Agricultural/Bioengineering Agricultural/Bioengineering: Food Engineering 2 — Questions and Answers
Question 1: Which heat transfer mechanism is primarily responsible for cooking food in a microwave oven?
- Convection
- Conduction
- Dielectric heating (Correct answer)
- Radiation
Correct answer: Dielectric heating
Microwaves cause polar molecules like water to rotate rapidly, generating heat internally through dielectric heating.
Question 2: The 'z-value' in thermal processing refers to:
- The temperature increase needed to reduce D-value by 90%
- The log reduction in microbial count at a given temperature
- The temperature increase needed to reduce D-value to 1/10th (Correct answer)
- The pH at which microbial death rate is maximized
Correct answer: The temperature increase needed to reduce D-value to 1/10th
The z-value is the temperature change required to achieve a 10-fold (one log) change in the D-value of a microorganism.
Question 3: Which of the following is NOT a colligative property exploited in food preservation?
- Osmotic pressure
- Boiling point elevation
- Freezing point depression
- Surface tension reduction (Correct answer)
Correct answer: Surface tension reduction
Surface tension is not a colligative property; colligative properties depend on solute concentration, not identity.
Question 4: In extrusion processing of food, the 'specific mechanical energy' (SME) input affects:
- Only the color of the extrudate
- Starch gelatinization, protein denaturation, and product expansion (Correct answer)
- Only product moisture content
- Only extruder throughput rate
Correct answer: Starch gelatinization, protein denaturation, and product expansion
SME drives the thermomechanical transformation of ingredients, affecting starch gelatinization, protein structure, and the expansion ratio of the extrudate.
Question 5: What is the primary purpose of blanching vegetables before freezing?
- To add color to the vegetables
- To inactivate enzymes that cause quality deterioration (Correct answer)
- To reduce microbial load to zero
- To increase the freezing rate
Correct answer: To inactivate enzymes that cause quality deterioration
Blanching inactivates enzymes such as peroxidase and lipoxygenase that would otherwise cause color, flavor, and texture degradation during frozen storage.
Question 6: The Maillard reaction in food processing requires which two types of reactants?
- Reducing sugars and amino acids (Correct answer)
- Oxidized lipids and free water
- Ascorbic acid and metal ions
- Polyphenols and oxygen
Correct answer: Reducing sugars and amino acids
The Maillard reaction is a non-enzymatic browning reaction between reducing sugars and free amino groups of amino acids or proteins.
Question 7: In food rheology, a fluid whose viscosity increases with increasing shear rate is classified as:
- Pseudoplastic
- Dilatant (Correct answer)
- Newtonian
- Bingham plastic
Correct answer: Dilatant
Dilatant (or shear-thickening) fluids exhibit increasing viscosity as shear rate increases, unlike pseudoplastic fluids which thin under shear.
Agricultural/Bioengineering Agricultural/Bioengineering: Food Engineering 2
Which heat transfer mechanism is primarily responsible for cooking food in a microwave oven?