Evaluation of Vacuum Steam Pasteurization to Inactivate Salmonella PT30, Escherichia coli 0157:H7, and Enterococcus faecium on Flaxseed

Introduction: With increasing demand for nutritious food, low moisture foods such as flaxseeds, sunflower seeds, and sesame seeds have been studied a great deal for their nutritious value. However, such foods are minimally processed and are usually consumed raw and several outbreaks due to Salmonella, and E.coli 0157:H7 have been attributed to them. Previous studies show that these pathogens are more resistant to dry heat in low moisture foods and processes such as chemical treatments and blanching may have negative effects on product quality and functionality. 

Purpose: Vacuum steam pasteurization is a technology that injects saturated steam under vacuum to supply heat which can be controlled to achieve desired temperatures. We wanted to determine the efficacy of this technology in inactivation of pathogens on flaxseeds. 

Methods: Flaxseeds were separately inoculated with bacterial lawns of Salmonella PT30, E.coli 0157:H7 and E. faecium to obtain a homogenous distribution. The inoculated flaxseed (25 g) were pasteurized at 75°C, 85°C, 95°C, and 105°C after 24 and 48 hours post inoculation. Three 25 g samples were run at each condition, and the experiment was repeated three times.

Results: Similar average log reductions of 5.5 ± 1.2, 5.7 ± 0.4, and 5.3 ± 0.5 was observed after 1 min at 75°C for Salmonella, E.coli 0157:H7 and E. faecium, respectively (P > 0.05). The optimum time and temperature for maximum log reduction was determined to be after pasteurization for 3 min at 85°C on flaxseeds. 

Significance: Steam vacuum pasteurization is an effective method for inactivation of these pathogens on flaxseed achieving a 5-log reduction after just 1 min at 75°C. Enterococcus faecium may be used as a surrogate for Salmonella, and E.coli 0157:H7 when evaluating vacuum steam pasteurization.