Molecular Weight Distribution and Antioxidant Activity of Enzymatic Hydrolysates from Rhopilema hispidum and Nemopilema nomurai Under Different Enzymatic Hydrolysis Conditions

Jellyfish, as high-biomass marine resources, frequently exhibit explosive proliferation in coastal waters and possess both nutritional functional factors and potential medicinal value. This study investigated the enzymatic hydrolysis of two jellyfish species, Rhopilema hispidum (R. hispidum) and Nemopilema nomurai (N. nomurai), using Alcalase, Flavourzyme, and Protamex, with a specific focus on the molecular weight distribution and antioxidant activity. The optimal hydrolysis conditions were systematically determined via single-factor experiments followed by orthogonal test optimization. The Flavourzyme hydrolysates had the highest proportion of low-molecular-weight peptides (<3 kDa) and exhibited the most potent antioxidant activity, while Protamex hydrolysates had more high-molecular-weight peptides (>3 kDa, >40%) with comparatively weaker antioxidant activity. R. hispidum hydrolysates exhibited stronger DPPH• and O2•− scavenging activities and contained a higher proportion of low-molecular-weight peptides (<3 kDa), whereas N. nomurai hydrolysates showed a higher degree of hydrolysis, and its hydrolysates demonstrated superior •OH scavenging activity. Chromatographic analysis confirmed low-molecular-weight peptides positively correlated with antioxidant potential. This study highlights molecular weight distribution, together with enzyme type, as a pivotal determinant of the antioxidant activity of jellyfish hydrolysates, providing insights for antioxidant peptide development.