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Milk tastes sour when kept in the open for sometime due to the formation of?
1. Malic acid
2. Citric acid
3. Lactic acid
4. Carbonic acid

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Correct Answer - Option 3 : Lactic acid

The correct answer is Lactic acid.

  • Lactic Acid
    • Like many other things, milk contains bacteria, Milk also naturally contains a kind of sugar known as lactose.
    • The bacteria that live in milk get energy from this special sugar and use it to reproduce to make even more bacteria.
    • When the bacteria use the lactose sugars to reproduce, they change it from lactose sugar into lactic acid, which tastes sour. Hence, Option 3 is correct.
    • Lactic Acid is an organic acid with the chemical formula C3H6O3.
    • It is also known as milk acid. When milk sugar (lactose) undergoes fermentation, the product obtained is lactic acid.
    • It is found in cottage cheese, leban, sour milk, yoghurt, and Koumiss.
    • Levo and Dextro are two forms of optical isomers of lactic acid.
    • In the year 1780, Carl Wilhelm Scheele a Swedish chemist isolated lactic acid from sour milk for the first time.
    • This compound is water-soluble and white in its solid state whereas it is colourless in its liquid state.
    • The soluble salt of lactic acid like calcium lactate can be used as a source of calcium.
    • The PH of 1 mM of lactic acid is about 3.51.
    • Uses of Lactic Acid
      • It is used in food and pharmaceuticals.
      • It is used in making plastics.
      • It helps in the coagulation of protein in milk.
      • It is used in textile dyeing and leather tanning.
      • Lactate plays an important role in the healing of traumatic brain injuries.
      • The release of norepinephrine in the brain is signalled by lactate.

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