Effect of different fermentation parameters on l-lactic acid production from liquid distillery stillage

Expansion of lactic acid applications, predominantly for the preparation of biodegradable polymers increased the research interest for new, economically favourable production processes. Liquid stillage from bioethanol production can be an inexpensive, valuable source of nutrients for growth of lactic acid bacteria. Utilisation of residual biomass with spent fermentation media as a functional animal feed can greatly influence the process value and its ecological aspect. In this paper, the kinetics of lactic acid and biomass production on liquid stillage by Lactobacillus rhamnosus ATCC 7469 was studied. In addition, the impact of temperature, inoculum concentration, shaking and pH control by addition of CaCO3 was evaluated. Maximal lactic acid yield of 73.4%, as well as high biomass production (3 × 108 CFU ml−1) were achieved under selected conditions (41 °C, 5% (v/v) of inoculum, 1% (w/v) of CaCO3, initial pH of 6.5 and shaking rate of 90 rpm). These results were achieved without supplementation of the stillage with nitrogen or mineral sources.