Utilization of renewables for lactic acid fermentation

Originally, lactic acid was produced from pure substrates like glucose. Increasingly, however, agricultural feedstocks such as grains and green biomass are also being used as raw materials for the biotechnological production of lactic acid. A high-productivity lactic acid bacterium strain was selected, process parameters were optimized for the batch fermentation on a laboratory scale, and its performance at cultivation on a barley hydrolysate medium together with different supplements was examined. The present results for the cultivation of the Lactobacillus paracasei on complex nutrient broth are in the same range as those for another strain of the same species with pure glucose, de Man, Rogosa and Sharpe medium (MRS) minerals, peptone and yeast extract. Under these conditions, this strain was able to accumulate more than 100 g lactate/L in the MRS medium. Medium optimization experiments showed that the main part of the nitrogen-containing nutrients in the medium (peptone, yeast extract) can be replaced by protein extracts from green biomass (lucerne green juice). The green juice after pressing fresh biomass contains a series of nitrogen-containing compounds and inorganic salts, which are essential for cell growth. Thus, on laboratory scale, we have demonstrated that it is possible to substitute synthetic nutrients by renewable resources like cereals and green biomass without any loss of productivity. This high biomass concentration together with the number of living cells could increase the productivity to higher levels compared to the well-adapted synthetic nutrients of MRS.