The Study Of Lactic Acid Production From Jerusalem Artichoke Powder By Lactobacillus Paracasei NJ Using Simultaneous Saccharification And Fermentation

Lactic acid,as an essential chemical in industry,has been widely used in various fields.As a raw material,it can be quickly and naturally degraded and regenerated polylactic acid fiber(PLA),which is currently considered as the most potential environmental material to replace traditional plastics.In recent years,due to the high cost of refining sugar substrates in traditional processes and the food safety problems caused by lactic acid fermentation using traditional foods as substrates,the search for cheap renewable resources as lactic acid fermentation substrates has become a hot topic.Jerusalem artichoke,a non-food crop,is widely cultivated in northwestern China.Inulin,the main component of Jerusalem artichoke tuber makes it a good resource for biorefinery.In this study,Lactobacillus paracasei NJ was employed as the fermentative strain by the reason of its ability to directly use Jerusalem artichoke powder(JAP)as a substrate to produce lactic acid.This research explored a fermentation process for the lactic acid production by using JAP as raw materials.The fermentation process does not require additional acid hydrolysis or enzymatic hydrolysis,external nitrogen sources,and sterilization.This straightforward and low-cost process yet with high-yield and high-purity L-lactic acid production makes Jerusalem artichoke tuber promising application prospects in the industrial production of lactic acid.The main results are as follows:(1)Lb.paracasei NJ was selected to be the fermentative strain in the production of lactic acid production due to the results of comparison of the conversion of inulin and JAP using different lactic acid bacteria.NJ had the highest yield of lactic acid produced by JAP and the highest conversion rate(32.65 g/L and 0.65 g/g JAP),showing the huge potential for directly efficient lactic acid production from JAP.Simultaneously,the growth curve of NJ under different carbon sources and the analysis of its ability to ferment different pure sugars showed that NJ could effectively ferment glucose,fructose.Moreover,it displayed high conversion rates of inulins with different polymerization degrees to lactic acid.(2)The effects of different p H,different temperature,different nitrogen sources,different concentration of JAP,the addition of enzymes,and the sterilization of culture medium on the production of lactic acid were investigated.The results demonstrated that the optimal conditions were p H 5.5,40?,corn steep powder(nitrogen source).The conversion rate of fermentation with no additional nitrogen source is considerable,lower than the result of corn steep powder group.The yield and conversion rates of sterilization fermentation and non-sterilization fermentation were at the same level.At the end of the non-sterilization fermentation,the species of Lb.paracasei accounted for more than 99% of the total bacterial count.(3)Lactic acid production from 215 g/L JAP by Lb.paracasei NJ was carried out in 5-L and 50-L bioreactor through simultaneous saccharification and fermentation.The L-lactic acid concentration,yield,and average productivity reached 144.08 g/L and 139.57 g/L,0.67 g/g JAP and 0.65 g/g JAP,4.37 g/L/h and 3.32 g/L/h,respectively in 5-L and 50-L bioreactor.The optical purity of L-LA reached as high as 99%.A conversion efficiency accounting for 99% of the theoretical yield.(4)The genome of Lb.paracasei NJ was sequenced,assembled,functionally annotated,and analyzed.By analyzing the metabolic pathways of NJ in the KEGG database,it was found that the genome contains a large number of genes involved in the phosphotransferase system and ABC transport system,as well as a variety of glycosidase genes,which means that the sugar transports and metabolism is active.Additionally,fructose/mannosemediated phosphotransferase system-related genes and two inulinase genes related to inulin degradation were predicted.Amino acid sequences comparisons showed that one of them shared complete 100% identity with extracellular ?-fructosidase(EC 3.2.1.80)and the other shared 82.9% identity with an intracellular sucrose-6-phosphate hydrolase or ?-fructofuranosidase(EC 3.2.1.26).