Microbiological risks of sandwiches
Recently, a number of food poisoning cases associated with eating of sandwiches from Taiwan arouse public concern. Some consumers may not be aware that sandwiches are high risk food items. Sandwiches can contain raw or fresh ingredients and preparation steps of sandwiches usually involve manual handling. Therefore, the ingredients used and cross-contamination during preparation are the two main pathways to contaminate the final products. Without proper storage, i.e. improper time and temperature control, pathogens may grow and multiply and cause food poisoning.
Potential microbiological hazards of sandwiches
Some high-risk ingredients, such as raw vegetables, eggs and salad dressing are commonly used in sandwiches. Pathogenic bacteria present in the soil or water may come into contact with raw vegetables during the growing stage. In addition, raw vegetables may also become contaminated after they are harvested, such as during preparation or storage. Properly cooked eggs are safe while undercooked egg may harbour Salmonella bacteria. For salad dressing, it may be prepared in advance and can become a source of contamination if not handled and stored properly. In addition, some salad dressing may contain raw egg as an ingredient.
As sandwich preparation often involves manual handling of ready-to-eat ingredients, good personal and environmental hygienic practices should be observed to minimise the chance of cross contaminations. Common pathogens transmitted through bare-hand handling include Staphylococcus aureus, which can be found on the human skin.
Prepared sandwiches should be properly stored, especially if they contain ingredients that allow bacteria to grow and multiply. As such, prepared sandwiches with high risk ingredients that support bacterial growth should be stored or displayed at 4oC or below. They should be discarded if stored above 4oC for more than 4 hours.
The Centre for Food Safety advises consumers and the trade to take necessary precautions to enhance food safety in preparation and consumption of sandwiches.
Advice to the consumers
- Patronise reliable and licensed food premises.
- Consume sandwiches as soon as possible.
- Keep sandwiches (including home-made ones) in the refrigerator at or below 4oC if they are not consumed immediately, and consume them within shelf-life.
Advice to trade
- Make reference to the Guidelines on Safe Production of Buns and Sandwiches to produce and sell wholesome and safe sandwiches.
- Purchase food ingredients from reliable sources.
- Estimate the demand for sandwiches as well as their fillings carefully to avoid over-production.
- Store perishable fillings at or below 4oC and avoid cross-contamination.
- Keep sandwiches with high risk ingredients that support bacterial growth in the refrigerator at or below 4oC or discard them after being kept at room temperature for more than 4 hours.
- Plan the production schedule ahead to avoid preparing sandwiches too far in advance.
- Always follow good personal hygiene practices.