Caracterización del aroma de una línea casi isogénica climatérica de melón respecto a su parental no climatérico con diferentes metodologías analíticas

Laburpena

Melon (Cucumis melo L.) as a cucurbitaceae model plant has been subject of researches in the last fifteen years. The vast majority of these researches have been focused on knowing the genetic basis involved in biochemical, growing and ripening levels, which take part in the quality of the melon fruits. This thesis is oriented in the research area of postharvest quality aimed to the breeding of melon fruits; particularly those aspects related to aromatic quality. The aroma profile was studied in two different seasons (with considerable environmental differences) in: one near-isogenic melon line (SC3-5-1) which is climacteric with respect to its no-climacteric parent, the “Piel de Sapo” Spanish cultivar (PS). The SC3-5-1 line shows two QTLs (quantitative trait loci) in the linkage groups (LG) III and VI. The combined effect of these QTLs has not been deeply studied and systematically beforehand. Two different extraction techniques were used and volatiles analyzed in juice samples of SC3-5-1 and PS: 1) static headspace solid-phase micro-extraction by gas chromatography-mass spectrometry (HS-SPME/GC-MS); 2) inside needle dynamic extraction by mass spectrometric-based electronic nose (INDEX/MS-E-nose). The last technique has not been evaluated previously in melon studies. The experimental data obtained by each technique and season were processed applied statistical techniques unsupervised and supervised, with the aim of determining the different volatile compounds between both lines (PS and SC3-5-1), also nonlinear analysis as correlation networks and hierarchical clustering were performed. The statistical analysis of supervised data, such as the criterion used for identifying the most discriminant variables importance in the projection (VIP) from partial least squares discriminant analysis (PLS-DA) or with the non-parametric classification technique random forest (RF). In general, the inductive techniques were adjusted satisfactory to selection in the volatile compound and discriminating ions. The applied techniques allowed to identify 137 volatile compounds: esters, alcohols, sulfur-derived esters and even some aldehydes, etc. for both evaluated seasons were found significantly higher concentrations the SC3-5-1 compared with PS within the identified compounds in both evaluated seasons. Those compounds were mostly esters and sulfur compounds. We also found the ions: m/z 74, 91, 104, 105, 106 y 108, in the SC3-5-1 line, these ions are derivate mainly from the phenylalanine precursor and are associated to the QTLs of this line. In the putative identification of the QTLs volatile compounds in the aroma-production regulation, a total amount of 104 and 86 for seasons 1 and 2, respectively. 65 available common QTLs were identified in both seasons and have a positive effect on the aroma production of the SC3-5-1 line compared with PS. The number and relative concentration, mainly in SC3-5-1, affected the relative abundance of ketones, aldehydes and esters and it was due to the differences between both seasons. The characterization of the volatile compounds allowed us to identify the presence in PS and the absence in SC3-5-1 of some compounds: pent-1-en-3-ol; pentanal; (2E,6Z)-nona-2,6-dienal; (2E,4E)-nona-2,4-dienal; β-cyclocitral; pent-1-en-3-one; 2-butylfuran; pentanal. Moreover, some compounds with a higher concentration in PS compared with SC3-5-1 were found: propanal; butanal; hexanal; (E)-5-ethyl-6-methylhept-3-en-2-one; non-3-en-1-ol; methanethiol; propan-2-one, 1-phenylethanone. The applied techniques for the extraction and analysis of aromas identified the differences by the kind of phenotype. However when comparing GC-MS and MS-E-nose, the former showed a higher utility for specifying the significant compounds in each profile and growing conditions. One drawback of the MS-E-nose was the common ions identification, as m/z 43; 44; 45; 57; 77, 79 y 66 or m/z 109, which belong to the chemical compounds: aldehydes, alcohols and esters. The differences in the aroma profiles between the SC3-5-1 and PS lines were significant, independently from the multivariante technique used. Better results were obtained by using the GC-MS in the discrimination of the volatile compounds