Improving the quality of agro-wastes by solid-state fermentation: enhanced antioxidant activities and nutritional qualities

Solid substrate fermentations of some agro-wastes, namely cocoa pod husk (CPH), cassava peel (CP), and palm kernel cake (PKC) were carried out for the production of fructosyltransferase (FTase) by a newly isolated fungal strain Rhizopus stolonifer LAU 07. The fermented substrate were studied for improved nutritional quality by determining the crude protein, crude fibre, ash and lipid contents, and antioxidant activities. The cyanide content of cassava peels was also determined. Some levels of value-addition occured as a result of the fermentation. The protein contents of the substrates increased by 33.3, 55.4, and 94.8%, while the crude fibre contents decreased by 44.5, 8.6, and 7.2% in PKC, CP, and CPH, respectively. The cyanide content of cassava peel was reduced by 90.6%. Generally, fermentation of the substrates by R. stolonifer LAU 07 increased the antioxidant activity in a DPPH (1,1-diphenyl-2-picrylhydrazyl) assay. The IC₅₀ (mg/ml) values of the methanolic extracts (fermented/unfermented) were obtained as 7.0/14.9, 4.4/10.6, and 5.5/14.7 mg/ml for PKC, CP, and CPH, respectively. Results herein reported showed that the nutritional qualities and antioxidant activities of all the investigated solid substrates were enhanced by fungal fermentation. Thus, scope exists for microbial upgrading of these low-quality agro-wastes and development of healthy animal feed supplements.