Purpose: This study evaluated the effect of hot water at various time and temperature points to establish a kill step for Salmonella and Escherichia coli O157:H7 during shelling of pecan.
Methods: Pecan samples from Louisiana farms were inoculated with a cocktail of nalidixic acid resistant strains of four serotypes of Salmonella enterica or five strains of E. coli O157:H7. Salmonella or E. coli O157:H7 inoculated pecan samples were then treated with hot water maintained at 70°, 80°, and 90°C for one, two, three, four, and five minutes. Enumeration was done in XLD agar plates for Salmonella and CT-SMAC plates containing nalidixic acid (50µg/ml) for E. coli O157:H7 .
Results: A six log reduction of E. coli O157:H7 was achieved within four minute of treatments at 70°C (6.5±1.0 log cfu/g), within three minutes at 80°C (6.5 to 7.6-log reduction) and within two minutes at 90°C (6.0 to 7.7-log reduction). However, for Salmonella inoculated samples >5.60±0.6 log reductions was achieved at 90°C for four and five minutes. Other time and temperature combination for Salmonella and E. coli O157:H7 inactivation was unable to achieve a five-log reduction. The decimal reduction time (D-values) for E. coli O157:H7 isolates were lower than for Salmonella isolates. At, 70, 80, and 90°C the D-values for E. coli O157:H7 were 0.68, 0.52, and 0.46 minites, respectively, and for Salmonella were 1.02, 0.9, and 0.7 minutes, respectively.
Significance: Utilizing proper time and temperature of hot water treatment during pecan shelling could significantly reduce the food safety risk associated with Salmonella and E. coli O157:H7.