Heat inactivation of Escherichia coli O157:H7 in apple cider containing malic acid, sodium benzoate, and potassium sorbate

The effect of pH modification and preservative addition in apple cider on the heat resistance of Escherichia coli O157: H7 was investigated. E. coli O157:H7 and various amounts of potassium sorbate (0 to 0.2%), sodium benzcaate (0 to 0.2%), and malic acid (0 to 1%) were added to apple cider. Thermal inactivation experiments were performed at 47, 50, and 53 degrees C, and D- and z-values were calculated, in apple cider without additives, the D-value at 50 degrees C (D-50) was about 65 min, but addition of preservatives and malic acid significantly (P < 0.01) decreased D-values. D-50-values decreased to 13.9 min in cider with 0.5% malic acid, 13.2 min with 0.1% sorbate, and 7.0 min with 0.1% benzoate added. Addition of both sorbate and malic acid had similar effects as either one alone, thus additive effects were not present. However, addition of both 0.2% benzoate and 1% malic acid did show additive effects, lowering D50 to 0.3 min. Addition of all three components (0.2% sorbate, 0.2% benzoate, and 1% malic acid) resulted in a D-50 = 18 s. The z-value of cider without additives was about 6 degrees C, whereas z-values of cider containing malic acid, benzoate, and/or sorbate ranged from about 6 degrees C to 26 degrees C. This increase may result in a longer 5-log reduction time at higher temperatures (i.e., 70 degrees C) in cider with benzoate as compared to cider without additives.