Submitted to: Journal of Food Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2003
Publication Date: 5/2/2003
Citation: NIEMIRA, B.A., SOMMERS, C.H., BOYD, G. EFFECT OF IRRADIATION AND FROZEN STORAGE ON INJURY AND SURVIVAL OF SALMONELLA ENTERITIDIS IN CONCENTRATED ORANGE JUICE. JOURNAL OF FOOD PROTECTION. 2003. V. 66 (10). P. 1916-1919.
Interpretive Summary: Extended storage at frozen temperatures reduces the surviving bacteria on frozen food products. Orange juice concentrate was inoculated with an outbreak strain of the human pathogenic bacterium Salmonella Enteritidis. The inoculated concentrate was then treated with various levels of ionizing radiation, a process that is known to effectively eliminate bacteria from foods. After irradiation, the inoculated concentrate was stored at 20C. Samples were taken at various times up to 14 d and assessed for bacterial survival and injury. Irradiation of inoculated frozen concentrated orange juice causes a reduction of initial pathogen population that is proportional to the radiation dose used. The total bacterial population in irradiated samples was lower than in non irradiated at all sampling times. Over the course of the study, irradiated samples suffered increasing mortality frozen storage at rates comparable to or somewhat less than non-irradiated controls. Irradiated samples tended to have greater levels of injury than non irradiated controls. Accumulation of injury during frozen storage was comparable in irradiated and non-irradiated samples. The antimicrobial interaction of irradiation with freezing and frozen storage was therefore determined to be additive in nature. In this study, irradiation did not predispose Salmonella Enteritidis to greater sensitivity to the effects of freezing.
Technical Abstract: Orange juice can be contaminated with pathogenic bacteria such as Salmonella. To determine the effect of combining two antimicrobial treatments, this study evaluated the combination of freezing and extended frozen storage with ionizing radiation. Frozen concentrated orange juice (FCOJ) was inoculated with an outbreak strain of Salmonella enteritidis. The inoculated concentrate was then treated with various levels of ionizing radiation. After irradiation, the inoculated FCOJ was stored frozen. Samples were taken at various times up to 14 days and assessed for bacterial survival and injury. Irradiation of inoculated FCOJ reduces the initial pathogen population at a rate proportional to the radiation dose used. Over the course of the frozen storage study, bacteria in irradiated samples died off at rates comparable to or somewhat less than non-irradiated samples. Surviving bacteria in irradiated samples tended to be more injured than bacteria in non-irradiated samples. The bacterial population in irradiated samples accumulated injury at rates comparable to non-irradiated bacterial populations. These data show that i) irradiation is effective at reducing the bacterial load in FCOJ, and ii) bacteria which survive irradiation are not predisposed to be more sensitive to the antimicrobial effects of frozen storage than non-irradiated bacteria. These results provide a more complete understanding of how irradiated bacteria respond to subsequent challenges. These results are expected to benefit the consumers of irradiated, frozen food products.