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:
Two visiting scientists were hired to work on the project. The effect of different does of UV-C on populations of human pathogens inoculated on apricots have been conducted. Experiments are underway to study the growth and survival of human pathogens during post-UV treatment storage in different temperature.