Enzymatic Fermentation Of Food Waste To Produce Medium-Chain Fatty Acids Research

With the rapid development of the economy and the continuous improvement of people’s living standards,the output of food waste in China is increasing day by day.If it is not standardized,it will have a serious impact and harm on the human body and the environment.Compared with incineration and landfill,the anaerobic fermentation method not only has less environmental pollution,but also realizes energy recovery.At the same time,medium-chain fatty acids are widely used in industry,agriculture,medicine and other fields,and can be used as drugs,lubricants,antibacterial agents,feed additives and biofuels.Ethanol and lactic acid have proven to be the most suitable electron donors for the production of medium-chain fatty acids,but ethanol as an electron donor requires additional CO₂ to provide a carbon source.Therefore,this study aims to produce medium-chain fatty acids using food waste as the substrate,and strives to prepare lactic acid fermentation broth by enzymatic digestion and fermentation of food waste in large and efficient quantities,explore the optimal conditions of enzymatic hydrolysis and fermentation stage,and then use lactic acid fermentation broth as substrate to prepare medium-chain fatty acids to study the influencing factors in the production of medium-chain fatty acids.The specific research content and results are as follows:（1）The most suitable conditions for the enzymatic hydrolysis and saccharification stage of food waste are optimized.According to the characteristics of large proportion of starch and cellulose components of selected food waste,the compound enzyme ofα-amylase and cellulase was selected for enzymatic hydrolysis experimental research.Through single factor and response surface optimization experiments,the optimal conditions for enzymatic hydrolysis of reducing sugars were obtained:the optimal enzyme dosage was 1.2%of the substrate,the ratio ofα-amylase and cellulase was 4.4:1,the enzymatic hydrolysis temperature was 44.6°C,and the enzymatic hydrolysis p H was 6.2,and the concentration of reducing sugars was increased by 213%compared with no enzyme under these conditions.（2）Optimal screening of lactic acid-producing microbial agents.Before exploring the optimal conditions in the fermentation stage,the most suitable lactic acid microbial agents were screened out.Firstly,the ability of a single bacterium to produce lactic acid was experimentally studied,and three bacterial agents were selected:acidophilus lactobacillus,Bacillus coagulans and yeast.The results showed that the lactic acid production capacity was Bacillus coagulans>acidophilus lactic acid bacteria>yeast.Then the three microorganisms were mixed to produce lactic acid,and the results showed that the complex agent did show better lactic acid production ability than a single bacteriological agent,and the lactic acid production capacity was:Bacillus coagulans+acidophilus>Bacillus coagulans+yeast>acidophilus lactic acid bacteria+yeast.Therefore,the optimal lactic acid complex agent is Bacillus coagulans+acidophilus.（3）Study on the influencing factors of complex bacteria on lactic acid produced by enzymatic hydrolysis fermentation of food waste.The optimal conditions were set for enzymatic hydrolysis of food waste,and after a period of time,Bacillus coagulans and acidophilus were inoculated to ferment lactic acid to produce lactic acid.It was determined that the inoculation amount of the compound bacterium was 10%,the inoculation ratio of Bacillus coagulans and acidophilus was 1:1,the interval between the addition of enzyme bacteria was1h,the fermentation temperature was 40°C,and the fermentation p H was 6.The inoculation amount,inoculation ratio,fermentation temperature and fermentation p H of the compound fungus were selected for response surface optimization,and the results were that the inoculation amount was 10%,the inoculation ratio was 1.08:1,the fermentation temperature was 39.2°C,the fermentation p H was 6.2,and the lactic acid concentration reached 8.246 g/L,which was176%higher than that without lactic acid bacteria.（4）Study on the influencing factors of the conversion of lactic acid fermentation broth into medium-chain fatty acids.The lactic acid fermentation broth was prepared under the above optimal conditions of enzymatic hydrolysis fermentation,and medium-chain fatty acids were prepared using the lactic acid fermentation broth as the substrate,and the effects of lactic acid concentration,additional electron donor ethanol,additional electron acceptor type,plus electron acceptor acetic acid and p H value on medium-chain fatty acids were explored.The results show that the lactic acid concentration of the obtained fermentation broth can undergo a chain growth reaction,which is in line with the low concentration range of medium-chain fatty acids.When the electron acceptor is acetic acid,it shows a better caproic acid production ability than n-butyric acid,and caproic acid cannot be used as a single electron acceptor.Therefore,when the concentration of lactic acid in the fermentation broth is about 8 g/L,the concentration of electron donor ethanol is 6 g/L,the concentration of acetic acid of the electron acceptor is 4 g/L,and the optimal p H value is 6,which is the best condition for the production of medium-chain fatty acids,and the product is mainly caproic acid.The results of this study show that medium-chain fatty acids can be prepared by using lactic acid-containing food waste fermentation broth,which can not only solve the environmental pollution of food waste,but also transform it into high-value products,which can be used in industrial production and alleviate the problem of insufficient resources.