Production of safe school lunchboxes

Common production systems

Common pathogens

Food safety problems

Production flow charts for school lunch boxes

Food safety measures

Other reference documents

Common production systems

l           Cook-serve (conventional) system

In a cook-serve system, most food items are prepared primarily from ingredients on the day they are to be served. However, since school lunchbox suppliers have to prepare a lot of lunchboxes before noon (number of lunchboxes may vary from a few hundred to a few thousand), they usually prepare foods 2 to 4 hours in advance of service time. The food items are then held hot until they are distributed to schools for consumption.

l           Cook-chill system

In a cook-chill system, a central kitchen cooks foods thoroughly and chills the foods rapidly in a blast chiller (e.g. below 4^oC within 1.5 hours) to prevent the growth of harmful bacteria. The foods are then stored at below 4^oC. On the next day, the foods are distributed to satellite kitchens (reheating centers at different districts) for reheating and then to schools for consumption.

Common pathogens

l           Staphylococcus aureus

Source              Humans are the primary reservoir of the pathogen which may be present in the nasal passages and throats and on the hair and skin of healthy individuals. After contamination, the pathogen grows on the prepared foods and produces toxin which, if ingested, may cause food poisoning.

Foods involved           Foods most frequently implicated are prepared foods that require considerable handling during preparation and that are kept at room temperature after preparation.  

Control Measures               In order to reduce the chance of staphylococcal food poisoning, prepared foods should be handled carefully. Food handlers should observe good personal hygiene practices and wash their hands frequently. Prepared foods should also been kept hot enough (60¢XC or above) or cold enough (4¢XC or below).

l           Clostridium perfringens

Source.             It is widely distributed in the environment and frequently occurs in the intestines of humans. Spores of the organism persist in soil, dust, and human and animal feces. They are likely to accompany any raw foods brought into a food preparation area.  (Note: a spore is a thick-walled structure formed under adverse conditions. It is resistant to heat, cold and chemical and is capable of becoming a vegetative cell under favourable conditions)

Foods Involved.         Cooked meats, meat products, and gravies are the foods most frequently implicated. The spores of C. perfringens are heat-stable and survive in foods after cooking. These spores germinate and multiply to food poisoning levels if the foods are subjected to long periods of slow cooling and non-refrigerated storage.

Control Measures.              In order to reduce the chance of food poisoning caused by C. perfringens, hot foods (intended to be stored cold) should be cooled quickly by (1) dividing and placing the foods into small and shallow containers, (2) reducing the amount of water in a recipe and adding ice as an ingredient, (3) using an ice bath, or (4) using a blast chiller. In addition, refrigerated foods should also be reheated thoroughly (i.e. to 75^oC or above) before consumption.

Food safety problems

To avoid food poisoning, school lunchbox suppliers should have a thorough understanding of the following food safety problems.

Cook-serve

1.           Inadequate cooking (i.e. food not thoroughly cooked)

Many pathogens may be present on raw food products. Foods that are not thoroughly cooked may contain these pathogens and cause food poisoning.

2.           Improper hot holding

This problem illustrates a twofold fault, namely, preparation of food too far in advance of service coupled with improper holding temperature.

3.           Post-cooking contamination

This is a mistake resulting from (a) using the same area for handling of both raw and prepared or ready-to-eat foods; (b) using the same equipment for handling of both raw and prepared or ready-to-eat foods; or (c) handling prepared foods (such as proportioning cooked foods into lunchbox containers) with unclean hands, etc.

4.           Improper cooling

Although most food items are prepared primarily on the day they are to be served, some suppliers choose to prepare gravy or soup one day ahead of the time of service. The gravy, if cooled improperly in a prolonged period of time, allows the spores of C. perfringens to germinate and multiply to food poisoning levels. Food poisoning may occur if the refrigerated gravy is not adequately reheated before consumption. To overcome the problem, suppliers should (1) prepare the gravy on the day of service and keep it hot until consumption; or (2) cool the gravy quickly after cooking and, on the next day, reheat the food thoroughly.

Cook-chill

1.     Inadequate cooking (i.e. food not thoroughly cooked)

Many pathogens may be present on raw food products. Thorough cooking will destroy pathogens and prevent food poisoning.

2.     Post-cooking contamination

This is a mistake due to the handling of cooked foods (e.g. during proportioning cooked food into lunchbox containers) with unclean hands, utensils, etc.

3.           Improper cooling

If cooked foods are cooled too slowly, spores or pathogens that survived the cooking step, or are introduced after cooking, are allowed to grow and multiply. In a cook-chill system, suppliers must be aware that the following factors will affect the cooling time/rate and the blast chillers must be able to cope with different cooling situations:

(a) the nature of foods (e.g. the denser/more viscous the food, the longer time required to chill),

(b) the nature of containers (e.g. foods contained in plastic containers take a longer time to cool than foods in stainless steel containers)

(c) covered foods will cool slower (but are less likely to be exposed to accidental contamination)

4.     Inadequate reheating

As mentioned above, cooked foods can become contaminated with pathogens after cooking. Some of these pathogens (e.g. Listeria monocytogenes) can grow slowly at refrigerated storage. Thoroughly reheating foods at the satellite kitchens can help kill any of these pathogens that might be present.

Cook-serve                                                                                     Cook-chill

In order to ensure the safety of foods, basic food hygiene/safety principles as well as the following suggestions should be followed:

Cook-serve system

l           purchase raw materials of good quality only and store all raw materials at appropriate temperature

l           avoid cross-contamination

l           observe good personal hygiene throughout the production

l           personnel handling food should wash hands frequently

l           use separate, identifiable sets of equipment (e.g. cutting boards, knives, etc.) to handle raw and cooked (or ready-to-eat) foods

l           cook foods thoroughly (i.e. to 75^oC or above)

l           use separate areas to process raw materials (e.g. the area for washing vegetables and chopping raw meats) and cooked foods (e.g. the area for portioning and packaging) to prevent cross contamination

l           after cooking, keep cooked foods at 60^oC or above until serving

l           upon arriving at schools, service of foods should commence as soon as possible

Cook-chill system

l           purchase raw materials of good quality only and store all raw materials at appropriate temperature

l           avoid cross-contamination:

l           observe good personal hygiene throughout the production

l           personnel handling food should wash hands frequently

l           use separate, identifiable sets of equipment (e.g. cutting boards, and knives) to handle raw and cooked food

l           cook foods thoroughly (i.e. to 75^oC or above)

l           use separate areas to process raw materials (e.g. the area for washing vegetables and chopping raw meats) and cooked foods (e.g. the area for portioning and packaging) to prevent cross contamination

l           after cooking, portion and package foods as soon as possible and the rapid chilling process should begin within 30 minutes of cooking

l           chill foods rapidly to below 4^oC within 1.5 hours

l           store chilled foods at below 4^oC

l           reheat foods to 75^oC or above

l           keep reheated foods at 60^oC or above during distribution

l           upon arriving at schools, service of foods should commence as soon as possible

Summary of important food safety points

Note: it is a good practice to check and record the temperature of the food during production; for example, when the food is cooked, chilled, reheated, hot-held and/or at schools.

Desserts and fruits

Recently, desserts (e.g. jelly, yoghurt, fruits juice, etc.) and fruits (e.g. oranges, apples, etc.) have been included in the menus of many suppliers. These food items will likely introduce new food safety issues if they are not prepared and handled properly and hygienically. Suppliers are advised to consider the following suggestions before providing the food items:

l           have adequate personnel, equipment and facilities to handle extra procedures involved in the preparation of desserts and fruits

l           consider purchasing desserts in a pre-packaged ready-to-serve form from other reputable and reliable commercial sources if adequate personnel, equipment or facilities are not available

l           select appropriate food items and avoid high risk items. In general, items that require temperature control (e.g. require refrigerated storage for safety reasons) have a higher risk of causing foodborne illness

l           following are some steps that suppliers can take to reduce the risk of foodborne illness if fruits are provided:

n           if possible, provide whole fruits. This is because the edible parts of cut fruits can be contaminated during cutting and storage.

n           discard fruits that are bruised or damaged

n           after purchase, refrigerate fruits promptly (note: fresh whole produce such as bananas do not need refrigeration.)

n           wash hands thoroughly with liquid soap and water before cutting fresh produces

n           food poisoning bacteria may be present on the outside of fruits, so wash all fruits with cool tap water. Don't use soap or detergents

n           wash and sanitize cutting boards, dishes, utensils, and counter tops before cutting fruits

n           use one clean cutting board and knife for fruits and a separate one for raw meat and poultry

n           cover and refrigerate cut fruits immediately after peeling or cutting

n           use thermal boxes or other appropriate means to keep the temperature of cut fruits low when distributing the fruits to schools

Other reference documents

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