Enhancement and bioavailability of phenolic content in Kappaphycus alvarezii through solid substrate fermentation

Abstract

Known as carrageenan, Kappaphycus alvarezii is a popular species of red edible seaweed which is mainly cultivated for its hydrocolloids. K. alvarezii is a good source of phenolics which are considered to be natural antioxidants that promote myriads of health benefits. Extraction of phenolic compounds using conventional solvent extraction may result in hazards and toxicological effect and low yield of bound phenolics. Therefore, this study was conducted to increase the release of bound phenolics through solid substrate fermentation. In the present study, three different varieties of K. alvarezii were fermented with Aspergillus oryzae through solid substrate fermentation (SSF) at 30 ℃ for 2 to 6 days. The changes of total phenolic content and antioxidant activity due to the effects of SSF were investigated. Results obtained revealed that the highest total phenolic content for green (10.022 mg GAE/g) and purple (4.037 mg GAE/g) varieties of K.alvarezii were on the fourth day of fermentation while for yellow (4.479 mg GAE/g) variety was on the sixth day of fermentation. A remarkable enhancement of antioxidant activity was discovered through DPPH radical scavenging activity on the fourth day of fermentation for all varieties of K. alvarezii tested. Total phenolic content also showed a significant correlation with antioxidant activity of fermented seaweed. Cellulase, xylanase, and β-glucosidase enzymes produced by A.oryzae during SSF were also investigated to see the relationship with the release of phenolic compounds after fermentation. The highest cellulase activity was observed on the fourth day of fermentation. The similar observation was also found for xylanase enzyme in yellow and purple varieties of K. alvarezii, except for green variety where the highest xylanase activity was on the sixth day of fermentation. The maximum β-glucosidase activity in yellow and green varieties was observed on the fourth day of fermentation while purple variety exhibited the maximum β-glucosidase activity on the sixth day. There are positive correlation between the enzymes studied and the polyphenols content in all varieties of K. alvarezii. This study demonstrated that fermented K. alvarezii contained more phenolic content compared to non-fermented seaweed.