Microbiological Quality of Rice and Noodles in Hong Kong
The Centre for Food Safety (CFS) and the Consumer Council (CC) have conducted a study on the microbiological quality of rice and noodles in Hong Kong . This study aimed to give an overview of the microbiological quality of some ready-to-eat rice and noodle products commonly available at variouslocal food premises and to increase awareness of safe preparation and handling of rice and noodles in the food industry.
2. Rice and noodles are the main staple foods of thelocal population. In general, rice and noodles are cooked before consumption. Thorough cooking can kill most dangerous microorganisms. However, rice and noodles may contain Bacillus cereus spores which are unlikely to be destroyed under normal cooking conditions. Improper storage or inadequate cooling of cooked rice and noodles will allow spores germination, bacterial growth as well as toxin production. In addition, lack of personal hygiene in food handlers and contamination after cooking may contribute to poor microbiological quality of rice and noodle products. Risk associated with cooked rice and noodles consumption may even be higher if they are prepared in bulk and in advance.
3. To provide assistance in the interpretation of microbiological analyses of ready-to-eat food, the CFS has developed a set of Microbiological Guidelines for Ready-to-eat Food (The Guidelines). The Guidelines stipulate criteria indicating the microbiological condition of the food concerned so as to reflect its safety and hygienic quality. According to the Guidelines, microbiological quality of food can be classified into one of the four classes * , namely Class A (satisfactory), Class B (acceptable), Class C (unsatisfactory) and Class D (unacceptable).
Methods and Results
4. In this study, a total of 114 ready-to-eat products (57 rice; 57 noodles) were collected from food premises, including chain and individual stores, located at different districts in Hong Kong . Four microbiological parameters, namely aerobic colony count (ACC), Escherichia coli (total), Staphylococcus aureus and Bacillus cereus, were tested by the Public Health Laboratory Services Branch of the Centre for Health Protection, Department of Health. The microbiological quality of the samples was assessed against the criteria stipulated in the Guidelines.
5. Most rice and noodle products (96%) in this study were of satisfactory (Class A) or acceptable (Class B) quality. For the three unsatisfactory (Class C) rice samples, two were found to contain 1.6 X 106 and 2.0 X 106 cfu/g ACC respectively and the other was found to contain 510 cfu/g Staphylococcus aureus . For the unsatisfactory (Class C) noodle sample, it contained 3.8 X 105 cfu/g ACC and 400 cfu/g Escherichia coli (total) . Prolonged storage at room temperature and post-cooking contamination could be the causes for the poor microbiological quality, highlighting the importance of good hygiene practices in the food industry.
Advice to the Public
- Patronise reliable and licensed food premises.
- Consume ready-to-eat rice and noodles as soon as possible.
- If products are not consumed immediately, keep them above 60 oC or at or below 4 oC.
- Cooked rice and noodles that are properly cooled should be refrigerated within two hours .
- Reheat refrigerated rice and noodles thoroughly, if applicable, to core temperature reaching 75 oC or above.
Advice to Trade
- Estimate the demand of rice and noodles carefully to avoid over-production.
- Plan the production schedule ahead to avoid preparing rice and noodle products too far in advance.
- If products are not served immediately, keep them above 60 oC or at or below 4 oC.
- Always follow good personal hygiene practices.
* Class A: the microbiological status of the food sample is satisfactory.
Class B: the microbiological status of the food sample is less than satisfactory but still acceptable for consumption.
Class C: the microbiological status of the food sample is unsatisfactory. Licensees of food premises should be advised to investigate and find out the causes and to adopt measures to improve the hygienic conditions.
Class D: the microbiological status of the food sample is unacceptable. The food sample contains unacceptable levels of specific pathogens that is potentially hazardous to the consumer .
Risk Assessment Section
Centre for Food Safety
Food and Environmental Hygiene Department