Inhibitory effect of ethanol and thiamine dilaurylsulfate against loosely, intermediately, and tightly attached mesophilic aerobic bacteria, coliforms, and Salmonella Typhimurium in chicken skin

Abstract

The effects of 3 ethanol levels (30, 50, and 70%) with and without thiamine dilaurylsulfate (TDS; 1,000 ppm) were evaluated for the reduction of natural mesophilic aerobic bacteria (MAB), coliforms, and inoculated Salmonella Typhimurium (S. Typhimurium) in chicken skin. The chicken skin was inoculated with a 7 log cfu/mL suspension of S. Typhimurium. Loosely, intermediately, and tightly attached cells were recovered from chicken skin through shaking at 200 rpm for 5 min, stomaching for 1 min, and blending for 1 min, respectively. Increasing the ethanol concentration reduced the number of MAB, coliforms, and S. Typhimurium on the chicken skin, whereas TDS treatment without ethanol was not effective. Intermediately and tightly attached microorganisms (total MAB, coliforms, and S. Typhimurium) were more resistant to chemical disinfectants than loosely attached microorganisms. The combination of 70% ethanol with TDS was most effective than the combination of TDS with lower concentrations of ethanol in reducing populations of loosely, intermediately, and tightly attached MAB (by 1.88 log cfu/g, 1.21 log cfu/g, and 0.84 log cfu/g, respectively), coliforms (by 1.14 log cfu/g, 1.04 log cfu/g, and 0.67 log cfu/g, respectively), and S. Typhimurium (by 1.62 log cfu/g, 1.72 log cfu/g, and 1.27 log cfu/g, respectively). However, the chicken skin treated with higher concentrations of ethanol was tougher (P < 0.05) and more yellow and less red (P < 0.05) than that treated with lower concentrations of ethanol or with water (control). On the other hand, a combination of 30% ethanol and TDS yielded the best results, showing the reduction greater than 0.5 log cfu/g in S. Typhimurium, with no negative effect on chicken skin color or texture. Thus, a combination of 30% ethanol and TDS appears to be the optimal treatment for reducing microbial contamination of skin-on chicken products to enhance poultry safety without decreasing food quality, and this treatment could be applied in the poultry industry.

Keywords: Salmonella Typhimurium; chicken skin; ethanol; food quality; thiamine dilaurylsulfate (TDS).

Figure 1

Field emission scanning electron microscopy (FE-SEM) images of S. Typhimurium attached to chicken skin (arrows; 10,000 × magnification). (a) Loosely attached S. Typhimurium on chicken skin. (b) Intermediately attached S. Typhimurium on chicken skin. (c) Tightly attached S. Typhimurium on chicken skin.

Figure 2

FE-SEM images of S. Typhimurium attached to chicken skin after 70% ethanol and TDS treatment (arrows; 20,000 × magnification). (a) Effect of sterile distilled water (control) on S. Typhimurium on chicken skin. (b) Effect of ethanol treatment on S. Typhimurium on chicken skin. (c) Effect of TDS treatment on S. Typhimurium on chicken skin. (d) Effect of combined ethanol and TDS treatment on S. Typhimurium on chicken skin. FE-SEM, field emission scanning electron microscopy; TDS, thiamine dilaurylsulfate.