Inoculation Protocols Influence the Thermal Resistance of Salmonella Enteritidis PT 30 in Fabricated Almond, Wheat, and Date Products

Abstract

Inoculation methods in pathogen inactivation studies ideally represent conditions that might occur in real-world scenarios. Surface contamination in or on low-moisture foods affects Salmonella thermal resistance, which is critically important for process validation applications. The objective of this study was to quantify the effect of inoculation protocol on the thermal resistance of Salmonella Enteritidis PT 30 in fabricated low-moisture foods. Almond meal, almond butter, wheat meal, wheat flour, and date paste were inoculated via prefabrication and postfabrication protocols. In the prefabrication protocol, kernels and fruits were surface inoculated and equilibrated to a target water activity (a) (0.40 for almond and wheat products, 0.45 for date products) before fabricating meal, butter, flour, or paste and then reequilibrating the samples to the target a. In the postfabrication protocol, meal, butter, flour, and paste were fabricated before inoculation and equilibration. All inoculated and equilibrated samples were subjected to isothermal treatment (80°C), pulled sequentially during processing, cooled, serially diluted, and plated to enumerate survivors. Log-linear and Weibull-type models were fit to the Salmonella survivor data and were compared via the corrected Akaike information criterion. Pre- and postfabrication protocols resulted in significant differences ( P < 0.05) in Salmonella thermal resistance in all products. Overall, the thermal resistance of Salmonella Enteritidis PT 30 in almond products was greater ( P < 0.05) than in wheat products, which was also greater ( P < 0.05) than in date paste. Additionally, Salmonella was more thermally resistant in almond products and date paste when inoculated pre- rather than postfabrication; however, the opposite was true for wheat products. These results indicate that the means of inoculation can significantly affect thermal resistance of Salmonella in low-moisture foods.

Salmonella and Enterohemorrhagic Escherichia coli Serogroups O45, O121, O145 in Wheat Flour: Effects of Long-Term Storage and Thermal Treatments

“…R 2 and greater SE values in general. Such variations have also previously been reported for Salmonella by Blessington et al (2013); Beuchat et al (2017), and Limcharoenchat et al (2018), who attributed the variations to inoculation method. In an extended study focusing on the effects of inoculation procedures on Salmonella thermal resistance in wheat flour, Hildebrandt et al (2016) reported that inoculation method impacted repeatability, population stability and inactivation kinetics of Salmonella in wheat flour, regardless of laboratory.…”

“…In another study δ-value of 5.1 min for pre-fabrication inoculated flour and 4.7 min, for post-fabrication inoculated flour both at 80°C were reported, respectively, emphasizing the effect of inoculation protocol on Salmonella thermal death kinetics (Limcharoenchat et al, 2018). However, defining the inoculation protocol that is the closest simulation of real contamination routes based on product type and pathogen of concern remains a challenging subject for further discussion and future research.…”

“…Due to the importance of inoculation method in challenge food studies and in particular dry foods (Hildebrandt et al, 2016; Esbelin et al, 2018; Limcharoenchat et al, 2018) a method based on application of concentrated cell suspension for inoculation was developed in our previous study (Forghani et al, 2018). This method could efficiently deliver as high as approximately 8 Log CFU/g inoculum level homogeneously, did not show variabilities which are of concern for inoculation (Blessington et al, 2013; Beuchat et al, 2017) and barely changed the water activity of post-inoculation wheat flour.…”

Effect of Physical Structures of Food Matrices on Heat Resistance of Enterococcus faecium NRRL-2356 in Wheat Kernels, Flour and Dough

“…For comparing the influence of graininess and powder structures of food matrices on the heat resistance of E. faecium, an aliquot of 10 µL bacteria suspension was inoculated in~0.7 g wheat kernels and flour by gently hand mixing for 1 min and then dried for~40 min inside a biosafety hood until the a w of the sample equaled to that of a non-inoculated sample [12,15]. By simulating bacterial liquid distribution with the blue ink, the inoculation uniformity was determined by the color distribution with photos that the deviations of the L* and b* values were less than 8% and 7%, respectively, according to preliminary tests.…”

“…To investigate the effect of graininess and paste structures of materials on most heat-resistant bacteria, about 0.9 g wheat kernels and dough were inoculated by the same steps as described above. The drying time was determined by preliminary tests according to the a w of the sample using the water activity meter [2,12,15]. After equilibrating, the inoculated samples were transferred into TDT cells and closed immediately.…”