Process Optimization For L-Lactic Acid Production From Food Waste

Lactic acid which belongs to the basic chemical raw materials for the production of both commodity and specialty chemicals is acknowledged as one of the most widely used organic acids worldwide.At present,95% of the L-lactic acid is obtained from food production.Food waste is recognized as a typical kind of raw material which has the characteristics of large quantity,extensive sources and abundant organic matter,and it can be the raw materials for the production of L-lactic acid.Food waste was taken as the object in this study.On the basis of screening advanced lactic acid bacteria,pretreatment of enzymatic hydrolysis on food waste and cooperative fermentation by corn stalk were carried out to optimize conditions of L-lactic acid production from food waste.The main research results were summarized as follows:1)An advanced lactic acid bacteria was isolated from plain yogurt on MRS agar.After identified by normally physiological and biochemical tests,the bacteria could be a homofermentative Lactobacillus plantarum species.It growed quickly and 6~9h was the logarithmic phase.In addition,its lactate production capacity could be up to 142g·L-1.2)The results of the pretreatment of enzymatic hydrolysis on food waste showed that the optimum proportion of enzyme preparation was 450U·gVS-1of ?-amylase,180U·gVS-1 of lipase and 90U·gVS-1 of trypsin,respectively.And the optimum hydrolysis condition was 45°C of temperature,5.0 of pH value,and 60 min of hydrolysis time.In this condition,the maximum yield of L-lactic acid was 0.246g·gVS-1,which was enhanced by86.4% more than that of the untreated food waste.3)The results of fermentation of food waste pretreated by enzymatic hydrolysis showed that the optimum parameter was 45°C of temperature,6.0 of initial pH value,1: 6of solid-liquid ratio,and 10% of inoculum size.Under this condition,the maximum yield of L-lactic acid was 0.325g·gVS-1 after 24-hour fermented.4)The results of cooperative fermentation of food waste and pretreated corn stalk showed that the optimum parameter was 50°C of temperature,6.0 of initial pH value,25:1of C/N ratio,and 10% of inoculum size.Under this condition,the maximum yield of L-lactic acid was 0.428g·gVS-1,which was enhanced by 31.7% more than the food waste pretreated by enzymatic hydrolysis directly.The fermentation time of cooperative fermentation was a half shorter than that of food waste alone,and the stability was also improved.