Unit 4: Analysis of Food

Nutritional Value of Foods

The nutritional value of food is determined by its content of macronutrients and micronutrients.

• Macronutrients: Needed in large amounts.
  • Carbohydrates: Primary source of energy (e.g., rice, bread, sugar).
  • Proteins: Used for building and repairing tissues (e.g., milk, eggs, pulses).
  • Fats: A dense source of energy, used for insulation and hormone production (e.g., oil, ghee, nuts).
• Micronutrients: Needed in small amounts.
  • Vitamins: Organic compounds for various metabolic functions (e.g., Vitamin C, Vitamin D).
  • Minerals: Inorganic elements (e.g., Calcium, Iron, Iodine).

Food Preservatives

Definition: Food preservatives are substances added to food to prevent or slow down spoilage (caused by bacteria, fungi, or mold) and maintain freshness.

They are broadly classified by FSSAI (Food Safety and Standards Authority of India) into:

• Class I Preservatives: Natural preservatives, not restricted.
  • Examples: Salt (NaCl), Sugar, Spices, Vinegar (acetic acid).
  • Mechanism: They create a hostile environment for microbes (e.g., by osmosis).
• Class II Preservatives: Artificial (chemical) preservatives. Their use is strictly regulated.
  • Examples: Sodium Benzoate (used in sauces, juices), Sulphites/Sulphur Dioxide (SO₂) (used in wine, dried fruits), Sorbates, Nitrates.

Food Adulteration

Definition: The practice of adding a foreign, inferior, or harmful substance (an adulterant) to a food item to increase its quantity or reduce its cost, thereby lowering its quality.

Adulteration is illegal and can be a major health risk.

Analysis of Milk

Milk is a near-complete food but is easily adulterated.

• Specific Gravity: Measured with a lactometer. Normal milk has a specific gravity of 1.028-1.034.
  • If water is added, the specific gravity *decreases* (becomes lower).
  • If fat is removed, the specific gravity *increases*.
• Fat Content: Determined by Gerber's method, which uses sulfuric acid and amyl alcohol in a special butyrometer tube.
• Common Adulterants:
  • Water: (See specific gravity).
  • Starch: Added to thicken milk (after adding water).
    Test: Add a drop of iodine solution. A blue-black color indicates the presence of starch.
  • Urea: Added to increase the non-protein nitrogen (NPN) content, which falsely inflates the protein reading.
    Test: Several chemical tests exist (e.g., using DMAB reagent).

Analysis of Ghee (Butter Fat)

Ghee is pure, clarified butter fat. It is often adulterated with cheaper fats, like hydrogenated vegetable oil (Vanaspati) or animal body fats.

• Rancidity: Ghee can go rancid (spoil) over time. This is measured by the Acid Value (titrating the free fatty acids with KOH).
• Test for Vanaspati Adulteration (Baudouin's Test):
  1. Take a sample of ghee.
  2. Add concentrated HCl and a 2% solution of furfural (in alcohol).
  3. Shake vigorously. Vanaspati contains traces of sesamolin, which reacts with furfural to produce a rose-red color in the acid layer. Pure ghee shows no color.

Analysis of Tea and Coffee

The primary active ingredient in both is the stimulant alkaloid caffeine.

• Adulteration:
  • Tea: Often adulterated with used, dried tea leaves, sawdust, or artificial coloring dyes.
  • Coffee: Often adulterated with powdered auto (chicory) or date seeds.
• Analysis (Estimation of Caffeine): Caffeine can be isolated from tea/coffee powder.
  1. Boil the powder with water and a base (like magnesium oxide) to free the alkaloid.
  2. Filter the hot mixture.
  3. Extract the caffeine from the water into an organic solvent (like chloroform or dichloromethane) using a separating funnel.
  4. Evaporate the solvent to obtain crude, white crystals of caffeine.

Analysis of Spices (Turmeric, Coriander, Chilli)

Spices are commonly adulterated to add weight and color.

• Turmeric Powder (Haldi):
  • Common Adulterant: Metanil Yellow, a cheap, non-permitted, and carcinogenic yellow dye.
  • Test: Add a few drops of concentrated HCl to a water slurry of the turmeric. A violet/magenta color which persists (and does not disappear on dilution) indicates Metanil Yellow.
• Coriander Powder (Dhania):
  • Common Adulterant: Dried horse dung powder or sawdust.
  • Test: Sprinkle the powder on water. The sawdust and dung will float, while the coriander powder will sink.
• Chilli Powder (Mirch):
  • Common Adulterant: Brick powder or sawdust, often colored with artificial red dyes.
  • Test: Sprinkle on water. Brick powder will settle at the bottom, and the dye will color the water.