Cinnamaldehyde Enhances the Killing Effect of High-pressure Processing against escherichia coli O157:H7 and Salmonella Enterica in Refrigerated (4°C) Carrot and Berry Juices

Introduction: Continuous operation of high pressure processing (HPP) equipment at 600 to 700 Mega Pascals (MPa) or higher to inactivate pathogens in foods can increase maintenance costs and decrease the life of pressure vessels. Simultaneous exposure of pathogens to a naturally derived antimicrobial and HPP might permit use of lower pressure treatments for effective microbial inactivation.

Purpose: A study was conducted to evaluate the efficacy of cinnamaldehyde (CA) combined with HPP to inactivate Escherichia coli O157:H7 and Salmonella entericain carrot juice (CRJ; pH 6.3) and a berry juice (BRJ; pH 3.6).

Methods: Both juices each with added CA at 0 (control), 0.10, 0.15 or 0.25 µl/ml were each inoculated with E. coli O157:H7 or S. enterica to obtain ~7.0 log₁₀CFU/ml. Juices were pressurized at 300 or 400 MPa for 60, 90 or 120 seconds at 4°C. Viability of pathogens in the juices were evaluated via serial dilution and plating of juice on appropriate selective agar before pressurization, after pressurization (within 1 h) and at set time intervals during storage (4°C) of the juices.

Results:  Addition of CA to juices increased the sensitivity of the pathogens to HPP with S. enterica exhibiting a greater loss in viability than E. coli to the CA/HPP (P < 0.05). CA (0.25 µl/ml) combined with 400 MPa (60 s) inactivated S. enterica by more than 5.5-log cycles in CRJ, whereas E. coli was inactivated by only 2.26 log cycles (P < 0.05). In the more acidic BRJ, CA (0.15 µl/ml) with a lower pressure (300 MPa for 120 s) resulted in complete inactivation (negative enrichment) and greater than a 5-log₁₀ CFU/ml reduction of both pathogens.

Significance:  Application of CA as low as 0.15 µl/ml combined with HPP can facilitate the use of lower pressures for effective inactivation of enteric pathogens in juices.