Bioconversion of sea cucumber (Stichopus japonicus) by Lactobacillus plantarum: enhancement of bioactive peptides, gamma-aminobutyric acid, and corresponding bioactivities.

The increasing demand for natural nutraceuticals has driven interest in marine resources like sea cucumbers (Stichopus japonicus), which are rich in proteins that can be biotransformed into bioactive compounds. This study investigated the bioconversion of Stichopus japonicus through fermentation with Lactobacillus plantarum to enhance its bioactive profile. Fermentation significantly altered the proximate composition, increasing protein content (51.25% dry basis) while reducing moisture, fiber, ash, and organic matter. The degree of hydrolysis reached 70.76%, resulting in elevated levels of free amino acids, bioactive peptides, and gamma-aminobutyric acid (GABA), which increased 2-3 fold across all molecular weight fractions. Bioactivity assays revealed potent antioxidant (IC₅₀ as low as 0.97 mg/mL), anti-inflammatory (IC₅₀ down to 1.11 mg/mL), and antidiabetic (IC₅₀ as low as 1.04 mg/mL) activities, with the < 3 kDa fraction consistently showing the highest potency. LC-HRMS analysis identified 25 novel peptides, all predicted as non-toxic, with several demonstrating high bioactivity potential. These results demonstrate that fermentation with Lactobacillus plantarum effectively valorizes Stichopus japonicus into a multi-functional ingredient enriched with protein, GABA, and bioactive peptides, offering promising applications in functional foods and nutraceuticals.