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Food Safety Focus (206th Issue, September 2023) – Article 1

Siu Mei and Food Safety

Reported by Arthur Yau, Scientific Officer,
Risk Communication Section, Centre for Food Safety

In June 2023, the Centre for Food Safety (CFS) investigated a cluster of food poisoning outbreaks related to consumption of siu mei. The affected persons complained of gastrointestinal (GI) symptoms including abdominal pain, diarrhoea and vomiting.  The incriminated food items were siu mei dishes and Salmonella was the suspected causative agent. Hygiene and food handling deficiencies were detected in the siu mei kitchen, including preparation of siu mei too far in advance, prolonged period in the Temperature Danger Zone, inadequate cooking temperatures and cross contamination with raw food.

Figure 1: Examples of good practices in the preparation and sale of siu mei

Common Pathogens in Siu Mei

Salmonella and Staphylococcus aureus were implicated in past siu mei food poisoning outbreaks. Salmonella causes GI illnesses within 6 to 72 hours after oral exposure, with symptoms like nausea, vomiting, abdominal cramps, diarrhoea, fever and headache. While the infection is usually self-limiting in healthy individuals, it may be lethal to susceptible populations. Salmonella can be found in contaminated water, soil, food contact surfaces and hands, and in the GI tracts of animals and in humans. It is often spread through the faecal-oral route and contaminated water. Slaughtering can also contaminate the meat.

On the other hand, Staphylococcus aureus bacteria are commonly found on the hair, skin, nasal cavity, throat and wounds of humans. S. aureus contaminates food through food handlers’ hands, especially after cooking.  With post-cooking cutting and prolonged storage at room temperature, the bacterium can grow exponentially and form heat-stable toxins.

Antimicrobial Resistance (AMR) Bacteria

AMR bacteria are not necessarily pathogens and can be commensal bacteria that derive benefits from their association with humans. Similar to other environmental organisms or commensal bacteria in humans, they can also contaminate food if food hygiene and hand hygiene issues are overlooked. Although infection by AMR bacteria can be asymptomatic, microorganisms gain resistance spontaneously by gene mutation or gene transfer among each other. The strategy as provided in “Five Keys to Food Safety” for the prevention of foodborne diseases can also effectively reduce the risk of contracting AMR bacteria.

Addressing Food Safety Issues Related to Siu Mei

While the pathogens can be easily killed by thorough cooking, some common malpractices can lead to contamination of siu mei.

  1. Unhygienic air-drying process, where siu mei can become contaminated due to dirty environment or prolonged drying time;
  2. Contamination due to poor protection of siu mei after cooking and in subsequent handling, including display, cutting and transportation;
  3. Dirty equipment and poor personal hygiene;
  4. Cross contamination by raw or partially-cooked food;
  5. Prolonged display of cooked siu mei due to over-production

Food Safety Measures for Production of Siu Mei

Plan production accurately ahead of time to prevent over-production and extended storage of cooked siu mei at room temperature. Have two or more sessions of roasting daily to cater to peak hours during lunch and dinner so that storage time can be minimised. Defrost frozen meat in a chiller at 4°C or under running water. Do not defrost at room temperature.

Post-production Handling
Designate a clean area away from raw food for the cooling and packing of cooked siu mei with a dedicated set of tools to prevent cross contamination. Keep the area clean. Vehicles for transporting siu mei should not be previously used for transporting raw food or chemicals to prevent contaminations. Keep the siu mei covered while maintaining adequate room to prevent moisture built-up.

Display and Sale
Minimise display time with accurate production planning. Siu mei should be displayed in insect- and dust-proof showcases. No raw food should be allowed in them. Stacking should be avoided. Follow the “2 hours / 4 hours” rule for display at room temperature.  Roasted siu mei should be cut upon purchase. Roasted products, especially pre-packaged ones, are preferred to be sold within 2 hours after cutting if kept in the Temperature Danger Zone.

Key Points to Note:

  1. Pathogens like Salmonella and Staphylococcus aureus can be present in meat and meat products as many animals harbour them naturally;
  2. Thorough cooking can kill many pathogens and AMR bacteria;
  3. Proper planning, production and handling of siu mei and maintenance of personal and environmental hygiene can prevent microbiological contaminations.

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