Question

Fresh milk has a pH of ${ 6 }$. How do you think the pH will change as it turns into curd?
a.) pH will reduce
b.) pH will increase
c.) It becomes same as milk
d.) None of these

Answer 1

Hint: The pH value of:
Basic solution is greater than ${ 7 }$.
An acidic solution is less than ${ 7 }$.
Neutral solution is equal to ${ 7 }$.

Complete answer:
It is given that the pH of fresh milk is ${ 6 }$, i.e., less than ${ 7 }$. So, it is acidic in nature. When the milk turns into curd then it will show all the properties of an acid. The milk is converted into curd due to the action of bacteria and lactic acid will be formed which is also acidic in nature. It turns sour and the pH decreases from ${ 6 }$. Hence, we can say that the pH of the milk is reduced as it turns into a curd.
The correct option is A.

Additional information:
Bacteria like Lactobacillus and Streptococcus lactic, etc are responsible to convert milk into curd as they release some organic acids which reduces the pH as the milk turns into curd.
Fermentation is the process by which we can convert milk into curd. Milk contains casein protein. When the chemical reaction occurs between lactic acid and casein protein then the curd is produced.
During this process, bacteria use enzymes to produce ATP energy from lactose.

Note: The possibility to make a mistake is that you can choose option C. The pH of the fresh milk is ${ 6 }$ (acidic) and when it is converted into curd it is acidic in nature. But the pH will decrease and not remain the same.