PRAKTIKUM UJI ZAT MAKANAN - LABORATORIUM BIOLOGI SMA N 1 SOKARAJA

Scientific concepts / nature phenomena presented

• Biochemical food composition testing (food substance analysis)

  • Testing common macronutrients in food samples:
    • Starch (carbohydrate)
    • Protein
    • Glucose
    • Fat

• Chemical indicators and reactions

  • Lugol’s reagent (used for starch testing) producing a color change.
  • Biuret reagent (used for protein testing) producing a color change to indicate protein presence.
  • Glucose test indicator
    • Changes color to red/orange after heating, implying a reducing sugar reaction such as glucose with an oxidizing reagent.
  • Fat detection via transparency
    • Translucent/transparent behavior of fat on paper is used as an indicator for fat presence.

• Underlying reaction idea (as described)

  • For protein: formation of a coordination complex between Cu (from CuSO₄) and nitrogen-containing groups (as implied by the biuret reaction), producing a purple color.

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Methodology / steps (as described in the practicum)

Preparation

• Prepare and process food samples (e.g., crushing/smoothing; optionally using a blender).
• Gather tools/materials, such as:
  • Porcelain dish
  • Test tubes
  • Stirrer
  • Spiritus burner
  • Pipette/drops
  • Distilled water
  • Opaque paper
• Use worksheets to record results.

1) Starch test (with Lugol’s reagent)

1. Mix the food sample with Lugol’s solution (about 5–10 drops).
2. Observe the color change:
   • Blackish-blue darker color → indicates more starch/carbohydrates.

2) Protein test (with Biuret reagent)

1. Crush/smooth the protein-containing sample for easier testing.
2. Add Biuret reagent (about 5–10 drops).
3. Observe the color change:
   • Purple → indicates protein present.
4. Described mechanism:
   • Complex formation involving CuSO₄ (copper) with protein-related groups.

3) Glucose test

1. Place the processed sample into a test tube with sufficient water (aquatest/distilled water implied).
2. Add the glucose reagent (not fully specified in the subtitles).
3. Heat using a spiritus burner.
4. Observe the color change:
   • Red/orange color → indicates glucose (reducing sugar) present.
5. Safety note:
   • Avoid spills/boiling over, since the heated mixture may eject from the test tube mouth.

4) Fat test

1. Prepare opaque paper.
2. Place/disturb the sample on/with distilled water on the paper (wetting/soaking preparation is implied).
3. After drying:
   • Transparent/translucent paper → indicates fat present.

Data recording

• Record observations during the practicum and use them to draw conclusions.

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Researchers / sources featured

• No specific researchers, institutions, or named scientific authors are featured in the subtitles.
• Only chemical reagents and general laboratory/testing procedures are mentioned (e.g., Lugol’s reagent, Biuret reagent, NaOH, CuSO₄), but no individual scientific sources are credited.