## 5 Case Study: Panel Test and E-Nose for the Determination of VOOs' Shelf Life
### Virgin Olive Oil Shelf Life Assessment
Although the panel test still represents the most effective and complete tool for the quality classification of a VOO [119,120] during production and storage, the correct application of VOO sensory assessment appears time consuming and difficult to apply during routine operations, especially considering small- and medium-sized enterprises [121,122]. Consequently, the development of instrumental methods for rapid screening could support the sensory analysis in discriminating samples close to the quality border (EVOO/VO and VO/LO). To this end, several promising analytical instrumental techniques, especially based on the detection of VOC markers, have been developed [123], and many E-nose tools with different chemical sensors, system designs and methods of data analysis have been tested for olive oil analysis. In this context, owing to its quickness, the flash gas-chromatography E-nose in combination with chemometrics is being revealed as one of the most encouraging and useful screening methods to support the sensory analysis [123]. E-nose equipped with QCM sensors was used to discriminate between different VOO categories (i.e., edible and non-edible olive oils) [124]. MOS and piezoelectric sensors were also used to discriminate over 140 samples of olive oil (VOO, non-virgin and seed oil) [125,126], whereas CP sensors were used to distinguish between olive oils of different qualities. This technique has been found to provide a good degree of selectivity and also the identification of specific features, considered as a quality fingerprint [127]. Eight compounds were identified by using an E-nose (i.e., 4-methyl-2-pentanol, (E)-2-hexenal, 1-tridecene, hexyl acetate, (Z)-3-hexenyl acetate, (E)-2-heptenal, nonanal and a-farnesene) to study the aroma fingerprint of 15 different EVOOs [128]. As far as SL evaluation is concerned, the degree of oxidation of volatiles is a key point for the use of E-nose. As discussed above, storage conditions (especially temperature and light) play a key role in maintaining olive oil quality over time. Many studies reported that it is indeed possible to discriminate between oils stored in different conditions. An E-nose based on 32 CP sensors was used to determine the rancidity of EVOO caused by the auto-oxidation process during storage [129]. The results obtained from the measurementsof different Italian olive oils by an E-nose with EC sensors show that oils can be easily distinguished between them. Additionally, changes in the aromatic profile due to the handling of the sample itself can be monitored. This aspect is of particular interest, considering the possibility to monitor changes during the ageing of the olive oil and whether it has been properly stored [130]. In a different study, a commercially available E-nose (equipped with MOS-FET sensors) was used to assess the oxidation degree of olive oil samples: EVOO was stored at 40 \({}^{\circ}\)C in the dark for two months and volatile compounds (by E-nose) and peroxide value (for comparison) were evaluated. The E-nose was able to discriminate among the different storage conditions and the results correlate well with peroxide values [11; 131]. Furthermore, other authors [132] used the E-nose equipped with 10 MOS sensors to distinguish oil samples characterized by different degrees of rancidity and fruitiness. The results obtained agree with those found during the intensity rating test carried out by a traditional panel test. Furthermore, the study demonstrated the capability of the E-nose in the monitoring of the evolution of oil flavor during storage. Marchal et al. (2021) [133] utilized a commercial E-nose (10 MOS sensors) to predict the intensity of the fruity attribute and off-flavors in VOOs, proposing to apply it for a fast screening of VOO quality. The authors of [134] compared the degree of oxidation in olive oil stored for up to 2 years in various lighting conditions. The results obtained using an E-nose equipped with MOSFET sensors are as precise as those obtained using reference methods (Reg EU 2568/1991). Lerma-Garcia et al.