| As a species of Probiotics in intestinal tract of human body, Bifidobacteria plays an important part in the health of human body. It has already been used in food industry. Countries in the world have made large amount of research on it during recent years, but development of Bifidobacteria in our country is lag becaause it requirs harsh culturing condition. Problems we confront with now are:the viable count is small and the retention period is short.In order to screen the excellent quality and high quality bacterial strain, We choose Bifidobacterium infantis as the raw material, screen the mutant strain by complex mutation, microencapsulate the mutant strain, optimize its culture medium. The details and the results are as follows:(1) Made research on the acid proof, bile salt endurance, antibiotic-resistance of Bifidobacterium infantis. Results indicates that the ultimate pH was 5.0, the ultimate consistency of bile salt was 2%, Bifidobacterium infantis can't propagate in the culture medium with antibiotic. Mutagenize the bacterial strain with U.V and DES, the mutant strain Bi-A54's characteristic were as follows: the ultimate pH was 3.8, the ultimate consistency of bile salt was 2.4%, can steadily propagate in culture medium with antibiotic (consistency 0.6 mg/mL). The physiological-biochemical test indicates that Bi-A54 can ferment gum sugar.(2) The single factor test defined the best growing evironment for mutant strain: the the optimum temperature was 37℃; the optimum inoculating amount was 3%; the best original pH was 6.4. The orthogonal test of optimizing culture medium indicates that the best mixture ratio: soy peptone 1.1%, yeast extract 0.5%, oligosaccharide 1.3%, glucose 0.6%, tomato juice 8.0%, carrot juice 7.0%. The viable count in the optimized culture medium was 2.68×109cfu/mL, it was 3.5 times as many as viable count in TPY (7.62×108 cfu/mL). The acidity of bacteria solution in the optimized culture medium increased from 115.69°T to 156.01°T(3) The best proportion of protective solute resulted from the orthogonal test:Fucose 12%, Glycerin4%, Glutin0.5% and Vitamin C 0.5%. Owing to optimized protective agent, the livability of Bi-A54 was 70.32% after being freezed and dried. After the experiment of freeze drying test and microencapsulation test, it could be testified that the number of viable organism in microcapsule reach at 2.53×1010cfu/g from 3.64×1010 at while the number of bacterial strain which have not been capsuled was 1.27x1010cfu/g. The livability of capsuled bacterial strain was 69.51% while the one of bacterial strain which have not been capsuled was 34.90%. This experiment promoted the livability of bacterial strain in production process which provides practical significance.The monofactorial test confirms that the best proportion of protective solute and bacterial strain was 3:1 and the best pH value of majorized protective solute was 6.5 and the best mixing time of protective solute and bacterial strain was 30 min.(4) The tolerance test of capsuled bacterial strain's resistant to gastric juice, cholate and intestinal juice. The results were listed as follows:the capsuled bacterial strain disintegrated in the artificial intestinal juice in 3h; the number of viable organism was 2.07×107cfu/g in artificial gastric juice (PH 6.5) after 4h; the livabilities were 76.90% and 84.06% respectively in artificial cholates of two different concentration (2% and 0.5%) after 12 h.
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