Original article

Volatile compounds of ditax ( J.F. Gmel) from Senegal

Nafissatou Diop NDIAYE1, Marc LEBRUN2, Manuel DORNIER3*

1 Inst. Technol. Alim., Route Volatile compounds of ditax fruit (Detarium senegalense J.F. Gmel) from Pères Maristes, BP 2765, Senegal. Dakar Hann, Sénégal Abstract – Introduction. Detarium senegalense J.F. Gmel is a forest found in Senegal 2 CIRAD, UMR95 QualiSud, TA whose are locally called ditax in Wolof. It is eaten fresh but it is widely used as nectar, B-95/16, 73 av. Jean François which is one of the most popular beverages in Senegal. However, the chemical characterization Breton, F-34398 Montpellier of ditax pulp remains incomplete. This paper describes the volatile compounds of ditax to cedex 5, France assess its organoleptic qualities. Materials and methods. Free volatile compounds of fresh ditax pulp were isolated by solvent-assisted flavor evaporation and analysis by GC-MS. Results 3 Montpellier SupAgro, UMR95 and discussion. Among the 53 compounds tentatively identified, 49 are reported for the first QualiSud, Inst. Rég. Chaudes, time in this fruit. In total, 17 aldehydes, 11 aliphatic alcohols, 1 terpene alcohol, 7 free fatty acids, 1101 av. Agropolis, BP 5098, 3 unsaturated hydrocarbons, 1 terpene hydrocarbon, 7 sesquiterpene hydrocarbons, 1 phenol, F-34093 Montpellier cedex 5, 2 ketones, 2 esters and 1 organic acid compound were tentatively identified in ditax fresh pulp. France, [email protected] The main volatiles identified in fresh ditax pulp were trans, cis-2,6-nonadienal (2.47 mg⋅kg–1), cis-2-heptenal (1.93 mg⋅kg–1), trans-α-bergamotene (1.11 mg⋅kg–1), bicyclo [2,2,0] hexane-1- carboxaldehyde (0.80 mg⋅kg–1), butyl octadecanoate (0.55 mg⋅kg–1) and trans-2-nonenal (0.47 mg⋅kg–1 fresh pulp). Conclusion. Among the volatile compounds identified, aldehyde compounds were widely predominant. To assess the aromatic qualities of ditax pulp, the pri- mary impact aromas should be determined by identifying the aroma-active compounds by GC- olfactometry. Senegal / Detarium senegalense / fruits / flavor / volatile compounds / solvent extraction Les composés volatils du fruit de ditax (Detarium senegalense J.F. Gmel) au Sénégal. Résumé – Introduction. Detarium senegalense J.F. Gmel est un arbre forestier, trouvé au Sénégal, dont les fruits sont localement appelés ditax en Wolof. Le fruit est directement consommé mais il est largement utilisé en nectar, l’une des boissons les plus populaires au Sénégal. Cependant, la caractérisation chimique de la pulpe de ditax reste incomplète. Cette étude décrit les composés volatils de la pulpe de ditax afin d’évaluer sa qualité organolep- tique. Matériel et méthodes. Les composés volatils libres de la pulpe de ditax fraîche ont été isolés par la technique d’évaporation assistée par solvant et analysés par GC-MS. Résultats et discussion. Parmi les 53 composés identifiés, 49 sont signalés pour la première fois dans ce * Correspondence and reprints fruit. Au total, 17 aldéhydes, 11 alcools aliphatiques, 1 alcool terpénique, 7 acides gras libres, 3 hydrocarbures insaturés, 1 hydrocarbure terpénique, 7 hydrocarbures sesquiterpéniques, Received 2 September 2013 1 phénol, 2 cétones, 2 esters et 1 acide organique ont été identifiés dans la pulpe de ditax Accepted 11 September 2013 fraîche. Les principaux composés volatils identifiés dans la pulpe de ditax fraîche ont été le trans, cis-2,6-nonadiénal (2,47 mg⋅kg–1), le cis-2-hepténal (1,93 mg⋅kg–1), le trans-α-bergamo- tène (1,11 mg⋅kg–1), le bicyclo [2,2,0] hexane-1-carboxaldéhyde (0,80 mg⋅kg–1), l’octadeca- –1 –1 Fruits, 2014, vol. 69, p. 181–188 noate de butyle (0,55 mg⋅kg )etletrans-2-nonénal (0,47 mg⋅kg de matière fraîche). © 2014 Cirad/EDP Sciences Conclusion. Parmi les composés volatils identifiés, les aldéhydes sont les composés majori- All rights reserved taires. Pour évaluer la qualité aromatique de pulpe de ditax, l’identification des composés DOI: 10.1051/fruits/2014007 d’impacts notamment par GC-olfactométrie serait une perspective intéressante. www.fruits-journal.org Sénégal / Detarium senegalense / fruits / flaveur / composé volatil / extraction RESUMEN ESPAÑOL,p.188 par solvant

Article published by EDP Sciences

Fruits, vol. 69 (3) 181 N.D. Ndiaye et al.

1. Introduction 2.2. Solvent-assisted flavor evaporation (SAFE) of ditax pulp The Detarium senegalense tree from the volatiles Ceasalpiniaceae family, an arboreal fruit , is still found wild in Senegal (West The solvent-assisted flavor evaporation Africa), in the Sine-Saloum islands and in (SAFE) technique was applied for careful Casamance [1]. Reaching (15 to 40) m, it is extraction of the ditax pulp volatiles. Vola- also found in the wet dense forest borders, tiles, preliminarily extracted in a solvent, the coastal and septentrional regions, and were evaporated at low temperature in high the Sudan-Guinean zone. The Detarium vacuum conditions (10–3 mbar) and con- senegalense fruit, locally called ditax in densed with a liquid nitrogen trap. Wolof, is one of the most important forest Forty g of fresh ditax pulp and 50 µL of fruit-bearing species with great economic internal standard solution (20 µL⋅20 mL–1 importance. The fruit (figure 1) appears in the form of a drupe with a diameter from H2O) of nonan-4-ol were combined with (3 to 8) cm and a mean weight of (49.2 ± 40 mL of distilled water and 80 mL of dichlo- 11.2) g. The epicarp (13% of the fruit romethane, and stirred for 30 min in an iced weight) is dark green and hard in unripe water bath under a nitrogen atmosphere. fruits, and light green, brown and brittle in The supernatant was collected and the res- ripe fruits. The pulp (34% of the fruit weight) idue was reextracted with 80 mL of dichlo- is green and entangled in a high-fiber net- romethane and 40 mL of distilled water for work firmly inserted on the stone (53% of 30 min again to achieve complete transfer the fruit weight), which contains one single of the volatile compound from the pulp. dark brown seed [1–4]. The pulp is very rich Organic phases were combined, dried over in ascorbic acid [from (1.2 to 2.2) g⋅100 g–1 anhydrous sodium sulfate and distilled at of fresh weight according to geographical 30 °C. After complete distillation, the system area]; sucrose (18–20% dry weight) is the was left for 1 h under vacuum. The distillate main component of the total sugars (23% dry was then concentrated in a water heating weight) and pheophytin a (128 mg⋅kg–1 bath at 40 °C using a Kuderna-Danish appa- fresh weight) is the major pigment of ditax ratus. Preliminary extractions were realized pulp [5, 6]. The fruit is eaten fresh but it is using a mixture of pentane-diethyl ether widely used as nectar (fruit pulp with water (50/50). and sugar), which is one of the most popular beverages in Senegal. However, the chem- 2.3. GC-MS analysis of safe extract ical characterization of ditax pulp remains incomplete. To the best of our knowledge, A tandem gas chromatograph 6890 / MSD only Haddad makes reference to the aroma 5973 / Gerstel Multipurpose Sample MPS-2 volatiles of ditax [3]. Therefore, our paper (Agilent Technologies, Palo Alto, USA) describes for the first time the volatile com- pounds of ditax to complete the chemical was used for volatile compound analysis. characterization data of this forest fruit and Injection (1 µL) was carried out in split to assess its organoleptic qualities. 1/10 mode at 250 °C using a DB-WAX polar column (J&W, 30 m × 0.25 mm × 0.25 µm) and a DB-1ms nonpolar column (J&W, 0.25 mm × 30 m × 0.25 µm) (Agilent Tech- 2. Materials and methods nologies, Palo Alto, USA). Helium was used as the carrier gas at 1 mL⋅min–1. Elution was realized with the following temperature 2.1. Fruits program: 3 °C per min from 40 °C to 170 °C, then 10 °C per min up to 240 °C and held Fresh ripe fruits were bought at the market for 10 min. Mass spectra were recorded in in September 2012, and after one week of EI+ mode at 70 eV within (15 to 300) Da. storage at –18 °C, pulps were extracted just The analyzer and source temperatures were before analysis. 150 °C and 250 °C, respectively.

182 Fruits, vol. 69 (3) Volatile compounds of ditax fruit

2.4. Identification of volatile compounds

Data were analyzed with the MSD Chem revD1 acquisition and data retreatment soft- ware. Peak identification was done by com- paring mass spectra with those of the NIST 2008 (National Institute of Standard Tech- nology) database [7]. Injection of n-alkane series C8-C20 (Sigma-Aldrich) was used for retention index (RI) calculations and their comparison with those found in the litera- ture, and on the Flavornet1 and Pherobase2 websites.

2.5. Quantification of volatile compounds

Semi-quantitative determinations were car- ried out by adding nonan-4-ol (Sigma Aldrich) as an internal standard at a concen- ⋅ –1 tration of 20 µL 20 mL H2O. The ratio of the response factor was considered to be equal to 1, thus allowing semi-quantification in µg⋅kg–1 fresh pulp using the equation:

()μ ⋅ –1 × AimIS mi gkg fresh pulp = 1000 ------AISmp explained by a longer storage in the freezer Figure 1. (17 d at –18 °C) before analysis on the DB- Fruit of Detarium senegalense with Ai = peak area of volatile com- 1ms. Among the 53 compounds tentatively J.F. Gmel: whole fruit, husked pound i; AIS = peak area of nonan-4-ol; mIS = identified, forty-nine are reported for the fruit (green pulp), fruit after pulp quantity of nonan-4-ol; mp = pulp quantity. first time in this fruit. In total, seventeen extraction (stone with fibrous aldehydes, eleven aliphatic alcohols, one network). terpene alcohol, seven free fatty acids, 3. Results and discussion three unsaturated hydrocarbons, one ter- pene hydrocarbon, seven sesquiterpene The aroma compounds were separated on hydrocarbons, one phenol, two ketones, two columns of different polarity (DB-WAX two esters and one organic acid compound and DB-1ms) (table I). Quantification on were identified or tentatively identified in both the DB-WAX and DB-1ms columns, ditax fresh pulp (table I). Aldehydes known (11 769 and 10 200) µg⋅kg–1, were quite to impart “green” and “grassy” notes were similar. This slight difference could be qualitatively and quantitatively the most important class of compounds in ditax fresh pulp, with a total concentration of 1 Acree T., Arn H., Flavornet and human 6 704 µg⋅kg–1 of fresh pulp (57% of the odor space, Gas chromatography–olfactom- total volatile fraction). Among them, trans, etry (GCO) of natural products, Datu Inc. cis-2,6-nonadienal was the main volatile, 2004, www.flavornet.org. representing 21% of the total volatile frac- 2 El-Sayed A.M., The Pherobase : Data- tion. Then followed cis-2-heptenal (16.4% base of Pheromones and Semiochemicals, of the total volatile fraction), bicyclo [2,2,0] www.pherobase.com, 2003–2012, The Phe- hexane-1-carboxaldehyde (6.8%), trans-2- robase. nonenal (4%) and trans-2-hexenal (3.8%).

Fruits, vol. 69 (3) 183 N.D. Ndiaye et al. , 1 1 1 1 1 1 ] 8 ] 1 ] 1 9 1 8 [ 1 1 1 1 1 ] 8 1 ]; green [ – – – – – – – – – – – 9 Odor Green Green [ Balsamic ]; grass, tallow, fat Leaf, green Mint, sweet 8 ]; resin, flower, green Biscuit, cream 9 Chemical, green Medicine, fruit Fat, citrus, rancid Leaf, fatty grass [ Fatty, citrus, green Fruit, leaf [ Almond, malt, pungent Cucumber, fatty, green Cucumber, waxy, green Strawberry, fruit, tomato Fruit [ Green [ of fresh pulp) 34.17 Traces 112.12 –1 12.34 ± 0.66 77.87 ± 2.76 52.60 ± 3.75 67.50 ± 5.05 49.14 ± 0.34 67.11 ± 0.37 35.82 ± 0.16 73.64 ± 0.60 31.85 ± 1.27 18.08 ± 0.49 12.13 ± 0.14 72.97 ± 3.06 20.31 ± 0.79 29.98 ± 0.11 16.00 ± 0.84 27.34 ± 4.58 37.60 ± 1.08 159.99 ± 4.43 105.79 ± 6.94 199.46 ± 9.40 803.85 ± 1.68 470.97 ± 1.96 Concentration kg 332.18 ± 10.98 452.18 ± 19.58 ⋅ 1929.56 ± 21.96 2474.08 ± 71.11 (µg b c – 658 669 730 740 774 844 858 870 945 950 674 773 724 801 885 815 826 885 927 921 1171 1015 1079 1031 1083 1112 1130 1137 Literature – – – – nd nd 814 814 859 870 867 950 948 824 804 823 887 847 851 878 931 916 1151 1009 1078 1024 1065 1132 1125 Retention indice non polar Experienced c a – – 935 1145 1181 1255 1313 1323 1401 1360 1400 1467 1714 1214 1093 1117 1132 1174 1187 1220 1230 1319 1385 1442 1444 1469 1480 1527 1605 Literature nd nd 937 1144 1155 1242 1314 1384 1353 1410 1469 1530 1756 1194 1096 1126 1137 1172 1186 1201 1220 1310 1372 1387 1425 1449 1463 1545 1602 Retention indice polar Experienced -2,4-heptadienal -2,6-nonadienal -3,6-nonadienal -2-hexen-1-ol -2-pentenal -2-hexenal -2-octenal -2-nonenal -2-penten-1-ol -3-hexen-1-ol -6-nonen-1-ol -3-hexenal -2-hexenal -4-heptenal -2-heptenal -6-nonenal 1-Butanol 1-Penten-3-ol 1-Pentanol Cis Cyclopentanol Cis 1-Hexanol Trans 1-Heptanol 6-Hepten-1-ol Cis 1,8-Cineole Pentanal Hexanal Trans Cis Heptanal Cis Trans Cis Cis Bicyclo [2.2.0] hexane-1-carboxaldehyde* Nonanal Trans Cis, cis Cis Trans, cis Trans Trans, cis Table I. Volatiles compounds identified or tentativelyon (*) in polar fresh and ditax non pulp polar after column. solvent-assisted flavour evaporation (SAFE) extraction and analysis Compounds Aliphatic alcohols Terpenic Alcohols Aldehydes

184 Fruits, vol. 69 (3) Volatile compounds of ditax fruit 1 1,2 1 1 1 1 1 1 1 1 1 1 1 1 – – – – – – – – – Odor Acid Paint Metal Phenol Rancid Rancid Balsamic Balsamic Fat, sweat Citrus, mint Woody, spicy Fish, pungent Woody, tea, warm Woody, citrus, sweet of fresh pulp) 11.21 5.5±1 –1 5.63 ± 0.03 1112 ± 6.17 82.96 ± 4.24 20.02 ± 1.20 26.73 ± 4.10 33.17 ± 0.03 87.76 ± 2.99 81.84 ± 5.97 39.54 ± 1.62 96.30 ± 6.15 98.83 ± 7.75 35.02 ± 4.31 60.41 ± 0.94 43.52 ± 1.51 273.24 ± 0.96 367.87 ± 3.11 552.07 ± 6.92 154.47 ± 9.88 114.07 ± 3.06 Concentration kg 202.39 ± 13.24 200.59 ± 41.76 ⋅ (µg c b - 890 673 678 756 846 876 961 1064 1258 1556 1950 2124 1977 2374 1022 1414 1419 1431 1448 1513 1440 Literature nd nd nd nd nd 864 882 958 1004 1125 1280 1501 1955 2093 2110 2257 1012 1404 1409 1425 1441 1465 1497 Retention indice nonpolar Experienced ]. 7 c a – – 1872 1990 1962 2202 2517 2940 3181 1272 1070 1124 1178 1580 1574 1779 1674 1726 1982 1479 1452 1 034 1 261 Literature and NIST 2008 [ 2 1879 1985 1996 2183 2613 2936 3184 1063 1266 2573 2733 1071 1121 1234 1182 1580 1581 1602 1692 1750 1777 2026 1450 Retention indice polar Experienced , Pherobase 1 fresh pulp. –1 kg ⋅ -bergamotene -farnesene* α β -2-hexanoic acid - -bergamotene α - :<5µg -Copaene -Santalene -Bisabolene* -Cadinene* Hexanoic acid Heptanoic acid Trans Nonanoic acid Dodecanoic acid* Hexadecanoic acid Octadecanoic acid 1-Penten-3-one 3-Hydroxy-2-butanone Butyl hexadecanoate* Butyl octadecanoate* Toluene Ethylbenzene Styrene Limonene α Cis α Trans Trans- β β Phenol Acetic acid linear retention index on DB-1ms. linear retention index on DB-wax. linear retention index from Flavornet Table I. continued. trace Compounds Free fatty acids Ketones Esters Unsaturated hydrocarbons Terpene hydrocarbons Sesquiterpene hydrocarbons Phenol Acid a b c nd: Retention indice (RI) experimented < 800 or not detected.

Fruits, vol. 69 (3) 185 N.D. Ndiaye et al.

Haddad reported that 2,6-nonadienal indices) are different from those from the lit- (42.3%), trans-2-heptanal (13.5%), cis-6- erature. These two compounds are esters of nonenal (7.5%), trans-2-nonenal (7.4%), fatty acid and represent 7.8% of the total vol- caryophyllene oxide (2.5%), humulene atile fraction of ditax fresh pulp. oxide (1.8%) and tetradecane (0.7%) were Free fatty acids represent 7% (839 µg⋅ kg–1) the main volatiles of essential oil extract of of the total volatile fraction, where hexa- ditax pulp obtained by hydrodistillation [3]. noic acid (273 µg⋅kg–1), n-hexadecanoic The following different flavors confirmed acid (202 µg⋅kg–1) and octadecanoic acid our perception; trans, cis-2,6-nonadienal is (201 µg⋅kg–1) were the main compounds. cucumber, violet, green and waxy; trans-2- nonenal is fatty, penetrating and waxy; Acetic acid represents 2.45% of the total melon or green melon and citrus are char- volatile fraction. acteristic of cis-6-nonenal and green and Other chemical compounds such as un- watermelon-like of cis, cis-3,6-nonadienal saturated hydrocarbons (1.7% of the total [10–15]. Hexanal and trans-2-hexenal odor volatile fraction) with styrene as the main is green [8]. It has been widely reported that compound; ketones (1.45% of the total vol- C9 odorant compounds were the result of atile fraction) and phenol (0.36% of the total lipoxygenase degradation of linoleic and volatile fraction) were also identified in di- linolenic acid, which occurs rapidly after tax pulp. tissue disruption [16, 17]. Sesquiterpene hydrocarbons represent the second class of compounds (12.9% of total volatile compounds), with trans-α-ber- 4. Conclusion gamotene being the major component, with 73% of total sesquiterpene hydrocarbons The major volatiles present in ditax pulp and 9.4% of the total volatile fraction. could explain why ditax is very popular, Aliphatic alcohols were the third class of especially for its strong cucumber-like compounds, with 8.8% of the total volatile aroma with gentle fruity, woody, herbal fraction for a total amount of 1 040 µg⋅kg–1 and green notes. Among the volatile com- of fresh pulp. Among them, 1-hexanol (flo- pounds identified, aldehyde compounds ral, green notes) was the main volatile (2.8% were widely predominant. Five volatiles of the total volatile fraction) followed by were responsible for over 38% of the total cyclopentanol (1.4%). However, other alco- volatile fraction: trans,cis-2,6-nonadienal, hols such as 1-butanol, cis-3-hexen-1-ol and (21%), cis-2-heptenal (16.4%), trans-α-ber- trans-2-hexen-1-ol have also been identi- gamotene (9.4%) and bicyclo [2,2,0] hex- fied in ditax pulp. They have already been ane-1-carboxaldehyde (6.8%). To assess the reported in many other fruits such as apricot aromatic qualities of ditax pulp, the primary [18–21], copoazù [22] and acerola [23]. impact aromas should be determined by identifying the aroma-active compounds by 1,8-Cineole (mint, sweet flavor) was the GC-olfactometry. only terpene alcohol identified in ditax pulp (0.3% of the total volatile fraction). 1,8-Cin- eole has also been identified in cantaloupe [24]. Alcohols and aldehydes of six carbon Acknowledgments atoms are responsible for the herbaceous odor of several fruits and vegetables [20, 25]. The authors thank Mrs Oumar Diémé, Ester compounds were represented by Babacar Dieng and Noël Diandy from the butyl hexadecanoate (368 µg⋅kg–1) and Inst. Food Technol. (Dakar, Senegal) for butyl octadecanoate (552 µg⋅kg–1); these their technical help and supplying fruits. We two compounds were tentatively identified also thank CIRAD and WAAPP 2 for their because the experimental RIs (retention financial and technical support.

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Los compuestos volátiles del fruto de ditax (Detarium senegalense J.F. Gmel) en Senegal. Resumen – Introducción. Detarium senegalense J.F. Gmel es una especie forestal que se encuentra en Senegal, cuyos frutos son denominados localmente ditax en Wólof. El fruto se consume directamente, pero también se emplea ampliamente en forma de néctar, una de las bebidas más populares de Senegal. Sin embargo la caracterización química de la pulpa de ditax permanece incompleta. El presente trabajo describe los compuestos volátiles de la pulpa de ditax con el fin de evaluar su calidad organoléptica. Material y métodos. Los com- puestos volátiles libres de la pulpa de ditax fresca se aislaron mediante la técnica de evapora- ción asistida con solvente y se analizaron mediante GC-MS. Resultados y discusión. Entre los 53 compuestos identificados, se señalaron 49 por primera vez en este fruto. En total se identificaron 17 aldehídos, 11 alcoholes alifáticos, 1 alcohol terpénico, 7 ácidos grasos libres, 3 hidrocarburos sesquiterpénicos, 1 fenol, 2 cetonas, 2 éster y 1 ácido orgánico en la pulpa fresca de ditax. Los principales volátiles identificados en la pulpa de ditax fresca fueron el trans, cis-2,6-nonadienal (2.47 mg⋅kg–1), el cis-2-heptenal (1.93 mg⋅kg–1), el trans-α-bergamo- teno (1.11 mg⋅kg–1), el biciclo [2,2,0] hexano-1-carboxaldehído (0.80 mg⋅kg–1), el octadeca- noato de butilo (0.55 mg⋅kg–1)yeltrans-2-nonenal (0.47 mg⋅kg–1 de materia fresca). Conclusión. Entre los compuestos volátiles identificados, los aldehídos son los compuestos mayoritarios. Para evaluar la calidad aromática de pulpa de ditax, una perspectiva interesante sería la identificación de los compuestos de impactos, sobre todo por GC-olfactometría.

Senegal / Detarium senegalense / frutas / sabor / compuesto volátil / extracción por disolventes

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