Influences of malic acid and nisin supplementations on the decimal reduction times of Escherichia coli O157:H7 in mildly-heated young coconut liquid endosperm

This study was conducted to determine the effects of malic acid (800-1500 ppm) and nisin (0-150 ppm) on the heat resistance of Escherichia coli O157:H7 in young coconut liquid endosperm. The Central Composite Rotatable Design was applied to determine the various combinations of the two supplements to be added to young coconut liquid endosperm. The lowest D55 value was observed in the combination of 1500 ppm malic acid and 75 ppm nisin at 14.89 ± 4.17 min, while highest was 27.04 ± 4.98 min in the combination of 1150 ppm malic acid and 75 ppm nisin. The D55 values established from the combinations tested did not significantly vary, indicating that within the ranges of supplementation tested, significant influences of both additives and their interaction on the heat resistance of the pathogen did not exist. It was however emphasized that all supplementation combinations resulted in D55 values significantly lower than that in the unsupplemented medium, reducing the heat resistance of the cells by as much as 3-folds. Therefore, thermal processes to be established in the supplemented liquid endosperm shall be less severe, and may be applied to preserve sensory attributes.