DETECTION BY HPLC/TOF-MS OF ISOBARIC LIGNANS FROM LAMPANTE AND REFINED OLIVE OIL AS POSSIBLE QUALITY MARKERS

Lignans are a group of polyphenolic substances widespread in plants; they belong to the class of phytoestrogens and showed some interesting activity for human health (1). This class is typical of Olea Europaea L. but, although their amount in the olive oils is comparable to the other classes of phenolic compounds, they were discovered only ten years after the first evidences on the presence of the oleuropein derivatives (2). Lignans are one of the most abundant groups of phenolic compounds in olive oils (3), and their concentration mainly depends on cultivar and agronomic conditions while extraction process doesn’t affect their amount in a significant manner (4). To date, it has not yet been clarified how they are transferred from the olives into the oils and how their amount changes after the chemical/physical treatment of the oils (5). The principal lignan of olive oil is the acetoxy-pinoresinol with minor amounts of pinoresinolo (6), hydroxy-pinoresinol and syringaresinol (7). According to the IOC (8), virgin olive oils (VOOs) are obtained from the fruit of the olive tree solely by mechanical or other physical means under conditions, particularly thermal conditions, that do not lead to alterations of the oil. Depending on chemical and organoleptic properties, they are classified as extra virgin olive oil, virgin olive oil, ordinary virgin olive oil or lampante virgin olive oil. The oils belonging to this latter category need to be refined to render it edible (9). The oil refining is a chemical–physical multi-step process that needs at least a deacidification treatment and a last step, namely deodorization. Regarding the olive oils it has been reported the disappearance of all the phenolic compounds, with the only exception of the lignans pinoresinol and 1-acetoxypinoresinol (9). However, the abundance of lignans in virgin olive oils or crude lampante olive oils is higher than in the refined olive oils (6,9). If compared with other edible vegetable oils, extra virgin olive oil is an high value vegetable oil and very attractive for fraudsters. For this reason there is a continuous research of new markers to detect the adulterations and to guarantee the quality and the safety of extra virgin olive oil. (10) This work is aimed to investigate on the impact of the refining process on the lignans profile by analyzing both commercial olive oils and different partially-refined samples from Italian and Spanish production. The lignans have been extracted by ethanol 70% v/v and then concentrated before the HPLC/DAD/MS analysis. Our results by HPLC/TOF confirmed that the typical phenolic compounds diminished step by step until to completely disappear in the final refined oil with the only exception for the lignans. An interesting and unexpected result from the refined oil was the evidence of three isobaric forms of the original lignans: two isobaric forms of 1-acetoxypinoresinol (figure 1) and one isobaric to pinoresinol (Figure 2). To the best of our knowledge this is the first report on the presence of isobaric forms of lignans produced during the refining process of olive oils. So, these isobaric forms of lignans could be proposed as new chemical markers in this field. The presence of these isobars, easily detected by HPLC/TOF-MS, can be an interesting tool to discover the application of not declared refining procedures in commercial extra virgin olive oils.