Submitted to: Journal of Food Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/4/2013
Publication Date: 4/30/2013
Publication URL: doi:10.1111/1750-3841.12098
Citation: Zhou, S., Sheen, S., Liu, L.S., Pang, Y., Yam, K.L. 2013. Antimicrobial effects of vapor phase thymol, modified atmosphere and their combination against Salmonella spp. on raw shrimp. Journal of Food Science. Volume 78(5):M725-M730. Interpretive Summary: Salmonella contamination is commonly found in raw shrimp which can lead to foodborne illness outbreaks. Salmonella are sensitive to some natural antimicrobial compounds, e.g. thymol. In this report, thymol (in vapor phase) and modified atmosphere were found to inhibit the growth of Salmonella spp. This process can be used commercially to reduce foodborne illness risk from consumption of potentially contaminated shrimp and other seafood. The developed growth models may be used in risk assessments for consumption of seafood products.
Technical Abstract: Salmonella contamination of raw shrimp is a food safety concern in the U.S. and other countries. This research evaluated the effects of vapor phase thymol, modified atmosphere (MA) and their combination against Salmonella spp. on raw shrimp. Growth profiles of a Salmonella spp. cocktail (6 strains), inoculated onto the surface of raw shrimp, treated with vapor phase thymol at three levels (0, 0.8 and 1.6 mg/l), or MA (60 percent CO2, 40 percent N2, +/- 1 percent each), both alone and in combination, at three temperatures (8, 12 and 16 degree C), were determined. Lag time and maximum growth rate of Salmonella spp. under each treatment were obtained using Baranyi & Roberts model. Results indicate that the combination of vapor phase thymol and MA was effective inhibiting the growth of Salmonella spp. For instance, at 8 deg C, lag time of Salmonella spp. was extended from 54.2 hrs (without treatment) to 143.9 hrs (with 1.6 mg/l vapor thymol + MA treatment), and maximum growth rate was reduced from 0.021 log CFU/g/hr (without treatment) to 0.0098 log CFU/g/hr (with 1.6 mg/l thymol + MA treatment). Synergistic antimicrobial effectiveness from the combination treatment was observed. For instance, at 12 deg C, lag time of Salmonella spp. was extended 59.6% by the combination treatment of 0.8 mg/l thymol + MA over the effects from 0.8 mg/l thymol treatment and MA treatment individually. Linear regression models of lag time and maximum growth rate for Salmonella spp. on raw shrimp under multiple stresses were also developed and validated.