Synergistic Action of Mild Heat and Essential Oil Treatments on Culturability and Viability of Escherichia coli ATCC 25922 Tested In Vitro and in Fruit Juice

Abstract

The strengthening effect of a mild temperature treatment on the antimicrobial efficacy of essential oils has been widely reported, often leading to an underestimation or a misinterpretation of the product’s microbial status. In the present study, both a traditional culture-based method and Flow Cytometry (FCM) were applied to monitor the individual or combined effect of Origanum vulgare essential oil (OEO) and mild heat treatment on the culturability and viability of Escherichia coli in a conventional culture medium and in a fruit juice challenge test. The results obtained in the culture medium showed bacterial inactivation with an increasing treatment temperature (55 °C, 60 °C, 65 °C), highlighting an overestimation of the dead population using the culture-based method; in fact, when the FCM method was applied, the prevalence of injured bacterial cells in a viable but non-culturable (VBNC) state was observed. When commercial fruit juice with a pH of 3.8 and buffered at pH 7.0 was inoculated with E. coli ATCC 25922, a bactericidal action of OEO and a higher efficiency of the mild heat at 65 °C for 5′ combined with OEO were found. Overall, the combination of mild heat and OEO treatment represents a promising antimicrobial alternative to improve the safety of fruit juice.

Lactiplantibacillus plantarum monolayer enhanced bactericidal action of carvacrol: biofilm inhibition of viable foodborne pathogens and spoilage microorganisms

“…After o/n incubation, 1 ml was transferred to 30 ml of fresh sterile medium. Starting from the refreshed culture, the initial concentration of 6 Log CFU/ml (Colony Forming Unit: CFU) for each microorganism was applied for subsequent analysis (Di Gregorio et al, 2022).…”

“…(Wang et al, 2015). The reduction in pH due to the synthesis of LAB organic acids promotes the hydrophobicity of carvacrol, allowing it to explain the bactericidal activity (de Carvalho et al, 2018;Di Gregorio et al, 2022). However, few studies have focused on the synergistic effect of lactic acid bacteria and EOs or their components, showing that the combined treatment may have better antimicrobial activity than single ones and lower concentrations could also be utilized to minimize unwanted side effects (Govaris et al, 2010;Sharma et al, 2022;Esposito and Turku, 2023).…”

“…Innovative approaches to assess the culturability and viability of food pathogens in complex matrices are needed to optimize the protocol used for food production and evaluate the effectiveness of preservation treatments (Fleischmann et al, 2021;Rubbens and Props, 2021). It is well-known that using traditional, culture-based microbiological approaches can lead to an overestimation of treatment efficacy (Di Gregorio et al, 2022). Cultivable methods coupled with FCM represent an important strategy for the study of antimicrobial treatment efficacy on both sessile and planktonic cells, providing a deeper understanding of the physiological state of microbial cells.…”

Effects of Ginger and Garlic Powders on the Physicochemical and Microbiological Characteristics of Fruit Juices during Storage

“…In the last years, the growing demand for healthy natural foods has led to an increase in the consumption of fresh fruit juices [ 20 ], which are rich in vitamins, minerals, pigments, antioxidants, and bioactive compounds [ 21 , 22 ]. Fresh fruit juices have a relatively short shelf-life which can be extended by using different thermal (conventional, microwave heating, ohmic heating, and infrared radiation) and non-thermal (high-pressure processing, pulsed electric fields, ultraviolet radiation, and sonication treatments) processing methods [ 21 , 22 , 23 , 24 ]. However, the nutritional compounds and organoleptic characteristics of fruit juices can be affected by preservation technologies [ 22 ].…”

“…Fresh fruit juices have a relatively short shelf-life which can be extended by using different thermal (conventional, microwave heating, ohmic heating, and infrared radiation) and non-thermal (high-pressure processing, pulsed electric fields, ultraviolet radiation, and sonication treatments) processing methods [ 21 , 22 , 23 , 24 ]. However, the nutritional compounds and organoleptic characteristics of fruit juices can be affected by preservation technologies [ 22 ].…”