Which of the following chemicals is not used as a fruit preservative?

A food preservative is a chemical added to food to slow microbial growth or oxidative spoilage and extend shelf life. For fruit products under Indian food-safety rules (FSSAI), the substances permitted for this purpose fall into a few approved functional classes -- chiefly sulphite salts, which supply antimicrobial, anti-browning sulphur dioxide, and benzoate salts, which are antimicrobial in the naturally acidic pH of fruit juices, squashes, and jams. A chemical counts as a fruit preservative only if it has a recognised preservative function and a permitted use.

• Potassium metabisulphite (K2S2O5) is a sulphite-class salt. Under the aqueous, mildly acidic conditions of fruit pulp it is acidified and liberates antimicrobial, anti-browning sulphur dioxide -- the basis of its use on light-coloured fruit products.

• Sodium benzoate (C6H5COONa) is a benzoate-class salt. In the naturally acidic pH of fruit juices and squashes it acts as an antimicrobial preservative, which is the basis of its permitted use.

• Sodium metabisulphite (Na2S2O5) is the sodium salt in the sulphite class; like other sulphite salts it liberates preservative sulphur dioxide under acidic aqueous conditions.

• Calcium bicarbonate (Ca(HCO3)2) is neither a sulphite salt nor a benzoate salt and has no antimicrobial or anti-browning action; its recognised additive roles (such as acidity regulator) are non-preservative, so it has no preservative functional class or permitted use as a fruit preservative.

Cross-checking against the recognised preservative classes confirms that sulphites (INS 223/224/228) and benzoates (INS 211) are permitted, functional food preservatives, whereas calcium bicarbonate carries only non-preservative additive roles under FSSAI / Codex GSFA and has no preservative functional class or permitted preservative use.

So the chemical that is not used as a fruit preservative is calcium bi-carbonate.