Screening Of Bacillus With Potential Probiotic Characteristics And Studies On The Fermentation Technology

Thirty-five strains of Bacillus were isolated from traditional sour gruel western area of Inner Mongolia. Bacillus licheniformis B₂ was screened out through comparation of the resistance of the strains to low pH, simulated gastrointestinal juice, bile salts and antimicrobial activities. Furthermore, biological property and growing conditions of the strain was systematically studied. The main results were showed as follows:(1)Among these thirty-five strains, twenty-five strains could survival in pH2.5 (71.4%)and 5 strains showed high tolerance to the simulated gastric juice (pH 2.0, 3h of incubation, survival rate >30%). And then these 5 strains were treated by simulated intestinal juice for 24h (pH8.0)with a slight loss of live cells. 5 strains also showed well tolerance to bile salts. In terms of antimicrobial activity, various activities were observed from strain to strain and only Bacillus licheniformis B₂ showed broad spectrum of activity against 5 food-borne pathogens.Its maximum inhibitory diameter was 13.5mm.(2)The tolerance to the maximum concentration of bile salt in medium of Bacillus licheniformis B₂ was 1.8g/100mL. This strain showed a high resistance to heat treatment and the survival rate were more than 63% after 100℃either dry heat or heat-moisture treatment. But the heat-moisture treatment had a severer damage to bacterial cells.(3)After incubated At optimization medium and culture conditions for 24h ,the viable count could reach 2.35×108cfu/mL.(4)The strain was continuous cultured in 5L fermenter without feeding in fermentation and with fixed parameter(spH7.8,air flow was 2L/min and stir speed was 200rpm).After 16h fermentation, the live bacterial cells of B₂ was as much as 4.62×10⁹cfu/mL,which was twenty times more than shake culture.(5)The spore forming rate could be increased significantly though increasing temperature and reducing the air dose at the later stage of fermentation. As come to our experiment, we increased the temperature to 55℃after incubating for 18 hours and turn off the air input at the same time. At the end of fermentation, the spore number reached 3.37×10⁹cfu/mL and the spore forming rate was 73%.