Long-Term Storage of Vegetable Juices Treated by High Hydrostatic Pressure: Assurance of the Microbial Safety

Abstract

Food business operators search for new, mild technologies, which extend the shelf life of product without changing the sensory and nutritional properties. High hydrostatic pressure (HHP) meets these requirements; however it also triggers sublethal injury of bacterial cells. Sublethal injuries could spoil the product during storage and potentially pose major public health concerns. This study aims to examine the changes of sublethally injured pathogens cells in two vegetable juices: carrot juice (pH 6.0-6.7) and beetroot juice (pH 4.0-4.2) that are induced by HHP (300-500 MPa). The possibilities of recovery of bacterial cells during 28 days of juices storage at two different temperatures (5°C and 25°C) were determined using plate count methods. During the entire period of storage of carrot juice at refrigerated temperature, the propagation and regeneration of L. innocua strains were observed. Storage at 25°C showed that the number of these bacteria drastically decreased between 14 and 21 days. The above phenomenon was not detected in E. coli case. There was no cells recovery during long-term refrigerated storage for all strains in beetroot juice. However, in some cases spoiling of this product intermittently occurred at 25°C storage temperature. This work demonstrates that carrot juice supports growth and regeneration of HHP-sublethally injured L. innocua, while beetroot juice can be classified as a safe product.

High-Pressure-Induced Sublethal Injuries of Food Pathogens—Microscopic Assessment

“…To attain the quality and safety standards of high-pressure-processed foods, particular attention should be paid to the potential presence of sublethally injured cells. Research efforts have been made to clarify the relationship between sublethal injuries and products spoilage during long-term storage [ 53 ]. However, further studies are crucial to understanding the characteristics of HHP-injured bacteria and physiological changes of individual cells.…”

Factors Affecting Microbial Inactivation during High Pressure Processing in Juices and Beverages: A Review

“…This will result in a reduced resistance of the bacteria injured by HPP treatment to low pH during storage (35). For example, in high-acid juices, pathogens like E. coli O157:H7 may survive the initial pressure treatment but will die off within a relatively short period of time during cold storage under acidic conditions (14,15,83). As a result of storage of beetroot juice (pH 4.0 to 4.2) treated with HPP (300 MPa for 10 min) at 58C for up to 28 days, additional reductions of 5.15 and 6.53 log CFU/mL after pressure treatment were obtained for L. innocua and E. coli, respectively (83).…”

“…For example, in high-acid juices, pathogens like E. coli O157:H7 may survive the initial pressure treatment but will die off within a relatively short period of time during cold storage under acidic conditions (14,15,83). As a result of storage of beetroot juice (pH 4.0 to 4.2) treated with HPP (300 MPa for 10 min) at 58C for up to 28 days, additional reductions of 5.15 and 6.53 log CFU/mL after pressure treatment were obtained for L. innocua and E. coli, respectively (83). That was in agreement with the results obtained by Buzrul et al (14), who studied the effects of storage temperature (4, 20, and 378C for up to 3 weeks) on the additional reduction of E. coli and L. innocua after HPP treatment (5 pulses of 350 MPa at 208C for 60 s) in kiwifruit and pineapple juices.…”

“…The storage period and temperature after HPP may influence the safety of HPP-treated fruit juices and beverages (14,55,83,126,131). Conflicting results have been published on recovery of pathogenic bacteria during storage after HPP.…”

“…The counts of a pressure-resistant strain (strain C9490) of E. coli O157:H7 in orange juice were reported to be reduced after the juice was treated with HPP at 500 MPa for 5 min and then held at 48C for 0, 3, 7, or 24 h (55). Other studies have shown that pathogens may recover and grow during shelf life (83,126,131). L. innocua survived and grew in HPP-treated (400 and 500 MPa for 5 min) carrot juice (pH 6.0 to 6.7) during the entire storage at 58C up to 28 days (83).…”