Standard stock solutions to be used in the analysis of the volatile compounds
Positive and negative sensory attributes in virgin olive oils (VOOs) strictly depend on the composition of the volatile fractions. To date, the organoleptic assessment in VOOs, in terms of the presence and intensity of these sensory attributes, is carried out according to a method known as Panel test. Given the possibility of disagreement in the VOOs classification by different panels, a confirmation/disconfirmation coming from the qualitative and quantitative analysis of specific volatile organic compounds (VOCs) responsible of the defects or the positive attributes, assumes great importance. In this context, the OLEUM project proposed methods for the analysis of volatile compounds in VOOs based on different analytical techniques: from the most consolidated SPME-GC-FID and SPME-GC-MS to the most innovative HS-GC-IMS, this last more adapt for a screening, which can be used for the classification of VOOs in the respective quality grade (extra virgin, virgin and lampante). A qualitative and quantitative instrumental analysis of volatile compounds may be relevant to support the Panel test in addition, once validated signals/markers, to establish limits of concentration of the relevant compounds, describing the off-flavor, for the different quality grades. On the basis of analytical investigations carried out within the OLEUM project, 18 volatile compounds were selected with the aim of having a set with a minimum number of highly diagnostic compounds easily available on the market. They were grouped into two Standard Matrices (SMA and SMB), dissolved in refined olive oil, to drastically reduce the number of analysis for the preparation of calibration curves. The selection of the 18 volatile compounds in SMA or SMB was based: i) on their usual occurrence in VOOs (high or low concentration) and ii) on the need to limit the possible overlaps between compounds, which would otherwise make it difficult to integrate the peaks, thus facilitating the inter-laboratory comparison of the results.
The same mixtures can also be used as calibration material to developing rapid screening methods; as recently published in Foods at least 15 of the 18 volatile compounds can be eluted and detected by a HS-GC-IMS. The composition of these matrices has been presented in some public events and is described in detail in another scientific article published in Food Control.