Efficacy of High Pressure Pasteurization as a Kill Step for Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes in Low and High Acid Juices and Almond Milk

Introduction: High pressure pasteurization (HPP) is a cold pasteurization process used extensively in the juice industry as a kill step to achieve the 5-log reduction of pertinent pathogens mandated by Juice HACCP (21CFR120). The efficacy of a standard HPP treatment to achieve a 5-log reduction of vegetative pathogenic microorganisms in a variety of juice and beverage products was evaluated.

Purpose: Evaluate effectiveness of HPP to achieve a 5-log reduction of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes in Carrot Mix Juice (pH = 4.12), Green Juice (pH = 3.86), Apple Juice (pH = 3.64), Carrot Juice (pH = 6.41), Coconut Water (pH = 5.37), and Almond Milk (pH = 8.43).

Methods: Products were separately inoculated with E. coli O157:H7, Salmonella, and L. monocytogenes. Inoculated products were HPP-treated at 85,000 psi for 180 seconds. Log reductions were determined immediately after HPP and after 24 h of storage at 4°C post-HPP using MPN methodology.

Results: For high acid juices (pH < 4.6), log reductions > 5 logs were achieved for all organisms in all products after 24 h of storage post-HPP. However, immediately after HPP, log reduction of E. coli O157:H7 in Apple Juice was 4.82 ± 0.48 logs (n = 3). For low acid products (pH > 4.6), log reductions > 5 logs were achieved for Salmonella and L. monocytogenes in Coconut Water and Almond Milk. However, a 5-log reduction of E. coli O157:H7 was not achieved in either of these products. HPP was the least effective for Carrot Juice, in which log reductions of E. coli O157:H7, Salmonella, and L. monocytogenes were 2.31 ± 0.16, 1.79 ± 0.00, and 3.91 ± 0.30 (n = 3), respectively.

Significance: The results of this study raise questions regarding the ability of HPP (as tested) to achieve the required 5-log reduction of E. coli O157:H7 in low acid juices or Almond Milk. For high acid juices, products may require an additional 24 h hold post-HPP to achieve a 5-log reduction of E. coli O157:H7.