## 3 Results and Discussion  
### Planning and Selection of Volatile Markers Suitable for Formulations  
The objective of preparing mixtures of chemical compounds to provide aromas that resemble sensory defects in VOOs can be carried out using volatile compounds that do not necessarily have to be among those identified in VOO or by using a matrix as carrier that can be different from the refined olive oil [15]. However, in order to obtain greater representativeness of the aroma, the objective of this work was addressed using volatiles identified in VOOs and were preferentially markers of the two sensory defects considered, i.e., rancid and winey-vinegary [18]. It is important to remember that a marker of a particular sensory defect is a compound that is identified in samples with that sensory defect and its presence is related to the associated off-flavor in an almost indubitable manner. When the sensory defect is perceived by a panelist when smelling a VOO, this marker should be identified. There is, in consequence, a causal relationship between the identification of this compound and the sensory defect or the biochemical/chemical processes that give rise to it [30; 31]. However, it does not mean that this compound is necessarily the only one responsible for the complex sensory notes defining the defect. In fact, the aroma perceived by the compound can be masked by other chemical compounds that also contribute to the aroma. Furthermore, in some cases, the aroma provided by the volatile marker can be far from the aroma of the corresponding sensory defect. In that case, the marker is useful to identify the presence of a sensory defect, because this compound is associated with the chemical/biochemical process causing the sensory defect, but it would not be suitable to emulate the sensory defect aroma (henceforth target aroma). Thus, under this premise, the RM can also be prepared with volatile compounds that may not be the most informative markers of the sensory defect but they can contribute in reproducing or enhancing the sensory descriptor of the target aroma. Figure 1 shows the scheme of the strategy used. The volatile compounds that are suitable to formulate the RMs are those resulting from the overlap between two subgroups of volatile compounds: sensory markers of the defect (subgroup 1), though not all can contribute to the sensory perception, and those that can contribute to the aroma of the sensory defect (subgroup 2), even if not all contribute exclusively to it or are always identified in oils with the corresponding sensory defect. In other words, the compounds that lie in the overlap of these two subgroups are those that provide aromas that are highly representative of the off-flavor of the sensory defect, regardless whether they are always present in natural VOOs with the defect. In addition, the strategy included the possibility to add other compounds that are not related with the defect, but that can be used to modulate the perception of certain sensory notes. These compounds can also be used to avoid \"a chemical perception\" and give a more \"natural\" aroma to the RM considering all the nuances of the target aroma. The process to produce optimal formulations of RMs for rancid and winey-vinegary defects required a flow diagram to make use of previous knowledge on the relationship between volatile compounds and sensory descriptors of VOOs [18]. Figure 2 shows the flow diagram designed for the development of RMs for sensory defects of VOOs. The background information refers to previous studies that established the scientific basis for the identification of volatile compounds that are responsible for several sensory defects and the determination of their concentration thresholds that contribute to the aroma of those VOO defects [18; 22; 32; 33]. Table 1 shows the main volatile markers selected for the two sensory defects studied, winey-vinegary and rancid.