Nutritional requirements and the impact of yeast extract on the D-lactic acid production by Sporolactobacillus inulinus

This study provides detailed insight into the impact of complex nutrient sources on the fermentation of Sporolactobacillus inulinus, a highly productive D-lactic acid producing bacterium. The composition of various yeast extracts and peptones was analyzed and compared to the cultivation results of S. inulinus. Special attention was paid to the utilization of peptides and free amino acids. It turned out that free amino acids are the limiting factor for the lactic acid production. This limitation could be prevented in a fedbatch experiment, in which the product concentration was increased to 222 g L-1 by the addition of free amino acids and vitamins. Furthermore, a synthetic medium based on the analytical data of the reference yeast extract was developed to elucidate the nutritional requirements in detail.