Step 1: Understanding the Concept:
Parboiling is a hydrothermal treatment given to paddy before milling. It involves three main steps: soaking, steaming, and drying. The question asks for the primary purpose of the steaming step.
Step 2: Detailed Explanation:
Let's look at the purpose of each step in the parboiling process:
1. Soaking (Hydration): Paddy is soaked in water to increase its moisture content to a certain level (around 30-35%). This step is also called hydration. This prepares the grain for the next step. So, (A) is the purpose of soaking, not steaming.
2. Steaming: After soaking, the paddy is treated with steam. The heat from the steam causes a crucial change within the rice kernel. The starch granules absorb the water present in the kernel and, under the influence of heat, they swell and burst, losing their crystalline structure and forming a fused, amorphous gel. This irreversible process is known as starch gelatinization.
3. Drying: After steaming, the paddy is carefully dried to a moisture content suitable for milling and storage. So, (B) is a separate step, not the purpose of steaming.
The main benefits of starch gelatinization during steaming are:
- It heals the cracks and fissures within the rice kernel, making the grain harder and more translucent. This significantly reduces the number of broken grains during milling, thus increasing the head rice recovery.
- It drives water-soluble nutrients (like vitamins, especially B vitamins) from the bran and germ layers into the endosperm (the starchy part). This makes parboiled rice nutritionally superior to raw milled rice.
- It makes the milled rice more resistant to insect attacks during storage.
(D) Starch retrogradation: This is the process that occurs during the cooling and drying of the gelatinized starch. The starch molecules re-associate into a more ordered structure. While it's part of the overall parboiling process (happening after steaming), the primary purpose and event {during} steaming is gelatinization.
Step 3: Final Answer:
The main purpose of the steaming step in the parboiling process is to achieve starch gelatinization. Therefore, option (C) is the correct answer.