Antimicrobial Potential of Carvacrol and Its Effect at Sub-lethal Concentration during Low Thermal Pasteurization of Fruit Juices

Aims: This study aimed at assessing the relationship between the initial antimicrobial activity of carvacrol and its effect at sub-lethal concentration when used for low thermal treatment of fruit juices.

Place and Duration of Study: Faculty of Food Science and Technology, University of Agricultural Science and Veterinary Medicine of Cluj-Napoca for a period of 5 months.

Methodology: The antimicrobial potential of carvacrol on Escherichia coli ATCC 25922; Listeria monocytogenes 56 LY and Zygosaccharomyces bailii was evaluated through the macrodilution method. The survival of these two latter strains grown in different acid conditions was also assessed after a treatment at 55°C in pineapple, orange and watermelon juices supplemented or not with carvacrol (30 µL/L) as performed in a previous study for E. coli. For each strain, the comparative length of treatment was the time required to reduce non-acid adapted cells in watermelon juice supplemented with carvacrol by 99.9%.

Results: Carvacrol exhibited a MBC value of 200 µL/L on E.coli; 1900 µL/L on L. monocytogenes, and a MFC value of 500 µL/L on Z. bailii. A prior growth of these microorganisms in acid conditions globally led to an enhancement of their survival ratio to heat treatment. Z. bailii inactivation was affected by the nature of the treated juice (higher in pineapple juice followed by orange juice). Supplementation of carvacrol at 30 µL/L had a positive impact on microorganisms thermal inactivation but with strength which appears to be inversely proportional to its MBC or MFC on the target strain (R2=0.98).

Conclusion: The choice of the natural aroma compound to use for such combined treatment of fruit juices should be made based on its antimicrobial potential on the contaminant microorganisms.