The Study Of The Dairy Product Fermented By Lactobacillus Helveticus

Lactobacillus helveticus and Streptococcus diacetilactis were selected as mix starter to produce yogurt to enhance its function and flavor in comparison to traditional starter L.bulgaricus and S.thermophilus. Some healthy function ingredient of skim milk fermented by the ropy strain Lactobacillus helveticus were detected, such as amino acid and biopeptide cart be liberated during fermentation owing to the L.h high proteolysis ability. Dehydrated Lactobacillus helveticus acidified milk powder was prepared by spray -drying process, which can be used for functional food and pharmaceutical preparations.Lactobacillus helveticus was used as new starter culture to prepare yogurt because of its rapid acidification and slime- forming capacity during milk fermentation, Streptococcus diacetilactis has the ability of utilize citrate for producing diacetyl of cream flavor. The two strains were combined as mix starter to produce a new style yogurt of typtical ketone flavor. Design of SAS(Orthogonal Array Design) was used to analyze yogurt sensory score made from different culturing condition after storing 24 h at 4 C, pH value, acidity, viscosity and plate counts were also checked. In addition, three major volatile armoa compounds, as acetaldehyde, ethyl acetate and diacetyl contents were determined by GC. The result indicated the optimal culture condition was when two strains in the proportion of 2:1 could grow well at 38 C in 12% skim milk by inoculating 4% starter. The sample had good coagulation and mouthfeel with desirable flavor. The plate count reached 2.32 1010cfu/ml. Laclobacillus helveticus displayed low bile acid resistance and growth was inhibited under the pH 3.0 controlled in vitro.Lactobacilluis helveticus was inoculated in 12% of the skim milk and cultivated three times at 43 C, dehydrated acidified milk powder was obtained by adding 0.02% CaCl2 as protector before spray-drying. The moisture was measured 4.57 %(w/w) after spraying and the viable counts can reach 109cfu /ml. After two times activation, the milk fermented by powered starter could coagulated within 5h, pH value 4.33, and the acidity reached 90?T, the taste was similar to that of common fermented yogurt.HPLC was used to detect the composition of the milk fermented by L. helveticus comparing to control, the result showed proline increased apparently and the molecular weight distribution of hydrolysate determined by gel filtration chromatography using a sephadex G-25 column were below 1000Da, the short peptides with proline may be released during fermentation and exopolysaccharide was not detected, the molecular and structure of the short peptide needs to be isolated and identified further.