The digestive stability of two natural antioxidant compounds present in virgin olive oil, hydroxytyrosol (HTy) and hydroxytyrosyl acetate (HTy-Ac) and a new series of hydroxytyrosyl ethers (methyl, ethyl and butyl hydroxytyrosyl ethers) was evaluated by a simulated digestion procedure. High recovery of all compounds after gastric digestion was obtained, although they showed a statistically significant lower stability after pancreatic-bile salts digestion. HTy-Ac was partially hydrolyzed into free HTy, whereas after intestinal digestion, HTy was converted into 3,4-dihydroxyphenyl acetic acid (DOPAC), and HTy-Ac was hydrolyzed to HTy and subsequently transformed into DOPAC. In contrast, no chemical modification of hydroxytyrosyl ethers during in vitro digestion was observed. In summary, HTy, HTy-Ac and hydroxytyrosyl ethers show high and interesting digestive stability and the new synthetic hydroxytyrosyl ethers showed enhanced chemical stability compared to HTy and HTy-Ac.

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At present, two systems have been usually used to identify olive oil aroma: the official panel test, according to the European Union Regulation [1], and the gas chromatographic method and its improvements. However, both types of techniques have two principal disadvantages: They need a long time for analysis and cannot be applied on‐line. Recently, there has been increasing interest in the development of a new device, the so‐called “electronic nose”. The aim of this work is to perform both a review of these techniques used for olive oil sensory analysis and their advantages and disadvantages.

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A sensor based on the technique of a piezoelectric quartz crystal microbalance (QCM) is analyzed for the detection of six organic volatile compounds with high olive oil sensory significance, such as hexanal, acetic acid, Z-3-hexenyl acetate, undecane, 1-octen-3-ol and 2-butanone. Four sample concentrations have been exposed to each QCM sensor constructed. The detection system is based on the sample adsorption on the forty sensing films coated at the surfaces of forty AT-cut gold-coated quartz crystals. Each sensing film has been prepared with different solution concentrations of ten materials, usually used as chromatographic sta-tionary phases. Sensing film coating process shows excellent repeatability, with coefficient values less than 0.50%. The frequency shifts of the piezoelectric crystals due to the adsorption of the volatile compounds have been measured as sensor responses, using a static measurement system. The results show that only five QCM sensors, with high sensitivity values, are enough to the detection of the volatile compounds studied. Therefore, the developed detection system presented herein provides a rapid identification of organic volatile compounds with elevated olive oil sensory connotation and it could be a substitute technique to the analytical methods normally used for the analysis of the olive oil flavor