Studies On Isolation And Identification Of Lactobacillus Acidophilus And Its Growth Characteristics In Fermented Soymilk

Lactobacillus acidophilus is an important microorganism in human intestinal tract.When there exist certain number of Lactobacillus acidophilus in intestinal tract,they play an important role to maintain healthy intestinal flora balance.Lactobacillus acidophilus is one of probiotics which current scholar attaches great importance to research and development.It is considered as the third generation starter for fermented milk.With more and more in-depth studies on the biological characteristics,functionality and application of Lactobacillus acidophilus by many scholars at home and abroad, people have been growing awareness to this microorganism's prebiotic characteristics.There have been increasing products containing Lactobacillus acidophilus,such as yoghurt,capsule,troche, powder and oral liquid.However,functional fermented soymilk through the fermentation of Lactobacillus acidophilus haven't been commercial produced and there are few reports on the growth characteristics of Lactobacillus acidophilus in fermented soymilk. In China,soymilk is a traditional food,but also a kind of cheap and easy accessible resource.But due to the impact of the traditional habits,people have been unable to recognize the benefits of soymilk. In addition,soymilk has heavier beany flavor,so that many consumers, especially teenagers and children have low level of acceptance. Therefore,the use of modern biological technique,it is of great significance to develop functional fermented soymilk beverages through the fermentation of lactic acid bacteria.These beverages can not only solve the problem of taste,but also provide high quality and inexpensive functional vegetable protein beverage for the regions which are short of milk.In this study,Lactobacillus strains were isolated from fresh infant feces.There were three Lactobacillus acidophilus strains through molecularly biological identification.This study is aim to provide Lactobacillus acidophilus strains with strong growth capacity, high active number and strong acid-producing ability for fermented soymilk.Besides,we explored the growth characteristics of Lactobacillus acidophilus in fermented soymilk,providing a theoretical basis and a scientific basis for industrialized production of fermented soymilk.By comparing the biological characteristics of the three strains, including the growth curve,acid-producing ability,gastric acid-resistant capacity,bile-resistant capacity,antibiotic resistance and antibacterial capacity,we choosed Lactobacillus acidophilus LA-5 as tested strain.The active number of Lactobacillus acidophilus LA-5 can reach to 4.33×10¹² cfu/mL after cultivated in MRS liquid medium for 14 hours.Lactobacillus acidophilus LA-5 has strong acid-resistant and bile-resistant capacity.The strain is highly sensitive to chloramphenicol,penicillin G,rifampicin and acheomycin,but is't sensitive to kanamycin.In vitro,The metabolites of Lactobacillus acidophilus LA-5 are obvious antagonism on E.coli,Salmonella and Staphylococcus aureus and Staphylococcus citreus.In order to develop a Lactobacillus acidophilus starter suitable for producing fermented soymilk,we studied on the growth promoting culture of Lactobacillus acidophilus LA-5 based on soymilk.The optimal growth promoting culture composition was as following:10% soymilk,1%glucose,8%tomoto juice,5%corn extract juice,2% carrot juice,2%juice of plerotus sapidus.According to the growth curve of Lactobacillus acidophilus LA-5 in the optimal growth promoting culture,the terminal time was at 10 hours.Lactobacillus acidophilus LA-5 got to 1.72×10⁹ cfu/mL in the culture for 10 hours at 37℃.After activated in the growth promoting culture for three times, Lactobacillus acidophilus LA-5 was inoculated in soymilk with 8% inoculum size.After fermented for 20 hours at 37℃,soymilk reached to the fermented end-point,and the parameters of fermented soymilk were as following:pH 3.57,titratable acidity 85.22°T,the cells reached to 3.62×10⁸ cfu/mL.The finished product was stored for 30 days at 4℃,as a result,the parameters of fermented soymilk were as following:pH 3.45,titration acidity 94.29°T,the cells reached to 7.04×10⁶ cfu/mL.