QDA and GCO analysis of total aroma extracts from ’Spring Bright’ nectarines sorted by TRS Giulia Bianchi, Anna Rizzolo, Paola Eccher Zerbini, Maristella Vanoli Istituto per la Valorizzazione Tecnologica dei Prodotti Agricoli (I.V.T.P.A.), via Venezian 26, I-20133 Milano (Italy) INTRODUCTION Sensory analysis of total extract per se is useful to point out the characteristics of the overall odour profile, while gas-chromatography/olfactometry (GCO) is a powerful tool to get information about the quality and the concentration of single compounds as well as about their odour thresholds. GCO is a combination between sensory and instrumental analysis, involving the chromatographic separation of total extracts with the simultaneous detection of their odour by the human nose. In a previous work (Bianchi et al., 2004) GCO was carried out on total extracts from four peach varieties using a semi-trained panel of assessors, which could use a freely chosen lexicon to describe the odours at the sniffing port. These GCO data were grouped in thirteen categories named ‘focus groups’ after LeFur et al. (2003) and identified in studies conducted on peach aroma analysis (Rizzolo et al., 1995). Then, the frequencies of each focus group within the GCO analysis were analysed using Generalized Procrustes Analysis (GPA) obtaining a consensus space that visualized the differences and the analogies among the samples. We used both techniques on total extracts of “Spring Bright” nectarines, previously shared in two size classes (Eccher Zerbini et al., 2003), to verify if the classification as “less mature” or “more mature” on the basis of TRS (time-resolved reflectance spectroscopy) absorption coefficient µa 670 as an harvest index is correct also from the odour profile point of view. MATERIALS AND METHODS Spring Bright , size 1 and 2 sorted by TRS as ‘less mature’ and ‘more mature’ (S1-LM, S2-LM, S1-MM, S2-MM) Quantitative Descriptive Analysis (QDA) QDA was carried out with 8 semi-trained panellists from the ITVPA staff in individual sensory evaluation booths. Cellulose stripes were dipped into total aroma extracts from S1-LM and S1-MM fruits and put in screw-capped Pyrex tubes (after Pompei and Lucisano, 1991). Panellists were asked to evaluate the intensity of five sensory attributes (herbaceous, sharp, fruity, floral, peach), as well as global intensity and global quality, using an unstructured line-scale with anchors near the extremes and in the middle. Data obtained were analysed with multifactor ANOVA and, after standardization, with PCA. solvent extraction (after Rizzolo et al., 1995) Sniffers could use descriptors freely chosen, that were shared out in ‘focus groups’: chemical, fruity, floral, buggy, sharp, herbaceous, sweet, fermented, fresh, earthy, creamy, roasted and spicy RESULTS Table 1 - Volatile compounds (g/kg) detected in total extracts of ‘Spring Bright’ nectarines sizes 1 (S1) and 2 (S2), sorted at harvest in ‘less mature’ (LM) and ‘more mature’ (MM) classes at the end of shelf-life. Within the same size, means followed by different small letters are statistically different at p<0.05 (Tukey’s test); within the same maturation class, means followed by different capital letters are statistically different at p<0.05 (Tukey’s test). All values are the average of two samples, each one analysed twice. Figure 1 - GCO analysis: cumulative number of odour events for every focus group in size 1 (S1) and size 2 (S2), ‘less mature’ (LM) and ‘more mature’ (MM) classes of total aroma extracts from ‘Spring Bright’ nectarines. In size 2 fruits more than 74% (MM) and 65% (LM) are included in focus groups fruity, chemical and creamy. In size 1, the odour events are included in all the groups (except buggy); the prevailing groups are herbaceous in LM fruits, and creamy, herbaceous and fruity in MM ones. compound S1-LM S1-MM S2-LM S2-MM hexanal 244.77 Aa 618.18 Ab 329.46 Ba 407.58 Aa (E)-2-hexenal 40.81 Aa 201.87 Aa 312.86 Bb 120.82 Aa (Z)-3-hexen-1-ol 39.03 Aa 427.04 Aa 118.24 Aa 536.43 Aa (E)-2-hexen-1-ol 45.94 Aa 289.14 Aa 203.34 Aa 21.21 Aa hexanol 418.21 Aa 2619.54 Ab 2050.17 Ba 2180.72 Aa -valerolactone 16.42 Aa 66.74 Ab 145.47 Aa 39.77 Aa benzaldehyde 41.80 Aa 62.81 Aa 73.47 Aa 29.82 Aa hexyl-acetate 25.78 Aa 30.41 Aa 30.88 Aa 16.51 Aa -phellandrene 0.0 Aa 6.60 Aa 231.15 Ba -hexalactone 334.13 Aa 756.64 Aa 358.92 Aa 393.27 Aa -terpinene 17.38 Aa 52.23 Ab 64.59 Ba 58.16 Aa -terpinene 7.74 Aa 33.29 Aa 43.30 Aa 29.06 Aa linalool 15.40 Aa 370.59 Aa -nonalactone 61.28 Aa 81.09 Ba 28.20 Aa -decalactone 78.08 Aa 440.27 Aa 476.00 Aa 271.12 Aa -decalactone 7270.30 Aa 11777.30 Aa 12028.50 Aa 14457.10 Aa -undecalactone 29.66 Aa 170.45 Aa 36.14 Aa 83.03 Ab -undecalactone 35.33 Aa 242.77 Aa 142.18 Aa 66.80 Aa -dodecalactone 5.29 Aa 23.93 Aa 45.97 Aa 5.52 Aa -dodecalactone 9736.88 Aa 12723.50 Aa 11132.00 Aa 8108.73 Aa Within the Size 1 fruits, the more mature ones have higher quantities of all the compounds detected. This situation is different for size 2 fruits. Figure 3 - GPA of GCO data: Position of the samples in the consensus space. Labels: chi=chemical, fru=fruity, flo=floral, cim=buggy, pun=sharp, erb=herbaceous, dol=sweet, ter=earthy, cre=creamy, cot=roasted and spe=spicy. G1PP1MOLTOMAT=S1-MM, G1PP1POCOMAT=S1-LM, G1PP2MOLTOMAT=S2-MM, G1PP2POCOMAT=S2-LM, Figure 2 - GPA of GCO data: Position of the focus groups in the consensus space for the assessors 1 and 2. Labels: che=chemical, fru=fruity, flo=floral, bug=buggy, sha=sharp, herb=herbaceous, swe=sweet, ear=earthy, fat=creamy, roa=roasted and spi=spicy. Numbers refer to assessors 1 and 2. The position of the samples in the consensus space is similar for both sniffers. Size 1 samples are in different position of the consensus space, so they are judged different by the sniffers; size 2 samples are close. Almost all focus groups are positioned differently, because the descriptors are used in a different frequence by the two sniffers. Table 2 and figure 4 –Sensory analysis of S1-LM and S1-MM total extracts. Means followed by different letters are statistically different at p<0.05 (Tukey’s test) a b LM extract was judged more herbaceous and sharp and with an higher global intensity. MM extract had higher floral and fruity notes and global quality. CONCLUSIONS Both GCO and QDA analysis were able to underline differences and similarities among the total extracts from ‘Spring Bright’ nectarines of two size classes sorted by TRS at harvest in maturity classes. GPA applied to GCO frequencies was useful to evaluate and compare the odour profiles belonging to different samples. It was confirmed the usefulness of TRS absorption coefficient µa 670 as an harvest index; from the aroma profile point of view, the sorting of nectarines into ‘less mature’ and ‘more mature’ classes at harvest was successful particularly for size 1 fruits. REFERENCES Bianchi, G., Rizzolo, A. & Eccher Zerbini, P. (2004). 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A new approach to examine the relationships between sensory and gas chromatography-olfactometry data using Generalized Procrustes Analysis applied to six French Chardonnay wines. Figure 5 – PCA of the odour descriptors: (a) loading plot and (b) score plot PC1 opposes sharp to the other descriptors and to global intensity and global quality. PC2 opposes global quality and herbaceous to global intensity and the other descriptors. Both function discriminate the samples.