The Screening And Research On The Mechanism Of Lactobacillus Bulgaricus With Low-postacidiifcation Ability

Lactic acid bacteria are a kind of bactercia which can convert carbohydrates into lactic acid.At present. Yoghurt fermented with lactic acid bacteria has a broad market in china. In the processof processing, transportation and storage of the yoghurt, Lactobacillus delbrueckii subsp.bulgaricus can metabolism lactose to produce lactic acid, affecting the quality of the yogurtseriously and shortening the shelf life greatly. There are many methods which can controlpostacidificaton, but they can’t solve the problem fundamentally. we nation has redundant LABresources, so we should screen much better functionality LAB endlessly, this is the fundamentalplan. Thus, it’s very important to screen the low postacidification Lactobacillus delbrueckii subsp.bulgaricus from the wild strains.The main research goal is to screen the Lactobacillus delbrueckii subsp. bulgaricus from thewild strains with low-postacidification, yoghurt was fermented with co-culture of Streptococcusthermophilus, we have tested the actual production verification in this paper, from the study of thegrowth performance of the strains in all respects in-depth, the glycometabolism metabolism andthe key enzymes in producing lactic acid, we can gain the the root cause of thelow-postacidification of the strains. This study provides some theoretical and experimentalguidance for solving the problem of postacidification pointed and preparing of DVS yoghurtstarter.First of all, the strains from four commercial starter culture domestic and overseas aresegregated and identified, the result is segregating two Lactobacillus delbrueckii subsp. bulgaricus,which are the comparison group. Then based on fifteen strains of Lactobacillus delbrueckii subsp.bulgaricus, selected two strains which reflect a low postacidification eventually, the strainsKLDS1.1006and KLDS1.1011were selected, the strain KLDS1.0207which has highpostacidification as reference.Then the growth capability of the strains were studied intimately. Results demonstrated thatthe growth performance has very close contact with postacidification, glucose conversion rate andlactic acid production are far lower than the strain KLDS1.0207, the strains which had highersensitivity to acid and salt tolerance, there is a strong correlation between them, it is clear thatthere is a close relationship between growth performance and postacidification. Weak growthperformance of the strains is one of the causes of the low postacidification. The glucose metabolism experiments showed that the metabolic pathway from lactose tolactic acid is the crucial factor that results in postacidification of yogurt, the strains which havestrong ability of metabolizing lactose also show serious postacidification, they have inability touilize galactose. Then we determine the enzyme activity of metabolic pathway from lactose tolactic acid of the strains. It was concluded that the fundamental causes that the strains ofKLDS1.1006and KLDS1.1011reflect weak growth performance are the weak enzyme activitiesof H+-ATPase and β-galactosidase, and there is a close relationship between them, which is thefundamental reason why KLDS1.1006and KLDS1.1011reflect weak postacidification. Lactatedehydrogenase and protease showed no obvious correlation with postacidification.Low-postacidification yoghurt was fermented with co-culture of Streptococcus thermophilus,After21days storage at4℃, pH of yoghurt fermented with KLDS1.1011and KLDS1.1006were4.4-4.5, and the titration acidity was85-880T, and all aspects of sensory evaluation is good,inoculated Lactobacillus acidophilus to the yogurts above, the viable counts were>107cfu·mL-1,improving the probiotics survival effectively.