## 4 Conclusions  
The formulation of mixtures to emulate aromas of foods requires combining knowledge from both compositional data (flavor compounds) and sensory analysis. Since the target was to reproduce the aroma of sensory defects at high intensity, the high concentrations of compounds renders volatile analysis difficult. However, the objective was not to reproduce the same volatile profile, but to obtain the same aroma with a reduced number of volatile compounds. Thus, the concentrations of the compounds were not limited by the natural values found in VOOs, but rather the concentrations needed to produce the aroma, overcoming problems of masking and enhancing the synergy. Working in the gap between chemical composition and aroma perception leads to some difficulties due to inherent particularities in the interface between chemical composition and physiological olfaction [30]. All of these aspects were carefully considered during formulation to avoid the risk of obtaining a non-representative RM. In summary, these particularities are: (1) the perception of the aroma of mixtures of volatile compounds, in particular when they are at high concentration, can be perceived as \"non-natural\" or \"chemical\" by assessors, even though the aroma of the mixture highly resembles the aroma of the sensory defect; (2) the perception of a mixture of volatile compounds can be \"analytical\" (different aromas are detected as parts of the global aroma) or \"holistic\" (a simple perception of one aroma resulting from the partial contribution of all compounds in the mixture), the second case being the desirable one; (3) the relationship of the response of human perception is non-linear with respect to increasing concentrations of substances; (4) the release of volatile compounds from an oily matrix has been scarcely studied (most studies were developed for water dilutions) and it concerns the temporal dimension of flavor perception; (5) some compounds (e.g., hexanal) provide different aromas at low/high concentrations; (6) some compounds, when added together, provide a different aroma compared to when they are in single dilutions due to complex interactions in perception (synergic/masking/different aroma), and thus the resulting aroma cannot be reduced to the sum of the partial aromas given by each volatile compound; (7) there is a strong dependence on the individual when defining an aroma (e.g., green or rancid for hexanal and nonanal) in the perception of some aromas and the RM of aroma should be perceived as homogeneously as possible by all assessors smelling it. Although the strategy described herein was designed for winey-vinegary and rancid aroma, it is valid to continue developing RMs for the other sensory defects of VOOs, which also need RMs for panel training and control. Once the RMs are developed, the next step, as described in Figure 2, is their validation using an evaluation process by panelists, ideally from panels from different parts of the world. This last step is currently being carried out by OLEUM project. Although the use of RMs is already described in current IOC norms for organoleptic assessment, it would be desirable to establish a perfected procedure for implementation of the RMs. Finally, the use of artificial RMs described in this work has the advantage of high reproducibility and availability since it is suitable for a defined formulation that can be produced on demand and/or marketed. Their use does not exclude the use of the current natural RMs if they are available to combine training in recognition of the defects, in the contextualization of a real oil and reproducible evaluation of their intensity. Conceptualization, R.A.-R., D.L.G.-G., T.G.T., and S.B. ; methodology, R.A.-R. and D.L.G.-G.; software, R.A.-R. and D.L.G.-G.; validation, R.A.-R., T.G.T., and S.B.