Lactic Acid Fermentation Lab Report

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Laboratory Report on Fermentation of Yogurt and Ginger Ale


Fermentation is a metabolic process in which an organism converts a carbohydrate, such as starch or a sugar, into an alcohol or an acid. There are two types of fermentation namely ethanol fermentation and lactic acid fermentation. Ethanol fermentation occurs when pyruvate from glucose metabolism is broken down into alcohol and oxygen. In lactic acid fermentation, pyruvate molecules are fermented into lactic acid (Helmenstine, 2014).
Examples of fermented products are yogurt and ginger ale. Yogurt is a sour milk product that is usually served with fruit toppings while ginger ale is a carbonated drink often mixed with alcoholic beverages.
This experiment aims to produce
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Explain the process of fermentation in the Yogurt and Ginger Ale.

Yogurt underwent lactic acid fermentation. During the making of yogurt, the lactose is broken down by Lactobacillus bulgaricus and Streptococcus thermophilus into these two glucose and galactose. The further processing of glucose and galactose results in the end products of lactic acid and acetaldehyde. The production of lactic acid and acetaldehyde decreases the pH which causes the milk to clot and produce the sour taste of the yogurt (Westminster College, n.d.). Ginger ale underwent ethanol fermentation. The yeast breaks down the glucose to form 2 pyruvate molecules. Before pyruvate can be converted to ethanol, it is first converted into an intermediary molecule called acetaldehyde. This releases carbon dioxide. Afterwards, acetaldehyde is converted into ethanol (, n.d.).

2. What common microorganisms is use in processing Yogurt.

The most common starter culture of yogurt is Lactobacillus bulgaricus and Streptococcus thermophilus. Streptococcus thermophilus is classified as a thermophile growing at 45°C, and higher, and is widely used in the manufacture of yoghurt while Lactobacillus delbrueckii subsp. bulgaricus is homofermentative, produces almost 2% w/v lactic acid in milk, has an optimum temperature of 42° and grows at temperatures of 45°C and higher (Mullan,

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