Fruit and Vegetable Processing Technology
What this domain tests
Expect questions on unit operations from washing to filling, the composition standards of jam, jelly, squash and ketchup, and the causes of failed products.
Unit operations
Receiving, sorting, grading, washing, peeling (manual, steam, lye, abrasive), trimming, cutting, blanching, pulping, juice extraction, finishing, deaeration, homogenization, pasteurization and filling. Blanching is usually 85-95°C for 1-3 minutes; it inactivates peroxidase and catalase, removes air, fixes colour and reduces surface microbes. Over-blanching causes nutrient and texture loss.
Product specifications (FPO-style minimums)
- Jam: at least 45% fruit pulp and 68% TSS.
- Jelly: at least 45% fruit juice and 65% TSS; pectin 0.5-1.0% and pH 3.2-3.4 for a good set.
- Marmalade: citrus peel and pulp, about 65% TSS.
- Squash: at least 25% juice, 40-45% TSS and about 1% acidity.
- Ketchup: about 12% TSS and 1.2% acidity.
- Pickle: salt 8-10% and enough acid to keep pH low.
Worked example
A guava jelly fails to set. Test the three setting factors: pectin by the alcohol test, pH by titration or meter, and sugar by refractometer. If pectin is low, add commercial pectin or blend with a pectin-rich fruit; if pH is above 3.5, add citric acid; if TSS is above 68%, add juice. Correcting only sugar will not repair a pectin or acid fault.
Traps that cost marks
Jam is made from crushed pulp, jelly from clear juice and marmalade from citrus with peel. Specifications are legal minimums, not targets. Enzymatic browning is caused by polyphenol oxidase plus oxygen, and is prevented by blanching, sulphites or ascorbic acid.