Oils and Fats

Changes in oil structure over time lead to rancidity and off-odours, which may lead to rejection by beneficiaries. Chemical analysis of FFA, peroxide value and p-anisidine value are usual.

• Vegetable oil is likely to have an FFA content of less than 0.05%, higher levels indicate that the oil has deteriorated.
• The peroxide value (PV) indicates the level of primary oxidation through measurement of the primary oxidation products. As the oil deteriorates further, these primary products (hydroperoxides) break down to give off-flavour and odour-producing compounds which are detected by the p-anisidine (AV) test. PV indicates the current oxidation state of the oil and the AV indicates its oxidation history.
• Neither figure should be relied on alone. Rather, they should be combined (AV + 2PV) to give the Totox value, which is an overall indicator of rancidity. A Totox value of about 10 is generally accepted as the upper limit for oil considered fit for human consumption.

Oils should be fortified with vitamin A and vitamin D, which should also be measured.