UV Tolerance of Spoilage Microorganisms and Acid-shocked and Acid-adapted E. coli in Apple Juice Treated with a Commercial UV Juice-processing Unit

Introduction: The enhanced thermal tolerance and survival responses of Escherichia coli O157:H7 in acid and acidified food products is a major safety concern in the production of low-pH products, including beverages. However, little is known about this phenomenon when using ultraviolet (UV) light treatments. Previous studies have shown that spoilage microorganisms present higher UV tolerance compared to pathogenic bacteria, but limited information has been published regarding the UV doses required to control these organisms when using commercial UV juice-processing units.

Purpose: We studied the effects of strains, acid shock and acid adaptation on the UV tolerance of E. coli O157:H7, as well as the UV tolerance of selected spoilage microorganisms using a commercial UV juice-processing unit for the treatment of apple juice.

Methods: The log reduction of five strains (E. coli O157:H7 C7927, ATCC^® 35150™, ATCC^® 43895™, ATCC^® 43889™ and E. coli ATCC^® 25922™) at three physiological states (unadapted-control, acid-adapted, and acid-shocked cells) was determined in apple juice treated with a CiderSure 3500 UV reactor and under the conditions stated in current FDA regulations. The UV tolerance of three spoilage microorganisms (Aspergillus niger, Penicillium commune, and Alicyclobacillus acidoterrestris) was also determined at UV doses between 0 and 70 mJ·cm^–2. Trials were performed in triplicate.

Results: A higher than 5-log reduction with E. coli was achieved under all tested conditions. A significant effect of strain (P = 0.01) was observed, but the physiological state did not affect UV inactivation (P = 0.96). Total reductions of 3.3, 3.8 and 5.0 logs with Aspergillus, Penicillium and Alicyclobacillus, respectively, at 70 mJ·cm^–2were observed.

Significance: These findings suggest that the use of unadapted E. coli is adequate to conduct challenge studies using UV light technologies, and support the relevance of a hurdle approach to extend the shelf life of UV treated beverages.