Agricultural/Bioengineering Food Processing Unit Operation 5

Question 1

In fluidized bed drying of particulate food, the minimum fluidization velocity is reached when:

Accepted Answer

The drag force on particles exactly equals their weight in the bed

Answer

At minimum fluidization velocity, upward drag and buoyancy forces exactly balance particle weight, causing the bed to expand and become fluidized.

Question 2

Which type of pump is most appropriate for moving a shear-sensitive food liquid such as whole berry yogurt without damaging the fruit pieces?

Accepted Answer

Positive displacement rotary lobe pump

Answer

Rotary lobe pumps move product gently through large cavities with minimal shear, preserving the integrity of delicate particulates.

Question 3

The D-value in food microbiology is defined as:

Accepted Answer

The time in minutes at a given temperature to reduce the microbial population by 90% (one log cycle)

Answer

D-value (decimal reduction time) is the time needed at a constant temperature to destroy 90% of a specific microbial population.

Question 4

In a pneumatic conveying system for flour, 'dense phase' conveying differs from 'dilute phase' primarily in that it:

Accepted Answer

Operates at lower velocities with higher product-to-air ratios, reducing particle degradation

Answer

Dense phase conveying uses high pressure at low velocity with high solid loading, minimizing particle breakage and attrition compared to high-velocity dilute phase.

Question 5

Water activity (aₓ) of a food product is defined as:

Accepted Answer

The ratio of the partial pressure of water in the food to the vapor pressure of pure water at the same temperature

Answer

Water activity equals p/p₀, the equilibrium relative humidity divided by 100, and determines microbial growth potential and chemical reaction rates.

Agricultural/Bioengineering Practice Test

Agricultural/Bioengineering Practice Test

Agricultural/Bioengineering Food Processing Unit Operation 5