## 3 Results and Discussion
### Building a Formulation as RM for the Rancid Defect
perceived as spicy and green with a rancid perception at the end of the smelling. A sample of nonanal, at identical concentration, was qualified as rancid or highly rancid, wood, and green. The concentration of those volatiles at 6000 mg/kg was perceived as a highly rancid, flat odor followed by lard and tallow perceptions, but also green aroma was reported despite the high concentration. As a consequence, it was concluded that the aroma of these two compounds may confuse tasters when trained for the rancid descriptor. It was decided to remove nonanal from the formulation and keep hexanal, although the reverse alternative would also have been valid. As a second approach to reformulate R1, a search for new compounds providing rancid aroma was carried out. Figure 4 shows the chromatogram of a VOO qualified with an intensity of rancid perception at Md = 9.5. The chromatogram shows that there are four other compounds (_E,E_-2,4-hexadienal, _E,E_-2,4-decadienal, _E_-2,4-decadienal and hexanoic acid) that contribute to rancid perception without the problems of the aldehydes as already pointed out and led to a major consensus in sensory evaluation by assessors. Thus, a new formulation was produced (R2, Table 4) in which _E,E_-2,4-hexadienal, _E,E_-2,4-decadienal and _E_-2-decenal was added at 600 mg/kg and hexanal was kept in the formulation although at low concentration (100 mg/kg). This new formulation was subjected to modified simplex. Concerning the set of volatiles to produce a green perception, the addition of these new aldehydes masked the bitter almond aroma of _E_-2-hexenal, and we opted for the pool of compounds used to formulate the vinegary defect. Formulations R2-R4 were sensory evaluated by assessors (Table 4) at three concentration levels (100, 50, and 35 mg/kg) of the compounds contributing to a green-fruity sensory perception (high -R2-, medium -R3- and low -R4), but without excessively masking the rancid perception, which was always perceived by all assessors. The sensory descriptions of the three formulations were similar, including green, rancid, and sweet notes (Table 4). However, when the concentrations of the compounds contributing to green aroma were reduced to 35 mg/kg, other sensory notes were perceived, such as ripe fruit, rancid nuts, and rancid aftertaste. To emphasize the rancid perception over the green aroma, it was decided to change the formulation by adding other volatiles which are also responsible for the rancid defect. The compounds selected were pentanoic and hexanoic acids. Modified simplex allowed checking results of decreasing the concentration of volatiles contributing to green-fruity perception in order to avoid disagreement among assessors if there was or not masking of the rancid perception by the essential VOO green aroma. The assessors agreed that the best result in terms of representativeness and odor persistence was R6 (Table 2), which was considered as the most promising as a RM for rancid defect in VOOs. Regarding the \"primary compound\" in the formulation (hexanal), when this formulation was analyzed by SPME-GC-FID, the relative chromatographic area was 20.268, which was approximately twice the relative area found in the IOC RM (8.396), but lower than the maximum found in VOOs (164.316).