Abstract
Marine bioactive compounds have been found in very different sources and exert a very vast array of activities. Squid skin, normally considered a discard, is a source of bioactive compounds such as pigments. Recovering these compounds is a potential means of valorizing seafood byproducts. Until now, the structure and molecular properties of the bioactive pigments in jumbo squid skin (JSS) have not been established. In this study, methanol–HCl (1%) pigment extracts from JSS were fractionated by open column chromatography and grouped by thin-layer chromatography in order to isolate antioxidant pigments. Antioxidant activity was determined by the 2,2-diphenyl-1-picrylhydrazyl (DPPH●) and 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS●+) radical scavenging assays and ferric reducing power (FRAP) assay. Fractions 11–34 were separated and grouped according to flow rate values (F1–F8). Fractions F1, F3, and F7 had the lowest IC50 against ABTS●+ per milligram, and fractions F3 and F7 showed the lowest IC50 in the FRAP assay. Finally, fraction F7 had the highest DPPH● scavenging activity. The chemical structure of the F7 fraction was characterized by infrared spectroscopy, 1H nuclear magnetic resonance, and electrospray ionization–mass spectrometry. One of the compounds identified in the fraction was xanthommatin (11-(3-amino-3-carboxypropanoyl)-1-hydroxy-5-oxo-5H-pyrido[3,2-a]phenoxazine-3-carboxylic acid) and their derivatives (hydro- and dihydroxanthommatin). The results show that JSS pigments contain ommochrome molecules like xanthommatin, to which the antioxidant activity can be attributed.
Highlights
Marine bioactive compounds show noteworthy and natural properties that support their nutraceutical and pharmaceutical potential and are regarded as more secure options in contrast to synthetic drugs and food additives
The aim of this work was to isolate and identify the pigments responsible for the antioxidant activity detected in squid skin (Dosidicus gigas)
The liquid-phase column to open column method resulted in the elution of 34 fractions from the raw extract
Summary
Marine bioactive compounds show noteworthy and natural properties that support their nutraceutical and pharmaceutical potential and are regarded as more secure options in contrast to synthetic drugs and food additives. Marine bioactive compounds have been isolated and characterized from different sources, like plants, microorganisms, algae and animals (vertebrates and invertebrates) [1]. Among the different invertebrates studied, one of the most notable for its commercial impact and Molecules 2019, 24, 3420; doi:10.3390/molecules24193420 www.mdpi.com/journal/molecules. As with most marine species, only the squid muscle is of economic importance. Obtaining clean squid filet requires the removal of skin and other anatomical regions. This process creates waste that accounts for over 40% of the total squid weight [3]
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