1a. Objectives (from AD-416):
To study the feasibility of UVC on tree-ripe (vine-ripe) fruits (apricot, peach, and raspberry). Specifically, we plan to determine the efficacy of UVC in inactivating human pathogens (E. coli O157:H7, Salmonella spp and Listeria monocytogenes) and study shelf-life and possible changes in fruit quality during post-UV storage.
1b. Approach (from AD-416):
Pathogens to be included in the study are E. coli O157:H7, Listeria monocytogenes and Salmonella. Isolates of the pathogens will be from ERRC’s culture collection and from recent outbreaks of foodborne illness. A cocktail of 3-5 strains of each pathogen will be used. Scientifically well established inoculation, recovery, and enumeration procedures will be used. Appropriate controls will be included in each experiment, and experiments will be replicated independently at least two times. Inoculation of fresh produce will be achieved by surface ‘spot inoculation’ where specific locations on the produce surface will be inoculated. The inoculated samples will be air dried in a biohood for 2-3 hrs before being subjected to different doses of UV treatments. Inoculation levels on the fruits and vegetables will be in the range of 106-108 cfu/ml. After treatment, the total number of viable bacteria will be determined using an overlay method (e.g. Thin Agar Layer Recovery Method) consisting of selective media such as Sorbitol MacConkey agar for E. coli O157:H7 and XLT-4 agar for Salmonella in the bottom of plates and non-selective media such as TSA on the top. In subsequent experiments, the study will be repeated using the commercial sized UV equipment. Our and other’s studies on UV have showed that that increases in UV doses will achieve a higher doses of pathogen reduction, but only to certain points. Fruits without human pathogens will be used for the quality and shelf-life study. Fruits after being treated with selective UV doses (as determined in pathogen reduction study) will be stored at 5 and 20 C for up to 21 days. Quality (color, firmness, decay, vitamin C, antioxidants, etc) will be assessed every week.
3. Progress Report:
Several experiments have been conducted to study the feasibility of UV-C technology for the sanitization of tree ripe apricots, including 1) Efficacy of UV-C in inactivating pathogenic and non-pathogenic E. coli O157:H7 and Salmonella spp., 2) The survival of pathogenic E. coli O157:H7 and Salmonella spp. during post-UV storage., and 3) Development of UV-C film dosimeter systems to evaluate dose uniformity. In addition, UV-C treatment system in a commercial packing line at the collaborator site was evaluated. The commercial UV-C treatment system was tested for UV-C intensity, reduction of surrogate bacteria, UV dose uniformity on apricot fruit, and fruit quality changes during post-UV storage. The film dosimeter system was used to study the dose uniformity on different locations of fruit surface in the commercial and lab settings. To increase dose uniformity, two rotation devices were developed and evaluated. The results from the research suggested that apricot fruit can tolerate high doses of UV-C without change in fruit quality. UV-C treatment reduced the population of human pathogens by as high as 99% in laboratory setting. In the commercial setting, the reduction was 70-80%. The project is complementary to the objective of in-house project to reduce the risk of foodborne illness associated with consumption of ready-to-eat products using physical, chemical or antimicrobial treatment or integrated treatment strategy while maintaining acceptable product quality and shelf-life.