Food Tests for Leaving Cert Biology

Overview

• Four practical food tests
• Key for studying nutrition chapter
• Important to know chemicals used and color changes

Test 1: Reducing Sugars

• Sugars: Glucose, Fructose, Galactose (Monosaccharides), Maltose, Lactose (Disaccharides)
• Non-reducing: Sucrose (Disaccharide)
• Chemical Reagent: Benedict's Reagent (Blue color)
• Control: Distilled water
• Procedure:
  • Add equal volume of distilled water and glucose solution in separate test tubes
  • Add Benedict's solution equally to both
  • Heat in hot water bath for 5 minutes
• Results:
  • Glucose: Color changes to brick red (Positive)
  • Distilled water: Remains blue (Negative)

Test 2: Starch

• Category: Polysaccharide
• Test: Iodine Test
• Control: Distilled water
• Procedure:
  • Add equal volume of distilled water and starch solution in separate test tubes
  • Add a few drops of iodine solution to both
• Results:
  • Starch: Turns blue-black (Positive)
  • Distilled water: Remains orangey (Negative)

Test 3: Proteins

• Test: Biuret Test
• Reagents: Sodium Hydroxide, Copper Sulfate Solution
• Control: Distilled water
• Test Sample: Milk or Egg White
• Procedure:
  • Add distilled water and sodium hydroxide to control
  • Add copper sulfate solution
  • Add milk and sodium hydroxide to test solution
  • Add copper sulfate solution
• Results:
  • Milk: Turns purple (Positive)
  • Distilled water: Remains blue (Negative)

Test 4: Lipids

• Tests: Brown Paper Test, Sudan 3 Test
• Control: Distilled water
• Test Sample: Vegetable Oil
• Procedure:
  • Add drops of water on first brown paper
  • Add drops of oil on second brown paper
  • Allow both to dry
• Results:
  • Oil: Permanent translucent stain on paper (Positive)
  • Water: No stain (Negative)

Key Points for Revision

• Understand initial and resulting color changes
• Be able to explain preparation of different food samples
• Practice with past papers and textbook
• Listen to teacher instructions

Note

• These notes are for educational purposes and not for commercial use.