Research On The Freeze-Drying Lactic Acid Bacteria

The starter is one of the key factors influenced the fermented dairy products and quality. Streptococcus thermophilus (S.t) and Lactobacillus bulgaricus (L.b) were the two important bacteria, ultra-concentration and freeze-drying LAB starter has such advantages as high activity, less dosage and polluted, plenty kinds, easy transportition and preservation. However, they are all commercially imported, study on this is not very fast and there is not a systematic research report yet, this certainly will bring heavier financial burden to dairy enterprise of our country.Six trials were conducted in the experiment, the objective is to exam the best LAB and ascertain the optimum industrilization conditions and this will have great ecnomical and far-reaching social benefits.The first experiment select the fine bacterial strains from own lab preserved and get the single colony after a lot of activations and purifications, then incubate repeatedly.In the second one, three sources of carbon, nitrogen and yeast extract powder were optimized with others same, it showed that the medium components of S.t and L.b were pancreas peptone ( 0.5% ) , glucose( 1 %) , yeast extract powder ( 0.7% ) and polypeptdn ( 0.5% ), lactose(l %), yeast extract powder ( 0.3%) , absorbance at 600nm of S.t and L.b were 0.5325 and 0.4732, colony were 2.2 +1 07mL-1 and 2.5 +106mL-1 respectively after incubation.The third one showed that the optimal condition of S.t is in common incubation, 41 C, pH5.6 and the L.b is in CO2 incubation, 37 C, pH5.8.In the fourth one, single factor experiment confirmed four better growing factors of either, on this basis, orthogonal design was used to study the interact influnce, S.t grows well in mushroom juice (14%), carrot juice (10%), maize fluid (0.6%), Vc (0.2%) and L.b in haerbin beer (10%), tomato juice (10%), carrot juice (15%), mushroom juice (16%) ,the colony of S.t and L.b were 2.9 + 109mL-1 and 3.5 + 108mL-1' in this medium.The four methods were used at the same time in the fifth experiment Absorbance at 600nm and pH of S.t and L.b were 0.858, 1.825 and 4.78, 4.07 after ultrafiltration; OD600 was increased 50% and 20% respectively after adding phosphate buffer, 20% Na2CO3 was added inthe incubation, the colony were 1010 and 109mL-1, the best centrifugation condition was 6000rpm.Cryoprotective agents (1000ml) consist of skimmed milk powder100g, monosodium glutamate10g, glycerol 10g, oligosaccharide 25g, lactose 12.5g, sucrose 12.5g, cystine 1g, Vc3g, after freeze drying, the products were used to ferment milk in the sixth trial, the quality of youghurt was nearlly the same as the liquid stater one, but the concreting time was longer,the state was good and viscosity was low. The flavor should be improved after regulating ratio of the freeze-drying LAB powder.Masterate student: Zhang Jianyou Major: Food Science Supervisor: Prof. Huo Guicheng...