Combining ultraviolet light and mild temperatures for the inactivation of Escherichia coli in orange juice

It is difficult to guarantee the effectiveness of UV technology to reach 5 Log(10) cycles of inactivation of Escherichia coli in a large amount of fruit juices with high absorption coefficients and turbidities, such as orange juice. The aim of this work was to overcome this limitation by combining UV light and mild temperatures. UV treatments were carried out in an equipment with eight individual annular thin film flow-through reactors connected sequentially and submerged in a thermostatic water bath. A treatment of 13.55 J/mL reached 0.25 +/- 0.04, 0.41 +/- 0.13, 0.84 +/- 0.32, 0.96 +/- 0.12, 2.57 +/- 0.05, 5.41 +/- 0.23, and more than 6 Log(10) cycles of inactivation of E. coli STCC 4201 suspended in commercial sterilized orange juice at 25.0, 40.0, 50.0, 52.5, 55.0, 57.5, and 60.0 degrees C, respectively. The comparison of UV resistance at 25 degrees C with heat resistance at mild temperatures demonstrated a synergistic effect of both technologies applied simultaneously. The maximum synergistic lethal effect was reached at 55 degrees C (68.03%). A UV light treatment (23.72 J/mL) at 55 degrees C (3.6 min) of freshly squeezed orange juice allowed reaching more than 5 Log(10) cycles of inactivation of a E. coli cocktail (STCC 4201, STCC 471, ATCC 27325, ATCC 25922, and O157:H7 Chapman strain). The selected treatment did not affect the pH, acidity, Brix, and color, and decreased 16.45% ascorbic acid content and 63.96% the Pectinmethylesterase activity. (C) 2012 Elsevier Ltd. All rights reserved.