After studies with powdered infant formula indicated that the enhancement of thermal inactivation of Cronobacter sakazakii by butyl para-hydroxybenzoate (BPB) was blocked by the presence of high protein levels, we hypothesized that BPB would retain its synergistic activity in foods with a limited protein content and lipid content. This hypothesis was explored by examining the ability of BPB to enhance the thermal inactivation of Cronobacter sakazakii 607 at 58 °C in commercial apple juice, including examining the effects of pH and the possible synergistic effects with malic acid. Apple juice was adjusted to designated pH values between 3.2 and 9.0, supplemented with selected levels of BPB (≤125 ppm), inoculated with early stationary phase C. sakazakii 607, and thermally treated (58 °C) for 15 min using submerged coil apparatus. The same methods were used to study the enhancement of thermal inactivation by malic acid. Samples were plated on Tryptic Soy Agar for recovery and enumeration. Survival curves were plotted, and D-values were calculated and compared using ANOVA. Our results indicated BPB significantly enhanced thermal inactivation in a concentration dependent manner, with D-values of a few seconds at the original pH (3.8). The enhancement of thermal inactivation was pH dependent over the range of pH 3.4 to 9.0. Malic acid enhanced thermal inactivation as the pH was decreased from 3.8 to 3.2. The study supports the hypothesis that BPB can enhance the thermal inactivation of C. sakazakii in low protein foods.

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