Viability of Listeria monocytogenes and Salmonella Typhimurium after isochoric freezing

Abstract

Isochoric freezing, different from isobaric (conventional) freezing, allows for storage below freezing temperatures without significant damage from ice formation. While several types of tissues have been successfully stored in sub-zero isochoric conditions, it is unknown how isochoric freezing affects pathogenic microorganisms. Thus, the objective of this study was to investigate the survival of Salmonella Typhimurium and Listeria monocytogenes at below freezing storage (<0 C) in isochoric conditions. Tested conditions included storage at −4, −7, and −15 C for 24 hr and at −15 C for 1, 2, 3, 6, 12, and 24 hr. A comparison of bacterial survival during isobaric freezing was included with every trial. Additionally, bacterial cells were examined for morphological damage using transmission electron and field-emission scanning electron microscopes. Isochoric freezing at −15 C for 24 hr reduced both species of bacteria down to unrecoverable levels and maximum efficacy achieved after the 6 hr timepoint for L. monocytogenes and the 12 hr timepoint for S. Typhimurium. When viewed using electron microscopy, S. Typhimurium cells were noticeably disfigured with regions of cytosol separated from the cell wall. The results of this study demonstrate that isochoric freezing is capable of substantial levels of pathogen reduction. Unlike conventional nonthermal interventions, isochoric freezing does not require additional devices such as elevated pressure machines or pulsed electric fields and can be achieved with simple, inexpensive, rigid closed volume containers such as household freezers or commercial cold storage facilities.

Isochoric freezing to extend the shelf life of pomegranate juice

“…However, Y&M counts for the IF juice stored at 4 and 24°C were lower than that for fresh pomegranate juice, which indicated the benefits of isochoric freezing treatment for extending the shelf life of pomegranate juice. The combination of pressure and storage at subfreezing temperatures during isochoric freezing had been previously shown to reduce native microbial populations in whole pomegranate fruits and extracted arils (Bilbao‐Sainz, Chiou, Takeoka, Williams, Wood, Powell‐Palm, Rubinsky, Wu, et al., 2022) as well as pathogens (Bridges et al., 2020). Other research groups had also reported that high pressures can reduce microbial growth in pomegranate juice.…”

“…Fruits and vegetables treated in this way had been shown to keep their original freshness with minimal changes in physicochemical and nutritional properties. Isochoric technologies had also demonstrated potential for inactivating microorganisms (Bridges et al., 2020; Powell‐Palm et al., 2018).…”

A comprehensive review on isochoric freezing: a recent technology for preservation of food and non-food items

“…Because it is a simple rigid, closed-volume device, the isochoric system can be used for preservation and microbial reduction in standard industrial chilling and freezing infrastructure without altering the present facilities. 38…”

Benefits of isochoric freezing for carrot juice preservation

“…Previous authors had shown that IF could be an effective technology to inactivate microorganisms (Bridges et al, 2020;Powell-Palm et al, 2018) and to preserve fruits and vegetables with similar qualities to those of fresh produce (Bilbao-Sainz et al, 2018Bilbao-Sainz, Sinrod, et al, 2020;Bilbao-Sainz, Zhao, et al, 2020;). In this study, we investigated IF as a nonthermal technology to enhance the safety and shelf life of liquid foods.…”