Protein isolates and hydrolysates from Atlantic sea cucumber (Cucumaria frondosa): characterization and bioactivities

Senadheera, Tharindu Ruchira Lakni (2020) Protein isolates and hydrolysates from Atlantic sea cucumber (Cucumaria frondosa): characterization and bioactivities. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

North Atlantic sea cucumber (Cucumaria frondosa) or orange-footed sea cucumber is a benthic marine echinoderm found in Northwest Atlantic waters. It is harvested mainly for its edible body wall and muscle bands. The aquaphyrangeal bulb or flower is considered as a secondary marketable product and internal organs including gonads, respiratory tracts and intestine are discarded as processing by-products, which generate a high volume of biological waste. However, all the body parts of the sea cucumber are rich in protein. The objective of this research was to recover the proteins from sea cucumber tissues and produce protein hydrolysates with bioactive properties associated with antioxidative and angiotensin-I-converting enzyme (ACE) inhibitory activities following a multidisciplinary approach. Proteins were isolated from the body wall, flower and internal organs of Cucumaria frondosa using a pH-shift method. Isolated proteins were evaluated for their physicochemical properties including solubility, emulsifying and foaming properties, water- and oil-holding capacities, surface hydrophobicity, content of sulfhydryl and disulfide groups along with FTIR analysis for identifying the functional groups of proteins and amino acid compositional analysis. Findings of this research revealed that sea cucumber-derived protein isolates could be used as a natural alternative to soy protein isolates as well as a source of balanced dietary proteins. Lyophilized protein isolates were then hydrolysed using food grade commercial enzymes, namely Alcalase, Corolase and Flavourzyme individually and in combination. The protein hydrolysates so prepared were evaluated for their antioxidant potential in different systems including radical scavenging assays such as the 2-2-diphenyl-1-picrylhydrazyl (DPPH) radical, the2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation, and hydroxyl radical scavenging assays. In addition, metal chelating, the reducing power, and -carotene bleaching assays in oil-in-water emulsion as well as thiobarbituric acid (TBA) assays in meat-model system were performed. Furthermore, hydroxyl and peroxyl radical induced DNA strand scission inhibitory activity assay and the cupric ion- induced human low-density lipoprotein (LDL) peroxidation inhibitory activity assays were performed. Finally, physicochemical properties of protein hydrolysates were evaluated based on their solubility, color and water holding capacity in a meat model system. The samples treated with a combination of Alcalase and Flavourzyme exhibited strong antioxidant potential and better functional properties compared to that of other treatments as well as their untreated counterparts of all tested sea cucumber body parts. The selected protein hydrolysates were also assessed for their ACE inhibitory activity to examine the potential multifunctional behaviour. All these findings along with the amino acid profiles demonstrated that the samples hydrolyzed with Alcalase and Flavourzyme exhibited more favourable properties. Results demonstrated that sea cucumber protein hydrolysates have great potential for use as nutritional supplements. Protein hydrolysates with highest antioxidant activity were further analysed for their molecular weight distribution and amino acid sequence using liquid chromatography- mass spectrometry (LC-MS/MS). The identified peptide sequences were then subjected to in silico analysis employing biotechnological tools PepRank, BIOPEP-UWM data base, ToxinPred and SwissADME. Virtual screening of bioactive peptides predicted that sea cucumber-derived peptides have the potential to develop as therapeutics in oral administration. Thus, the findings of the current study revealed the potential applications of sea cucumber-derived protein isolates, hydrolysates and bioactive peptides in functional food, nutraceutical, dietary supplement as well as natural therapeutics.

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