Experimental Design Lab--Bacteria E. Coli

Experimental Design Lab--Bacteria E. Coli

Extended Essay Experimental Design
October 2008

Research Topic: Chemical “artificial” preservatives effectiveness in comparison to natural known preservatives

Research Question: Are chemical preservatives and/or natural preservatives effective at controlling the growth of bacteria on raw red meat?

Independent variable: Multiple types of food preservatives

Dependent variable: Raw red meat sample

Controlled variable: Agar/Petri dish set-up, incubation area and temperatures

Background knowledge:

Natural Preservatives-
“When foods are very salty or sugary, they draw water out of bacteria, which either kills the bacteria or keeps their numbers down. Thus sugar and salt keep in the pantry indefinitely. Many sweet or salty foods will also keep for long periods. Many types of candy, stored in a tightly closed container, last for a long time on the shelf.”

“Foods containing enough alcohol, a general disinfectant, can also live long on your pantry shelves. It is the presence of alcohol that keeps your vanilla, almond extract, and other flavoring extracts, as well as alcoholic beverages, safe for long periods on your shelves without refrigeration.”

“Acidity and dryness also discourage bacteria. Vinegar, with a pH ranging from 2.4 to 3.4, is too acidic to be friendly to bacterial growth, so you ordinarily need not refrigerate it, and it will last safely on your pantry shelf for as long as a year. (But see the book.) Pickling and brining use a potent combination of salt and vinegar or other acid to preserve and flavor foods at the same time. Nowadays we refrigerate our pickled foods after opening them so as to keep them crisper and better-tasting. But pickles always used to be stored in the pantry-in the pickle barrel or jar-and some stores still sell pickles from the barrel, at room temperature.’

Chemical-
“Nisin is a kind of food antiseptic, and it can efficiently inhabit Gram-positive germs which causes food putrescent. It...