Comparative evaluation of antioxidant pigments and collagen biomaterials from wastes of two edible sea urchin species

Around 75000 tons of different sea urchins species are exploited worldwide for their edible gonads1. The sea urchin Paracentrotus lividus is the main Mediterranean edible species. By applying a circular economy approach, we have recently demonstrated that non-edible parts of P.lividus (up to 70-90% of their mass) represent wastes that can be fully valorized towards high added value products. Particularly we exploited this waste as a source of potent antioxidant pigments2, namely polyhydroxynaphthoquinones (PHNQ), and native fibrillar collagen3, which are currently used to develop innovative biomaterials for biomedical applications. The aim of this work was to assess if waste from other species of edible sea urchins, i.e. Sphaerechinus granularis, can be similarly valorized. To this purpose, we performed a comparative study on PHNQ and collagen extracted from the two sea urchin species. Particularly, we identified and compared the different PHNQ relative abundances of their extraction yields (by UPLC-ESI-MS). Subsequently, antioxidant activities were assessed (by ABTS assay) and correlated to specific PHNQ presence (e.g. Spinochrome E). Similarly, collagen extraction yields were evaluated and the obtained collagen-based biomaterials were compared in terms of ultrastructural features and porosity (by SEM and squeezing method), degradation kinetics and mechanical resistance to compressive stress. Results showed that the PHNQ profile was partially similar in the two species, but while P.lividus PHNQ yield was significantly higher, the antioxidant activity was better in S.granularis. Furthermore, while P.lividus samples showed higher collagen extraction yield, minor differences in the ultrastructural organization of the obtained collagen biomaterials, as well as higher stability and resistance to compression, were observed in S.granularis scaffolds. In conclusion, wastes from both species can be successfully valorized for PHNQ and collagen extraction, although with different yields. The slightly different features of PHNQ and biomaterials might lead to different applications in biomedical field, according to specific technical requirements.