14A-38

F. R. MATTOS¹, O. O. Fasina, L. D. Reina, G. S. Damasceno, H. P. Fleming, and F. Breidt, Jr. (1) U.S. Department of Agriculture, ARS, Department of Food Science, NC State University, Raleigh, NC 27695-7624

Fresh fruits and vegetables may contain numerous microorganisms that relate to spoilage and food safety concerns. Although most evidence indicates that the microbial population is located near the fruit surface, there have been reports of internal location. Methods that will be effective in the inactivation of these organisms will require information on their location.

The objective of this study was to develop a method for determining microbial distribution in fresh cucumbers based on a heat transfer-microbial kinetic (HTMK) model.

The HTMK model combines two-dimensional transient heat transfer and microbial inactivation kinetics equations. Thermal death time (F_t^z) at any location within the cucumber was calculated from the model and used to predict microbial reduction when cucumbers were blanched in hot water. Cucumbers (45-55 mm diameter) were blanched at temperatures of 60, 80, and 90^oC for various times. Blanched cucumbers were homogenized and plated to determine cell counts for total aerobic microflora and aerobic spores. Experimental results for total aerobes were compared to predicted results from the HTMK model.

There was no statistically significant difference (P greater than/equal to 0.05) between experimental and predicted log reduction values at the blanching temperatures used. Blanching did not reduce the number of microbial spores. Variation in thermal death time (F_t^z) with location, as obtained from the HTMK model, showed that total aerobic microorganisms were located within 0.65 mm of the fruit surface. Microbial load depth was based on simulation results for cucumbers blanched to achieve 2 and 3 log reductions at specified temperatures.

The HTMK model should be useful in determining minimal thermal process for inactivation of cucumber microflora. However, the 5-log reduction (recently recommended by the U.S. Food and Drug Administration for selected commodities) could not be attained experimentally due to limiting initial numbers of microorganisms on/in cucumbers and the presence of heat resistant spores.