| Currently,lactic acid has a wide range of applications and is widely applied in food,environmental protection,medicine,feed,daily necessities,chemical industry and other fields.There are several raw materials for the production of lactic acid,food waste as a potential renewable raw material which is rich in carbohydrates and protein can be used as raw material for lactic acid production.The traditional treatment of food waste not only causes pollution to the environment,but also wastes a lot of biomass energy.In this study,we use Bacillus coagulans strain LA204 that can efficiently ferment the substrate to produce lactic acid.This strain has the characteristics of high temperature resistance.It can ferment food waste to produce lactic acid to achieve reasonable using food waste resources.The results of this study are showed as follows:1.The salt tolerance and lactic acid production capacity of LA204 were analyzed.The salt concentration was controlled at 0.0%-2.0% to define range of salt tolerance.Then,the salt concentration was controlled at 0.0%-0.5%,and the growth and acid production of LA204 were detected.The results showed that when the salt concentration was higher than 0.5%,the growth of LA204 and lactic acid production were significantly decreased and the utilization efficiency of glucose was significantly reduced.It indicated that the salt tolerance of LA204 was not good.When the salt concentration was controlled within0.5%,the growth and production of lactic acid were basically the same,and the lactic acid liter was about 10.5 g/L.Therefore,the salt concentration in the medium should be controlled within 0.5% for lactic acid fermentation by LA204.2.The use of the main nutrient components(starch,protein,and lipids)in food waste was studied.The lipids had a certain inhibitory effect on the growth of LA204.When the medium contained 1% lipid with lipase,LA204 grew well for using it,but it did not produce acid;and the optimized wheat starch and protein ratio was 4:1.The medium contained 80 g/L starch and 20 g/L protein with addition of α-amylase,glucoamylase and protease,and 57.84 g/L glucose and 4.55 g/L maltose and a large number of amino acids were produced after incubation.Carbon-nitrogen source can be used for lactic acid fermentation by LA204,the residual glucose concentration was 30.44 g/L and a little maltose,the lactic acid liter was 20.72 g/L,the lactic acid yield was 0.26 g/g,and the lactic acid productivity was 0.20 g/L/h.Using the shake flasks to ferment had a lot of sugar residued and the lactic acid titer and yield were low.3.Lactic acid fermentation from low-level nutrients in food waste was conducted in a 5-L anaerobic bioreactor.The substrates were 80 g/L gelatinized wheat starch and 20g/L protein with α-amylase,glucoamylase and protease.The lactic acid liter,yield,productivity were 58.26 g/L,0.73 g/g,2.42 g/L/h respectively.The results showed that LA204 can efficiently utilize starch and protein for lactic acid fermentation under the action of enzymes.4.Simultaneous saccharification and batch feeding of lactic acid fermentation with food waste nutrients.The substrates were 80 g/L of gelatinized wheat starch and 20 g/L protein.One was fed unprocessed wheat starch,the other was fed gelatinized dried wheat starch.The fermentation was fed twice and the final substrate concentration was 160 g/L.Feeding unprocessed wheat starch experimental group showed that the lactic acid liter,yield,productivity were 65.67 g/L,0.41 g/g,0.91 g/L/h respectively;feeding elatinized dried wheat starch experimental group showed that the lactic acid liter,yield,productivity were 92.31 g/L,0.57 g/g,0.96 g/L/h respectively.The results showed that the nutrient substances in food waste should be gelatinized and dried by α-amylase,and the lactic acid liter and yield had been greatly improved.The use of simultaneous saccharification and fed-batch fermentation can greatly increase lactic acid titer. |
