The effect of molecular weights on the survivability of casein-derived antioxidant peptides after the simulated gastrointestinal digestion

A two-stage in vitro gastrointestinal (GI) digestion model was used to assess the survivability of antioxidant peptide fractions with different molecular weights (MW). Research on MW distribution showed that peptides above 3000 Da were more easily digested by gastric digestion than those below 3000 Da. And peptides tended to be more hydrolyzed by intestinal digestion than by gastric digestion. Determination of free amino groups suggested that peptide bonds in the peptides above 3000 Da were more inclined to be cut off during the GI digestion. However, the amount of free amino acid (AA) increased as the MW decreased and accounted for 30%–40% (w/w) of the GI digests. The peptides below 1000 Da exhibited the best initial and surviving antioxidant activities in 2, 2′-azinobis (3-ethylbenzothiszoline-6-sulphonic acid) diammonium salt (ABTS+), hydroxyl radical scavenging and ORAC value. In conclusion, casein-derived antioxidant peptides below 1000 Da were a promising antioxidant administered orally.Industrial revelance: Numerous products are already on the market or under development by food companies, exploiting the potential of food-derived bioactive peptides. To exert physiological effects in vivo, bioactive peptides must survive the gastrointestinal (GI) digestion, and then reach their target sites after absorption. So far, only a few among the numerous bioactive peptides displaying activities in vitro have been proven effective in vivo. The real bioavailability of quite an amount of marketed products containing bioactive peptides is unclear.However, our research conducted further examination of bio-accessibility of casein-derived antioxidant peptides and assessed the effect of MW on the survivability of casein-derived antioxidant peptides after the simulated GI digestion. The survivability of peptides was above 60% after the GI digestion. And the casein-derived peptides below 1000 Da exhibited the best initial and surviving antioxidant activities. The enriched antioxidant peptide fraction above could be a promising candidate for dietary supplements and nutraceuticals with good GI survivability and bio-accessibility.

► Peptides with higher molecular weight were easier digested by gastric digestion.
► The higher the molecular weight, the more peptide bonds were cut off.
► Amounts of free amino acid in digests increased as the molecular weight decreased.
► The changing trend of activity in two stages of digestion were different.
► Peptides below 1000 Da with the best surviving activity are a promising antioxidant.