Q.“Curd is easier to digest by humans than milk.” Justify, giving two suitable reasons.
Curd is easier to digest than milk primarily because its proteins are partially pre-digested by bacteria, and its lactose content is significantly reduced during fermentation.
The transformation of milk into curd is a classic example of microbial fermentation, a process that not only changes the texture and flavour of food but also often enhances its digestibility and nutritional value. In the case of curd, Lactic Acid Bacteria (LAB), such as Lactobacillus, play a crucial role. These beneficial microorganisms act upon the milk, leading to changes that make curd a more digestible food item for humans compared to fresh milk.
Here are two primary reasons why curd is easier to digest:
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Partial Digestion of Milk Proteins: Milk contains complex proteins, primarily casein. During the fermentation process, Lactic Acid Bacteria produce lactic acid. This acid causes the casein proteins in milk to coagulate and curdle. More importantly, the acidic environment and enzymatic activity of LAB lead to the partial breakdown or denaturation of these complex milk proteins into simpler, more easily digestible forms. When we consume curd, our digestive system receives proteins that are already partially broken down, requiring less effort and fewer digestive enzymes to process them further into amino acids for absorption.
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Reduction of Lactose Content: Milk naturally contains lactose, a disaccharide (milk sugar). Many individuals, particularly adults, have varying degrees of lactose intolerance due to insufficient production of the enzyme lactase, which is necessary to break down lactose into simpler sugars (glucose and galactose) for absorption. During curd formation, Lactic Acid Bacteria actively consume lactose as their energy source, converting it into lactic acid. This process significantly reduces the lactose content in curd compared to fresh milk. Consequently, curd becomes much easier to digest for individuals who are lactose intolerant, and even for those with normal lactase levels, the reduced lactose load contributes to smoother digestion.
Beyond digestibility, LAB also improve the nutritional quality of curd by increasing the content of certain vitamins, such as Vitamin B12, as stated in the NCERT textbook. They also play a beneficial role in our stomach by checking the growth of disease-causing microbes.
In short, curd is easier to digest than milk because the Lactic Acid Bacteria partially digest the milk proteins and reduce the lactose content during fermentation, making it less taxing on the human digestive system.
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