Free and Bound Flavor Constituents of White-Fleshed Nectarines

reduction of 3-oxo-a-ionol (10 mg) with palladium black (5 mg) i n 10 mL ..... of blacktail deer. (20). £-. Tetradecalactone has been found to occur ...
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Chapter 10

Free and Bound Flavor Constituents of White-Fleshed Nectarines 1

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Gary R. Takeoka, Robert A. Flath , Ron G. Buttery, Peter Winterhalter, Matthias Güntert , David W. Ramming, and Roy Teranishi 3

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Agricultural Research Service, U.S. Department of Agriculture, 800 Buchanan Street, Albany, CA 94710 Lehrstuhl für Lebensmittelchemie, Universität Würzburg, Am Hubland, D-8700 Würzburg, Germany Research Department, Haarmann and Reimer GmbH, Postfach 1253, D-3450 Holzminden, Germany Agricultural Research Service, U.S. Department of Agriculture, 2021 South Peach Avenue, Fresno, CA 93727

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The volatiles of white-fleshed nectarine (Prunus persica nectarina) were studied by capillary gas chromatography and combined capillary gas chromatography-mass spectrometry (GC-MS) using dynamic headspace sampling of intact fruit, direct extraction of juice, and simultaneous vacuum and atmospheric d i s t i l lation-extraction of blended fruit. Enzymatic hydrolysis of the glycoside fraction obtained from nectarine juice by adsorption on Amberlite XAD-2 resin followed by elution with ethyl acetate and methanol led to the identification of the following C norisoprenoids: 3-oxo-αionol, 3-hydroxy-7,8-dihydro-ß-ionol, 3-hydroxy-ß-ionone, 3-oxo-7,8-dihydro-α-ionol, 3-oxoretro-α-ionol, vomifoliol, and 7,8-dihydrovomifoliol. 13

T h e r e h a v e o n l y b e e n l i m i t e d s t u d i e s on t h e volatile constituents of nectarine (1,2). While the flavor c o n t r i b u t i o n o f l a c t o n e s i n n e c t a r i n e s has been c l a r i f i e d ( 1 ) , f l a v o r d i f f e r e n c e s between w h i t e and y e l l o w - f l e s h e d nectarines have yet to be explained. White-fleshed n e c t a r i n e s t y p i c a l l y p o s s e s s an a d d i t i o n a l f l o w e r y n o t e w h i c h i s l a c k i n g i n t h e y e l l o w - f l e s h e d v a r i e t i e s . One g o a l of this study was to determine what compounds are r e s p o n s i b l e f o r t h i s unique odor c h a r a c t e r i s t i c i n w h i t e fleshed nectarines.

0097-6156/92/0490-0116$06.75/0 © 1992 American Chemical Society

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TAKEOKA ET AL.

Flavor Constituents of White-Fleshed Nectarines

The p r e c u r s o r a n a l y s i s a p p r o a c h h a s b e e n d e m o n s t r a t e d t o be a u s e f u l complement t o c o n v e n t i o n a l methods o f f r u i t flavor research (3) . R e c e n t s t u d i e s on v a r i o u s Prunus s p e c i e s s u c h a s a p r i c o t , p e a c h , y e l l o w p l u m (4) a n d s o u r c h e r r y (5) h a v e shown t h a t t h e s e f r u i t s c o n t a i n c o n j u g a t e d forms o f monoterpenes, C13 n o r i s o p r e n o i d s a n d s h i k i m i c a c i d d e r i v e d m e t a b o l i t e s and t h a t t h e s e c o n j u g a t e s p l a y an i m p o r t a n t r o l e a s f l a v o r p r e c u r s o r s . T h i s work r e p o r t s on t h e f l a v o r c o n s t i t u e n t s l i b e r a t e d and p r o d u c e d d u r i n g e n z y m a t i c and a c i d h y d r o l y s i s o f t h e g l y c o s i d e f r a c t i o n o f white-fleshed nectarines.

Experimental M a t e r i a l s . F r e s h t r e e - r i p e n e d n e c t a r i n e s (Prunus persica nectarina), c u l t i v a r Ρ 8 9 - 5 6 , were o b t a i n e d f r o m o r c h a r d s of t h e H o r t i c u l t u r a l Crops Research L a b o r a t o r y o f t h e U . S . Department o f A g r i c u l t u r e , F r e s n o , CA. Ρ 89-56 i s a w h i t e f l e s h e d e x p e r i m e n t a l c u l t i v a r b e i n g t e s t e d i n F r e s n o , CA and was grown u n d e r s t a n d a r d c u l t i v a t i o n methods with flood i r r i g a t i o n . Sample P r e p a r a t i o n . 1. Dynamic H e a d s p a c e S a m p l i n g . I n t a c t f r u i t ( t o t a l w e i g h t 3 . 9 kg) were p l a c e d i n a 9 - L P y r e x g l a s s c o n t a i n e r . A P y r e x h e a d was a t t a c h e d t o t h e t o p o f the c o n t a i n e r which allowed p u r i f i e d a i r t o e n t e r the b o t t o m o f t h e chamber ( v i a a T e f l o n t u b e ) a n d e x i t o u t t h e t o p t h r o u g h a T e n a x t r a p (14 cm. l e n g t h X 2 . 2 cm i . d . ; 10 g o f Tenax [ A l l t e c h A s s o c i a t e s , Deerfield, I L ] ) . The s a m p l i n g was c o n t i n u e d a t room t e m p e r a t u r e ( c a . 2 4 ° C ) f o r 24 h a t 3 L / m i n . The c o l l e c t e d v o l a t i l e s were e l u t e d f r o m t h e T e n a x t r a p w i t h 100 mL o f f r e s h l y d i s t i l l e d d i e t h y l e t h e r c o n t a i n i n g c a . 0.001% E t h y l a n t i o x i d a n t 330 ( 1 , 3 , 5 t r i m e t h y l - 2 , 4 , 6 - t r i s (3 , 5 - d i - t e r t - b u t y 1 - 4 hydroxybenzyl)benzene). 2. S i m u l t a n e o u s D i s t i l l a t i o n - E x t r a c t i o n ( S D E ) . T h e washed f r u i t was c u t a n d t h e s t o n e s were r e m o v e d . T h e s k i n a n d p u l p ( 1 . 0 2 kg) were b l e n d e d w i t h 1500 mL o f w a t e r i n a W a r i n g b l e n d e r f o r 15 s . 4-Nonanone (1 μ ΐ ) was a d d e d a s an i n t e r n a l s t a n d a r d and t h e m i x t u r e was b l e n d e d f o r an a d d i t i o n a l 15 s . The m i x t u r e was s u b j e c t e d t o SDE f o r 2 h w i t h p e n t a n e - d i e t h y l e t h e r ( 1 : 1 , v / v ) u s i n g t h e SDE h e a d d e s c r i b e d by S c h u l t z e t a l . (6) . The e x t r a c t was d r i e d o v e r anhydrous sodium s u l f a t e and c o n c e n t r a t e d w i t h a V i g r e u x c o l u m n t o a f i n a l volume o f 0 . 2 - 0 . 3 mL. 3 . Vacuum S D E . The s k i n and p u l p ( 3 . 1 8 k g , s t o n e s removed) were b l e n d e d w i t h 3500 mL o f w a t e r i n a W a r i n g b l e n d e r f o r 15 s . 4 - M e t h y l p e n t - 2 - y l a c e t a t e and 4 - n o n a n o n e (final c o n c e n t r a t i o n - 0.8 ppm e a c h r e l a t i v e t o f r u i t w e i g h t ) were a d d e d t o t h e f r u i t s l u r r y a s i n t e r n a l s t a n d a r d s . T h e s l u r r y was b l e n d e d f o r an a d d i t i o n a l 15 s a n d t h e n a d d e d

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to a 12 L r o u n d - b o t t o m e d f l a s k . Eighty m i l l i t e r s of a n t i f o a m s o l u t i o n was a d d e d t o t h e f l a s k . T h e a n t i f o a m s o l u t i o n was p r e p a r e d by a d d i n g 10 mL o f H a r t w i c k a n t i f o a m 50 e m u l s i o n t o 1000 mL o f w a t e r a n d b o i l i n g u n t i l t h e v o l u m e was r e d u c e d t o c a . 700 mL t o remove volatiles. Vacuum SDE was p e r f o r m e d (60 mmHg) w i t h h e x a n e o v e r 2 h u s i n g t h e SDE h e a d d e s c r i b e d b y S c h u l t z e t a l . ( 6 ) . T h e e x t r a c t was f r o z e n ( - 2 0 ° C ) t o remove r e s i d u a l w a t e r a n d c o n c e n t r a t e d under reduced p r e s s u r e w i t h a V i g r e u x column t o a f i n a l v o l u m e o f 0 . 8 - 1 . 0 mL. 4. XAD-2 C o l u m n . A m b e r l i t e XAD-2 (20-60 mesh) was c l e a n e d by s u c c e s s i v e e x t r a c t i o n s i n a Soxhlet apparatus with p e n t a n e , e t h y l a c e t a t e a n d m e t h a n o l ( e a c h f o r 8 h) . T h e s l u r r y was f i l l e d i n t o a g l a s s c o l u m n ( 2 . 5 cm i . d . X 53 cm, b e d h e i g h t - 33 c m ) . 5. I s o l a t i o n o f G l y c o s i d e s w i t h XAD-2 Column ( 7 ) . Fruit p u l p a n d s k i n (1 kg) were h o m o g e n i z e d w i t h N a C l (700 g) and w a t e r (1 L) i n a W a r i n g b l e n d e r . T h e homogenate was centrifuged at 3200 rpm f o r 20 min. The resulting s u p e r n a t a n t s o l u t i o n (1000 mL was a d j u s t e d t o pH 5 w i t h 3 Ν NaOH s o l u t i o n . The pH a d j u s t e d j u i c e was d i l u t e d w i t h 700 mL w a t e r and p a s s e d t h r o u g h f i l t e r p a p e r . T h e f i l t r a t e was t h e n l o a d e d on t h e A m b e r l i t e XAD-2 c o l u m n w h i c h h a d b e e n j u s t p r e v i o u s l y washed w i t h 500 mL o f w a t e r . After t h e f i l t r a t e h a d p a s s e d o n t o t h e r e s i n t h e c o l u m n was washed w i t h 2200 mL o f w a t e r f o l l o w e d b y 600 mL o f p e n t a n e . T h e g l y c o s i d e s were o b t a i n e d by e l u t i o n w i t h 800 mL o f e t h y l a c e t a t e f o l l o w e d by 600 mL o f m e t h a n o l . T h e e t h y l a c e t a t e a n d m e t h a n o l e l u a t e s were e a c h d i v i d e d i n t o h a l v e s ; one h a l f was s u b j e c t e d t o SDE a n d t h e o t h e r h a l f was u s e d f o r e n z y m a t i c h y d r o l y s i s . 6. A c i d H y d r o l y s i s o f G l y c o s i d e s . E a c h s o l v e n t eluate ( e t h y l a c e t a t e and m e t h a n o l ) was c o n c e n t r a t e d t o d r y n e s s on a r o t a r y evaporator and t r e a t e d separately. Each g l y c o s i d e f r a c t i o n was d i s s o l v e d i n 0.2 M p h o s p h a t e b u f f e r (200 mL, pH 3 . 0 ) a n d s u b j e c t e d t o c o n t i n u o u s l i q u i d - l i q u i d extraction (16 h) with d i e t h y l ether to remove any v o l a t i l e s . T h e aqueous g l y c o s i d e s o l u t i o n was s u b j e c t e d t o SDE f o r 2 h w i t h p e n t a n e : e t h e r ( 1 : 1 , v / v ) u s i n g t h e SDE h e a d d e s c r i b e d by (6) . T h e e x t r a c t s were d r i e d o v e r a n h y d r o u s s o d i u m s u l f a t e and c o n c e n t r a t e d w i t h a V i g r e u x c o l u m n t o a f i n a l v o l u m e o f 0 . 1 - 0 . 2 mL. 7. E n z y m a t i c H y d r o l y s i s o f G l y c o s i d e s . Each s o l v e n t e l u a t e ( e t h y l a c e t a t e and m e t h a n o l ) was t a k e n t o d r y n e s s o n a r o t a r y e v a p o r a t o r and t r e a t e d s e p a r a t e l y . E a c h g l y c o s i d e f r a c t i o n was d i s s o l v e d i n 160 mL o f 0.2 M p h o s p h a t e b u f f e r (pH 5 . 0 ) a n d c o n t i n u o u s l y e x t r a c t e d (16 h) w i t h d i e t h y l e t h e r t o remove any v o l a t i l e s . β - G l u c o s i d a s e (25 mg; C a r l Roth KG, K a r l s r u h e , ca. 310 U/mg) was a d d e d a n d t h e m i x t u r e was s t i r r e d f o r 33 h a t 3 6 ° C . The l i b e r a t e d

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aglycons were removed by continuous liquid-liquid extraction (16 h) w i t h d i e t h y l e t h e r . A f t e r d r y i n g and concentration the extract was ready for analysis. P e c t i n a s e (70 mg, R o h a p e c t C , Rohm T e c h . , I n c . ) was a d d e d to the previously enzyme (β-glucosidase) hydrolyzed g l y c o s i d e s o l u t i o n . T h e m i x t u r e was s t i r r e d f o r 50 h a t 3 6 ° C . R e l e a s e d a g l y c o n s were removed by c o n t i n u o u s l i q u i d l i q u i d e x t r a c t i o n (16 h) w i t h d i e t h y l e t h e r . T h e e t h e r extract was dried and concentrated in the manner previously described. 8. I s o l a t i o n o f P o l a r C o n s t i t u e n t s by C o n t i n u o u s L i q u i d L i q u i d E x t r a c t i o n . N e c t a r i n e j u i c e was p r e p a r e d i n t h e same way a s f o r t h e i s o l a t i o n of g l y c o s i d e s . T h e pH adjusted juice (pH 5 . 0 ) was subjected to continuous l i q u i d - l i q u i d e x t r a c t i o n w i t h p e n t a n e f o r 22 h . T h e j u i c e was t h e n e x t r a c t e d w i t h d i e t h y l e t h e r f o r 18 h t o i s o l a t e t h e p o l a r c o n s t i t u e n t s . The e t h e r e x t r a c t was d r i e d o v e r a n h y d r o u s s o d i u m s u l f a t e and c o n c e n t r a t e d t o 1 mL o n a Vigreux column. C a p i l l a r y Gas C h r o m a t o g r a p h y . A H e w l e t t - P a c k a r d 5890 g a s chromatograph equipped w i t h a flame i o n i z a t i o n d e t e c t o r (FID) was u s e d . A 60 m X 0.32 mm ( i . d . ) D B - 1 f u s e d s i l i c a c a p i l l a r y c o l u m n (d - 0 . 2 5 μπι, J&W S c i e n t i f i c , F o l s o m , CA) was e m p l o y e d . The i n j e c t o r and d e t e c t o r t e m p e r a t u r e s were 180 ° C a n d 2 6 0 ° C , r e s p e c t i v e l y . T h e o v e n t e m p e r a t u r e was programmed f r o m 30 ° C (4 m i n i s o t h e r m a l ) t o 2 4 0 ° C a t 2 ° C / m i n . T h e h e l i u m c a r r i e r g a s l i n e a r v e l o c i t y was 3 3 - 3 5 cm/s ( 3 0 ° C ) . f

C a p i l l a r y Gas C h r o m a t o g r a p h y - M a s s S p e c t r o m e t r y (GC/KS). Two d i f f e r e n t s y s t e m s were u s e d . The f i r s t s y s t e m was a F i n n i g a n MAT 4500 GC/MS/INCOS s y s t e m ( F i n n i g a n MAT, San J o s e , CA) e q u i p p e d w i t h t h e same t y p e o f c o l u m n u s e d i n t h e GC a n a l y s e s . The o v e n t e m p e r a t u r e was programmed f r o m 5 0 ° C t o 2 5 0 ° C a t 2 ° C / m i n . F o r t h e hexane e x t r a c t ( o b t a i n e d by vacuum SDE o f b l e n d e d f r u i t ) t h e o v e n t e m p e r a t u r e was programmed f r o m 3 0 ° C t o 2 0 0 ° C a t 2 ° C / m i n . T h e i n s t r u m e n t was o p e r a t e d i n t h e e l e c t r o n i m p a c t mode a t a n i o n i z a t i o n v o l t a g e o f 70 e V . The s e c o n d s y s t e m c o n s i s t e d o f a HP 5890 g a s c h r o m a t o g r a p h c o u p l e d t o a HP 5970B q u a d r u p o l e mass s p e c t r o m e t e r ( c a p i l l a r y d i r e c t i n t e r f a c e ) . A 60 m X 0 . 2 5 mm ( i . d . ) DB-1 f u s e d s i l i c a c a p i l l a r y column (d 0.25 Mm) was u s e d . The o v e n t e m p e r a t u r e was programmed f r o m 3 0 ° C (4 m i n i s o t h e r m a l ) t o 2 1 0 ° C a t 2 ° C / m i n . B o t h s y s t e m s u t i l i z e d h e l i u m as t h e c a r r i e r g a s . f

R e f e r e n c e Compounds. R e f e r e n c e s t a n d a r d s were o b t a i n e d commercially, synthesized by established methods or received as gifts. (E)-2-hexenyl octanoate had the f o l l o w i n g mass s p e c t r u m : 2 2 6 ( M , 3), 197(4), 183(2), 155(5), 142(2), 128(9), 127(100), 125(6), 109(10), 100(5), +

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97(8), 83(28), 82(28), 67(45), 57(93), 55(71), 54(12), 43(24), 41(66). M a n d e l o n i t r i l e , prepared according to the method o f H i r v i a n d Honkanen ( 8 ) , h a d t h e f o l l o w i n g mass spectrum: 133(76, M ) , 132(50), 116(29), 115(43), 106(44), 105(100), 79(47), 78(37), 77(95), 51(68), 50(46), 39(19). Vomifoliol, prepared by NaBH reduction of d e h y d r o v o m i f o l i o l a c c o r d i n g t o t h e method o f S e f t o n e t a l . ( 9 ) , h a d t h e f o l l o w i n g mass s p e c t r u m : 1 6 8 ( 7 ) , 166(2), 151(5), 150(11), 149(4), 135(10), 125(9), 124(100), 122(11), 111(7), 107(11), 95(7), 94(7), 91(8), 79(16), 77(10), 69(8), 55(11), 43(29). 7,8-Dihydrovomifoliol, p r e p a r e d by t h e r e d u c t i o n o f v o m i f o l i o l a c c o r d i n g t o t h e method o f S e f t o n et a l . (9), had the f o l l o w i n g mass spectrum: 208(3), 193(2), 183(2), 170(29), 166(6), 153(29), 152(58), 125(26), 111(69), 110(100), 109(31), 107(28), 96(31), 82(24), 69(21), 68(23), 55(23), 45(22), 43(50). 3-0xo-a-ionol h a d t h e f o l l o w i n g mass s p e c t r u m : 193(2), 175(1), 165(2), 153(2), 152(13), 135(7), 109(27), 108(100), 95(10), 91(13), 79(12), 77(11), 67(7), 65(6), 55(6), 45(14), 43(21). 3-Hydroxy-B-ionone had the f o l l o w i n g mass s p e c t r u m : 2 0 8 ( M , 5 ) , 1 9 4 ( 1 3 ) , 193(100), 175(30), 149(10), 147(11), 133(11), 131(14), 121(13), 109(14), 105(22), 91(24), 79(14), 77(15), 55(9), 43(44). 3-Hydroxy-7,8-dihydro-6-ionol had the following mass spectrum: 212(M , 3), 194(4), 179(6), 162(5), 161(36), 153(7), 137(28), 136(33), 135(17), 123(16), 121(100), 119(76), 109(25), 107(29), 105(35), 95(31), 93(43), 91(29), 81(29), 79(27), 77(16), 69(23), 67(28), 55(28), 4 3 ( 3 4 ) , 4 1 ( 3 9 ) . 3 - O x o - 7 , 8 - d i h y d r o - a - i o n o l , p r e p a r e d by t h e r e d u c t i o n o f 3 - o x o - a - i o n o l (10 mg) w i t h p a l l a d i u m b l a c k (5 mg) i n 10 mL e t h y l a c e t a t e (1 h r e a c t i o n t i m e , 3 p s i H ) h a d a mass s p e c t r u m w h i c h was i n good a g r e e m e n t w i t h literature data (48). 3-Oxo-retro-a-ionols, prepared a c c o r d i n g t o t h e method o f H e r d e r i c h a n d W i n t e r h a l t e r (66) , h a d mass s p e c t r a c o n s i s t a n t w i t h t h a t p r e v i o u s l y r e p o r t e d (66). I s o m e r 1 a n d i s o m e r 2 h a d K o v a t s ' r e t e n t i o n indices (DB-1) o f 1663 a n d 1718, r e s p e c t i v e l y , transM a r m e l o l a c t o n e h a d t h e f o l l o w i n g mass s p e c t r u m : 1 6 6 ( M , 28), 151(11), 138(15), 124(11), 123(40), 109(20), 107(12), 97(23), 96(27), 95(27), 93(42), 91(29), 81(34), 80(24), 79(27), 77(27), 69(39), 68(100), 67(43), 53(19), 42(36), 41(40). cis-Marmelo lactone had t h e following mass spectrum: 166(M , 35), 151(12), 138(16), 124(12), 123(43), 109(20), 107(13), 97(24), 96(29), 95(28), 93(49), 91(31), 81(34), 80(24), 79(28), 77(28), 69(39), 68(100), 67(43), 53(18), 42(34), 41(39). (Z)-2,6-Dimethylocta-2,7-diene1 , 6 - d i o l , p r e p a r e d f r o m l i n a l o o l a c c o r d i n g t o t h e method o f B e h r e t a l . (10), h a d t h e f o l l o w i n g mass s p e c t r u m : 137(8), 123(4), 121(5), 119(16), 110(9), 109(7), 107(5), 105(7), 97(5), 96(15), 95(13), 93(12), 91(7), 84(16), 83(9), 82(19), 81(15), 79(14), 71(57), 69(11), 68(19), 67(49), 57(11), 55(32), 53(14), 43(100), 41(40). (E)-2,6Dimethylocta-2,7-diene-l,6-diol, p r e p a r e d from l i n a l o o l +

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TAKEOKA ET A L

Flavor Constituents of White-Fleshed Nectarines

a c c o r d i n g t o t h e method o f B e h r e t a l . (10), h a d t h e f o l l o w i n g mass s p e c t r u m : 1 5 2 ( 1 ) , 1 3 7 ( 8 ) , 1 2 3 ( 4 ) , 1 2 1 ( 6 ) , 119(13), 110(9), 109(8), 107(4), 105(5), 97(5), 96(12), 95(8), 94(8), 93(16), 91(9), 84(10), 83(8), 82(16), 81(13), 79(19), 71(59), 69(11), 68(20), 67(50), 57(10), 55(34), 53(16), 43(100), 41(37). The i s o m e r i c p - m e n t h - 1 e n - 9 - a l s were p r e p a r e d by s u b j e c t i n g (E)-2,6-dimethylocta2,7-diene-l,6-diol t o SDE f o r 2 h i n 0.2 M p h o s p h a t e b u f f e r , pH 3 . 0 . The a l d e h y d e s ( i s o m e r s n o t s e p a r a t e d ) g a v e an *H NMR s p e c t r u m consistant with that previously reported (49). p - M e n t h - l - e n - 9 - a l (isomer 1) had the f o l l o w i n g mass s p e c t r u m : 9 5 ( 1 7 ) , 9 4 ( 1 0 0 ) , 9 3 ( 1 1 ) , 9 1 ( 1 3 ) , 81(12), 80(9), 79(93), 77(21), 68(13), 67(30), 55(15), 5 3 ( 1 6 ) , 4 1 ( 1 7 ) , 3 9 ( 2 1 ) . p - M e n t h - l - e n - 9 - a l ( i s o m e r 2) h a d t h e f o l l o w i n g mass s p e c t r u m : 9 5 ( 1 6 ) , 94(100), 93(11), 91(10), 81(11), 80(7), 79(93), 77(16), 68(12), 67(27), 65(9), 55(18), 53(18), 41(17), 39(20). C o n i f e r y l a l c o h o l h a d t h e f o l l o w i n g mass s p e c t r u m : 1 8 0 ( M , 6 7 ) , 162(9), 152(10), 147(14), 138(11), 137(100), 131(18), 124(69), 119(32), 109(21), 107(12), 105(10), 103(27), 91(58), 89(12), 77(28), 65(27), 63(13), 55(16), 53(13), 51(20), 39(19). Dihydroconiferyl alcohol, prepared by the reduction of c o n i f e r y l alcohol (10 mg) w i t h p a l l a d i u m b l a c k (5 mg) i n 7 m l o f a b s o l u t e e t h a n o l (2 h r e a c t i o n t i m e , 1 atm H ) , h a d t h e f o l l o w i n g mass s p e c t r u m : 182 ( M , 44), 164(4), 149(6), 139(6), 138(33), 137(100), 123(11), 122(18), 107(10), 94(14), 91(17), 77(18), 65(10), 51(10), 39(11) . +

+

2

O d o r T h r e s h o l d D e t e r m i n a t i o n s . T h e s e were d e t e r m i n e d ( w i t h reference standards purified by preparative gas chromatography) with a panel of 16-22 members using procedures described p r e v i o u s l y (11). Results

and D i s c u s s i o n

V o l a t i l e constituents of fresh, white-fleshed nectarines ( e x p e r i m e n t a l c u l t i v a r Ρ 89-56) were i s o l a t e d by h e a d s p a c e s a m p l i n g o f i n t a c t f r u i t , vacuum SDE o f b l e n d e d f r u i t a n d d i r e c t e t h e r e x t r a c t i o n o f j u i c e . Sample c o n s t i t u e n t s w e r e i d e n t i f i e d by c o m p a r i s o n o f t h e compound's K o v a t s i n d e x , I (12) a n d mass s p e c t r u m w i t h that of a reference standard. Headspace Sampling. Table I shows the constituents i d e n t i f i e d by d y n a m i c h e a d s p a c e s a m p l i n g o f t h e intact f r u i t . T h e s e v a l u e s s h o u l d be c o n s i d e r e d a s a p p r o x i m a t e s i n c e sample c o n s t i t u e n t s c o e l u t e d w i t h s o l v e n t p e a k s , and s a m p l e b r e a k t h r o u g h d u r i n g t r a p p i n g was n o t d e t e r m i n e d . Esters comprised a substantial portion of the volatiles, w i t h l a r g e amounts o f t h e f o l l o w i n g : (Z)-3h e x e n y l a c e t a t e (15.99%), e t h y l o c t a n o a t e (10.72%), e t h y l acetate (6.47%), hexyl acetate (2.61%), ethyl (Z)-4-

111

122

FLAVOR PRECURSORS

T a b l e I . Headspace C o n s t i t u e n t s Nectarine

of

Intact,

Tree-Ripened

jDB-l

Constituent

exp.

ref.

%

area*

ethyl acetate 3-hydroxy-2-butanone propyl acetate toluene 2-methylpropyl acetate hexanal e t h y l butanoate (Z)-3-hexenol ethylbenzene m-xylene hexanol 3-methylbutyl acetate styrene o-xylene pentyl acetate 3-methylbut-2-enyl acetate methyl hexanoate benzaldehyde propylbenzene e t h y l m e t h y 1 b e n ζ ene 1,3,5-trimethylbenzene 1,2,4-trimethylbenzene e t h y l hexanoate ( Ζ ) - 3 - h e x e n y 1 acetate (E)-2-hexenyl acetate + hexyl acetate γ-hexalactone (monoterpene) e t h y l heptanoate linalool methyl (E)-4-octenoate methyl octanoate naphthalene ( Ζ ) - 3 - h e x e n y 1 butanoate ethyl (E)-4-octenoate e t h y l octanoate 7-octalactone ethyl (E)-2-octenoate