Question

State whether the following statements are true or false. Curd is sour in taste due to the presence of an acidic substance.

Short answer

Answer: The statement is true.

Step-by-step solution

Understand the statement

First, we need to understand the statement. The statement is: "Curd is sour in taste due to the presence of an acidic substance."

Investigate the taste of curd

Curd, also known as yogurt, is known for its sour taste. This is due to the fermentation process that it goes through, in which bacteria convert lactose (a sugar found in milk) into lactic acid.

Determine the presence of an acidic substance

As mentioned earlier, the fermentation process produces lactic acid. An acid is a substance that donates hydrogen ions (H+) to a solution, making it acidic. Lactic acid has a sour taste and is indeed an acidic substance.

Evaluate the statement

Now that we know that curd has a sour taste due to the presence of lactic acid, an acidic substance, we can conclude that the given statement is true. So, the answer is: The statement is true.

Key concepts

Fermentation Process

Fermentation is a metabolic process that converts carbohydrates to alcohols, gases, or acids under anaerobic conditions (without oxygen). Different types of fermentation exist, but when it comes to curd, what's particularly interesting is the process known as lactic acid fermentation.
During the fermentation that happens with curd, specific bacteria, typically from the Lactobacillus family, are introduced to milk. These bacteria then feed on lactose, which is the sugar found in milk. As they metabolize the lactose, they produce lactic acid as a byproduct. It is this production of lactic acid that not only gives the curd its distinct sour taste but also assists in coagulating the milk proteins, which thickens the milk into curd. Furthermore, the acidity created by the lactic acid helps preserve the curd by preventing the growth of harmful bacteria.

Fermentation in Daily Life

Many foods and beverages undergo fermentation, leading to their unique flavors and textures. Examples include the making of bread with yeast or the fermentation of grapes into wine. In each case, microorganisms play a crucial role, transforming basic ingredients into products with increased shelf life and nutritional value. The process is both a natural preservative and a means to enhance the organoleptic properties of foods.

Lactic Acid

Lactic acid, scientifically termed as 2-hydroxypropanoic acid, is an organic acid that plays a significant role in various biochemical processes. Structurally, it is a molecule that includes a carboxyl group ((COOH)), which is characteristic of all acids. In the context of food science, lactic acid is primarily known for its contribution to the sour taste of fermented dairy products like curd.
Lactic acid develops in milk when specific bacteria ferment lactose during the making of curd. These bacteria, through the fermentation process, produce lactic acid which lowers the pH of milk, causing it to curdle and form the familiar texture and flavor of curd. Apart from its role in food, lactic acid is also involved in our metabolism, particularly during exercise, where it is produced in muscle tissue and can lead to the sensation of fatigue.

Commercial Uses of Lactic Acid

Besides its natural occurrence in foods, lactic acid is also commercially produced and used as a preservative, flavoring, and pH regulator in various industries, including food, pharmaceutical, and cosmetic industries.

Properties of Acids

Acids are a group of substances with common characteristics and properties. They are known to have a sour taste, and when dissolved in water, they increase the concentration of hydrogen ions ((H+)), making the solution acidic. This is apparent in foods such as lemons and vinegar, and it is similarly the case with curd's sour flavor being attributable to lactic acid.
One of the hallmark properties of acids is their pH level. The pH scale measures how acidic or basic a substance is, with levels below 7 indicating acidity. Lactic acid, like other acids, contributes to the lowering of the pH level in the environments where it's present. Acids also have the ability to conduct electricity in their aqueous solutions, react with metals to produce hydrogen gas, and cause color changes in pH indicators. For example, blue litmus paper turns red when introduced to an acidic solution.

Acid-Base Reactions

Acids participate in chemical reactions known as acid-base reactions where they react with bases to form salt and water. This neutralization process is an integral aspect of various chemical experiments and industrial applications. Understanding these properties helps in identifying acids and their functional roles in various contexts, such as in the sourness of curd due to lactic acid, or in broader scientific and industrial practices.