Cost-effective lactic acid production by fermentation of agro-industrial residues

The substrate cost is a hurdle in the lactic acid (LA) manufacturing by microbial fermentations. Thus, this work aimed to optimize the production of LA by Lactobacillus amylovorus and Lactobacillus acidophilus in a culture medium containing agro-industrial wastes, cassava bagasse (CB, 6-18%, w/v) and corn steep liquor (CSL, 4-12%, v/v). Initially, the optimal medium composition was defined; different fermentation times were also assessed. CB was used in natura or hydrolyzed by Rhizopus oligosporus' amylase. In a batch process without pH control, the LA maximum concentration (31.6 g/L-h) and productivity (0.11 A) were obtained by L. amylovorus using 14% (w/v) hydrolyzed CB and 10% (v/v) CSL. However, when a Fed-batch process was performed with pH control and using the optimized culture medium composition, high volumetric productivity (0.46 g/L-h) was achieved. The optimized medium's cost is 0.05 US$/L. These findings suggest a promising bioprocess for LA manufacturing from agro-industrial wastes.