Research Paper On Yoghurt

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Abstract – Yogurt is a product of lactic acid and lactose. In order to produce yogurt, milk is pasteurized (at 45 degrees Celsius) and the inoculum is added followed by incubation. Over a period of 7 days, yoghurt fermentation was attempted using lactobacillus cultures. A liter of milk was supplied and plain yoghurt was used as a starter culture as it contains the necessary bacteria to ferment lactose and produce lactic acid. The milk was added to a flask: then boiled, cooled and inoculated. The milk was incubated for a week and all the while the milk was tested for changes in pH, density, mass and physical changes. The values obtained were then used to determine the growth kinetics of Lactobacillus bulgaricus.


Fermentation …show more content…

Worldwide, yoghurt production is a multi-billion dollar industry. Although yoghurt is known for its high sugar content, some doctors and scientists suggest that it is a necessary part of the diet, especially for growing children.
No one really knows exactly how yoghurt was discovered. (Dworsky, 1978) say the Lactobacillus bacteria may have come into contact with the milk by accident, a random occurrence. Some of the earliest recordings of yoghurt date back to the 11th century, crediting the Greeks and nomadic Turks with the discovery. Around 1878 and the years that followed, a Bulgarian medical student Stamen Grigov discovered that yoghurt contained Lactobacillus. This discovery influenced the industrial production of yoghurt
Yoghurt is basically a product of lactose fermentation (a milk sugar) to produce lactic acid. The decrease in pH due to the formation of acid, causes the milk to change physically and form the soft gel that we associate with the physical characteristics of yoghurt (Pillsbury et al, …show more content…

Glucose and lactose are the most preferred carbon sources (Dickinson, 1999)

Microorganisms used in Yogurt production
The bacterial cultures used in yogurt production are mainly Streptococcus thermophiles and Lactobacillus bulgaricus.

Lactobacillus bulgaricus
These are gram positive bacteria which are found in acidic condition of pH 4 to 4.5 – acidophilic. Figure 1: An image of Lactobacillus bulgaricus viewed under electron microscope: source-

Lactobacillus bulgaricus bacteria was first isolated from the leaves of a green plant called a snowdrop flower by scientist named makovnkov and Dr. Stamen Grigov.
L bulgaricus has shown the ability to cause homofermentation of lactic acid, meaning the lactic acid produced is the on byproduct. In a study conducted by (wheater ,1974) the strains of l bulgaricus grow optimally at temperatures between 45 and 50 degrees Celsius and they do not prefer environments high in salt concentrations
L. bulgaricus are used as starter cultures during yogurt fermentation and are regarded as probiotics (Perna et al, 2008)

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