Growth and survival of Bacillus cereus in mageu, a sour maize beverage

Abstract

The growth and survival of B. cereus, a known pathogen commonly found in cereals, during lactic acid fermentation of mageu, a sour maize beverage, was studied. In the mageu base inoculated with both the starter culture and B. cereus, the acidity developed to pH less than or equal to 4.00 and 0.10% titratable acidity after 24 h; the growth of B. cereus was reduced from 10(6) c.f.u./ml to 10(2) c.f.u./ml within 24 h; after the first 6 h of fermentation, the rate of inhibition of B. cereus was correlated to the rate of decrease in pH (r = 0.85, p < 0.05); the redox potential (E-h) decreased from 463 to 149 mV within the first 12 h. The control mageu base to which neither starter nor lactic acid was added had a pH of 6.50, titratable acidity of 0.015% and lowest E-h of 244 mV. In the mageu base to which lactic acid and B. cereus were added, the pathogen was inhibited to < 10(1) c.f.u./ml. The B. cereus in the mageu base to which no starter culture nor lactic acid was added, grew to over 10(7) c.f.u./ml after 12 h. The decrease in E-h seemed to have no inhibitory effect on the growth and survival of B. cereus. No strains of lactic acid bacteria were found to produce bacteriocins antagonistic to Bacillus cereus. Low pH and acidity were found to be the major factors inhibiting growth of Bacillus cereus in mageu.