Enhancing the antibacterial activity of thyme oil against Salmonella on eggshell by plasma-assisted process

Abstract

Salmonella is the main source of microbial contamination on eggs. In the present study, the eggshells infected with Salmonella were employed as the test subjects. Thyme oil and cold nitrogen plasma (CNP) were introduced to treat Salmonella on eggshells. Both thyme oil and CNP showed low antimicrobial activities against microorganisms when they individually acted to infected eggs for short time. On the contrast, the loss of bacterial viability was obviously enhanced by combined treatment. The subsequent experiments demonstrated that thyme oil concentration and CNP treatment time were positively correlated with antibacterial effects. By CNP assist, thyme oil can effectively inhibit the multiplication of Salmonella on eggs under low concentrations. Among various combination groups, 0.5 mg/mL thyme oil and 400 W CNP exhibited the best synergistic antibacterial activity when they were applied for 20 min and 1 min, respectively. The populations of Salmonella enteritidis and Salmonella typhimurium were reduced below 10 CFU/egg. More importantly, the treatment in combination limited the growth of bacteria on eggs below undetected level during 14 days of storage at different temperatures (4, 12 and 25 °C).