Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/9/2005
Publication Date: 8/29/2005
Citation: Fan, X., Sokorai, K.J., Sommers, C.H., Niemira, B.A., Mattheis, J.P. 2005. Effects of calcium ascorbate and ionizing radiation on the survival of listeria monocytogenes and product quality of fresh-cut “gala” apples. Journal of Food Science. M352-358.
Interpretive Summary: The browning of cut fruit slices and product contamination with pathogens are major concerns of the fruit salad industry. The browning of cut apple slices is routinely controlled by antioxidant compounds. On the other hand, antioxidants may increase the resistance of pathogens to ionizing radiation, a non-thermal technology that effectively eliminates the pathogens. As a result, higher doses of radiation may be required to eliminate pathogens on apple slices that have been treated with antioxidants. However, too high doses of radiation may soften apple slices and promote tissue browning. This study was conducted to investigate the impact of a common antioxidant (calcium salt of Vitamin C) on the radiation resistance of Listeria monocytogenes, a pathogen associated with foodborne illness, and on the quality attributes of apple slices. The results show the antioxidant increased radiation resistance of the pathogen artificially inoculated on apple slices and in solution. But radiation at a dose that killed 99.999% of the pathogen did not have significant influence on the overall quality of apple slices that had been pre-treated with the antioxidant. Our results demonstrated that combination of antioxidants and irradiation will result in a microbiologically safe and quality product. The information will help the industry to enhance product safety and extend shelf-life of fruit salads.
Technical Abstract: The interactive effects of calcium ascorbate (CaA) and ionizing radiation on viability of Listeria monocytogenes inoculated in solutions and on ‘Gala’ apple slices were investigated. Quality changes in ‘Gala’ slices resulting from the treatments were also studied. CaA significantly increased radiation resistance of the pathogen both in solution and on apple slices. The D10 values (radiation doses that inactivate 90% of the bacterial population) for L. monocytogenes inoculated in water, 3.5, and 7.0% of CaA solutions were 0.32, 0.61 and 0.58 kGy, respectively. The D10 values for the pathogen inoculated on the surface of apple slices by dipping in the inoculated solutions were 0.24, 0.32, and 0.32 kGy, respectively. To determine the impact of CaA and irradiation on quality of apple slices, apple slices treated with 0, 3.5%, and 7.0% CaA were exposed to 1.6 kGy gamma radiation (a dose that produced a 5-log reduction of L. monocytogenes), and stored under modified atmosphere at 4 °C for 14 d. CaA at levels of both 3.5 and 7.0% prevented the browning of the apple slices. The apple aroma intensity, however, decreased as the concentration of CaA increased. Irradiation at 1.6 kGy did not significantly affect color, soluble solid content, titratable acidity, or apple aroma intensity. The only negative effect of irradiation on apple slices appeared to be a loss of firmness. However, firmness of irradiated samples treated with 3.5 or 7.0% CaA was similar compared to the non-irradiated samples that were not treated with CaA. Our results suggest that CaA, used as an antibrowning agent, protected L. monocytogenes from radiation both in solution and on apple slices, but radiation doses sufficient to inactivate 5-log of the bacterium did not significantly influence product quality attributes except for the loss in firmness.