M: Food Microbiology & Safety JFS M: Food Microbiology and Safety Efficacy of Pulsed UV-Light for the Decontamination of Escherichia coli O157:H7 and Salmonella spp. on Raspberries and Strawberries K.L. BIALKA AND A. DEMIRCI ABSTRACT: Small fruits are increasingly being implicated in outbreaks of foodborne illness, and fresh produce is now the 2nd leading cause of foodborne illness in the United States. Conventional methods of decontamination are not effective, and there is a need to evaluate novel technologies. Pulsed ultraviolet (UV)-light is one such technology. In this study, pulsed UV-light was applied to strawberries and raspberries at varying UV doses and times. On rasp- berries, maximum reductions of Escherichia coli O157:H7 and Salmonella were 3.9 and 3.4 log 10 CFU/g at 72 and 59.2 J/cm 2 , respectively. On the surfaces of strawberries, maximum reductions were 2.1 and 2.8 log 10 CFU/g at 25.7 and 34.2 J/cm 2 , respectively. There was no observable damage to the fruits at these UV doses. The results obtained in this study indicate that pulsed UV-light has the potential to be used as a decontamination method for raspberries and strawberries. Keywords: novel processing, pathogens, ultraviolet Introduction E ach year, foodborne illnesses cost the U.S. economy $6.9 billion of loss in productivity and medical expenses (ERS 2005). Fresh produce has been increasingly implicated as the vehicle of trans- mission and is now the 2nd leading cause of foodborne illnesses, with 639 outbreaks during 1990 to 2004 (CSPI 2006). An estimated 73000 cases of E. coli O157 infections (Frenzen and others 2005) and 2000000 salmonellosis infections are reported each year in the United States (Frenzen and others 1999). With increasing numbers of outbreaks tied to fresh foods, there is a need to evaluate novel processing technologies that do not de- stroy the integrity of the product: pulsed ultraviolet (UV)-light is one such technology. Pulsed UV-light, also referred to as pulsed light, broad-spectrum white light, high intensity light, or pulsed white light, utilizes electromagnetic radiation from 100 to 1100 nm (Green and others 2003). Pulsed UV-light is produced by storing electrical energy in a capacitor and releasing it in short bursts, which magnifies the power. These short pulses are believed to make pulsed UV-light a more efficient and effective method of appli- cation compared to conventional or continuous UV-light (Miller and others 1999). It has been reported that an equivalent level of inactivation can be achieved with pulsed UV-light up to 6 times faster than conventional UV-light (Fine and Gervais 2005). As with conventional UV-light, the predominant inactivation mechanism is through the formation of thymine dimers within the cells DNA (photochemical), which prevents the cell from replicating (Rowan and others 1999). However, with pulsed UV-light, additional modes of inactivation have been proposed: photothermal and photophys- ical (Krishnamurthy and others 2007). The efficacy of pulsed UV-light has been well documented for inactivating foodborne microorganisms in suspension as well MS 20070652 Submitted 7/24/2007, Accepted 2/26/2008. Authors are with Dept. of Agricultural and Biological Engineering and Author Demirci is also with The Huck Inst. of Life Sciences, The Pennsylvania State Univ., Uni- versity Park, PA 16802, U.S.A. Direct inquiries to author Demirci (E-mail: demirci@psu.edu). as in/on food. Rowan and others (1999) investigated the effects of pulsed UV-light on food-related microorganisms. Populations of Listeria monocytogenes, E. coli, Salmonella Enteritidis, Pseu- domonas 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. Reduc- tions between 2 and 6 log 10 CFU/mL were attained using 200 pulses with low UV content and high content, respectively. Krishnamurthy and others (2004) investigated the use of pulsed UV-light to inac- tivate S. aureus in buffer solution and on agar seeded plates. They found a 7 to 8 log 10 CFU/mL reduction of S. aureus on seeded agar plates and buffer solution at treatment times less than 5 s without significant temperature increase. Sharma and Demirci (2003) ex- posed alfalfa seeds inoculated with E. coli O157:H7 to pulsed UV- light. They found that when a seed layer of 1.02-mm thickness was treated for 30 s, a 4.80 log 10 CFU/g reduction was achieved. Small fruits such as raspberries and strawberries have been im- plicated in several notable outbreaks. Raspberries have been im- plicated in at least 5 outbreaks of Cyclospora cayetanensis (CDC 1997b), and strawberries have been implicated in 3 outbreaks of hepatitis A (CDC 1997a). While there have been no recorded bac- terial outbreaks associated with small fruits, the possibility exists, since the contamination routes responsible for previous outbreaks are the same for bacterial pathogens. A U.S. Food and Drug Admin- istration (FDA) survey found that 1 out of 143 imported strawberry samples tested positive for Salmonella (FDA 1999). Also, research has shown that both Salmonella and E. coli O157:H7 are capable of surviving on fresh strawberries for over 7 d (Knudsen and others 2001). Throughout the production of small fruits, the opportunity for contamination exists due to improper sanitation, infected pickers, contaminated irrigation water, and manure fertilized fields (Han and others 2004). In spite of these risks, small fruits are not washed prior to delivery to market, due to the negative effect on fruit quality and shelf life. However, washing alone has been shown to have limited efficacy at removing both spoilage and pathogenic C  2008 Institute of Food Technologists Vol. 73, Nr. 5, 2008—JOURNAL OF FOOD SCIENCE M201 doi: 10.1111/j.1750-3841.2008.00743.x Further reproduction without permission is prohibited