Question

Drying of fruit pulp can be accomplished by which of the following dryer?
A. Fluidized bed dryer
B. Drum dryer
C. Spray dryer
D. LSU dryer
E. Baffle dryer
Choose the correct answer from the options given below:

• A. A only
• B. B only
• C. B and C only
• D. D and E only

Hint:

To dry liquid or paste-like food materials (such as milk, fruit pulps, or purees), only drum dryers (for viscous pastes) and spray dryers (for pumpable liquids) are used commercially.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Fruit pulps are highly viscous, heat-sensitive food slurries that contain high levels of sugars, organic acids, and moisture.
Drying these materials requires specialized drying systems capable of handling sticky, liquid-phase feeds without causing thermal degradation, carmelization, or clogging of the dryer.

Step 2: Detailed Explanation:
Let us evaluate the suitability of the listed dryers for fruit pulp:
- A. Fluidized bed dryer: This dryer is used for particulate solid foods (like grains, peas, or diced vegetables) that can be suspended (fluidized) in an upward-flowing stream of hot air. It cannot handle liquid or highly viscous pulps.
- B. Drum dryer: This is highly suitable. In drum drying (roller drying), the viscous fruit pulp is applied as a thin layer onto the surface of rotating, steam-heated metal drums. The moisture evaporates rapidly, leaving a dry sheet of pulp that is scraped off by a doctor blade and ground into powder.
- C. Spray dryer: This is also highly suitable. For spray drying, the fruit pulp is diluted or mixed with a carrier agent (like maltodextrin) to reduce its viscosity. It is then atomized into a fine mist inside a drying chamber, where it encounters hot air and dries almost instantly into fine powder.
- D. LSU (Louisiana State University) dryer: This is a continuous-flow, mixing-type column dryer designed specifically for drying cereal grains (like paddy). It is not designed for liquid or paste-like materials.
- E. Baffle dryer: This is a gravity-flow dryer used for granular or particulate materials, and is unsuitable for viscous slurries.
Therefore, drum drying and spray drying are the appropriate methods for drying fruit pulp.

Step 3: Final Answer:
The correct option is (C).