Embedded portable instruments for olive oil quality analysis: determination of free acidity, peroxide value and

total phenol content

Marco GrossiDepartment of Electrical Energy and Information Engineering

University of Bologna, Italyhttp://www.researchgate.net/profile/Marco_Grossi

European Union represents the biggest producers of olive oil in the world (about 80% of the world production).

Olive oil market

Olive oil qualityThe determination of olive oil quality is carried out by means of

laboratory analytical methods and sensorial analysis.

Free acidity (expressed as grams of oleic acid in 100mg of oil) is an indicator of the quality of the olives used to produce the oil

and the procedures in the oil production.

Peroxide value (expressed as milliequivalents of O2 in 1kg of oil)is an indicator of the oil oxidation.

Bad storage conditions lead to increase of peroxide value.

Total phenol content (expressed as mg of gallic acid in 1kg of oil)Phenols are soluble polar compounds responsible for the oil

organoleptic properties and are important due to their anti-oxidant properties (beneficial for human health)

Depending on the measured quality parameters, the olive oil can be classified according to different categories.

ProductProduct Free acidityFree acidity Peroxide valuePeroxide value

Extra Virgin Olive OilExtra Virgin Olive Oil ≤ ≤ 0.8 %0.8 % ≤ ≤ 2020

Virgin Olive OilVirgin Olive Oil 0.8 % - 2 %0.8 % - 2 % ≤ ≤ 2020

Lampante Olive OilLampante Olive Oil > 2 %> 2 % --

Refined Olive OilRefined Olive Oil ≤ ≤ 0.3 %0.3 % ≤ ≤ 55

Reference techniques for olive oil quality analysis are generally complex and need trained personnel and a laboratory

environment.

Such techniques are not suitable to be implemented in olive oil production centers also due to the use of toxic reagents.

To improve the quality assessment of olive oil with in-situ measurements the following requirements are needed:

1.Quick and simple measurements that can be performed also by non trained workers

2.The technique must be implemented in the form of a portable electronic system

3.The electronic system must be built with low cost electronics

• A polypropylene vial modified to feature two stainless steel electrodes is filled with 15 ml of hydroalcoholic solution (9ml

ethanol 6ml distilled water).

• 1ml of the olive oil under test is added to the reagent and all is stirred to create the emulsion.

Measurement of free acidity in olive oil

• In presence of the reagent the free fatty acid molecules are ionized leading to an increase of the electrical conductance (Gm)

of the emulsion.

• The electrical conductance (Gm) of the emulsion is measured and the olive oil free acidity is estimated.

4 3828.3561.8822.1 AcidityAcidityGm

A portable battery-operated electronic system has been built

To watch a video of the instrument performing a measure:

https://www.youtube.com/watch?v=2C55F4w8mBs&feature=youtu.be

To watch a video of the instrument performing a measure:

https://www.youtube.com/watch?v=2C55F4w8mBs&feature=youtu.be

To watch a video of the instrument performing a measure:

https://www.youtube.com/watch?v=2C55F4w8mBs&feature=youtu.be

To watch a video of the instrument performing a measure:

https://www.youtube.com/watch?v=2C55F4w8mBs&feature=youtu.be

Measurement of peroxide value and total phenol content in olive oil

The aqueous reagent is mixed with 0.5ml of the oil under test to create an emulsion

The optical absorbance is measured and used to estimate the parameter of interest

A Led is used to provide the incident radiation and a photodiode to measure the intensity of the transmitted radiation

Total phenol content

Reagent: 1ml of Folin-Ciocalteu reagent + 1ml of Na2CO3 15% + 13ml of distilled waterλpeak,LED = 835 nm

Peroxide number

Reagent: 8ml of ferrous ion oxidation xylenol orange (FOX) + 7ml of distilled waterλpeak,LED = 569 nm

A portable battery-operated electronic system has been built

Peroxide value: correlation between the value measured with the reference technique and the intensity of transmitted radiation

Total phenol content: correlation between the value measured with the reference technique and the logarithm of the intensity of

transmitted radiation

References

[1] Grossi M., Di Lecce G., Gallina Toschi T., Riccò B. (2014). Fast and accurate determination of olive oil acidity by electrochemical impedance spectroscopy. IEEE Sensors Journal, 14 (9), 2947-2954.

[2] Grossi M., Di Lecce G., Gallina Toschi T., Riccò B. (2014). A novel electrochemical method for olive oil acidity determination. Microelectronics Journal, 45, 1701-1707.

[3] Grossi M., Di Lecce G., Arru, M., Gallina Toschi T., Riccò B. (2015). An opto-electronic system for in-situ determination of peroxide value and total phenol content in olive oil. Journal of Food Engineering, 146, 1-7.