Antioxidant and gastrointestinal cytoprotective effect of edible polypeptide poly-γ-glutamic acid

The antioxidant effects and cytoprotection of the poly-γ-glutamic acid (γ-PGA) were investigated. γ-PGA with a molecular weight of ~400 kDa showed hydroxyl radical (OH^•) averting capacity (HORAC), 85.2% at 1 mg/mL, which was caused by the chelation of transition metal ions and scavenging hydrogen peroxide. Moreover, this γ-PGA showed 94.1% superoxide anion radical (O₂^•-) scavenging and 96.0% lipid peroxidation inhibition activity at the same concentrations. The IC₅₀ values were 130 ± 4.2, 107 ± 3.5 and 128 ± 3.8 μg/mL against OH^•, O₂^•- and lipid peroxidation, respectively. There was no significant variation in the HORAC of γ-PGA after 9 h, the end point of the simulated digestion model. Furthermore, γ-PGA showed a completely protective effect in Caco-2 cells and probiotic bacteria against oxidative damage at 1 mg/mL. These data suggest that γ-PGA has a potential use as a cytoprotectant in food and feed supplements, cosmetics and biomedical fields.