Evaluation of olive oil quality grade using a portable battery operated sensor system

Olive oil is a vegetable lipid highly appreciated for its beneficial effects on human health. Olive oil quality is normally assessed by chemical analysis as well as sensory analysis to detect the presence of organoleptic defects. Two of the most important parameters that define the quality of olive oil are the free acidity, that is affected by the quality of the olives used to produce the oil as well as the production process, and the peroxide index, that is an indicator of the oil primary oxidation and is affected by the storage conditions. These chemical parameters are usually determinated by manual titration procedures that must be carried out in a laboratory by trained personnel. In this paper, a portable sensor system to evaluate the quality grade of olive oil is presented. The system is characterized by small dimensions (11 x 15 x 5 cm), light weight (350 g), quick measurement response (30 seconds) and can be powered by USB or batteries. The working principle is based on the measurement of the electrical conductance of an emulsion between an hydroalcoholic solution (60% ethanol 40% distilled water) and the olive oil sample under test. In the case of fresh olive oil samples, characterized by low values of peroxide index, the olive oil free acidity can be estimated from the electrical conductance of the emulsion. In the case of oxidized olive oil samples, the measured electrical conductance is also function of the oxidation level due to the presence of non-volatile compounds (such as aldehydes, ketones and hydrocarbons) produced by oxidation. Tests have been carried out on a set of 17 olive oil samples and the results have shown how the proposed system can be a low-cost alternative to standard laboratory analysis to evaluate the quality grade of olive oil.