Bioconversion of agro-residues to make extracellular polysaccharides in solid state fermentation via Trichoderma hamatum using response surface methodology: Antioxidant and α-glucosidase inhibitor activity

Agro-residues, including banana peel, pineapple peel, mango peel, apple peel, and coconut husk, were utilized to produce extracellular polysaccharide (EPS) via solid state fermentation(SSF) by the fungus, Trichoderma hamatum. EPS production was highest in pineapple peel (84.2 ± 0.4 mg/g), followed by mango peel (70.3 ± 0.41 mg/g) (p<0.01). The SSF bioprocess was optimized via a two-level full factorial design and response surface methodology. The effects of five selected variables on EPS biosynthesis, namely, the concentrations of glucose (10 to 30%), ammonium sulphate (0.1 to 1%), yeast extract (0.5 to 2%), MgSO4 (0.01 to 0.1%), and medium pH (4.5 to 6.5), were analyzed via a full factorial design (FFD). The EPS production ranged widely from 15.3 to 576.2 mg/g substrate. Three significant variables affecting EPS production were assessed in central composite design (CCD) to optimize concentrations of MgSO4, and glucose, and the pH. The designed CCD model was fitted to the quadratic model and was significant (p<0.0001). For 50 μL of EPS, the scavenging ratio was 43.4 ± 4.1% at a concentration of 200 μL (78.5 ± 6.9 μL) (p<0.01). The extracted EPS exhibited an alpha-glucosidase inhibitory effect (p<0.001). Solid-state fermentation allows the utilization of low-cost biomass for EPS production and the application of T. hamatum EPS as a natural antioxidant and α-glucosidase inhibitor.