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Name:Lisa 
Status: Student
Age: 15
Location: N/A
Country: N/A
Date: N/A 


Question:
Hi, I'm planning on doing an experiment to test what sort of substances can prevent meat from rotting (eg. salt, sugar, vinegar, vegetable oil), and trying to find some background info before I start.

Could you tell me: what types of bacteria are in meat - what are they called and what are they like? which meats have them? (what is a good meat to use?) which ones and how do they make the meat 'rot'? how is this prevented chemically? (a bit of a dumb question now) how can I tell that the meat has rotted? - what do I look for? how long does it usually take?

Sorry for asking so many questions. I'm just having a bit of a hard time finding the answers. Thanks :)



Replies:
What type of bacteria are IN meat? none, or the animal that produced the meat (muscles, mostly) must have been VERY ill. But on the surface of the meat you'll find lot's of bacteria that found their way there during slaughter, preparation, storage of the meat. These can be all kinds, but due to the slaughtering process, fecal bacteria will be overrepresented.

Most meat is treated to prevent bacterial growth during processing, especially by drying and heating. The best meat to use in your case is chicken, because that can not be dried as beef or pork: it would change color and would not look nice (hence would not sell). Chances are you get pathogenic (ill-making) bacteria on chicken meat, especially Campylobacter and Salmonella, so wear gloves whenever you handle the meat, and carefully clean and desinfect all utensils afterwards.

Which bacteria make meat 'rot'? Lactobacilli would turn the meat sour, any food-poisening bacteria would make the meat unfit for consumption (and dangerous to handle). The bad smell that warns you meat is 'off' are biochemical compounds produced by the bacteria when they grow, but also degradation compounds produced by enzymes released by the meat itself, as part of the natural decaying process.

You can speed up the process by increasing the temperature. 37 C is the optimum, and at this temperature meat will begin to smell very soon, rotting takes place within 24 hrs. Don't do this experiment in the vicinity of food stuff, and don't eat or drink anything during practical handling. Carefully wash hands afterwards.

How to tell the meat is rotten? check texture (punch it), smell, color. Measure the weight (does it remain constant?). If you can grow bacteria, Take a swab of a standardized square of the surface with a sterile swab and put this in a standardized amount of broth. Culture this on an agar plate and see how many, and what different, colonies grow.

For more bacteriological background on the dangers of bacteria growing on meat and other foodstuff, check the subject 'food safety' in the Virtual Museum of Bacteria, at www.bacteriamuseum.org (or go there directly:

www.bacteriamuseum.org/niches/foodsafety/foodsafety.shtml

Trudy Wassenaar
Curator of the VMB



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