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The objective of this study was to identify a suitable decontamination method for chicken meat. For this, investigations on a combination of physical and chemical interventions were carried out in the laboratory, and further experiments were done in the process-line of a poultry meat producing enterprise.
Initial trials determined the appropriate temperature, contact time and treatment solution for the immersion treatments which are based on sensory attributes such as the surface appearance, taste, odor and texture of the chicken meat. The antimicrobial effect of bacterial reduction in pure culture and of artificially contaminated chicken meat further was investigated. Trials which imitated natural contamination were designed for and evaluated in an experimental process-line within an enterprise. The applications by immersion were composed of hot water, hot lactic acid, hot and cool water and chlorinated water. Concerning the industrial tests, vacuum tumbling and freezing were further process steps.
In terms of reduction of the microbial counts, immersion in a hot lactic acid solution did enhance the antimicrobial effect. The application of a 2-3% hot lactic acid immersion at 70 and 75◦C for 10 - 30 seconds contact time was able to reduce the number of Salmonella on artificially contaminated chicken breast surfaces significantly more effectively compared to water immersion. The highest reduction of Salmonella (2.01 log10 MPN per gram meat) was achieved by a 3% lactic acid treatment at 75◦C for 20 seconds contact time.
Hot water treatment alone eliminated 1 – 2 log10 CFU Salmonella Typhimurium per ml pure culture and 1 log10 CFU per gram contaminated meat. Notably, bacterial reductions achieved in the experiments in the enterprise were lower than in the laboratory experiments. The ranges of bacterial reductions by heat treatment at 80◦C for 15 - 30 seconds with and without 3% lactic acid solution were for mesophilic aerobic bacteria between 0.2 to 0.3 and 0.1 to 0.3, for Enterobacteriaceae between 0.1 to 0.8 and 0.1 to 0.4, for coliforms between 0.4 to 0.9 and 0.0 to 0.4, and for pseudomonads between 0.4 to 0.6 and 0.0 to 0.4 log10 CFU per gram meat for each of the two respective treatments.
Vacuum tumbling employed before the immersion in 3% lactic acid soluion (TLHL) did effectively decontaminate the natural contamination with mesophilic aerobic bacteria and with pseudomonads (p≤ 0.05). Similarly, vacuum tumbling used after the hot water immersion (HLT) also significantly reduced natural contaminations, but for Enterobacteriaceae and coliforms in this case. Hot water followed by cool water in the enterprise experiments resulted in a reduction of bacterial counts of mesophilic aerobic bacteria of 0.02 to 0.53, of Enterobacteriaceae of 0.04 to 0.28, of coliforms of 0.10 to 0.37 and of pseudomonads of 0.08 to 0.96 log10CFU per gram chicken meat. Two-time treatment with hot water at 70°C for 15 seconds and cool water, followed by tumbling and freezing, did reduce bacteria more effectively than one-time treatment with hot water followed by cool water.
Based on these low antimicrobial effects, the following immersion methods are not recommended for practical application: hot water at 80°C for 15 seconds (HW1); hot water at 75°C for 15 seconds and then cool water followed by tumbling for 15 minutes (HCS2 and HCK2); two-times treatment with hot water at 70°C, 15 seconds and cool water (HCD2) without tumbling.
In terms of the microstructure of meat, collagen fibers started to denature at 80°C for 15 seconds in a hot lactic acid immersion and at 80°C for 20 seconds in a hot water immersion without lactic acid. With regard to the sensory attributes of treated chicken breast surfaces, aiming at results that almost equal the visual surface of raw chicken meat, the best treatment was two-time hot and cool water immersion. In contrast, TLHL clearly did reduce the natural bacterial contamination of chicken breast. Unfortunately, this method caused unacceptable taste and appearance changes. Treatment with 3% lactic acid did not make the meat sour but led to a change of the meat texture.
In the chemical treatment experiment, chlorinated water inactivated Salmonella Typhimurium in culture 3 log10 CFU per ml. However, chlorinated water did not reduce bacteria on chicken breasts very efficiently. Additionally adverse sensory effects occurred.
Concerning the decontamination of raw chicken breasts minimizing a compromise must be found for minimizing tissue damage and sensory alterations on the one hand and maximizing antimicrobial effects on the other hand.