© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Eur. J. Lipid Sci. Technol. 105 (2003) 403–408 DOI 10.1002/ejlt.200300780 403 Research Paper 1 Introduction In the recent years, extra virgin olive oil has acquired a distinguished position on the shelves of retail and deli- catessen stores all over the world. The increasing de- mand is related to some preference of consumers for the ingredients of the Mediterranean diet and the nutritional benefits expected, due to the presence of valuable phyto- chemicals, such as phenolic antioxidants, squalene and carotenoids. Virgin olive oil (VOO) has a high price in comparison to other vegetable oils due to its high production cost. Thus, to fulfil the expectations of consumers for this expensive product, a careful quality control is obligatory throughout the production line. The quality of virgin olive oil is moni- tored via the measurement of analytical parameters for which certain limit values are set. Thus it is possible to classify edible and non-edible virgin olive oil types [1, 2]. It is not easy to answer the rhetoric questions “what is vir- gin olive oil quality“ or “how can quality be objectively de- termined”. However, such questions are posed by the in- dustry that seeks for well-documented and realistic an- swers. It is generally accepted that VOO quality is direct- ly related to organoleptic characteristics. This explains why evaluation of organoleptic characteristics has been included in the relevant EC Regulation and its amend- ment [3]. Extended presentations of the merits of this cri- terion can be found in a review by Angerosa [4]. It also has to be stressed that the oxidative status of the oil is strongly connected to organoleptic defects. Thus, the control of oxidation products (e.g. peroxide values (PV), K 232 , anisidine value, hexanal content) is also a realistic means for quality evaluation. In all cases the authenticity of the oil is taken for granted. The International Olive Oil Council (IOOC) created by olive oil producing countries to raise olive productivity and improve olive oil quality, has proposed a conventional in- dex which expresses numerically the quality of the oil and provides indirectly a warranty for its authenticity. This in- dex takes into account authenticity criteria (K 270 ), quality characteristics (acidity and PV) as well as the organolep- tic score [5]. In our view the overall quality of virgin olive oil from the moment of its production till consumption is strongly relat- ed to its oxidative stability. Oxidative deterioration leads to development of unpleasant organoleptic characteristics. Therefore, it is of utmost importance to be able to evalu- Eleni Psomiadou a , Konstantinos X. Karakostas b , Georgios Blekas a , Maria Z. Tsimidou a , Dimitrios Boskou a a Laboratory of Food Chemistry and Technolo- gy, School of Chemistry, Aristotle University of Thessaloniki, Thessaloniki, Greece b Department of Mathematics- University of Ioannina, Ioannina, Greece Proposed parameters for monitoring quality of virgin olive oil (Koroneiki cv) The overall quality of virgin olive oil (VOO) is closely related to its oxidative stability that is usually evaluated through the stability index measured by the Rancimat apparatus. Quality characteristics and also pro-oxidant and antioxidant content for 52 Greek VOO samples (Koroneiki cv) were used to build up a model capable of predicting stability. Collinearity diagnostics, variable selection, and regression analysis were applied to the experimental data to locate the contribution of each parameter to the keeping quality of the samples. The predictive ability of the model was confirmed for a second VOO sample set of the same cultivar. It was found that except for the peroxide value, which negatively influences the stability, other important parameters were α-tocopherol, total polar phenol and total chlorophyll content. It is concluded that the colorimetric determi- nation of total polar phenols, the spectrometric determination of total chlorophylls and the high-performance liquid chromatography analysis of α-tocopherol, not presently in- cluded in the established methods of official analysis, can be used for a better evalua- tion of VOO quality. These parameters, which can be easily adopted as routine meth- ods by the industry, seem to be of utmost importance for shelf life prediction and expi- ration dating if applied for the promotion of the most competitive products in the inter- national olive oil market. Keywords: Virgin olive oil, stability, total polar phenols, α-tocopherol, total chloro- phylls. Correspondence: Maria Z. Tsimidou, Laboratory of Food Chem- istry and Technology, School of Chemistry, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece. Phone: +23-109-977- 96, Fax: +23-109-977-79; e-mail: tsimidou@chem.auth.gr