The global consumption of sea cucumber has increased rapidl y due its impressive nutritional profiles with multiple medicinal properties. Sea cucumber contains numerous essential high-value nutraceuticals and pharmaceuticals, which show unique biological properties such as antithrombotic, anticoagulant, anticancer, anti-inflammatory, and antidiabetic activities . For example, orange-footed sea cucumber (Cucumaria frondosa ) is abundant in the northwest Atlantic, which has been harvested in recent years for commercial purposes. This species is comprised of numerous compounds, namely lipids (PUFAs), proteins (collagen and peptides), vitamins, polysaccharides (chondroitin sulfate), saponins, and phenolics. The body wall is the major marketable portion (~50%) of this echinoderm.
However, during the processing of sea cucumber, several visceral by-products are produced, including gonads, respiratory tracts, and intestines, that are ultimately discarded as waste. These discards represent up to 50% of the sea cucumber biomass and are a rich source of fatty acids and amino acids as well as bioactive compounds, mainly carotenoids and phenolics. Therefore, utilization of these discards is crucial in order to address both the environmental concerns and economic sustainability of sea cucumber industries .
The aim of this work was to examine the free, esterified, and insoluble-bound phenolics of sea cucumber processing discards for the first time in any species of sea cucumber . The contents of total phenolics and flavonoids were determined, and antioxidant potential, including ABTS (2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid), DPPH (2,2-diphenyl-1-picrylhydrazyl), and hydroxyl radical scavenging activities, was assessed. The metal chelating ability of different phenolic fractions was also monitored. Furthermore, bioactivities such as LDL-cholesterol oxidation inhibition, inhibition of peroxyl and hydroxyl radical-induced supercoiled DNA strand scission, anti-tyrosinase activity, anti- glycation activity, and α-glucosidase inhibitory activity were investigated. Moreover, the antioxidant activity of the phenolic extracts was also evaluated in a fish model system using thiobarbituric acid reactive substance (TBARS)
assay.
It was found that the sea cucumber processing discards are a good source of phenolic compounds. The highest amount of phenolics, antioxidant activity, and bioactivity was observed in the free phenolic fraction. Moreover, phenolic extracts improved the shelf-life of Atlantic salmon up to 9 days during refrigerated storage by inhibiting lipid oxidation. A strong positive correlation was found between total phenolics and various in vitro antioxidant ass ays, suggesting that sea cucumber phenolics showed antioxidant activity. Additionally, 18, 14, and 16 compounds were identified using UHPLC-QTOF/MS-MS from the free, esterified, and insoluble-bound fractions, respectively. Phenolic acids, mainly p-coumaric acid, protocatechuic acid, hydroxygallic acid, and chlorogenic acid, and flavonoids, including quercetin and catechin, were the major compounds found in the free phenolic fraction.
Therefore, sea cucumber processing discards may serve as a viable source of functional food ingredients with protective antioxidant properties.