Lactic acid fermentation of potato pulp by the fungus Rhizopus oryzae.

Thirty-eight strains of the fungus Rhizopus oryzae were grown on potato pulp, an agricultural by-product of the starch industry. Either lactic acid or fumaric acid and ethanol were formed, and the ratio differed among the strains tested. The highest amount of L(+)-lactic acid (10 mg/g fresh matter) was observed in the pulp fermented for six days by Rhizopus oryzae IFO 4707. The IFO 4707 strain rapidly reduced the hardness and pH of potato pulp within one day followed by the gradual synthesis of lactic acid. A composition analysis showed that the enzymes secreted from the fungal cells hydrolyzed starch efficiently with partial degradation of the cell wall. Rhizopus oryzae may be used as an inoculant for ensiling potato pulp and other agricultural by-products containing starch.