Fruit and Vegetable Processing
Fruit and vegetable processing preserves perishable produce as canned, frozen, dried, juiced or concentrated products. The exam tests blanching, canning, jam and jelly making, total soluble solids, acidity, pectin, browning control and hygiene.
Core rules
- Blanching inactivates enzymes such as polyphenol oxidase and peroxidase before freezing or drying.
- Enzymatic browning is controlled by heat, acidification, exclusion of oxygen or use of ascorbic acid.
- Canning relies on adequate heat treatment, correct headspace, seam integrity and cooling. Low-acid vegetables need a pressure process.
- Jam, jelly and marmalade depend on the balance of sugar solids, acid and pectin. A typical jam has about 65% total soluble solids, pH below 3.5 and sufficient pectin.
- TSS is measured with a refractometer and expressed as °Brix. Brix is not identical to total solids in all products.
Worked example
100 kg fruit pulp at 10% TSS is to be made into jam at 65% TSS. Let final mass = M. Sugar added = M − 100. Solids balance: 0.65M = 10 + (M − 100). Thus 0.65M = M − 90, so 0.35M = 90 and M = 257.1 kg. Sugar added = 157.1 kg. The reasoning conserves soluble solids.
Traps
- Confusing °Brix with total solids in every product.
- Making jam without checking acidity and pectin.
- Ignoring headspace in canned products.
- Blanching for too long and losing nutrients.
- Assuming all canned vegetables need the same process.