Abstract
Virgin olive oil quality is assessed by chemical as well as sensory analysis. Two of the most important parameters that define the quality of virgin olive oils are the free acidity and the peroxide index. These chemical parameters are usually determined by manual titration procedures that must be carried out in a laboratory by trained personnel. In this paper, a portable sensor system to support the quality grade assessment of virgin olive oil is presented. The system is battery operated and characterized by small dimensions, light weight and quick measurement response (about 30 s). The working principle is based on the measurement of the electrical conductance of an emulsion between a chemical reagent and the olive oil sample. Two different chemical reagents have been investigated: (1) a hydro-alcoholic solution (HAS), made of 60% ethanol and 40% distilled water; (2) 100% distilled water (DW). Tests have been carried out on a set of 40 olive oil samples. The results have shown how, for most of the fresh virgin olive oil samples (31 samples out of 40), the free acidity can be estimated with good accuracy from the electrical conductance of the emulsion using HAS as the reagent. In the case of the full set of samples, the emulsion electrical conductance, using HAS as the reagent, is a function of both the sample free acidity as well as the compounds produced by oil oxidation, and a compensation method based on the measured electrical conductance, using DW as the reagent, has been introduced to improve the accuracy in the estimated free acidity. Tests have also been carried out on the full set of samples, using a k-nearest neighbors algorithm, to demonstrate the feasibility of olive oil classification according to the quality grade. The results have shown how measurements carried out using only the HAS reagent provide better classification accuracy than measurements carried out using both the HAS and DW reagents. The proposed system can be a low-cost alternative to standard laboratory analyses to evaluate the quality grade of virgin olive oil.
Highlights
The portable sensor system was used to evaluate the quality grade of a set of 40 virgin olive oil samples
All samples were tested with the portable sensor system, and the quality parameters were determined using the reference manual titration techniques; the oil quality category (EVOO, Virgin Olive Oil (VOO) or Lampante olive oil (LOO)) was defined based on the results of these two parameters
This is a simplification, since the quality grade of a virgin olive oil sold in the EU can be established by considering all the parameters as reported by the EU Reg. 2019-1604 [36]
Summary
Olive oil is a vegetable lipid, highly appreciated for its beneficial effects on human health [1], mainly due to the presence of a high content of oleic acid and polyphenols [2]. Studies from the literature have shown how mortality from breast and colorectal cancer [3], as well as from coronary heart diseases [4], is lower in countries with high olive oil consumption. Virgin olive oil quality is normally assessed by chemical as well as sensory analysis. Two of the most important parameters that define the quality of virgin olive oils are free acidity, defined as the amount of fatty acids no longer linked to their parent triglyceride
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