Evaluation of the Weevil-damaged Sweet Potato as Substrate for Microbial Protein Obtaining

Abstract

The production of microbial protein from agricultural and agroindustrial wastes is an important way to supply the demand of this essential nutritional principle. Sweet potato (Ipomea batata) tubercles damaged by weevil (Cylas formicarius) are considered a waste due to their unpleasant flavor. This research deal in the characterization of sweet potato damaged by weevil, as an alternative substrate
for the culture of the fodder yeast Candida utilis. It was found that the damaged tubercle had a similar composition that the healthy one, concerning dry matter, total reducing sugars, nitrogen and minerals; the high content of reducing sugars (30-40 % dry weight) recommends the use of this waste as a substrate for single cell protein production. Several fungal strains were assayed to enzymatic degradation of sweet potato polysaccharides; from these ones, Aspergillus oryzae H/28-1 and Neurospora sp. were the more actives to release reducing sugars to the culture medium, being the last one the more prominent. The
yeast Candida utilis showed a satisfactory growth in media formulated in basis to weevil-damaged sweet potato, reaching reducing sugar consumptions over 80 % and biomass yields of 37-58 %; addition of urea as nitrogen source improved both parameters of the growth. The fermentation’s end-product acquired a pleasant flavor, which suggests a better palatability.