Question Bank • QB_APE_DRY_012 MSQ • 2 Marks

Section 6: Agricultural Process Engineering

Evaporation and Drying

Subtopic: Drying and milling of cereals, pulses and oilseeds

Question Statement:

Which of the following statements regarding the extraction of oil from oilseeds (soybean, rapeseed, sunflower) are CORRECT?

Options:

  • (A) Mechanical screw pressing (expelling) typically leaves $5\%\text{--}8\%$ residual oil in the cake, whereas solvent extraction with hexane reduces residual oil to below $1\%$.
  • (B) Pre-treatment of oilseeds by flaking ($0.2\text{--}0.3\text{ mm}$ thickness) and cooking ruptures plant cell walls and shortens solvent diffusion paths.
  • (C) The Desolventizer-Toaster (DT) uses direct and sparge steam to strip residual hexane solvent from defatted meal and inactivate antinutritional factors (e.g., urease).
  • (D) Hexane extraction is performed at atmospheric boiling temperatures above $120^\circ\text{C}$.

Answer Key:

A, B, C

Step-by-Step Solution & Explanation

Analysis of oil extraction processes: - Option A is CORRECT: High mechanical pressures in screw presses leave $5\text{--}8\%$ residual oil due to physical entrapment, while liquid-liquid/solid-liquid extraction with solvent recovers
gt; 99\%$ of oil (
lt; 1\%$ residual). - Option B is CORRECT: Rolling seeds into thin flakes creates microscopic fractures, rupturing cellular oleosomes and providing a large surface area for mass transfer. - Option C is CORRECT: The DT unit recovers expensive volatile solvent and simultaneously toasts the meal at $100\text{--}105^\circ\text{C}$ to destroy antinutrients (trypsin inhibitors, lectins). - Option D is INCORRECT: Commercial n-hexane has an atmospheric boiling point of approximately $68.7^\circ\text{C}$; extraction is safely conducted at $50\text{--}60^\circ\text{C}$.
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