Agricultural/Bioengineering Food Processing Unit Operation 2

Question 1

In a counterflow heat exchanger used for milk pasteurization, which configuration provides the greatest thermal efficiency?

Accepted Answer

Counterflow with product and heating medium flowing in opposite directions

Answer

Counterflow configuration maintains a more uniform temperature driving force along the entire exchanger length, maximizing heat transfer efficiency.

Question 2

The Reynolds number in a food processing pipeline is 1,800. What flow regime is present?

Accepted Answer

Laminar flow

Answer

A Reynolds number below 2,100 indicates laminar (streamline) flow in a pipe, where fluid layers move parallel without mixing.

Question 3

Which drying method preserves heat-sensitive nutrients best while achieving very low final moisture content?

Accepted Answer

Freeze drying (lyophilization) under vacuum

Answer

Freeze drying removes water by sublimation at low temperatures, minimizing thermal degradation of vitamins, flavors, and bioactive compounds.

Question 4

In centrifugal separation of cream from milk, increasing the bowl speed by a factor of 2 increases the centrifugal force by a factor of:

Accepted Answer

4

Answer

Centrifugal force is proportional to the square of angular velocity (F = mω²r), so doubling speed quadruples the separating force.

Question 5

What is the primary purpose of blanching vegetables before freezing?

Accepted Answer

To inactivate enzymes that cause quality deterioration during frozen storage

Answer

Blanching inactivates peroxidase, lipoxygenase, and other enzymes that cause off-flavors, color changes, and texture degradation during frozen storage.

Agricultural/Bioengineering Practice Test

Agricultural/Bioengineering Practice Test

Agricultural/Bioengineering Food Processing Unit Operation 2