Lactic Fermentation of Media Containing High Concentrations of Yeast Extracts

Yeasts extracts (YE) were supplemented with whey permeate and citrate (YPC) as substrates for lactic acid and diacetyl production. Lactococcus lactis ssp. lactis AD was selected for high production of lactic acid and diacetyl. High correlation (r 2 = 0.88) occurred between acidification and population increases in YPC containing 70 g/L YE. Media with 100 g/ L YE were inhibitory to growth. YPC supplementation with M17 or MRS had little effect on growth but reduced diacetyl. Increasing incubation temperature to 25°C stimulated fermentation but a temperature rise to 30°C only increased lactic acid. With 2L fermenters (20°C/110 rpm) on YPC (70 g/L YE) maximal diacetyl was obtained between 12-16h, and maximal population was obtained after 22h. Fermenter-production of diacetyl in YPC was comparable to that in milk (1 to 10 ppm) but less than that in shake flasks (32 ppm).