Complete bioconversion of hemicellulosic sugars from agricultural residues into lactic acid by Lactobacillus pentosus

On the basis of previous knowledge, different agroindustrial wastes were submitted to dilute-acid hydrolysis with H2SO4 to obtain hemicellulosic sugars and then employed for lactic acid production by Lactobacillus pentosus. Toxic compounds released from lignin did not affect lactic acid fermentation when hydrolysates from trimming vine shoots, barley bran husks, or corncobs were employed as carbon source, and complete bioconversion of hemicellulosic sugars was achieved. Nevertheless, Eucalyptus globulus hydrolysates had to be submitted to a detoxification process with activated charcoal. Maximum lactic acid concentration (33 g/L) was reached employing barley bran hydrolysates, whereas corncobs, trimming vine shoots, and detoxified E. globulus hydrolysates yielded 26, 24, and 14.5 g/L of lactic acid, respectively. The maximum product yield from pentoses (0.76 g/g) was achieved using hydrolysates from trimming vine shoots, followed by hydrolysates from detoxified E. globulus (0.70 g/g), barley bran (0.57 g/g), and corncob (0.53 g/g). These results confirm that L. pentosus can be employed to ferment hemicellulosic sugars (mainly xylose, glucose, and arabinose) from acid hydrolysates of most agricultural residues without appreciable substrate inhibition.