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 <i>jellyfish</i> species, <i>Rhopilema hispidum</i> (<i>R. hispidum</i>) and <i>Nemopilema nomurai</i> (<i>N. nomurai</i>), 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. <i>R. hispidum</i> hydrolysates exhibited stronger DPPH• and O₂•^- scavenging activities and contained a higher proportion of low-molecular-weight peptides (<3 kDa), whereas <i>N. nomurai</i> 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.