The inactivation of Shiga toxin-producing Escherichia coli (STEC) and Listeria monocytogenes using isochoric freezing in raw milk and carrot juice

Authors: Lacombe, Alison; HARVEY, BEATRICE - Hispanic Association Of Colleges & Universities (HACU); Van Blair, Jared; CHAPMAN, NATALIE - Hispanic Association Of Colleges & Universities (HACU); Bilbao-Sainz, Cristina; McHugh, Tara; RUBINSKY, BORIS - University Of California Berkeley; Wu, Vivian

Submitted to: Food Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/18/2024
Publication Date: 10/25/2024
Citation: Lacombe, A.C., Harvey, B.L., Van Blair, J.B., Chapman, N., Bilbao-Sainz, C., McHugh, T.H., Rubinsky, B., Wu, V.C. 2024. The inactivation of Shiga toxin-producing Escherichia coli (STEC) and Listeria monocytogenes using isochoric freezing in raw milk and carrot juice. Food Control. 618. Article 110957. https://doi.org/10.1016/j.foodcont.2024.110957.
DOI: https://doi.org/10.1016/j.foodcont.2024.110957

Interpretive Summary: Isochoric freezing is a new food-saving method that maintains quality by applying low temperatures and high pressures. Raw milk and carrot juices are foods that are vulnerable to contamination by pathogenic bacteria. This work attempts to recreate traditional pasteurization conditions with isochoric freezing that produce a 99.999% reduction of Shiga toxin-producing Escherichia coli (STEC) and Listeria monocytogenes. Raw milk and carrot juice samples were inoculated with either STEC or L. monocytogenes frozen using the isochoric method. Following treatment, the product was sampled for surviving pathogens. The results demonstrated that a 99.999% reduction of both pathogens can be achieved for raw milk and carrot juice without adverse effects on quality. Decreasing the temperature increases the effectiveness of treatment. Listeria inactivation was easier to achieve than STEC. In addition, pathogens inoculated into carrot juice demonstrated quicker inactivation than raw milk. Isochoric freezing could be an option for milk and carrot juice processors that wish to achieve a reduction of pathogens similar to pasteurization without applying heat. This method is not a one-size-fits-all solution and the time and temperature will need further optimization depending on the target pathogen and intended food product.

Technical Abstract: Isochoric freezing is a novel food preservation method that maintains the quality and safety of the product by simultaneously applying low temperatures and high pressures. Raw milk and carrot juices are commodities that are vulnerable to pathogen contamination and require post-harvest treatment to remove microorganisms. This work aims to determine the variables of isochoric freezing that produce a five-log reduction of Shiga toxin-producing Escherichia coli (STEC) and Listeria monocytogenes. Raw milk and carrot juice samples were inoculated with cocktails of either STEC or L. monocytogenes, then subjected to isochoric freezing conditions in pressurized chambers set at -5, -10, and -15C. The chambers were held for 1, 5, 7, or 10 days. Following treatment, the product was sampled for surviving pathogens. The results demonstrated that a 5-log reduction of both STEC and L. monocytogenes can be achieved for raw milk and carrot juice without adversely affecting quality. For STEC inoculated in raw milk, both the linear and Weibull models suggest that 10 days is required to achieve 5-log reduction at -10C. Decreasing the temperature to -15C led to accelerated log reduction but induced phase separation in the milk. Listeria in raw milk demonstrated a biphasic reduction, indicating 1.3 days is required for a 5 log reduction at -10C. In comparison, pathogens demonstrated faster log reduction in carrot juice. The survival curves for STEC inoculated in carrot juice demonstrated that the 5-log reduction times were 6.94 days at -10C and 3.83 days at -15C. L. monocytogenes in carrot juice required 1.51 days at -10C for a 5-log reduction and was eliminated (7 log cfu/ml) within 24 hours at -15C. Isochoric freezing could be an option for milk and carrot juice processors that wish to achieve a 5-log reduction of pathogens without applying heat. This method is not a one-size-fits all solution and the time and temperature will need further optimization depending on the target pathogen and intended commodity.