M: Food Microbiology & Safety JFS M: Food Microbiology and Safety Decontamination of Escherichia coli O157:H7 and Salmonella enterica on Blueberries Using Ozone and Pulsed UV-Light K.L. BIALKA AND A. DEMIRCI ABSTRACT: Efficacy of gaseous ozone, aqueous ozone, and pulsed UV-light was evaluated for the purpose of decon- taminating blueberries artificially contaminated with either Escherichia coli O157:H7 or Salmonella. Blueberries were exposed to 4 different gaseous ozone treatments: continuous ozone exposure, pressurized ozone exposure, and 2 combined treatments. Maximum reductions of Salmonella and E. coli O157:H7 after 64-min pressurized or 64- min continuous exposure were 3.0 and 2.2 log 10 CFU/g, respectively. Aqueous ozone experiments were conducted at 20 ◦ C and 4 ◦ C and zero plate counts were observed for E. coli O157:H7 and Salmonella after 64 min of ozone exposure at 20 ◦ C. Finally, pulsed UV-light was evaluated at 3 different distances from the light. Maximum reductions of 4.3 and 2.9 log 10 CFU/g were observed at 8 cm from the light after 60 s of treatment for Salmonella and E. coli O157:H7, respectively. A sensory analysis as well as color analysis was performed on blueberries from each treatment agent; neither analysis detected a difference between treated and untreated blueberries. The results presented in this study indicate that ozone and pulsed UV-light are good candidates for decontamination of blueberries. Keywords: blueberries, decontamination, E. coli, novel technologies, pathogens Introduction I n 2003, the amount of fresh fruit consumption increased to 57.3 kg per person (NASS 2005). As the consumption of fresh produce has risen, so has the number of associated foodborne illnesses. Fresh produce is now the 2nd leading cause of foodborne illness, with 639 outbreaks from 1990 to 2004 (CSPI 2006). Small fruits such as blueberries, strawberries, and raspberries are important agricultural commodities and are worth over a billion dol- lars each year. Blueberries alone are worth over $497 million (NASS 2005). Small fruits that are destined for the fresh market are not treated or processed before sale, in order to increase the shelf life of the product. There are many opportunities for contamination of the fruits during production, such as irrigation water, soil, equipment, pickers, and food handlers (Han and others 2004). Despite risks of foodborne illnesses, washing berries is not a viable option, and con- ventional sanitizers have shown little promise. Research by Yu and others (2001) compared 5 sanitizers for the purpose of decontami- nating strawberries. The most effective sanitizer was determined to be hydrogen peroxide, which gave a reduction of 2.2 CFU/g. The ineptitude of conventional sanitizers has opened the door for the evaluation of novel methods of decontamination. Ozone and pulsed UV-light are 2 technologies that show promise. Ozone has been used since the late 19th century for the purification of drinking water (Graham 1997), and has the ability to oxidize organic materi- als. Ozone has been successfully used in both gaseous and aqueous forms for the decontamination of foods. In 2001, ozone was ap- proved by the U.S. Food and Drug Administration for the treatment of raw commodities (Federal Register 2001). Ozone gas has been MS 20070386 Submitted 5/21/2007, Accepted 8/12/2007. Author Bialka is with Dept. of Agricultural and Biological Engineering, and authors Bialka and Demirci are with The Huck Inst. of Life Sciences, The Pennsylvania State Univ., Univ. Park, PA 16802, U.S.A. Direct inquiries to author Demirci (E-mail: demirci@psu.edu). found to increase the shelf life of fruits. Bazarova (1982) found that when apples were exposed to 0.06 ppm of ozone gas for 4 h each day, there was a reduction in both weight loss and spoilage. An 80% reduction in the spoilage of blackberries by Botrytis cinerea was seen when the fruits were exposed to 0.1 and 0.3 ppm ozone gas for 12 d (Barth and others 1995). The use of aqueous ozone has also been shown to successfully decontaminate foods. Sharma and others (2002) found that aque- ous ozone was effective at inactivating Escherichia coli O157:H7 on alfalfa sprouts and seeds at a concentration of 21 ppm. Koseki and Isobe (2006) found that the natural flora on lettuce could be reduced by 1.4 log 10 CFU/g after treatment with 5 ppm of aqueous ozone. Fur- thermore, when an aqueous ozone treatment was combined with a hot water dip, a decrease in browning was observed during storage. Selma and others (2006) found decreases in Yersinia enterocolitica and Listeria monocytogenes on the surfaces of potatoes after 1 min of treatment. With 5 ppm aqueous ozone, reductions of 1.6 and 0.8 log 10 CFU/g were observed for Y. enterocilitic and L. monocytogenes, respectively. The use of aqueous ozone has also been found to in- crease the shelf life and sensory attributes of produce. Zhang and others (2006) found that celery treated with 0.18 ppm ozone exhib- ited decreased respiration rates during storage and that the sensory quality of the treated celery was better than the untreated celery. Pulsed UV-light has been found effective at inactivating food- borne microorganisms in suspension as well as on foods. Rowan and others (1999) investigated the effects of pulsed UV-light on food- related microorganisms. Populations of Listeria monocytogenes, E. coli, Salmonella Enteritidis, Pseudomonas aeruginosa, Bacillus cereus, and Staphylococcus aureus that were seeded on tryptone soya yeast agar media were exposed to pulsed light having either high or low content UV-light. Reductions between 2 and 6 log 10 CFU/mL were attained using 200 pulses with low UV content and high con- tent, respectively. Krishnamurthy and others (2004) investigated the use of pulsed UV-light to inactivate St. aureus in buffer solution and C  2007 Institute of Food Technologists Vol. 72, Nr. 9, 2007—JOURNAL OF FOOD SCIENCE M391 doi: 10.1111/j.1750-3841.2007.00517.x Further reproduction without permission is prohibited