Pasteurization of Apple Juice Contaminated with Escherichia coli by a Combined UV-Mild Temperature Treatment

The bactericidal efficacy of ultraviolet (UV) treatments to fruit juices is limited because of their low UV transmittance; therefore, it is necessary to design combined processes to improve their lethality. This investigation was carried out to determinate the lethal effect of UV-C treatments at mild temperatures (UV-H treatments) on the UV-resistant Escherichia coli strain Spanish Type Culture Collection (STCC) 4201 suspended in apple juice. A synergistic effect was observed and the optimum temperature for the combined process was established. Subsequently, the effect of the optimized treatment on the lethality of an E. coli cocktail (STCC 4201, STCC 471, American Type Culture Collection (ATCC) 27325, ATCC 25922, and O157:H7 Chapman strain) and on freshly squeezed apple juice quality was evaluated. A UV treatment of 20.33 J/mL reached 0.61 +/- 0.01, 0.83 +/- 0.07, 1.38 +/- 0.04, 1.97 +/- 0.06, 3.72 +/- 0.14, 5.67 +/- 0.61, and more than 6 log(10) cycles of inactivation at 25.0, 40.0, 50.0, 52.5, 55.0, 57.5, and 60.0 A degrees C, respectively. The optimum conditions for exploiting the synergistic effects were UV doses of 27.10 J/mL, temperature of 55.0 A degrees C, and 3.58 min of treatment time. This treatment guaranteed more of 5 log(10) reductions of the cocktail of five strains of E. coli without affecting pH, A degrees Brix, and acidity of freshly squeezed apple juice. The UV-H treatment did not increase the loss of ascorbic acid compared to the same UV treatment at room temperature but approximately doubled the inactivation of polifenoloxidase.