expression of IRS-2, alleviating neuronal apoptosis and inhibiting inflammation in the hippocampus of T2DM mice. Taken together, our results demonstrated that EPS103 may be a potential therapeutic agent for the treatment of T2DM.