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
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.