Agricultural/Bioengineering Agricultural/Bioengineering: Food Engineering 5 — Questions and Answers
Question 1: The 'glass transition temperature' (Tg) of a food system is important because below Tg:
- Microbial growth accelerates rapidly
- Molecular mobility is greatly reduced, improving stability (Correct answer)
- Lipid oxidation is maximized
- Enzymatic reactions proceed at maximum rate
Correct answer: Molecular mobility is greatly reduced, improving stability
Below Tg, the amorphous food matrix becomes a rigid glass with very low molecular mobility, dramatically slowing diffusion-limited deterioration reactions and microbial growth.
Question 2: In the context of frying, the 'oil uptake' by a fried food product is primarily driven by:
- Osmosis through the crust
- Condensation vacuum created as steam exits and the product cools after frying (Correct answer)
- Diffusion of oil across the intact surface during frying
- Capillary rise through starch channels during frying
Correct answer: Condensation vacuum created as steam exits and the product cools after frying
Most oil uptake occurs post-frying as the product cools: steam that had been escaping condenses, creating a partial vacuum that draws surface oil into the porous crust.
Question 3: Which analytical technique is most commonly used to determine fat content in food products by solvent extraction?
- Karl Fischer titration
- Soxhlet extraction (Correct answer)
- Kjeldahl digestion
- Dumas combustion
Correct answer: Soxhlet extraction
The Soxhlet method uses repeated cycling of an organic solvent (e.g., hexane or petroleum ether) to continuously extract fat from a dried food sample.
Question 4: The pasteurization of egg products at 60°C for 3.5 minutes is designed primarily to destroy:
- Clostridium botulinum spores
- Salmonella species (Correct answer)
- Listeria monocytogenes biofilms
- Mycotoxin-producing molds
Correct answer: Salmonella species
Liquid egg pasteurization targets Salmonella, the primary pathogen of concern in shell eggs, using the minimum time-temperature combination that achieves a sufficient log reduction.
Question 5: In food fermentation, heterofermentative lactic acid bacteria (LAB) produce lactic acid and also:
- Only CO2 as a byproduct
- CO2 and ethanol or acetic acid as byproducts (Correct answer)
- Only acetic acid as a byproduct
- Propionic acid as the sole byproduct
Correct answer: CO2 and ethanol or acetic acid as byproducts
Heterofermentative LAB use the phosphoketolase pathway, producing equimolar amounts of lactic acid, CO2, and either ethanol or acetic acid from glucose.
Question 6: The Fickian diffusion model is applied in food engineering primarily to predict:
- Heat transfer rates during sterilization
- Mass transfer of solutes or moisture within food matrices (Correct answer)
- Pressure drop across filtration membranes
- Centrifugal force on fat globules
Correct answer: Mass transfer of solutes or moisture within food matrices
Fick's second law describes transient diffusion of moisture or solutes through food, enabling prediction of drying curves, salt penetration, and flavor migration.
Question 7: Which statement best describes the function of transglutaminase (TG) enzyme in food processing?
- It breaks peptide bonds to tenderize meat
- It crosslinks glutamine and lysine residues to restructure proteins (Correct answer)
- It hydrolyzes triglycerides to free fatty acids
- It converts glucose to fructose for sweetener production
Correct answer: It crosslinks glutamine and lysine residues to restructure proteins
Transglutaminase catalyzes covalent isopeptide bonds between glutamine and lysine residues in proteins, enabling restructured meat production and improved gel texture.
Agricultural/Bioengineering Agricultural/Bioengineering: Food Engineering 5
The 'glass transition temperature' (Tg) of a food system is important because below Tg: