Chemical structure and antioxidant activity of cephalopod skin ommochrome pigment extracts

Abstract

Significant opportunities exist in the use of seafood by-products to create new beneficial products. Moreover, cephalopod skin is a good source of bioactive compounds. The present study compares the chemical structure properties and antioxidant activity of pigments extracted from the skin of Octopus vulgaris (OVS) and Dosidicus gigas (DGS) with methanol-HCl (T1) and ethanol-HCl (T2). The solubility and spectroscopic analysis (UV-Vis and 1 H NMR) indicated that extracted pigments belonged to the ommochrome family. Xanthommatin, dihydroxanthommatin, and kynurenine compounds were identified in the extracts using correlated homonuclear spectroscopy (COSY). The results showed that OVS yielded a higher recovery rate of pigments with antioxidant activity (DPPH, ABTS, and FRAP) than DGS in both solvents. T1 extracted the highest level of antioxidant pigments. The kynurenine proportion and proton peaks observed at 3.0-5.0 ppm (amino-aromatics) in the 1 H NMR spectra may explain the differences in antioxidant activity of OVS and DGS.

First Evidence of Ommochromes in Bivalves: the Case of the Edible Oyster Crassostrea Gigas

“…They also differ from those of porphyrins since no Soret band at ≈ 400 nm is distinguishable. These pro les turn out to be comparable to those of ommochromes which present a large band from 400 to 600 nm and a smaller one around 310 or 380 nm depending on the pH and the pigment in question 19,22,30 .…”

“…In this study, we noted that at least two groups of acid-soluble pigments were involved in the purple colour of shells of the oyster C. gigas. Among possible groups proposed from the identi cation of genes associated with their biosynthesis 9 , while the presence of acid-soluble porphyrins represented here by uroporphyrin I or III is now well established 7,8 , the presence of carotenoids and eumelanin could be ruled-out, their solubility being not compatible 1,30,38,39 . Besides, after separations of porphyrins from the set of acid-soluble pigments, the resulting PF was slightly soluble at 1 mg/mL in methanol, turning fully soluble with the addition of HCl (aq) , a typical property of ommochrome pigments.…”

“…While ommatins have an absorption band with a λ max around 450-500 nm, ommin A absorbs around 520 nm. The wide absorption band of PF, from 400 to 600 nm with λ max at 464, 496 and 552 nm, can result from a combination of various ommochromes pigments 30 (ommatins and ommins, at least). The discrimination between pheomelanin and ommochromes was then conducted by alkaline oxidation of PF, where none of pheomelanin markers were identi ed.…”

Improving the shelf life of chicken burgers using Octopus vulgaris and Dosidicus gigas skin pigment extracts

“…The head skin, considered a by-product, was manually collected, freeze-dried (Labconco, Kansas City, MO, USA), and kept at −18 ± 2 °C. Pigment extracts were prepared from 100 mg of freeze-dried skin samples via extraction with 1% HCl-methanol solution (v/v), as described elsewhere (Esparza-Espinoza et al, 2021). The samples without solvent were freeze-dried, packaged in polyethene bags, and stored at −18 ± 2 °C.…”

“…This behavior could be due to the presence of antioxidant compounds in the pigments, which may exert a certain level of lipid oxidation inhibition. This capacity is based on the configuration of ommochromic compounds present in the pigment extracts (Esparza-Espinoza et al, 2021). Ommochromes can act as free radical acceptors, thereby decreasing oxidation and forming new radicals in the oxidation process (Romero & Martínez, 2015).…”