Purpose: The objective of this study was to quantify Escherichia coli O157:H7 inactivation in date paste subjected to low-energy X-ray treatment.
Methods: Vacuum packaged whole dried dates were obtained from the Date Palm Research Center (Saudi Arabia) and were stored at 4 °C until tested. For the pathogen challenge test, a six-serovar cocktail of Escherichia coli O157:H7 was prepared, centrifuged, and re-suspended in sterile peptone water. The inoculum was mixed with 200 g of dates to be ground. The inoculated and ground sample (~3 g) was placed in a plastic bag and rolled to a 1 mm thickness to maximize X-ray dose uniformity. Five dose levels of X-ray (70 kV, 57 mA) were applied to achieve 1 to 5 log reductions in triplicate. After irradiation, samples were homogenized and plated on Petrifilms™ E. coli/Coliform Count Plates (3M, St. Paul, MN), with colonies enumerated after incubation at 35 ± 2 °C for 48 h.
Results: Initial concentration of E. coli O157:H7 was 7.42 log CFU/g in the date paste. The reciprocal of the slope of the regression line was calculated as the D10-value (0.37 ± 0.04 kGy). Based on this measurement, a 5-log reduction can be attained with 1.85 kGy. The X-ray treatment had minimal effect on the visual color of the date paste.
Significance: Low-energy X-ray was able to inactivate E. coli O157:H7 in date paste with a reasonable dose, suitable for potential commercial operations. Therefore, low-energy X-ray is considered as a viable method for ensuring microbiological safety of this low-moisture product.