Food Processing Unit Operation Flashcards
7 cards from real Agricultural/Bioengineering practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Food Processing Unit Operation flashcards as text
In fluidized bed drying of particulate food, the minimum fluidization velocity is reached when:
Answer: The drag force on particles exactly equals their weight in the bed
At minimum fluidization velocity, upward drag and buoyancy forces exactly balance particle weight, causing the bed to expand and become fluidized.
Which type of pump is most appropriate for moving a shear-sensitive food liquid such as whole berry yogurt without damaging the fruit pieces?
Answer: Positive displacement rotary lobe pump
Rotary lobe pumps move product gently through large cavities with minimal shear, preserving the integrity of delicate particulates.
The D-value in food microbiology is defined as:
Answer: The time in minutes at a given temperature to reduce the microbial population by 90% (one log cycle)
D-value (decimal reduction time) is the time needed at a constant temperature to destroy 90% of a specific microbial population.
In a pneumatic conveying system for flour, 'dense phase' conveying differs from 'dilute phase' primarily in that it:
Answer: Operates at lower velocities with higher product-to-air ratios, reducing particle degradation
Dense phase conveying uses high pressure at low velocity with high solid loading, minimizing particle breakage and attrition compared to high-velocity dilute phase.
Water activity (aₓ) of a food product is defined as:
Answer: The ratio of the partial pressure of water in the food to the vapor pressure of pure water at the same temperature
Water activity equals p/p₀, the equilibrium relative humidity divided by 100, and determines microbial growth potential and chemical reaction rates.
In aseptic processing and packaging of juice, the product is sterilized:
Answer: Continuously in a heat exchanger before being filled into pre-sterilized containers
Aseptic processing sterilizes product and packaging separately in continuous flow, then combines them in a sterile environment, enabling UHT treatment with minimal quality loss.
The overall heat transfer coefficient (U) in a food heat exchanger is most significantly reduced when:
Answer: A fouling layer deposits on the heat transfer surface
Fouling deposits act as an insulating layer with very low thermal conductivity, adding fouling resistance that dramatically reduces the overall U value.