Surface pasteurisation of fresh chicken meat using UV-C technology : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology at Massey University, Albany, New Zealand
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Fresh chicken meat is highly susceptible to contamination by spoilage and pathogenic microorganisms due to its high-water activity and rich nutrients. Following processing, aerobic mesophilic count (AMCs) on the surface of fresh chicken samples ranges from 3.00 to 4.00 log CFU/cm2. The New Zealand food safety guidelines stipulate that aerobic mesophilic counts (AMCs) present on surfaces of fresh chicken portion should be <6 log CFU/cm2 by end of shelf-life (6-7 days) when stored at 4°C. Hence, the safety and shelf-life of fresh chicken meat pose challenges for the industry. The UV-C technology, is a novel food processing technique that has lethal germicidal capability at 280-290 nm. Therefore, the technology has a potential to decontaminate suitable food products including the surfaces of fresh poultry portions. This study investigated the effect of UV-C light processing on untreated fresh skinless and skin-on chicken portions. The study was conducted in 2 phases to optimise the processing technology and determine its effects on fresh chicken samples during storage (4°C). One day old fresh chicken samples (skinless breast fillet, skinless thigh fillet, skin-on breast fillet, and skin-on thigh fillet) were obtained from a commercial processing factory and transported to Massey University, Auckland Campus, under chilled conditions (4°C) within an hour. In phase one, the fresh chicken samples were treated with four UV-C dosages (50, 100, 200, and 300 mJ/cm2) at ambient temperature (20°C) using a commercial UV disinfection system. AMCs were determined by swabbing the fresh chicken samples using swabs and 5-cm2 templates. Suitable dilutions (10-1 up to 10-6) of the swabbed samples were enumerated on standard plate agar with incubation at 30°C/72 h and grown colonies were expressed as log CFU/cm2. Temperature of the chicken samples before and after UV-C treatments was measured using a 20-cm probe thermometer. Treatment time was recorded automatically by the UV-C equipment. Phase one results showed that 50 mJ/cm2 was capable of maximum microbial reduction (skinless: 1.69 log CFU/cm2; skin-on: 0.21 log CFU/cm2) with minimal temperature changes (skinless: 3.14°C; skin-on: 3.32°C) and lowest exposure times (skinless: 2.17 minutes; skin-on: 2.22 minutes.). Therefore, 50 mJ/cm2 was selected as the optimum dosage for skin-on and skinless fresh chicken samples. In phase 2, the effect of optimised UV-C light dosage (50 mJ/cm2) on fresh chicken samples stored at 4°C/7 days was investigated. Instrumental color analysis, AMCs and lipid oxidation were determined at 4 different time points (day 0, 3, 5, 7) during storage (4°C). AMCs were analysed as previously described. The detection of E.coli, S. aureus, L. monocytogenes, Campylobacter spp. and Salmonella spp. were conducted at 0 and 7 days of storage using standard methods, while colour was measured by a colorimeter. Lipid oxidation was analysed by the thiobarbituric acid (TBA) method. Consumer sensory evaluation was carried out to evaluate raw and cooked chicken samples during storage. Raw chicken samples were evaluated by a focus group consisting of 5 semi-trained panelists at days 1, 5, and 7 while cooked samples were evaluated on days 1 and 7 by 30 panelists using a 9-scale hedonic test. For cooked chicken portions, samples were cooked to an internal temperature of 75°C using a convection oven. The cooked chicken samples were cooled to between 30 – 40°C before being served to the sensory panelists. The result of phase 2 showed that the initial mean AMCs were 3.31 ± 0.11 (skin-on) and 3.80 ± 0.35 (skinless) log CFU/cm2. After UV-C treatment, the AMCs of UV-treated chicken samples were reduced to 1.87 ± 0.98 (skinless) and 3.07 ± 0.34 (skin-on) log CFU/cm2, indicating that the AMCs for skinless and skin-on chicken samples decreased by 1.93 log and 0.24 log CFU/cm2 after UV-C (50 mJ/cm2) treatment, respectively. At the end of storage, the AMCs on skin-on chicken breast samples were 8.57 ± 0.34 (untreated) and 7.48 ± 0.07 (UV- treated) log CFU/cm2. Whereas, AMCs on skinless breast fillet were 8.62 ± 0.35 (untreated) and 6.73 ± 1.10 (UV-treated) log CFU/cm2, respectively. The results indicated that the growth of AMCs on untreated chicken samples exceeded the recommended limit on day 5, while UV-treated chicken samples were higher than the recommended limit on day 6 (skin- on) and day 7 (skinless). In addition, the AMCs results suggested that UV-C treatment was more effective on skinless chicken portion. Furthermore, pathogenic bacteria (E.coli, S. aureus, L. monocytogenes, Campylobacter spp., and Salmonella spp.) were not detected on untreated and UV-treated chicken samples on days 0 and 7 of storage, indicating the effectiveness of the chlorinated chilling processing step. Based on the Hunter L*, a*, b* colour readings and TBA (TBARS) results, the applied UV-C dose (50 mJ/cm2) had minimal impact on the color and lipid oxidation of both skin-on and skinless chicken samples during storage. However, a faint burnt odor was detected by sensory panelists during evaluation of UV-C treated fresh (raw) chicken samples stored (4°C) for day 1. The panelists did not detect any unpleasant odor from the cooked chicken samples during storage. Therefore, the results suggested that UV-C light may offer good prospects for shelf-life extension of fresh chicken samples. In addition, the results also indicated that UV-C light surface pasteurisation was more effective for skinless chicken samples, compared to its skin-on counterparts.
Figures 2.1 & 2.2 were removed for copyright reasons but correspond to Figures 1 & 2 in Thompson (2003).
Meat, Radiation preservation, Contamination, Chicken industry, Health aspects, Ultraviolet radiation, Industrial applications, Food, Pasteurization