Chemicals in Food — Revision Notes

⚡ 30-Second Revision

Preservatives:

- Sodium Benzoate ($C_6H_5COONa$): Antimicrobial, acidic foods (jams, juices). - Sodium Metabisulphite ($Na_2S_2O_5$): Antimicrobial, antioxidant, jams, squashes. - Propionates: Anti-mould in bread.

Artificial Sweeteners:

- Saccharin: First, 550x sucrose, metallic aftertaste, stable. - Aspartame: Dipeptide, 100x sucrose, heat unstable, PKU concern. - Sucralose: Trichloro derivative of sucrose, 600x sucrose, heat stable. - Alitame: Dipeptide, 2000x sucrose, more stable than aspartame.

Antioxidants:

- BHA (Butylated Hydroxyanisole), BHT (Butylated Hydroxytoluene): Prevent oxidative rancidity in fats/oils.

Flavour Enhancer:

- MSG (Monosodium Glutamate): Umami taste, intensifies flavour.

2-Minute Revision

Chemicals in food are additives used for preservation, sweetening, enhancing flavour, and improving appearance. Preservatives like sodium benzoate (effective in acidic foods against yeasts/moulds) and sodium metabisulphite (antimicrobial and antioxidant) extend shelf life by preventing spoilage.

Artificial sweeteners offer sweetness without calories; key examples include saccharin (first, stable), aspartame (dipeptide, heat-unstable, contains phenylalanine), sucralose (sucrose derivative, heat-stable), and alitame (high potency).

Antioxidants, such as BHA and BHT, prevent oxidative rancidity in fatty foods by scavenging free radicals. Edible food colours enhance visual appeal, while flavour enhancers like monosodium glutamate (MSG) intensify existing savoury tastes.

Remember the specific function and any unique properties or limitations for each major chemical.

5-Minute Revision

Let's quickly review the essential 'Chemicals in Food' for NEET. We categorize them by their primary function.

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Food Preservatives: — These are crucial for extending shelf life and ensuring food safety. Key examples include:

* **Sodium Benzoate ($C_6H_5COONa$):** Highly effective in acidic foods (pH 2.5-4.0) like fruit juices, jams, and pickles. It primarily inhibits yeasts and moulds by forming benzoic acid, which disrupts microbial cell function.

* **Sodium Metabisulphite ($Na_2S_2O_5$):** Used in jams, squashes, and dried fruits. It acts as both an antimicrobial and an antioxidant, releasing sulfur dioxide. * Propionates (e.g., Calcium Propionate): Specifically used in baked goods like bread to prevent mould growth.

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Artificial Sweeteners: — These provide intense sweetness with minimal or no calories, serving as sugar substitutes.

* Saccharin: The oldest artificial sweetener, about 550 times sweeter than sucrose. It's stable but can have a metallic aftertaste. * Aspartame: A dipeptide methyl ester (aspartic acid + phenylalanine), about 100 times sweeter than sucrose.

Crucially, it is unstable at cooking temperatures and in acidic solutions, breaking down into its constituent amino acids and methanol. Avoided by PKU patients. * Sucralose: A trichloro derivative of sucrose, about 600 times sweeter.

It boasts excellent heat and pH stability, making it suitable for baking. * Alitame: A high-potency dipeptide sweetener, around 2000 times sweeter than sucrose, more stable than aspartame.

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Antioxidants: — These prevent oxidative degradation, particularly rancidity in fats and oils.

* BHA (Butylated Hydroxyanisole) & BHT (Butylated Hydroxytoluene): Synthetic phenolic compounds that act as free radical scavengers, preventing lipid peroxidation. Used in fatty foods like chips and cereals.

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Edible Food Colours: — Added for visual appeal and to restore colour lost during processing.

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Flavour Enhancers: — Intensify existing flavours.

* Monosodium Glutamate (MSG): Sodium salt of glutamic acid, provides 'umami' (savoury) taste. Used in processed foods and Asian cuisine.

Worked Mini-Example: If a question asks which artificial sweetener is suitable for baking, you should immediately think of Sucralose due to its heat stability, and rule out Aspartame due to its instability. If it asks about a preservative for fruit juice, Sodium Benzoate is the prime candidate due to its efficacy in acidic conditions against yeasts and moulds.

Prelims Revision Notes

For NEET, 'Chemicals in Food' requires precise factual recall. Organize your notes by additive type:

I. Food Preservatives:

Definition: — Prevent microbial spoilage (bacteria, yeast, mould) and chemical degradation (oxidation). Extend shelf life.
**Sodium Benzoate ($C_6H_5COONa$):**

* Function: Antimicrobial, primarily against yeasts and moulds. * Conditions: Most effective in acidic medium (pH 2.5-4.0). * Uses: Fruit juices, soft drinks, jams, pickles. * Mechanism: Undissociated benzoic acid enters microbial cells, disrupting metabolism.

**Sodium Metabisulphite ($Na_2S_2O_5$):**

* Function: Antimicrobial and antioxidant. * Uses: Jams, squashes, dried fruits, wine. * Mechanism: Releases $SO_2$, which inhibits microbial growth and enzymatic browning.

Propionates (e.g., Calcium Propionate):

* Function: Anti-mould agent. * Uses: Baked goods, especially bread.

Nitrites/Nitrates: — Used in cured meats (e.g., sodium nitrite) to prevent botulism and fix colour.

II. Artificial Sweeteners:

Definition: — Provide sweetness with negligible calories. Much sweeter than sucrose.
Saccharin (o-sulfobenzimide):

* Sweetness: ~550 times sweeter than sucrose. * Properties: First artificial sweetener, stable, metallic aftertaste.

Aspartame (Aspartyl-phenylalanine methyl ester):

* Sweetness: ~100 times sweeter than sucrose. * Properties: Dipeptide derivative. Heat unstable (not for cooking/baking). Breaks down into aspartic acid, phenylalanine, and methanol. Caution for PKU patients (due to phenylalanine).

Sucralose (Trichloro derivative of sucrose):

* Sweetness: ~600 times sweeter than sucrose. * Properties: Highly heat and pH stable (suitable for cooking/baking). Passes through body largely unchanged.

Alitame:

* Sweetness: ~2000 times sweeter than sucrose. * Properties: Dipeptide derivative, more stable than aspartame but less than sucralose.

Neotame:

* Sweetness: ~7000-13000 times sweeter than sucrose. * Properties: Aspartame derivative, heat stable, safer for PKU patients (minimal phenylalanine release).

III. Antioxidants (Food):

Definition: — Prevent oxidative rancidity in fats and oils, preserving flavour and quality.
BHA (Butylated Hydroxyanisole) & BHT (Butylated Hydroxytoluene):

* Function: Synthetic phenolic antioxidants. Scavenge free radicals, interrupting lipid peroxidation. * Uses: Fatty foods (chips, chewing gum, cereals, butter).

Natural Antioxidants: — Ascorbic acid (Vitamin C), Tocopherols (Vitamin E).

IV. Edible Food Colours:

Function: — Enhance visual appeal, compensate for colour loss. No nutritional value.
Examples: — Tartrazine (yellow), Sunset Yellow FCF (orange-yellow).

V. Flavour Enhancers:

Definition: — Intensify existing flavours, do not add new ones.
Monosodium Glutamate (MSG):

* Chemical Nature: Sodium salt of glutamic acid (an amino acid). * Function: Provides 'umami' (savoury) taste. Intensifies flavour. * Controversy: 'Chinese Restaurant Syndrome' (headaches, flushing) reported by some, but generally recognized as safe.

Vyyuha Quick Recall

To remember the key artificial sweeteners and their properties:

Sweet Apple Slices Always Nice

Saccharin: Stable, Slightly bitter.
Aspartame: Amino acid derivative, Always avoid Heat (unstable), PKU concern.
Sucralose: Sucrose derivative, Super Stable (for baking).
Alitame: Almost All-purpose (more stable than aspartame, high potency).
Neotame: New, No PKU issue, Nice and stable.