Last reviewed 1 Oct 2026 · Facts as of 1 Oct 2026 · 9 min read
Why process fruits and vegetables?
Fruits and vegetables are highly perishable (water content 80–95 %, active respiration, soft tissue). A significant part is lost after harvest (commonly quoted in the range of about 5–20 % or more, depending on crop and study). Processing extends shelf life, adds value, reduces gluts, creates year-round supply and employment, and allows transport and export.
Principles of preservation (hurdles):
| Principle | Methods |
|---|---|
| Heat | Pasteurisation, canning, blanching |
| Low temperature | Refrigeration, freezing |
| Removal of water | Drying, dehydration, concentration |
| Osmotic pressure | Sugar (jam, candy), salt (pickle) |
| Acidity (low pH) | Pickling, vinegar, fruit acids |
| Chemical preservatives | SO₂, benzoic acid, sorbic acid |
| Fermentation | Lactic or acetic acid fermentation |
| Packaging and atmosphere control | Airtight, MAP, aseptic |
| Irradiation | Specified products |
Common unit operations (pre-processing)
- Receiving and sorting — remove damaged or immature produce; grading by size, colour, maturity.
- Washing — water, brushes, spray or bubbling; removes dirt, pesticide residue, and microflora (chlorinated water, 50–100 ppm, commonly used).
- Peeling — hand, knife, mechanical abrasion; steam; hot lye (1–3 % NaOH, 90–100 °C for 1–3 min) followed by washing/neutralising; flame; enzymatic; cryogenic.
- Cutting/slicing/pitting/coring — uniform size.
- Blanching — brief heating in hot water or steam (85–100 °C for 1–5 min) to inactivate enzymes (polyphenol oxidase, peroxidase, catalase, pectin esterase), soften tissue for packing, expel air, fix colour, and reduce microbes; tested by the peroxidase or catalase test; followed by rapid cooling.
- Prevention of browning — dips in citric acid or ascorbic acid solutions, sulphiting (potassium metabisulphite, KMS), blanching, vacuum or inert atmosphere.
- Extraction/pulping — pulper/finisher, juice extractors, presses, enzymatic clarification (pectinase).
- Formulation — sugar, acid, pectin, preservatives, spices.
- Heat treatment, filling, sealing, cooling (see Thermal Processing & Evaporation).
- Packaging, labelling and storage.
Enzymatic browning (cut apple, banana, potato) occurs when phenols are oxidised by polyphenol oxidase (PPO) in the presence of oxygen; controlled by acid dips, antioxidants (ascorbic acid), sulphiting, blanching, or excluding oxygen.
Sulphiting — SO₂ (from KMS or sulphur dioxide gas) is an antioxidant and antimicrobial; used for dried fruits, juice squash and jam (limits laid down); may bleach anthocyanins and destroy thiamine, and must be declared (allergen-like sensitivity in some people).
Fruit gels — jam, jelly and marmalade
A gel forms when high-methoxyl pectin (about 0.5–1.5 %) is cooked with sugar (about 60–68 % total soluble solids) at a low pH (about 3.0–3.4). The acid and sugar dehydrate and neutralise the pectin molecules so that they cross-link into a network holding the sugar solution.
| Product | Description | Typical standard (FPO / FSSAI; check current values) |
|---|---|---|
| Jam | Fruit pulp or fruit cooked with sugar to a thick consistency (with or without pectin) | Fruit not less than 45 %; total soluble solids (TSS) not less than about 68.5 % |
| Jelly | Clear, firm gel from fruit juice, sugar and pectin | Fruit juice about 45 parts per 55 parts of sugar; TSS about 65 % |
| Marmalade | Jelly or pulp with suspended strips of citrus peel | Fruit about 45 %; TSS about 65 % |
| Preserve (murabba) | Whole or large pieces in thick sugar syrup | Fruit pieces in syrup |
| Fruit cheese / fruit bar (toffee) | Pulp cooked to a stiff mass | Higher solids |
End-point determination: refractometer or hand refractometer (TSS 68.5 % for jam), temperature of boiling (about 104–105 °C at sea level), sheet test (a spoonful leaves in a sheet), drop test, weight method (final mass). Low-pectin fruits (strawberry, ripe papaya) need added pectin; high-pectin: apple, guava, citrus peel, plum. Overcooking inverts sugar and spoils the set; undercooking causes weak gels, and ‘crystallisation’ appears if sugar inversion is inadequate (invert sugar should be about 30–50 % of the total sugars; the acid assists inversion).
10 kg of fruit pulp containing 12 % TSS is cooked with 10 kg of sugar to a final TSS of 68.5 % (assume the sugar and pulp solids are all counted as TSS).
- Total solids kg.
- Final mass of jam .
- Water in the pulp kg; water in the jam kg; so water evaporated .
- Fruit content in the final jam pulp by mass of the raw ingredients (meets a minimum of 45 % fruit).