Inactivation results obtained in heat treatment experiments are subjected to a variability which depends on several factors. These latter are enhanced by the increase of vapour pressure caused by heat which, in turn, increases their solubility in cell membrane, the first target of their antimicrobial activity 12, 13. In this perspective, the use of essential oils or their constituents (added below their minimum inhibitory concentration) can be a suitable approach: the presence of thymol, carvacrol, citral, (E)-2-hexenal, vanillin is reported to increase the inactivation rate of thermal treatments 6, 7, 8, 9, 10, 11, due to cumulative antimicrobial effects of heat and aroma compounds.
Therefor strategies based on synergistic effects of thermal treatment with antimicrobials are exploited to avoid excessive heat damages. On the other hand, the application of high temperature may have negative effect on the sensory, nutritional, and textural characteristics of food that may be contaminated by L. Recently, revision of literature confirmed this variability in D-value 4, indicating that it may change in relation to temperature suggesting non-linear inactivation dynamics 5. However, the inactivation kinetics can be very different, with D 65 ranging from 0.2 to 2 min according to ANSES (2012) 3. Temperatures above 50 ☌ are needed for thermal death of L. In many cases, the control of this microorganism relies on thermal processing of foods. Due to these characteristics, the risk of listeriosis is high in ready-to-eat foods (meat and dairy products) but relevant outbreaks has been associated also to fruit and vegetables (cantaloupe, celery, mung bean sprouts, stone fruits) 2. Its wide environmental distribution, resistance to low pH and NaCl concentration, facultatively anaerobic metabolism and psychrotrophicity make this species one of the greater challenges for food industry 1. Listeria monocytogenes is a ubiquitous bacterium responsible for a disease (listeriosis) which is among the major foodborne illnesses characterized by a high case-fatality rate (approximately from 20 to 30%).
Finally, our study clearly indicated that VBNC cells can resuscitate under favorable conditions on a food matrix, becoming a threat for consumer’s health. In conclusion, we found a connection between the cell history and sensitivity toward an antimicrobial treatment, underlying the importance to standardize the experimental procedures (starting from the cells to be used in the assay) in the assessment of cell sensitivity to a specific treatment. Our results suggest that only Gorgonzola rind allowed a partial recovery of the culturability of cells previously heated in presence or not of terpens. monocytogenes cells to recover their culturability (on ALOA agar medium) and to growth on the food matrix stored at 4 ☌ for 7 days. Therefore, to mimic the worst scenario, these latter were selected to contaminate Gorgonzola rind and roast beef slices and we evaluated the ability of L. The mild heat treatment combined or not with terpenoids mainly affected culturability rather than viability, although the culturability of cells from single colony was less impacted.
monocytogenes towards antimicrobial treatment. Our results showed that the cell origin significantly impacted viability and culturability of L. After treatment, culturability on BHI medium and viability assessed by flow cytometry were evaluated.
In this study we investigated how cell origin could affect the efficacy of an antimicrobial treatment (mild heating combined with terpenoids) in Listeria monocytogenes Scott A, considering cells from: 1.
0 kommentar(er)
