Tullia Gallina. Bologna University.

Tullia Gallina Toschi^1,2, Patricia Garcia-Salas¹, Federico Ferioli¹, Enrico Valli^1,2 and

 Alessandra Bendini^1,2

¹Department of Agricultural and Food Sciences, Alma Mater Studiorum, University of Bologna

²Interdepartmental Centre for Industrial Agrofood Research, University of Bologna

Extra virgin olive oil (EVOO) is a typical Mediterranean food product characterized by high nutritional properties and unique sensory notes. Its characteristic flavour is markedly different from those of other edible fats and oils and the positive nutritional characteristics are especially related to its high content of polar phenolic compounds. In particular, polar phenolics have been related to free radical scavenging, as well as antioxidant, anticarcinogenic, cardioprotective, and antimicrobial properties.

Among polar phenolic compounds, hydroxytyrosol (Htyr) and tyrosol (Tyr) are phenyl ethyl alcohols naturally occurring in Olea europaea L. fruits and leaves as free forms and, to a greater extent, as bound derivatives belonging to the class of secoiridoids (e.g. oleuropein and ligstroside). These molecules, together with their derivatives, are valuable since they have been reported inhibit the oxidative damage of LDL. For this reason, in May 2012, the European Commission authorized a health claim for olive oil containing at least 5 mg of Htyr, Tyr and their derivatives (e.g. oleuropein complex) per 20 g of olive oil. Thus, it is important to address the requirement set by EC Regulations to bear the health claim on olive oil so called "polyphenols” in the label through the application of dedicated and robust analytical methods. In this sense, several analytical approaches have been tested and proposed by experts, but an official method has not yet been established by EU regulation.

Published analytical protocols are based on HPLC separation of the phenolic compounds differing each other with regard to the extraction procedure. The International Olive Council (IOC) has proposed two methods to determine phenolic compounds in olive oil: one is based on a liquid-liquid extraction, whereas the other method employs a solid phase extraction to purify and isolate phenolics. The main drawback of these methods is represented by the HPLC final analysis and is related to the poor resolution of some of the peaks related to complex phenols; this peak overlapping may lead to a worsening of integration accuracy. According to the olive oil polyphenols health claim, the quantification should be strictly referred to Htyr, Tyr and their derivatives. For this reason, several researchers focused their attention on developing analytical approaches targeted at the determination of these specific simple compounds calculating the others (their derivatives) by using correction factors. Some of these investigations proposed an acid hydrolysis of the bound forms of Htyr and Tyr as a preliminary step, and, after a HPLC separation, a successive calculation that took into account the different molecular weight of free and bound forms of phenolics. In this sense, the International Organization for Standardization (ISO) adopted a method wherein the phenolic fraction is extracted by applying a liquid-liquid procedure followed by the application of an acidic hydrolysis. Another method is based on the use of the ultra-high performance liquid chromatography (UHPLC) which was set up to speed up the overall analysis time thus increasing its sustainability. The analytical procedure was in-house validated in the framework of the EU H2020 project OLEUM (www.oleumproject.eu) and was proposed to the olive oil sector as a suitable method for supporting the health claim; this analytical approach is in line with guidelines recommended by relevant standardization bodies.

Concerning the positive attributes perceived during sensory analyses of EVOOs, in the scientific literature the bitter taste has been related to certain phenolic compounds, especially oleuropein aglycone and ligstroside aglycone derivatives, whereas the presence of the dialdehydic form of decarboxymethyl elenolic acid linked to tyrosol (oleocanthal) has been linked to the pungency of the EVOO.

To confirm the relationships between these sensory attributes and the composition of the phenolic fraction, a set of EVOOs has been studied in the herein presented research. For these oils, the intensities of those positive sensory attributes assessed by Panel test (namely bitter and pungent) have been correlated with the secoiridoid profile, the phenolic fractions after hydrolysis (derivatives of hydroxytyrosol and tyrosol) and the total phenolic compounds content. The analysed oils included eight monovarietal EVOOs produced from 100% Nostrana di Brisighella, a native variety of olives from orchards located in a limited area of the Emilia-Romagna region, in the north-central part of Italy. These olives were harvested at four different ripening degree and related monovarietal oil samples have been preserved for 12 months and stored under two different types of packaging.

In addition, although it is scientifically proven that phenolic compounds of EVOOs can play an important role in human health, it is well-known how consumers consider bitterness and pungency in a different way than the trained panellists, and that they usually are familiar and do not appreciate such positive attributes. So, it is important an effective research dissemination in order to enable consumers to appreciate bitterness and pungency as health-related substances, making familiar their taste and tactile perception (i.e. pungent). In this sense, a preliminary research work will be herein presented, highlighting how consumers evaluate bitter and pungent when they are informed or not about the health claim of such products and its meaning. For this study, three EVOOs were used with different bitter and pungent values, such as to be identified as robust, medium and delicate.

In conclusion, in this abstract, either the phenolic composition of the EVOO, related to the health claim, or the sensory quality perceived by consumers are reviewed, evaluated and discussed with the aim of identifying innovative ways to make the best quality of olive oil more familiar to the consumer.