Bioconversion of lignocellulosic by-products to L(+)-lactic acid by Lactobacillus cultures.

摘要

The bioconversion of lignocellulosic by-products such as municipal solid waste to fuels and chemicals has economic and environmental advantages. Technologies which can convert lignocellulose to fermentable sugars are currently available. The challenge is to screen suitable microorganisms which can use these lignocellulosic-derived sugars to produce commercial fuels and chemicals in huge quantities at low cost. Recent developments, particularly in the field of biodegradable plastics, have aroused new potential interest in L(+)-lactic acid, which can be used as a feedstock to manufacture biodegradable polylactic plastic (PLA).; Eight Lactobacillus cultures were screened for potential industrial production of L(+)-lactic acid from acid hydrolyzed municipal solid waste (MSW). Screening criteria included carbohydrate utilization, lactic acid production and the percentage of L(+)-lactic acid isomer produced. Of the eight cultures, L. pentosus NRRL B-227 showed the most promise for L(+)-lactic acid production. This culture fermented glucose, mannose and galactose and produced the highest concentration of lactic acid (21.2 mg/ml) in MSW substrate containing 41.3 mg/ml of carbohydrates. About 91% of the lactic acid produced was the L(+) isomer.; The optimum conditions for the bioconversion of MSW hydrolysate to lactic acid were evaluated. Calcium hydroxide treatment of MSW hydrolysate removed 45-95% of microbial inhibitors such as furfural, hydroxymethylfurfural and phenolic compounds and improved lactic acid production. Under the optimum fermentation conditions, consisting of 1% inoculum, 32{dollar}spcirc{dollar}C, static fermentation, initial carbohydrate of 80-105 mg/ml, 0.28% nitrogen nutrient provided by tryptone and yeast extract or soybean meal, and 5% calcium carbonate as the acid neutralizing reagent, L. pentosus NRRL B-227 produced 58.7-75.4 mg/ml lactic acid in MSW substrate, an 80 to 93% yield based on carbohydrate utilization. Using the immobilized culture fermentation technique, about 110.1 mg/ml of lactic acid was produced from MSW hydrolysate containing 131 mg/ml of carbohydrate by immobilized L. pentosus B-227.