Olive oil acidity

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Separation of oil and water during processing reduces the formation of acids

fatty acids (meaning not attached to other fatty acids in the form of a triglyceride). Free acidity is an important parameter that defines the quality of olive oil. It is usually expressed as a percentage of oleic acid (the main fatty acid present in olive oil) in the oil. As defined by the European Commission regulation No. 2568/91 and subsequent amendments,[1] the highest quality olive oil (extra-virgin olive oil) must feature a free acidity lower than 0.8%. Virgin olive oil is characterized by acidity between 0.8% and 2%, while lampante olive oil (a low quality oil that is not edible) features a free acidity higher than 2%.[2]
The increase of free acidity in olive oil is due to free fatty acids that are released from triglycerides.

Free fatty acids formation

Diagram of fatty acid synthase

The presence of free

harvesting and storage before processing. The lipolysis reaction is greatly enhanced by the presence of an aqueous phase, so when oil is separated from water during processing, lipolysis
slows down and stops.

Measurement of free acidity

Free acidity is a defect of

accuracy
.

Manual titration

The official technique to measure free acidity in olive oil (as defined by the European Commission regulation No. 2568/91) is a manual titration procedure: a known volume of the oil to be tested is added to a mix of ether, methanol and phenolphthalein. Known volumes of 0.1 M potassium hydroxide (KOH) (the titrant) are added until there is a change in the color of the solution. The total volume of added titrant is then used to estimate the free acidity. The official technique for acidity measure in olive oil is accurate and reliable, but is essentially a laboratory method that must be carried out by trained personnel (mainly because of the toxic compounds used). Hence it is not suitable for in situ measurements in small oil mills.

Near-infrared spectroscopy

One of the most promising methods is based on optical

spectrophotometer and the need of calibration
for different types of oil (produced by olives of different varieties, different geographical origin, etc.).

Electrochemical impedance spectroscopy

Another approach

ice-cream mixes, the measure of meat ageing,[8] and the investigation of ripeness and quality in fruits.[9][10]

References

  1. ^ "Regulation (EEC) No 2568/91 on the characteristics of olive oil and olive-residue oil and on the relevant methods of analysis".
  2. S2CID 10659764
    .
  3. ISBN 978-1-118-46045-0
    .
  4. PMID 17631115
    .
  5. ^ "NIR Olive Analyzer T-38 Mini". www.claudiovignoli.com. Retrieved 2018-10-25.
  6. S2CID 13168066
    .
  7. doi:10.1016/S0260-8774(03)00054-2
    .
  8. doi:10.1016/j.jfoodeng.2007.07.026
    .
  9. doi:10.1111/j.1365-2621.2011.02636.x
    .
  10. doi:10.1080/01140671.1997.9514001
    .
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