Formulating the racemic lactic acids-free nitrogen ingredients from plant proteins for cellulosic chiral lactic acid fermentation.

Nitrogen additive is an important factor for chiral lactic acid fermentation for low-cost and high optical purity of final chiral lactic acid product. This study tried to formulate a low-cost and racemic lactic acids-free nitrogen ingredient for lactic acid bacterium strain using wheat straw as carbon source. Eight available plant proteins were evaluated as potential nitrogen additives for chiral lactic acid fermentation by proteinase catalyzed hydrolysis to release the free amino acids and short peptides. Soybean meal was selected as the most promising nitrogen additive by its high protein content and lactic acids free composition. The plant proteins derived nitrogen additives was found that the inherent deficiency of amino acids in plant proteins led to the insufficient lactic acid fermentation. A minimal yeast extract was added to the plant protein hydrolysates to compensate the amino acid deficiency, and the use of the combinational nitrogen ingredients resulted in the final cellulosic L-lactic acid titer reached 122.9 ± 0.4 g/L with the yield of 88.1% and the optical purity of 99.7% using wheat straw feedstock. Comparing with yeast extract as nitrogen additive, the combinational ingredients substituted 75% of yeast extract with 56.7% cost reduction. This study provides a cost-effective solution of nitrogen ingredients for cellulosic chiral lactic acid production in industrial biorefinery process. • Plant proteins were screened as racemic lactic acids-free nitrogen additives. • A combinational nitrogen ingredient was designed for chiral cellulosic lactic acid fermentation. • 75% of yeast extract was substituted by plant proteins with 56.7% cost reduction. [ABSTRACT FROM AUTHOR]