Factors Affecting X-ray Inactivation of Salmonella in Low-moisture Foods

Introduction: Microbial safety of low-moisture foods is an important goal in the food processing industry. Ionizing irradiation, like x-rays, electron beams, or gamma-rays, can inactivate bacteria within the product without significant impact on the quality of the food. However, it is necessary to identify the factors affecting inactivation of pathogens in low-moisture food products, for improved process modeling, design, and validation.

Purpose: The objective was to quantify the effect of X-ray dose, dose rate, and food structure on Salmonella inactivation in wheat products.

Methods: Wheat kernels, meal, and flour were inoculated with Salmonella Enteritidis PT30, conditioned to 0.4 a_w, and irradiated at three dose levels with high (6.17 Gy/s) or low (0.617 Gy/s, only for flour sample) dose rate using a 70 kV X-ray food irradiator. Treated samples (~1 g) were plated on modified tryptic soy agar, incubated, and enumerated.

Results: Dose rate (high/low) did not affect Salmonella inactivation in wheat flour at 0.4 a_w (P > 0.05) However, D₁₀-values (up to 2 log reduction) were 0.51, 0.60, and 0.40 kGy for wheat kernel, meal, and flour, respectively, which implies that structural differences can affect X-ray inactivation of Salmonella in low-moisture products.

Significance: Considering the fact that low-moisture raw materials are processed to various particle sizes, the parameters of X-ray irradiation should be validated for each product type, even if the chemical compositions are identical.