PHYSIOCOCHEMICAL PROPERTIES AND NUTRIENT CONTENT OF FERMENTED SWEET POTATO (IPOMOEA BATATAS L.)

Abstract

Sweet potato pulp was fermented using pure strains of four monoculture fungi: Aspergillus niger, Rhizopus stolonifer, Neurospora and Saccharomyces cerevisiae by solid substrate fermentation method.  Results of proximate analysis showed significant (P≤0.05) increased protein (from 2.34±0.07% in the control to values ranging from 11.46±0.10 to 12.62±0.09% in the fermented samples) and lipid contents (from 2.89 0.04% in the control to 3.77±0.11 and 5.57±0.14 in the fermented samples).  Significant decreases were recorded in ash, crude fibre and carbohydrate contents.  Reducing, non-reducing and total sugar, starch and amylopectin contents were significantly reduced, while amylase content increased as a result of fermentation.  Mineral analysis showed increased Zn, Fe and Na contents while Mg, Ca, P and K were reduced. The pH of the samples reduced as fermentation progressed except in Saccharomyces cerevisiae-fermented samples. Highly significant negative correlation was obtained between fermentation time and pH of samples fermented with Aspergillus niger, Rhizopus stolonifer and Neurospora sitophila while Saccharomyces cerevisiae-fermented samples was highly significantly and positively correlation with fermentation time. Bulk density was reduced as a result of fermentation, ranging from 3.00 to 13.43%. Overall, Aspergillus niger appeared to be the most nutritionally-enriching of the four fungi used in the study.