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THE STUDY OF PH ADJUSTMENT EFFECT TO BACILLUS CEREUS ATCC 11778 GROWTH INHIBITED BY BIFIDOBACTERIUM METABOLITES FOR PREBIOTIC ACTIVITY ASSESSMENT

Boris Karetkin

Abstract

Bacillus cereus is known could cause intestinal diseases as typical sporogenous contaminant of foods. On the other hand, probiotics form a number of factors to inhibit bacilli growth, e.g. short-chain fatty acids. The patterns of Bacillus cereus ATCC 11778 bacilli specific growth rate reduction by metabolites of bifidobacteria (both in pure substances and when produced in mixed culture) were applied for the model development. These regularities were supposed to be appropriate for prebiotic activity assessment in vitro. Meanwhile, both fermentation with pH adjustment and simple batch fermentation (pH is not controlled) can be carried out for study a prebiotic activity. In last case, both the pH reductions caused by the formed acids and concentrations of acid anions will influence to bacilli growth. In the experiments with pure culture it was established that the complex effect is more significant and the constants of inhibition are greater. More of that, the lactate (up to concentration of 5 g/L) is not inhibit Bacillus cereus ATCC 11778 growth at pH of fermentation about 6.8. To research the effect of pH adjustment in mixed culture of bacillus and bifidobacteria fermentations were carried out in Minifors (Infors HT, Switzerland) bioreactors at N2 atmosphere. The growth of bacilli was compared at constant pH of 6.8 and with free pH reductions. The oligofructose (Orafti P95, Beneo Ingredients, Belgium) was used as the standard of prebiotics. The specific growth rate of bifidobacteria and substrate consumption were not significantly differed. The specific growth rate of Bacillus cereus was constant and significantly greater at pH adjustment conditions. Bacilli growth was stopped when pH of fermentation was dropped to about 5.7 by bifidobacteria that are produced the acids. Thus, the pH adjustment during the fermentation should be took into consideration for prebiotic activity assessment both with faecal culture and mixed culture with the limited number of bacteria.

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DOI resolver: doi.org/10.5593/sgem2018/6.2/s25.099

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