MICROBIOLOGICAL ASSESSMENT OF CHICKEN MEAT SOLD AT CHICKEN RICE STALLS IN SINGAPORE

Prior surveillance of food prepared at food stalls in Singapore suggested that chicken meat, particularly boiled chicken meat, may be undercooked and of unsatisfactory microbiological quality. Therefore, we conducted three studies of chicken meat, between 2010 and 2013 at chicken rice stalls using convenience sampling method in 5 areas of Singapore to evaluate chicken meat safety in order to guide food safety program. The first study compared the microbiological quality of the boiled, deep-fried and soy-sauced chicken meat by evaluating it using standard plate count (SPC) and detecting Escherichia coli, Staphylococcus aureus and Bacillus cereus counts. This was performed on 30 boiled, 30 deep-fried and 10 soy-sauced whole chicken meat samples obtained from 30 chicken rice stalls. Ninety percent of the samples had a SPC <5.0 log colony forming units per gram of meat, which is the Singapore regulatory limit. E. coli was detected in 10% (3/30) of the boiled chicken samples, 10% (1/10) of the soy sauced chicken samples and none of the deep-fried chicken samples. The boiled chicken samples (3/30) exceeded Singapore's regulatory limit. The first study revealed unsatisfactory levels of bacterial contamination, especially in boiled chicken meat. The second study assessed the microbiological safety of boiled chicken meat by examining for the presence of Salmonella or Campylobacter species among samples taken from the tail of the chickens near where the cloaca is found. We examined 136 samples obtained from 61 stalls, with a maximum of three samples per stall. Salmonella species were found in 1.5% (2/136) of samples and Campylobacter was not found in any of the tested samples. This study revealed a relatively low percentage of contaminated samples, but there is still room for improvement given the pathogenicity of Salmonella. The third study evaluated the presence of bacterial growth among chicken meat samples prepared by boiling and deep-frying. However, with this study, we took culture samples for SPC and E. coli counts from both groups every 2 hours for a total of 6 hours after food preparation was finished. A total of 29 boiled chicken meat samples and 29 deep-fried chicken meat samples were examined. The median SPC among boiled chicken meat samples at 0, 2, 4, and 6 hours were 2.9, 3.4, 3.4 and 3.3 log CFU/g. The number of bacteria present did not increase significantly between 0 and 2 hours (p>0.05), but did increase significantly from 0 to 4 hours (p<0.05) and between 0 and 6 hours (p<0.01). The median SPC among the deep-fried chicken meat samples at 0, 2, 4 and 6 hours were 1.6, 2.5, 2.6 and 2.5 log CFU/g, respectively. The numbers of bacteria increased significantly between 0 and 2 hours (p<0.05), between 0 and 4 hours (p<0.01) and between 0 and 6 hours (p<0.05), respectively. These findings suggest boiled and deep-fried chicken meat should be sold for consumption only within the first 2 hours after preparation, but not afterward. Our 3 studies of chicken meat show there is room for improvement in hygiene, especially boiled chicken. It also suggests the meat should be sold for consumption no more than 2 hours, if displayed under ambient conditions, after preparation.