Research On High Cell Density Culture Of Lactic Acid Bacteria Under Salt Stress And Activity Protection During Freeze Drying Process

In recent years, there is a rapid development of China's dairy industry, especially in the production of yoghurt starter cultures. In order to improve the competitive of domestic yoghurt starter cultures, we need to develop highly active, high-quality products to meet growing consumer's demands. Streptococcus thermophilus and Lactobacillus bulgaricus are major strains to the production of yoghurt starter. This paper study several key points, including the selection of lactic acid neutralizer during culture process, acclimate lactic acid bacteria tolerant sodium lactate, the nutritional needs and freeze-dried injury of lactic acid bacteria, provides a theoretical basis for the production of the high activity yoghurt starter cultures.In this study we compared the grows of Streptococcus thermophilus St sp1.1 and Lactobacillus bulgaricus Lb 34.5 in skim milk medium and synthetic medium respectively and determined 12% skim milk is the better condition for all the two strains, the maximum viable count were 2.8 times and 2.6 times respectively compared with that in the synthesis medium. Use skim milk as the based medium, selected the best lactic acid neutralizer by fermentor, the results showed that use 20% Na2 CO 3 as neutralizer, the two bacteria can reach the highest viable cells and maximum specific growth rate; Experiments also show that sodium lactate has a great negative impact on cell growth, acclimated lactic acid bacteria to Sodium lactate tolerance can further enhanced cell density, the viable count of St sp1.1 from 4.85×10 cfu/mL increased to 5.83×10 cfu/mL, Lb 34.5 from 1.28×10~9 cfu/mL increased to 1.75×10~9 c fu/mL.Choosed the stimulants for these two strains and determined adenine, sodium formate, L-cysteine hydrochloride significantly increased the viable count. 50μmol / L adenine promoted growth significantly for both St sp1.1 and Lb 34.5; 5 mmol / L sodium formate obvious promoted growth of St sp1.1, 10 mmol/L sodium formate obvious promoted growth of Lb 34.5; 50 mg/L L-cysteine hydrochloride promoted growth significantly for both St sp1.1 and Lb 34.5, when the concentration up to 250 mg/L, the growth of both strains were inhibited. Use HPLC determined purine content of several materials which can promote growth of these two strains, the results showed, beer, wort, yeast extracts contain a certain concentration of adenine, while the peptone, beef powder were not detected in the experimental conditions, and under the supplemented of adenine, the viable count was further increased, indicating that these compounds can not only provid carbon, nitrogen and other substances, but also the contain of adenine can better promote cell growth.In this study we also preliminary study the damage of lactic acid bacteria during freeze-dried, cleared that 10% trehalose combination with 1% glycine as protectants can significantly improve the survival rate of frozen and freeze-drying, reduce the loss of key enzymes in cell membranes and have a role in maintaining the cell membrane integrity.