|MadSci Network: Biochemistry|
"Rotting" is the decomposition of food by the action of spoilage bacteria, fungi or viruses. When microbes eat food, they break down the proteins into smaller parts, generate acids, and poison the food with toxins that keep other microbes from growing in competition. "Rotten" food is waste and partially digested result from microbes! Some chemical changes occur due to enzymes (proteins that speed up reactions) that are naturally present in the food. This happens with ripening of fruit and aging of meat. Observing the "rotting" of food can be done in a variety of ways. You just have to focus on one of the measurable properties of the food that changes: 1. Color. (Compare different stages. Example: banana.) 2. Appearance. (Compare different stages. Example: fruit, lettuce.) 3. Bacterial growth. (This requires measuring how many bacteria are present.) 4. Acidity. (This requires measurement of pH or acidity using chemistry lab equipment. Example: measure pH of meat by pH-paper.) 5. Taste. (You don't want to do this one, except for early stages!) 6. Toxins. (Requires special chemical procedures.) 7. Texture. (Strength or stretchiness. Example: measure weight needed to push pencil into food.) Color and appearance are very easy to do, and can be recorded with photographs and simple comparisons. Remember bacteria growth at different speeds depending on presence of air (oxygen), amount of humidity, presence of chemicals (salt) and temperature. You will cause the food to spoil in different ways if kept warm, or at room temperature, or refrigerated. In your experiment, you will be observing spoilage at room temperature with oxygen present. The spoilage will probably be fairly rapid, with bacteria the cause, unless the food is dry (bread, pie), in which case molds are the usual spoilage microbe. If you add salt, you slow down spoilage by allowing only certain bacteria and fungi to grow easily. If you add FRESH garlic, almost all microbes will be protected against, as fresh garlic contains a potent antibiotic. Other preservatives to try are fresh rosemary or mustard or white vinegar. Many foods we eat today are actually "spoiled" or "rotten" in some way. This includes yogurt and cheese (bacteria), pickles and sauerkraut (bacteria), wine and beer (yeast), and salami (bacteria). Good luck on your experiment!
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