Experiment No. 03 Date:
Name of the experiment:
Aerobic plate count (APC) and total coliform count of supplied yogurt sample.
To determine the aerobic plate count and total coliform count of the supplied yogurt sample.
Yogurt squeezed or extracted from milks are more or less acidic, depending on the product, the pH generally ranges from about 2.4-4.2 and contain sugar (4.7g), fat (3.3g), carbohydrates (4.7g), and proteins (3.3g). Although molds can and do grow on the surface of yogurt if the yogurt are exposed to air, the high moisture contents favors the faster-growing yeasts and bacteria. The deficiency of vitamin B discourages some bacteria. The normal change to be expected in raw yogurt in room temperatures is an alcoholic fermentation by yeasts, followed by the oxidation of the alcohol and yogurt acids by film yeast or molds growing on the surface if it is exposed to air or the oxidation of the alcohol to acetic acid if acetic acid bacteria are present. In additional to the usual alcoholic fermentation, yogurt may undergo other changes caused by microorganisms: 1. The lactic acid fermentation of sugars, mostly by heterofermentative lactic acid bacteria such as Lactobacillus pastorianus, Lac. bevis and by homofermentative lactic acid bacteria such as Lac. arabinose. 2. The fermentation of organic acids of the yogurt by lactic acid bacteria e.g., Lac. pastorianus, malic acid to lactic and sucsinic acids, citric acid to lactic and acetic acids. 3. Slime production by Leuconostics mesentoroides, Lac. bevis. As contamination and spoilage of yogurt is very common, it is necessary to check its quality before distribution, marketing and consumption. The main reasons for quality testing include- * To determine the presence of pathogenic bacteria.
* To determine the presence of coliform bacteria which indicate fecal contamination? *...
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