Betaine Improves Polymer-Grade D-Lactic Acid Production by Sporolactobacillus inulinus Using Ammonia as Green Neutralizer

The traditional CaCO₃-based fermentation process generates huge amount of insoluble waste. To solve this problem, we have developed an efficient and green D-lactic acid fermentation process by using ammonia as neutralizer. The 106.7 g/l of D-lactic acid production and 0.89 g/g of consumed sugar were obtained by Sporolactobacillus inulinus CASD with a high optical purity of 99.7% by adding 100 mg/l betaine in the simple batch fermentation. The addition of betaine was experimentally proven to protect cells at high concentration of ammonium ion, increase D-lactate dehydrogenase specific activity and thus promote the production of D-lactic acid.