Agricultural/Bioengineering Agricultural/Bioengineering: Food Engineering 4 ā Questions and Answers
Question 1: In centrifugal separation of cream from milk, the separation efficiency depends primarily on:
- Temperature and density difference between fat and skim milk (Correct answer)
- pH of the milk only
- Protein content of the milk
- Lactose concentration only
Correct answer: Temperature and density difference between fat and skim milk
Stokes' law governs centrifugal separation; efficiency increases with temperature (reduces viscosity) and with the density difference between the fat globules and the continuous skim milk phase.
Question 2: Ohmic heating of food products works by passing electric current through the food, which:
- Generates heat only on the surface
- Generates heat uniformly throughout the volume due to electrical resistance (Correct answer)
- Induces cavitation in liquids
- Generates heat only at the electrodes
Correct answer: Generates heat uniformly throughout the volume due to electrical resistance
Ohmic heating converts electrical energy to heat throughout the food volume as current flows through it, enabling rapid and relatively uniform internal heating.
Question 3: The 'retrogradation' of starch during bread staling results from:
- Mold growth on the bread surface
- Recrystallization of amylopectin chains during storage (Correct answer)
- Oxidation of lipids in the crumb
- Loss of CO2 from the bread structure
Correct answer: Recrystallization of amylopectin chains during storage
Retrogradation occurs as gelatinized amylopectin chains realign and form crystalline structures during storage, increasing stiffness and perceived staleness.
Question 4: In ultrafiltration (UF) membrane processing of whey, the retentate is enriched in:
- Lactose and minerals
- Whey proteins (Correct answer)
- Lactic acid
- Water
Correct answer: Whey proteins
UF membranes (typical MWCO 10ā100 kDa) retain large whey protein molecules in the retentate while lactose, minerals, and water pass through as permeate.
Question 5: Which food additive functions as a chelating agent to improve the efficacy of antimicrobials and retard lipid oxidation?
- Sodium benzoate
- EDTA (ethylenediaminetetraacetic acid) (Correct answer)
- Sodium nitrite
- Potassium sorbate
Correct answer: EDTA (ethylenediaminetetraacetic acid)
EDTA chelates pro-oxidant metal ions like iron and copper, slowing lipid oxidation and destabilizing gram-negative bacterial outer membranes to enhance antimicrobial effectiveness.
Question 6: The critical control point (CCP) concept in HACCP is defined as a step at which:
- A hazard is merely monitored but not controlled
- Control can be applied to prevent, eliminate, or reduce a food safety hazard to acceptable levels (Correct answer)
- Product quality is evaluated for commercial standards only
- Raw material suppliers are audited
Correct answer: Control can be applied to prevent, eliminate, or reduce a food safety hazard to acceptable levels
A CCP is a processing step where a control measure can be applied and is essential to prevent or eliminate a food safety hazard or reduce it to an acceptable level.
Question 7: Pulsed electric field (PEF) technology inactivates microorganisms primarily by:
- Thermal denaturation of cell proteins
- Electroporation ā creating pores in the cell membrane (Correct answer)
- UV-induced DNA damage
- Osmotic lysis from salt addition
Correct answer: Electroporation ā creating pores in the cell membrane
PEF applies short, high-voltage pulses that cause electroporation ā the formation of irreversible pores in microbial cell membranes ā leading to cell death.
Agricultural/Bioengineering Agricultural/Bioengineering: Food Engineering 4
In centrifugal separation of cream from milk, the separation efficiency depends primarily on: