Microbial Lactic Acid Production from Renewable Resources

Abstract

Lactic acid is widely used in the food, chemical, textile, and pharmaceutical industries. New applications of lactic acid for the manufacture of biodegradable polymers have increased the demand for it. Lactic acid can be produced from cheese whey and starchy and lignocellulosic biomass via microbial fermentation with lactic acid bacteria (LAB) or fungi. Pure sugar and cheese whey can be directly fermented by lactic acid bacteria, while liquefaction and enzymatic saccharification of starchy biomass and pretreatment and enzymatic hydrolysis of lignocellulosic biomass are required for lactic acid production from biomass. Amylolytic lactic acid bacteria can direct convert starchy biomass to lactic acid. Lactic acid bacteria and methods used for lactic acid production from different feedstocks are summarized in this paper. Lactic acid productivity of 6.34 and 4.87 g/l·h and yields of 0.98 g/g lactose and 0.97 g/g glucose were obtained from cheese whey and wheat starch, respectively, using cell-recycle repeated batch fermentation by Lactobacillus sp. RKY2. Lactic acid bacteria such as Lactobacillus pentosus, Lactobacillus brevis and Lactococcus lactis can ferment glucose to lactic acid by homolactic fermentation and also effectively convert xylose or arabinose to lactic acid and acetic acid by heterolactic fermentation. The process for lactic acid production from lignocellulosic biomass needs to be improved to increase the lactic acid yield and productivity.