Effect of High-Pressure Processing (HPP) on Phenolics of Sea Cucumber (Cucumaria frondosa) and their Bioactivities

The global consumption of sea cucumber has increased drastically due to its nutritional value. The most common sea cucumber species found in the northwest Atlantic is Cucumaria frondosa, which has been harvested commercially in recent years. The body wall is the major marketable portion of this species. 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 body weight and are a rich source of lipid and protein as well as bioactive compounds, mainly phenolic compounds. Therefore, utilization of these discards is crucial to minimize the processing waste and produce value-added products. This study aimed at investigating the free, esterified, and insoluble-bound phenolics from different body parts (body wall, flower, and internal organs) of sea cucumber (C. frondosa), as affected by high-pressure processing (HPP). Sea cucumbers were pretreated with high-pressure (2000, 4000, and 6000 bar for 5, 10, and 15 min) followed by freeze-drying. The contents of total phenolics and flavonoids were determined, and antioxidant activity of various phenolic fractions evaluated using in vitro free radical scavenging methods, namely DPPH (2,2-diphenyl-1-picrylhydrazyl), ABTS (2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid)), and hydroxyl radicals. The metal chelating activity of phenolics was also monitored. Furthermore, bioactivity of different phenolic fractions, including LDL-cholesterol oxidation inhibition, inhibition of peroxyl and hydroxyl radical-induced supercoiled DNA strand scission, antiglycation activity, and α-glucosidase activity were investigated. Individual phenolic profile was identified using ultra high performance liquid chromatography, coupled with a quadrupole time-of-flight mass spectrometry (UHPLC-QTOF-MS/MS). The HPP treated samples exhibited significantly higher total phenolics, flavonoids, and antioxidant activities compared to untreated samples. The best results were obtained for samples subjected to 6000 bar pressure for 10 min. The highest amount of phenolics, antioxidant activity, and bioactivity was observed in the free phenolic fraction. Phenolic acids and flavonoids were the major phenolic compounds found in all samples.