Effects of nutrient supplements on simultaneous fermentation of nisin and lactic acid from cull potatoes.

The feasibility of using cull potatoes as substrate for the simultaneous production of nisin, a natural food preservative, and lactic acid, a raw material for biopolymer production, was studied. Cull potatoes are potato tubers unacceptable for food processing because of size or damage caused by bruising or disease. Although cull potatoes are enriched in various nutrients including starch, minerals, and proteins, they alone still cannot provide enough essential nutrients for the growth and metabolism of Lactococcus lactis subsp. lactis (ATCC 11454). Stimulation of bacterial growth, nisin biosynthesis, as well as lactic acid production was observed when additional nutrients such as yeast extract, peptone from meat, peptone from soy (PS), corn steep solid (CSS), and distillers' dried grains with solubles were provided. Considering the cost and availability, PS and CSS were selected as nutrient supplements for nisin and lactic acid coproduction. The conditions for nisin biosynthesis and lactic acid coproduction by L. lactis subsp. lactis in a cull potato-based medium were subsequently optimized using a statistically based experimental design.