Bioconversion of macroalgae by enzymes from associated fungi into hydrolysates with cumulative antioxidant and antiglycemic properties for effective diabetes management.

Enzyme-assisted extraction is an emerging sustainable alternative to solvent based methods for recovering bioactive molecules from seaweed or macroalgal biomass. This study investigated the macroalgae-associated fungi as sources of extracellular enzymes for bioconversion of macroalgal biomass and the concurrent enhancement of bioactive properties. About 100 fungal isolates associated with macroalgae were isolated and characterized based on qualitative plate assays and quantitative enzyme activity for the production of cellulase, xylanase, agarase, alginate lyase, and ulvan lyase. Based on enzyme activity ranging from 1063 to 10,234 U ml- 1, four yeast isolates and one filamentous fungus were selected for solid-state fermentation of macroalgae Gracilaria corticata, Sargassum cinereum and Chaetomorpha antennina. The biochemical composition of reducing sugar, total phenolic and protein content in the seaweed hydrolysates obtained from solid state fermentation was significantly higher than the uninoculated control. The enzymatic hydrolysates of all the three macroalgal biomass, exhibited almost twice the antioxidant activity than its non-enzymatic control. However, antiglycemic activity was observed only in S. cinereum hydrolysate which ranged about 20 to 40%, which was significantly higher than the control. Significant correlation between the biochemical constituents and antioxidant activity was observed in the enzymatic hydrolysates of G. corticata, S. cinereum and C. antennina. Positive correlation was also observed between the protein content with antioxidant and antiglycemic activity in the hydrolysate of S. cinereum. This shows that the microbial enzymes have the potential for the bioconversion of macroalgal biomass, into bioactive molecules for sustainable diabetes management and for related health care applications.