MISSISSIPPI STATE -- Kids may think a lunch box's primary purpose is to look cool while holding food, but parent's should be sure the lunch box is actually a safe place for food.

Dr. Melissa Mixon, human nutrition specialist with Mississippi State University's Extension Service, said packing a safe, healthy lunch for school children can be a bit tricky. Whatever is packed must be able to survive several hours without refrigeration before lunchtime.

"Hot foods must stay hot and cold foods cold in order for the meal to be safe," Mixon said. "The best way to ensure youth have a safe lunch is to either pack shelf-stable foods or use insulated containers with a cold source or an insulated bottle for hot foods."

Perishable food has a very short time limit and temperature range it can tolerate before it becomes unsafe to eat. When in doubt about the safety of food, throw it out.

"If the food has been exposed to temperatures between 40 to 140 degrees longer than two hours, throw it away," Mixon said. "That's all the time needed for bacteria or other microorganisms to multiply to dangerous levels. Bacteria seldom change the taste, color or appearance of the food, but they can multiply to the millions in a few hours and cause illness."

Foods that are safe for any occasion include peanut butter sandwiches, cookies, crackers, commercially-dried fruit, some cans of fruit or pudding, juice boxes and whole fruit.

Foods that perish need to be temperature protected.

"When shopping for lunch boxes or bags, choose one that is insulated to keep hot foods hot and cold foods cold," Mixon said. "Include a frozen gel pack to keep foods chilled. Discard food kept past lunch as the gel packs generally thaw and don't keep foods safe past a few hours."

Mixon said another trick is to make perishable sandwiches or foods the night before and put them in the freezer. In the morning, place these frozen foods in the insulated lunch box. They'll thaw by lunchtime, but still be safe to eat. The same came be done with individual juice boxes or plastic containers of foods such as apple sauce. These will help keep the food cool until they've thawed by lunchtime.

Hot foods are best stored in insulated bottles. Prepare these by filling first with boiling water for a few minutes, then pour it out and fill with the hot food. Keep the bottle closed until lunchtime and the food will be warm when the student is ready to eat.

"Take precautions when preparing and packing a school lunch, but be sure to not eat any leftovers. Perishable food packed in a lunch box or bag that is not eaten at lunch should be thrown away," Mixon said. "Don't try to save it by bringing it back home. The chances are high that it is no longer safe to eat."

Parents who want to make sure the lunch box will keep their child's food safely can do a test run by packing a lunch and storing the box under normal conditions. At lunchtime, test the food temperatures with a kitchen thermometer to see if the meal is still safe to eat.