Impaginato 105 Adv. Hort. Sci., 2018 32(1): 105-111 doI: 10.13128/ahs-22807 Volatile compounds from different fruit parts of two cultivars of Cydonia oblonga C. Taiti 1, E. Giordani 1, E. Palm 1, W.A. Petrucci 1, G. Bennati 2, G. Gestri 2, E. Marone 3 (*), E. Azzarello 1, S. Mancuso 1 1 D i p a r t i m e n t o d i S c i e n z e d e l l e P r o d u z i o n i A g r o a l i m e n t a r i e dell’Ambiente, Università degli Studi di Firenze, Viale delle Idee, 30, 50019 Sesto Fiorentino (FI), Italy. 2 Associazione oasi apistica le buche, Via Regina Margherita, 26, 59016 Poggio a Caiano (PO), Italy. 3 Facoltà di Bioscienze e Tecnologie Agro-Alimentari e Ambientali, Università degli Studi di Teramo, Via R. Bazarini, 1, 64100 Teramo, Italy. Key words: f r u i t t i s s u e s , p r o t o n T r a n s f e r r e a c t i o n T i m e - o f - F l i g h t m a s s Spectrometer, physicochemical fruit parameters, quince, VoCs. Abstract: Quince is characterized as a fragrant fruit which, unlike other pomes (apple, pear), is not used for fresh consumption due to its astringency and com- pactness, but only in its processed form (jams, jelly, distillery products, and nutraceutical compounds). As a consequence, there is little knowledge current- ly available concerning the characteristics of the fruit, and in particular its aro- matic and chemotaxonomic patterns. In this work, carpometric, chemometric and spectrophotometric measurements were performed on quince fruits. VOCs emitted by different tissues or parts of the fruit were studied to describe its aromatic profile. The study was carried out on the fruits of an old, well-known cultivar (‘Gigante di Wranja’, commonly called ‘Wranja’) and a new Tuscan accession. Intact, halved and solely pulp (cubed) samples were evaluated for each individual fruit. Data obtained from VOC analysis through Proton Transfer Reaction Time-of-Flight Mass Spectrometer (PTR-ToF-MS) were evaluated by multivariate statistical analysis. The spectra obtained from the intact fruit sam- ples showed a higher amount of masses corresponding to terpenes or ter- penoid compounds, which fundamentally characterize the aroma of this type of fruit; these substances were found to be much less present in the VOCs emitted by the pulp, where high values of masses linked to the maturation processes were instead found. 1. Introduction plants are not only a dietary source for both human beings and ani- mals but also serve as medicinal, nutritional, and ornamental purposes (*) Corresponding author: emarone@unite.it Citation: TAITI C., GIordAnI e., pAlm e., peTruCCI w.A., bennATI G., GeSTrI G., mArone e., AZZArello e., mAnCuSo S., 2018 - Volatile compounds from different fruit parts of two cultivars of Cydonia oblonga. - Adv. Hort. Sci., 32(1): 105-111 Copyright: © 2018 Taiti C., Giordani e., palm e., petrucci w.A., bennati G., Gestri G., marone e., Azzarello e., mancuso S. This is an open access, peer reviewed article published by Firenze university press (http://www.fupress.net/index.php/ahs/) and distribuited under the terms of the Creative Commons Attribution license, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Competing Interests: The authors declare no competing interests. received for publication 2 december 2017 Accepted for publication 6 march 2018 AHS Advances in Horticultural Science Adv. Hort. Sci., 2018 32(1): 105-111 106 (Ashraf et al., 2016). The potential of plants as medi- cine is supported by abundant scientific evidence (lattanzio et al., 2009) and researchers are currently focused on isolating new aromas and active phyto- chemicals produced by different plant organs. Quince is the fruit of an ancient tree, Cydonia oblonga miller of the rosaceae family, and has a very wide origin area that ranges from Anatolia to the Caucasus. It was known to the Greeks and romans, and it seems that the name of the genus Cydonia comes from the ancient name of the town of Chania on the island of Crete (roversi, 1991). It is a climacteric, large-sized (up to 500 g) fruit, namely pome (false fruit), and generally oblong (pyriform types) or rounded (apple- shared types) (bellini et al., 2007). The harvest is still carried out by hand, although the desire to mecha- nize this operation with systems similar to those used for the mechanical harvesting of the apple tree is increasing (Fiorino et al., 2010). when ripening, the color of the fruit epidermis turns from greenish-yel- low to bright yellow when fully ripe. The pulp is very firm, and not directly edible due to the presence of tannins and pectic substances (bellini et al., 2007). ripe fruits are commonly used as a source of pectin, and to produce jam or jelly, liquors, and distilled products with aromatic notes typical of quince (Silva et al., 2004). The fruits can also be beneficial to human health thanks to their high phytochemical content (Ashraf et al., 2016). many studies have reported Cydonia oblonga as an excellent natural source of phenolic and flavonoid compounds which are considered potent antioxidants (Silva et al., 2004; oliveira et al., 2007). Quince fruit is considered an important dietary source of health-promoting com- pounds due to its antioxidant, antimicrobial and antiulcerative properties (magalhães et al., 2009). Although the aroma is one its most important fruit-derived parameters, only a few studies have focused on the volatile emission by Cydonia (Tateo and bononi, 2010), and in particular, by different tis- sues of the fruit. Indeed, the intense and pleasant aroma released by Cydonia may represent an impor- tant starting point in the genetic improvement of this species. recently, proton Transfer reaction-Time of Flight- mass Spectrometry (pTr-ToF-mS) was proposed as an innovative analytical technology for volatile organ- ic compound (VoC) detection and quantification on fruit matrices due to its capacity to rapidly provide a comprehensive mass spectrum with high-time reso- lution and without sample treatment (mayr et al., 2003; Taiti et al., 2017 a). The aim of the current study was to analyze the aroma profile of different fruit parts of two Cydonia oblonga genotypes, both grown in Italy, to increase the chemotaxonomic knowledge, fruit management and quince product trade. 2. Materials and Methods Plant materials Quince fruits belonging to an old, well-known cul- tivar (‘Gigante di wranja’, commonly called ‘wranja’) and a new Tuscan accession were harvested in Tuscany (Italy) in the last week of September 2017. For each cultivar, 12 homogeneous and healthy fruits were selected, gently brushed to eliminate the hair cover and washed in deionized water. Fruits were stored in a climatic chamber (14±1°C, 85-90% relative humidity) for three days prior to laboratory analysis. For all the fruits, color, weight, maximum diameter and height were determined. Six fruits were used for the spectrophotometric tests by pTr-ToF-mS and the remaining six for the physicochemical measure- ments. For chemical analyses (lugol starch test and refractometric grade), fruits were divided in half so that one half of each fruit was used for the starch test and the other to evaluate refractometric grade. Color and physicochemical fruit parameters Peel color. The identification of the different peel color of quince fruits was assessed using a minolta Cr-200 Chroma-meter (minolta, ramsey, nJ, uSA) a c c o r d i n g t o t h e H u n t e r s c a l e , a s p r e v i o u s l y described by Taiti et al. (2017 b). Fruits dimensions and firmness. For each cultivar, the weight (g), maximum diameter (cm), and height (cm) of twelve samples were measured. The firmness of each fruit (expressed as kgf) was measured as the force needed to reduce fruit diameter by 2 mm using a penetrometer (model 53205d, Turoni, Italy). Total soluble solids (TSS). To evaluate TSS concen- tration, six quince halved fruits for each genotype were squeezed to collect a few drops of juice; then TSS levels were measured with an n1 Atago refrac- tometer (Atago Co., Japan) and expressed as °brix. Starch Iodine Test. Starch-iodine test (lugol solu- tion) was performed by visual evaluation on halved fruits and by scoring samples on a ‘Golden delicious’ standardized 1-9 scale (Smith et al., 1979). Volatile compounds detection VoCs analyses were carried out with a high-reso- Taiti et al. - VOCs from different fruit parts of two quince cultivars 107 lution pTr-ToF-mS (IonICon Analytik GmbH, Austria) using H3o + as ion donor. For each genotype, six fruits were used; the same fruit was first analyzed as intact whole, then divided into two parts, analyzing the halves together; finally, two cubes were got from each one of the halved fruit respectively, without peel (5 × 5 × 5 cm, about 10 g each one); all the mea- surements were performed in triplicates on the same sample. All whole and halved samples were weighed, and the VoCs data were based on 100 g samples for whole and halved samples to allow for comparisons between the obtained results. The drift tube of pTr-ToF-mS instrument was set to 80°C and operated with a drift pressure of 2.30 mbar and a voltage of 550 V. These settings lead to an e/n ratio (e, electric field strength in the drift tube; n, buffer gas number density in the drift tube) e q u a l t o 1 3 5 T o w n s e n d s ( 1 T d = 1 0 1 7 V c m 2) . mass/charge ratio of peaks detected at m/z 21 (sig- nal for H3o +) and m/z 37 [signal for water clusters (H2o)H3o +] were monitored during all measurements to check the instrument’s stability and cluster ion formation. To reach a good mass accuracy (up to 0.001 Th), internal calibration was based on three points and was performed off-line. Acquisition and post-processing data were performed as reported by marone et al. (2017). Statistical analyses one-way analyses of variance (AnoVA) were per- formed (1) to compare the physicochemical parame- ters of two quince genotypes, and (2) to compare the VoC emission profiles whole, halved, and cubed fruit samples. Separation of means was performed by the Fisher’s lSd test (p= 0.05). Computations were per- formed by Statgraphics Centurion XV v. 15.0.04. A principal Component Analysis (pCA) was applied to the whole spectral data of 36 quince samples, previ- ously submitted to a logarithmic transformation and mean centering as pre-processing. Computations were performed by plS-Toolbox v. 8.0.2 (eigenvector research Inc., west eaglerock drive, wenatchee, wA) for mATlAb_ r2015b (mathworks Inc., natick, mA, uSA). A Correspondent Analysis (CA) was applied to the spectral data of the 36 quince samples to build up a simultaneous ordination of quince samples and protonated m/z, thus facilitating the evaluation of their reciprocal relationships. The analysis preserves the Χ2-distances between the data matrix rows and columns. data were weighted using the symmetric option (module HIerCluS, SYn-TAX 2000 program package). 3. Results and Discussion Physicochemical analyses The results of the physicochemical analyses on the different cultivars are reported in Table 1, and are largely in agreement with a previous study on dif- ferent cultivars (leonel et al., 2016). Among the physicochemical parameters analyzed, some signifi- cant differences were observed between the two Cydonia accessions, with regard to firmness, °brix val- ues and starch contents. In particular, the °brix con- tent was lower for ‘wranja’ (12.2±0.9) compared to Tuscan accession (17.2±0.9); vice versa the starch content was higher for ‘wranja’. The starch and sugar contents measured for the Tuscan accession indicate that these fruits may have been further along in the ripening process than the ‘wranja’ fruits. VOCs headspace analysis Samples (whole, halved and cubed) belonging to two different Cydonia genotypes were analyzed by pTr-ToF-mS detecting a total of 67 peak signals (Fig. 1). These signals represent different groups of volatile compounds including hydrocarbons, esters, alcohols, terpenoids, aldehydes, ketones and lac- tones. These results show that, even if no different volatile compounds were identified, different emis- sion intensities were found between the two geno- types (Fig. 1). on the other hand, among fruit tissues, both differences in number and emission intensity of each detected compound were instead observed. Figure 1 shows that for both cultivars, the intensity and number of compounds emitted were higher in Table 1 - one-way analysis of variance (AnoVA) related to the quince fruits physicochemical parameters (average ± sd) different lowercase letters within a column indicate differences by the lSd test at the 95% confidence level (p= 0.05). Cydonia accessions weight (g) Ø (mm) High (mm) Firmness (kgf) °brix Starch overcolor background color l* A* b* l* A* b* wranja 268.9 82.8 77.8 6.1 12.2 4.25 77.7 -12.5 62.6 72.6 -15.9 58.4 ±54.5 ±7.0 ±4.5 ±0.9 a ±0.9 a ±0.5 a ±2.4 ±2.4 ±3.3 ±4.1 ±2.3 ±3.1 Tuscan 320 86.5 85.4 7.6 17.2 2.75 76.9 -13.1 57.6 76.6 -12.8 60 ±92.6 ±9.2 ±9.7 ±0.4 b ±0.9 b ±0.5 b ±4.7 ±2.3 ±5.6 ±2.6 ±2.2 ±2.9 Adv. Hort. Sci., 2018 32(1): 105-111 108 the whole fruit followed by halved fruit, and lowest in cubed fruit. These results are in agreement with a previous study of Imayoshi et al. (1995) on nashi pear, where differences in the total number of VoCs among pulp, peel, and whole fruit were found. Indeed, as reported by paillard (1981) for many fruits species, VoC production changes among different fruit tissues, being highest in the skin and nearby tis- sues. It is noteworthy that fruit’s aroma depends on the combination of VoCs produced, and on the con- centration and odor threshold of each in the blend. A further investigation of the spectral data was per- formed by a multivariate ordination. The pCA (Fig. 2) approach applied to the whole dataset (ppbv) of 67 detected protonated masses (data not shown) give a general view of the quince sample ordination, based on the analysis of defined fruits parts (intact, halved, and cubed fruits) related to the two chosen acces- sions (Tuscan accession and ‘wranja’). The first three components accounted for 96.4% of the total vari- ability (66.1%, 17.7%, 12.7%, respectively). A strong effect related to the type of the sample used rather than the cultivar is evident. The whole fruit samples of both cultivars, joined in the lower right quadrant of the diagram, strongly differ from those obtained from the head space of the pulp only, both correlat- ed with the negative part of the x-axis (pC1), but clustered based on the cultivar, and respectively related to the positive part (Tuscan accession) and to the negative part (wranja) of the y-axis (pC2). The halved fruit group is placed in the upper right quad- rant, with the two cultivars partially overlapped, indi- Fig. 1 - Typical pTr-mS mass spectrum (average, n=6) obtained by different fruit parts of two cultivars of Cydonia. (A) Tuscan accession, (b) ‘wranja’; (1) whole fruit, (2) halve fruit, (3) cube fruit. Fig. 2 - pCA scores of the quince samples based on the full spec- tra distribution of the ‘Tuscan accession’ and ‘wranja’. (A1) = ‘Tuscan accession’ whole fruits; (A2) = ‘Tuscan accession’ halved fruits; (A3) = ‘Tuscan accession’ cube fruits; (b1) = ‘wranja’ whole fruits; (b2) = ‘wranja’ hal- ved fruits, (b3) = ‘wranja’ cube fruits. Taiti et al. - VOCs from different fruit parts of two quince cultivars 109 cating a greater similarity of masses with the intact whole fruit, even if positively correlated with pC2. To better evaluate the effect of specific chemical family compounds, the 20 masses with statistically signifi- cant (p= 0.05) discriminating power among the differ- ent parts of the fruit were selected by AnoVA within t h e w h o l e s p e c t r u m ( T a b l e 2 ) , u p o n w h i c h a Correspondence Analysis was subsequently applied. The join plot from CA (Fig. 3) simultaneously dis- plays quince different sample and protonated m/z ordinations based on the results of the variable selec- tion. The intact fruits of both cultivars are character- ized by a group of masses in which terpenes and ter- penoids are well represented. In particular, the high- est presence of monoterpene (m/z 135, m/z 137), terpenoid (m/z 153) and sesquiterpene (m/z 205) compounds distinguished the whole fruit from the other two types of cut samples. According to Taiti et al. (2017 b), the higher emission intensity and num- ber of VoCs detected in whole fruits was associated to the presence of the peel. It is well known that a great diversity of VoCs linked to the pericarp tissue of the peel are emitted, such as esters, alcohols, a l d e h y d e s a n d t e r p e n e s ( C h e r v i n e t a l . , 2 0 0 0 ; rodriguez et al., 2013). The VoCs linked to cutting, such as the green leaf volatiles (GlVs) (i.e., hexenal, hexanal), are highest in halved and cubed fruits, compared to intact fruits where the intensities of these signals were very low (Table 2), and confirmed by the fact that these com- pounds were well represented in pulp tissue. moreover, halved fruits occupy an intermediate position, while cubed fruit samples are shifted to the right in the diagram (Fig. 3), with a differentiation along the axis of the y (axis 2) determined by the masses m/z = 45.033, m/z = 47.049 and m/z 33.033 (only for the Tuscan accession). As reported by Taiti et al. (2015) the methanol emission in fruits increase Table 2 - protonated selected masses discriminating whole, halved and cubed fruit samples, identified via pTr-ToF-mS: mass/charge (m/z) ratios, chemical formula, tentative identifications, minimum and maximum values detected (ppbv) and VoC, as previou- sly reported in the literature (Cydonia*; pTr-mS#) no. protonated m/z Chemical formula Tentative identification min detected value (ppbv) max detected value (ppbv) references 1 33.033 CH 5 o+ methanol 11.7 2724.1 Khoubnasabjafari and Jouyban (2011)* 2 45.033 C 2 H 5 o+ Acetaldehyde 35 16416.9 umano et al. (1986)* 3 47.049 C 2 H 7 o+ ethanol 1.5 199.8 umano et al. (1986) 4 55.054 C 4 H 7 + C4 aldehydes fragment 65.3 433.1 Taiti et al. (2017 b)# 5 57.033 C 3 H 5 o+ Alkyl fragment (hexanal/hexyl acetate) 8.5 25.4 Taiti et al. (2017 b)# 6 57.069 C 4 H 9 + Alkyl fragment (Hexanol/valeric acid) 18.1 75.2 Taiti et al. (2017 b)# 8 75.044 C 4 H 11 o+ 2-butanol/2-methyl-1-propanol 0.5 19.7 umano et al. (1986)* 9 81.069 C 6 H 9 + Terpenes and C6 fragments 49.8 203.5 maleknia et al. (2007) # 10 83.085 C 6 H 11 + C6 fragments /hexenol fragment 8.8 50.7 maleknia et al. (2007)# 11 85.064 C 5 H 9 o+ 2-methyl-2-butenal/1-penten-3-one 4.6 26.2 Khoubnasabjafari and Jouyban (2011)* 12 99.080 C 6 H 11 o+ (e)-2-hexenal 1.6 8.9 umano et al. (1986)* 13 101.096 C 6 H 13 o+ Hexanal/(Z)-3-hexen-1-ol 1.7 44.8 Tateo and bonomi (2010)* 14 109.101 C 8 H 13 + Terpene fragments 0.4 23.6 maleknia et al. (2007) # 15 117.091 C 6 H 13 o 2 + Isobutyl acetate/ethyl butyrate/butyl acetate 1.5 176.7 Tateo and bonomi (2010)* 16 135.116 C 10 H 15 + p-Cymene 0.4 11.9 Tateo and bonomi (2010)* 17 137.132 C 10 H 17 + monoterpenes (e.g. limonene, g-terpinene) 0 5.1 Tateo and bonomi (2010)* 18 145.122 C 8 H 17 o 2 + ethyl hexanoate 0.5 153.9 Tateo and bonomi (2010)* 19 153.127 C 10 H 17 o+ oxygenated Terpenes (e.g. geranial) 0 0.4 Tsuneya et al. (1983)* 20 205.195 C 15 H 25 + Sesquiterpenes (e.g. bergamotene) 1.1 49.8 Tateo and bonomi (2010)* Fig. 3 - Join plot from Correspondence Analysis. (A1) = ‘Tuscan accession’ whole fruits; (A2) = ‘Tuscan accession’ halved fruits; (A3) = ‘Tuscan accession’ cube fruits; (b1) = ‘wranja’ whole fruits; (b2) = ‘wranja’ halved fruits, (b3) = ‘wranja’ cube fruits. numbers correspond to the pro- tonated m/z. Adv. Hort. Sci., 2018 32(1): 105-111 110 steadily throughout the ripening process. on the other hand, ethanol is the product of anaerobic metabolism and, together with acetaldehyde, accu- mulates in pome fruit under imposed hypoxia and poor gas exchange in the pulp tissue (pinto et al. 2001). pome fruit contains ethanol and acetaldehyde as part of their aroma (ritenour et al. 1997) and as reported by rapparini and predieri (2003) these com- pounds increase together with the ripening process and their emission increased at a faster rate with the onset of fruit senescence. 4. Conclusions The typical quince fruit aroma depends on a mix of volatile compounds which originate by different parts of the pome. by the analyses of different fruit tissues, differences in VoCs number and in their emission intensity were observed, while little dif- ference was observed between the two varieties analyzed. moreover, it has been shown that the intensity and number of compounds emitted was highest in the whole fruit, followed by halved fruit and cubed fruit. Through multivariate analysis, some masses have been highlighted that determine the differentiation of the spectral composition between the VoCs emitted by the pulp (halved and cubed fruit samples) and those obtained from intact fruit that could be specifically responsible for the particular aroma of quince fruit. The four mass- es referring to terpenes and terpenoids are prevalent in the peel, and are moderately related to the culti- var. 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