0 100 200 300 400 500 600 700 Surface area (cm2)
FIGURE 24.2 Relationship between weight and surface area of tomato fruit and lettuce leaf. (From Beuchat, L.R., Farber, J.M., Garrett, E.H., Harris, L.J., Parish, M.E., Suslow, T.V., and Busta, F.F., J. Food Prot, 64, 1079, 2001. With permission. Copyright International Association for Food Protection, Des Moines, IA.)
can exist among various types of produce, making this approach unreasonable in terms of assessing log10 reductions against risk of illness that may result from consumption of a given weight of produce. Relationships between the weight (g) and surface area (cm2) of iceberg lettuce and tomato (Figure 24.2) illustrate this point. Recognizing that the weight:surface area will vary, depending on the thickness of the lettuce leaf and variations in shape of both vegetables, this figure simply shows that large differences in ratios in weight:surface area can exist among fruits and vegetables. Ratios for other fruits and vegetables with geometric configurations other than a two-sided plane (lettuce) or a sphere (tomato) would fall somewhere between these extremes. A decontamination process designed to achieve, for example, a 3log10 reduction in CFU/g of lettuce or tomato would theoretically result, respectively, in approximately 0.11 and 18log10 reductions in CFU/cm ; a 3log10 reduction in CFU/cm2 of lettuce or tomato would result, respectively, in approximately 79 and 0.5log10 reductions in CFU/g .
A standard procedure for calculating and reporting populations of microorganisms on fruits and vegetables needs to be established and, if guidelines or limits for maximum populations of pathogens are to be considered, calculation should be done on a standard basis (CFU/g or CFU/cm2). The number of log10 reductions in CFU resulting from a processing or decontamination treatment should likewise be based on a standard procedure for calculation. Regardless of the procedure used, if guidelines or limits and log10 reductions for specific pathogens are established, differences in weight and geometric configuration of fruits and vegetables should be considered. Data need to be subjected to appropriate statistical analysis to determine significant differences in populations of pathogens or spoilage microorganisms recovered from produce that has been subjected to various treatment or storage conditions.
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