Autochthonous Fermentation of Amaranth Flour Increments Bioaccessibility and Antioxidant Activity of Proteins

Background and Objectives Amaranth seeds are an abundant source of bioactive compounds. Spontaneous fermentation represents a simple and cost‐effective strategy to enhance these properties. In this study we investigated the effects of spontaneous fermentation of amaranth flours with different particle sizes on protein bioaccessibility and the production of antioxidant peptides. Findings Fermented flours were prepared by incubating 22.2% w/w flour/water dispersions for 24 h at 37°C, followed by pasteurization (60°C, 30 min). Fermentation promoted lactic acid bacterial growth (9–10 log cfu/g), reduced the pH from approximately 6.2 to 4.2, and induced proteolysis (22%–25%), thereby increasing soluble protein and low‐molecular‐weight peptides (< 6.5 kDa). After simulated gastrointestinal digestion (COST‐INFOGEST), fermented flours reached proteolysis degrees of 48%–49%, with almost complete polypeptide hydrolysis. Fermentation increased the contents of soluble protein and free amino groups after each gastrointestinal digestion step, as well as the antioxidant activity (ORAC and ABTS) both before and after complete digestion. The effects of seed storage time and particle size were minimal. Conclusions Spontaneous fermentation substantially enhances protein bioaccessibility and antioxidant capacity of amaranth flours. Significance and Novelty This study demonstrates, for the first time, that naturally fermented amaranth flour is a promising functional antioxidant ingredient, suitable for incorporation into diverse food formulations.