*Article* **Barrel Jellyfish (***Rhizostoma pulmo***) as Source of Antioxidant Peptides**

**Stefania De Domenico 1, Gianluca De Rinaldis 1,2, Mélanie Paulmery 3, Stefano Piraino 4,5 and Antonella Leone 1,5,\***


Received: 31 January 2019; Accepted: 19 February 2019; Published: 23 February 2019

**Abstract:** The jellyfish *Rhizostoma pulmo*, Macrì 1778 (Cnidaria, Rhizostomae) undergoes recurrent outbreaks in the Mediterranean coastal waters, with large biomass populations representing a nuisance or damage for marine and maritime activities. A preliminary overview of the antioxidant activity (AA) of *R. pulmo* proteinaceous compounds is provided here based on the extraction and characterization of both soluble and insoluble membrane-fractioned proteins, the latter digested by sequential enzymatic hydrolyses with pepsin and collagenases. All jellyfish proteins showed significant AA, with low molecular weight (MW) proteins correlated with greater antioxidant activity. In particular, collagenase-hydrolysed collagen resulted in peptides with MW lower than 3 kDa, ranging 3–10 kDa or 10–30 kDa, with AA inversely proportional to MW. No cytotoxic effect was detected on cultured human keratinocytes (HEKa) in a range of protein concentration 0.05–20 μg/mL for all tested protein fractions except for soluble proteins higher than 30 kDa, likely containing the jellyfish venom compounds. Furthermore, hydrolyzed jellyfish collagen peptides showed a significantly higher AA and provided a greater protective effect against oxidative stress in HEKa than the hydrolyzed collagen peptides from vertebrates. Due to a high reproductive potential, jellyfish may represent a potential socioeconomic opportunity as a source of natural bioactive compounds, with far-reaching beneficial implications. Eventually, improvements in processing technology will promote the use of untapped marine biomasses in nutraceutical, cosmeceutical, and pharmaceutical fields, turning marine managemen<sup>t</sup> problems into a more positive perspective.

**Keywords:** invertebrate proteins; biological activity; antioxidants; collagen; pepsin hydrolysis; collagenase hydrolysis; oxidative stress; keratinocytes; cytotoxicity
