## 3 Results  
### Pear Chromatogram Contour Plot Analysis  
A representative three-dimensional (3D) GC\(\times\)G-ToFMS total ion chromatogram contour plot of \"Rocha\" pear is illustrated in Figure 2a. Here, it shows the pear headspace metabolite separation according to physicochemical characteristics, namely, through volatility (first dimension) and polarity (second dimension), when a non-polar and polar set of columns is used. In this way, a structured chromatogram is obtained, in which structurally related analytes occupy similar two-dimensional (2D) spaces. The GC\(\times\)GC configuration also results in the resolution of many peaks that otherwise would be overlapped in a one-dimensional (1D) chromatogram. An example of such advantage can be observed in Figure 2b. analytes with similar volatility (\({}^{1}\)\({}_{\text{R}}\) - 460 s) such as MHO and \(\beta\)-myrcene can be effectively separated by the second column according to their polarity (\({}^{2}\)\({}_{\text{R}}\) of 1.894 and 0.850 s, respectively). From each pear analyzed, a chromatogram, with approximate 550 instrumental features, was obtained. These features were constituted mostly by minor peaks and a few major ones. Major peaks detected on uncoated pears at nine days were 1-butanol, 1-hexanol, butyl acetate, pentyl acetate, hexyl acetate, butyl butanoate. and \(\alpha\)- and \(\beta\)-farnesene (Table S1). From the total instrumental features obtained, a total of 57 compounds were identified and selected for further analysis. Selected metabolites are listed in Table 1 along with the respective odor descriptors obtained from literature. Selected compounds were comprised of metabolites belonging to several chemical families commonly identified in pear volatile profiles, namely, alcohols, aldehydes, esters, and mono- and sesquiterpenes [6]. Such chemical families are known to be the major volatiles emitted by pears and the main contributors to the pear aroma [6]. Among these, straight-chain esters, alcohols, and aldehydes, which are generally regarded to be a result of fatty acid metabolism, are produced in pears during fruit development and maturation [38]. From the set of compounds selected, esters were qualitatively the most representative chemical family. Other compounds associated with SC development such as \(\alpha\)-farnesene and MHO were also identified [6]. For the selected compounds, at the first sampling time of the pilot scale assay (\(t\) = 9 days), uncoated pears' headspace volatiles were mainly composed of sesquiterpenes (71.5%), followed by esters (23.0%), alcohols (3.7%), monoterenes (0.8%), aldehydes (0.6%), and ketones (0.3%). A previous study on the headspace volatiles of ripe \"Rocha\" pears identified a total of 25 compounds with butyl acetate and hexyl acetate accounting for 66.5% of total volatiles peak area [25]. A total of 17 out of these 25 reported volatile compounds were successfully identified in the present study and included in the metabolites to be analyzed (Table 1). Figure 2: (**a**) Three-dimensional GC\(\times\)GC total ion chromatogram plot of an uncoated pear at 9 days, used to illustrate the “Rocha” pear volatile profile; (**b**) Enlargement of a part of GC\(\times\)GC chromatogram contour plot of the pear showing the separation of metabolites with the same retention time. The 111 milliseconds wide 6-methyl-5-hepten-2-one (MHO) GC\(\times\)GC peak is easily defined and identified at a mass spectral acquisition of 125 spectra/s. Spectral quality at this high acquisition rate is maintained due to the ToFMS with continuous full-range mass spectral acquisition rate. As observed, the MHO mass spectrum is very similar (similarity value of 912/1000) as compared with the [PERSON] database.