Impact Of Products In Hydrolysate Of Corn Stalk On L-lactic Acid Fermentation

So far sugars and starches have been used as the main material for fermenting productionof L-lactic acid. As compared with them, the crops straw taking a representative oflignocelluloses biomass with cheap, abundant biomass sources of features is the recognizedsources of the raw materials for the scale development of L-lactic acid in the future. Duringthe hydrolysis procedure of lignocellulosic materials such as corn stalk, hemicellulose ishydrolyzed into monosaccharide, and meanwhile, toxic by-products are simultaneouslygenerated, which may influence L-lactic acid fermentation thereafter. Foreign scholars havestudied the kinds of inhibiting factors in the lignocellose hydrolysate, and researched theimpact of them on some yeast stain growth and alcoholic fermentation. At present, thedomestic related research mainly focus on the discussion of technology, the study ofinhibitory action of by-products is rare. The degree to which some inhibitors are tolerated bymicrobial strains is varies greatly. On this basis, this paper examined the influence ofinhibitors on the Rhizopus oryzae growth and L-lactic acid fermentation.This paper ferments the hydrolysate of corn straw by Rhizopus oryzae (AS3.819) forL-lactic acid. In this study, three by-products, acetic acid, vanillin, and furfural which wereidentified in the hydrolysate of local corn stalk, were added into the medium at differentconcentrations to study their impacts on the growth and L-lactic acid fermentation of aRhizopus oryzae (AS3.819).The results indicated that the biomass and L-lactic acid production were inhibited by thethree by-products，and the effects were different. Acetic acid inhibition enhanced with theincreasing of its concentration. When the content is3g/L, the glucose consumption, biomassand L-lactic acid production were inhibited obviously; Vanillin at low content (0.2g/L) ispresented inhibition against biomass growth. Lower than0.5g/L, glucose consumption waspromoted. At0.8g/L, glucose consumption and L-lactic acid production were decreasedobviously; Furfural at0.2～0.8g/L, promoted the glucose consumption, caused a muchlonger lag-phase in growth, decreased the L-lactic acid production. At1g/L, the biomassgrowth and L-lactic acid generation were completely inhibited. Thus, for the target product- L-lactic acid，vanillin and furfural is strong inhibitory factor; The tolerance of Rhizopusoryzae (AS3.819) against acetic acid is strong relatively, furfural secondly, vanillin isweakest.In this experiment, the fermentation results of hydrolysate which is the substrate werecompared with that of its concentrate. It found that, by-products in common with differentconcentrations have great impact on fermentation，and their inhibition degree are various. Thefermentation effect of hydrolysate2was better than others.Studies on the inhibitory effects of the by-products on L-lactic acid fermentation are ofpractical use for further improvement of L-lactic acid yield from lignocellulosic materials.