BIOSCIENCE EDUCATION

DETERMINATION OF PHOSPHATE IN FOOD (VANADOMOLYBDATE METHOD)

AIM:
To determine phosphate content in a food sample.

APPARATUS:
Test tubes, colorimeter.

REAGENT:
Ammonium molybdate, ammonium vanadate, nitric acid.

PRINCIPLE:
Phosphate reacts with vanadomolybdate reagent to form a yellow complex.

PROCEDURE:

• Prepare sample extract.

• Add reagent and incubate for 10 minutes.

• Measure absorbance at 400–420 nm.

CALCULATION:
Compare with phosphate standard curve.

DETERMINATION OF VITAMIN A (COLORIMETRIC METHOD)

AIM:
To determine the vitamin A content in margarine or food sample.

APPARATUS:
Test tubes, colorimeter, pipettes.

REAGENT:
Chloroform, antimony trichloride reagent (Carr-Price reagent).

PRINCIPLE:
Vitamin A reacts with antimony trichloride to form a blue complex, measurable colorimetrically.

PROCEDURE:

• Extract sample with chloroform.

• Add 2ml of Carr-Price reagent.

• Measure absorbance at 620 nm.

• Compare with vitamin A standard.

CALCULATION:
Use standard calibration curve to estimate µg vitamin A.

DETERMINATION OF SUGAR IN HONEY (FEHLING’S TEST)

AIM:
To detect reducing sugars in honey.

APPARATUS:
Test tubes, burette, water bath.

REAGENT:
Fehling’s A and B solutions.

PRINCIPLE:
Reducing sugars reduce Cu²⁺ to Cu₂O (red precipitate).

PROCEDURE:

• Mix equal volumes of Fehling A and B.

• Add honey solution gradually while boiling.

• Observe brick-red precipitate.

CALCULATION:
Compare against known glucose standards.

Tollen’s Reagent

Purpose: Detects aldehydes (reducing agents).

Procedure:

1. Prepare fresh before use:

   • Mix 2 ml of 0.1 M silver nitrate solution.

   • Add a few drops of dilute NaOH to form Ag₂O precipitate.

   • Add dilute ammonia dropwise until the precipitate just dissolves.

DETERMINATION OF PROTEIN (KJELDAHL METHOD)

AIM:
To determine total protein content in a sample.

APPARATUS:
Digestion flask, distillation unit, titration setup.

REAGENT:
Concentrated H₂SO₄, NaOH, boric acid, indicator.

PRINCIPLE:
Nitrogen is converted to ammonia, distilled, and titrated to estimate protein.

PROCEDURE:

• Digest sample with H₂SO₄ + catalyst.

• Neutralize, distill ammonia into boric acid.

• Titrate with HCl.

CALCULATION:
% Protein = Titre × 1.4 × 6.25 / Sample weight

Seliwanoff’s Reagent

Purpose: Differentiates between aldose and ketose sugars.

Procedure:

1. Dissolve 0.05 g resorcinol in 100 ml of 3M HCl.

2. Store in an amber bottle.