Effect of high-pressure processing (HPP) on phenolics and their antioxidant activities of Atlantic sea cucumber (Cucumaria frondosa)

Hossain, Abul (2021) Effect of high-pressure processing (HPP) on phenolics and their antioxidant activities of Atlantic sea cucumber (Cucumaria frondosa). Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Sea cucumber belongs to the phylum Echinodermata and Holothuroidea class, which contains numerous bioactive compounds, including phenolics. In particular, body wall, aquapharyngeal bulb/ flower, and internal organs/ viscera are rich sources of phenolics. Sea cucumber is harvested mainly for its body wall and muscle bands. However, during sea cucumber processing, several visceral by-products are produced, including gonad, respiratory tract, and intestine, which are ultimately discarded as waste. These visceral by-products represent up to 50% of the sea cucumber biomass and are a rich source of bioactive compounds, mainly phenolics. The most common sea cucumber found in the North Atlantic region is the orange-footed sea cucumber (Cucumaria frondosa, Gunnerus, 1767). However, this species is under-explored for its bioactive compounds, especially its polyphenolic composition. Hence, this study investigated the free, esterified, and insoluble-bound phenolics from different commercial body parts (tentacles and body wall) and processing discards of sea cucumber (C. frondosa), as affected by high-pressure processing (HPP) pre-treatment. For that, sea cucumber was subjected to high-pressure (2000, 4000, and 6000 bar for 5, 10, and 15 min), followed by separation into the three aforementioned fractions. The contents of total phenolics and flavonoids were determined, and antioxidant activity reflected in scavenging of DPPH (2,2-diphenyl-1-picrylhydrazyl), ABTS (2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid), and hydroxyl radicals was monitored. The metal chelating ability of various phenolic fractions was also evaluated. Moreover, bioactivities such as inhibition of peroxyl and hydroxyl radical-induced supercoiled DNA strand scission, LDL-cholesterol oxidation inhibition, antiglycation activity, and α-glucosidase activity were examined. Furthermore, thiobarbituric acid (TBA) assay in a fish-model system was performed. Compared to untreated samples, those treated with HPP exhibited significantly higher total phenolics, flavonoids, and antioxidant activities. Treatment of 6000 bar for 10 min offered the optimal results. The free phenolic fraction was the predominant form present in all body parts examined. The highest amount of phenolics and antioxidant activity was observed in flower in the free phenolic fraction, whereas esterified and insoluble-bound phenolic fractions were more abundant in the body wall. Besides, in terms of bioactivities, all phenolic fractions showed strong inhibitory properties, mainly those that were in the free phenolic fraction. Additionally, 31, 23, and 20 phenolic compounds were identified from the flower, internal organs, and body wall, respectively, using UHPLC-QTOF-MS/MS. 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 different phenolic fractions of Atlantic sea cucumber. The highest amount of phenolic compounds of sea cucumber was observed as free phenolic in internal organs based on the UHPLC-MS analysis. Thus, this investigation enhances the fundamental understanding of the full utilization of Atlantic sea cucumber species and leads to the production of a multitude of value-added products.

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