Thermal Generation of Aromas - American Chemical Society

Chapter 32

Aroma Composition of Canned Black Truffles

Downloaded by TUFTS UNIV on June 4, 2018 | https://pubs.acs.org Publication Date: October 3, 1989 | doi: 10.1021/bk-1989-0409.ch032

T. Talou, M . Delmas, and A. Gaset Laboratoire de Chimie des Agroressources, Ecole Nationale Supérieure de Chimie, Institut National Polytechnique de Toulouse, route de Narbonne 31077 Toulouse Cédex, France

The volatile constituents of canned Black Perigord Truffles (Tuber Melanosporum) were analysed by dynamic headspace concentration gas chromatography - mass spectrometry. A total of 36 compounds were identified and described for the first time as canned black truffle aroma constituents. The modification of flavor and the possible formation of the compounds due to the heating treatment are discussed.

Black Perigord t r u f f l e s (Tuber Melanosporum) a r e underground mushrooms t h a t grow i n s y m b i o s i s w i t h c e r t a i n t r e e s , e s p e c i a l l y oaks. One f i n d s them i n Europe, p a r t i c u l a r l y i n France where t h e i r aroma i s v e r y much a p p r e c i a t e d by gourmets. Due t o t h e i r limited h a r v e s t i n g season (mainly d u r i n g w i n t e r ) , t r u f f l e s must be t h e r m a l l y p r o c e s s e d f o r c u l i n a r y use through the y e a r . We have p r e v i o u s l y c a r r i e d out s t u d i e s on f r e s h b l a c k truffle aroma by s t r i p and t r a p / dynamic headspace a n a l y s i s . Experiments were c a r r i e d out w i t h t r u f f l e f l e s h ( 1 , 2 ) , e n t i r e t r u f f l e s ( Talou, T. e t a l . , P r o c . 19th I n t e r n a t i o n a l Symposium on E s s e n t i a l O i l s and o t h e r N a t u r a l S u b s t r a t e s , i n p r e s s ; T a l o u , T. e t a l , J . S c i . Food A g r i c . , i n p r e s s ) and by atmospheric c a p t u r e o f s t o r e d truffles aroma ( T a l o u , T. e t a l , P r o c . 3rd C h e m i c a l Congress o f North America, i n p r e s s ) . Since cooks r e p o r t t h a t p r o c e s s e d b l a c k t r u f f l e s have a p a r t i c u l a r aroma which i s d i f f e r e n t and s t r o n g e r than f r e s h t r u f f l e aroma, we d e c i d e d t o i n v e s t i g a t e the v o l a t i l e s o f canned b l a c k truffles. For t h i s purpose, we developed a m o d i f i e d dynamic headspace t e c h n i q u e f o r the a n a l y s i s o f t r u f f l e f l e s h and the a r o m a t i c liquid released during cooking. The aim o f t h i s study was t o i d e n t i f y the v o l a t i l e s o f canned b l a c k t r u f f l e s by c a p i l l a r y gas chromatography - mass spectrometry i n order t o a s s e s s the m o d i f i c a t i o n o f aroma due t o t h e t h e r m a l processing. 0097-6156/89/0409-0346$06.00/0 ο 1989 American Chemical Society Parliment et al.; Thermal Generation of Aromas ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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Experimental.


M a t e r i a l . F r e s h B l a c k P e r i g o r d T r u f f l e s ( Tuber Melanosporum) were purchased by Pebeyre L t d . ( C a h o r s , F r a n c e ) , a company s p e c i a l i z e d i n truffle m a r k e t i n g . These t r u f f l e s were c o l l e c t e d m a i n l y i n the South East o f F r a n c e . They were f u l l y r i p e (3) and r e l e a s e d t h e i r characteristic aroma. The t r u f f l e s were r e c e i v e d t h e day a f t e r g a t h e r i n g i n w i c k e r - b a s k e t s , and then s t o r e d i n c o l d s t o r a g e . A f t e r b r u s h i n g and a d d i t i o n a l h a n d - s o r t i n g , t r u f f l e s were p l a c e d i n 1/8 cans (100 mL) and then i n d u s t r i a l l y p r o c e s s e d by heat treatment a t 115°C f o r 90 min. The w e i g h t s o f a n a l y s e d canned t r u f f l e s ranged from 30 t o 50 g. Sample P r e p a r a t i o n . D u r i n g the t h e r m a l p r o c e s s i n g , t r u f f l e s r e l e a s e d l a r g e amount o f water (25$ o f t h e i r w e i g h t ) . The h i g h l y aromatic juice obtained, called truffle juice, was c h a r a c t e r i s t i c a l l y flavoured. Sampling was c a r r i e d out i m m e d i a t e l y a f t e r the can was opened on b o t h t r u f f l e f l e s h and j u i c e . Headspace Sampling Technique. The method used a new gas chromato g r a p h i c d e s o r p t i o n - c o n c e n t r a t i o n - GC i n t r o d u c t i o n d e v i c e (D.C.I.) based on dynamic headspace a n a l y s i s and a v a i l a b l e from Delsi Instruments ( P a r i s , F r a n c e ) . T h i s a p p a r a t u s made i t p o s s i b l e t o i s o l a t e v o l a t i l e s from b o t h s o l i d and l i q u i d samples ( 4 ) . In the case o f the t r u f f l e j u i c e , a 1 mL sample was put i n a washing bottle topped by a condenser which was k e p t a t 6°C by c i r c u l a t i o n o f c o l d water.Above t h i s was l o c a t e d a f i x e d Tenax t r a p (0,2 g Tenax GC, 60-80 mesh) packed i n t o a 7 cm by 2 mm i . d . s t a i n l e s s s t e e l tube.The system was h e l d a t a c o n t r o l l e d temperature (75°C) and low p r e s s u r e (0.05 p s i ) , w h i l e the washing b o t t l e was purged by a 25 mL/min f l o w o f h e l i u m f o r 12 min. The a p p a r a t u s i s shown i n F i g u r e 1. The t r u f f l e v o l a t i l e s were then c o n c e n t r a t e d and t r a p p e d i n the Tenax t r a p c o o l e d a t -40° C by c i r c u l a t i o n o f l i q u i d nitrogen. By s w i t c h i n g a r o t a r y v a l v e t h e c a r r i e r gas was b a c k f l u s h e d through the t r a p and i n t o the GC column. U s i n g t h e r m a l d e s o r p t i o n a t 240°C aroma v o l a t i l e s were d i r e c t l y t r a n s f e r r e d onto the GC column. A diagram o f the D.C.I, d e v i c e has been r e p o r t e d p r e v i o u s l y (1_). In the case o f the canned t r u f f l e f l e s h , the washing b o t t l e was r e p l a c e d by a d e s o r p t i o n oven and the sample was put i n t o a v e s s e l which was p l a c e d i n the oven. The method was t h e same as we d e s c r i b e d p r e v i o u s l y f o r the study o f f r e s h t r u f f l e f l e s h and c o n d i t i o n s o f a n a l y s i s a r e the same a l s o ( 2 ) . Combined C a p i l l a r y Gas Chromatography-Mass S p e c t r o m e t r y . A GIRDEL 31 gas chromatograph equipped w i t h a D.C.I. system (Delsi I n s t r u m e n t s , P a r i s , F r a n c e ) was c o u p l e d by means o f a g l a s s l i n e d interface t o a NERMAG R10-10B quadrupole mass f i l t e r spectrometer (Nermag L t d . , P a r i s , F r a n c e ) . The system was connected o n - l i n e t o a d e d i c a t e d d a t a p r o c e s s i n g system c o n s i s t i n g i n a D i g i t a l Equipment Co. PDP8 Computer, u s i n g SIDAR s o f t w a r e i n c o r p o r a t i n g the NIH/EPA l i b r a r y o f mass s p e c t r a l d a t a ( 5 ) . The capillary column used was 50 m χ 0.32 mm ( i . d . ) f u s e d s i l i c a UC0N 75H 90000 w a l l c o a t e d cplumn. ( D e l s i I n s t r u m e n t s , Paris,

American Chemical Society Library 1155

15th St., N.W.

Parliment et al.; Thermal Generation Washington, O.C. 20036of Aromas ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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F i g u r e 1. Schematic diagram o f the d e s o r p t i o n f l a s k a) purge g a s ; b) c o l d water 1) washing b o t t l e ; 2) condenser ( w a t e r - j a c k e t ) .

Parliment et al.; Thermal Generation of Aromas ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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France) . The column oven temperature was h e l d 10 min then programmed from 30 t o 180°C a t a r a t e o f 3°C/min w i t h a f i n a l 10-min h o l d . Column i n l e t p r e s s u r e o f h e l i u m was 7 p s i and the splitter f l o w 30 mL/min. S i g n i f i c a n t Mass S p e c t r o m e t r y o p e r a t i o n a l parameters were as f o l l o w s : i o n i z a t i o n v o l t a g e , 70 eV; i o n i z a t i o n c u r r e n t , 200//Λ; source t e m p e r a t u r e , 200°C; e l e c t r o n m u l t i p l i e r v o l t a g e , 1,9 kV; i n t e g r a t i o n t i m e , 1 ms/a.m.u.. For optimum sample t r a n s f e r , a t r a n s f e r temperature o f 200°C was employed.


Reagents. Helium was p u r i f i e d by passage through c h a r c o a l , m o l e c u l a r s i e v e , and an O x i s o r b t r a p . Tenax adsorbent was o b t a i n e d from A l l t e c h A s s o c . Inc ( D e e r f i e l d , 111, USA). C h e m i c a l compounds f o r comparisons o f mass s p e c t r a and GC r e t e n t i o n times were o b t a i n e d from commercial s o u r c e s ( A l d r i c h , Milwankee, Wis, USA). Sensory V a l i d a t i o n o f Sampling and GC Techniques. The sensory e v a l u a t i o n was c a r r i e d out by a p a n e l o f t h r e e judges (employees o f Pebeyre L t d . ) . F o r t h i s s t u d y , an e x t e r n a l odor p o r t was a t t a c h e d t o the gas vent o f the D.C.I, system. A f t e r the t h e r m a l d e s o r p t i o n o f the v o l a t i l e s from the t r a p , the r o t a r y v a l v e was p o s i t i o n e d so t h a t the u n r e s o l v e d aroma i s o l a t e went t o our s n i f f i n g p o r t . The response was mesured as s i m i l a r i t y o r d i s s i m i l a r i t y t o canned b l a c k t r u f f l e aroma. R e s u l t s and D i s c u s s i o n . O p t i m i z a t i o n o f the s a m p l i n g and a n a l y t i c a l t e c h n i q u e s . A l t h o u g h Tenax adsorbent was h y d r o p h o b i c , l a r g e amount o f water could condense on a c o l d Tenax t r a p (6) and then i n t e r f e r e w i t h the a n a l y s i s i n two ways: i ) by p h y s i c a l l y b l o c k i n g a significant portion of the a v a i l a b l e t r a p p i n g s u r f a c e reduced trapping e f f i c i e n c y , d e g r a d i n g b o t h s e n s i t i v i t y and r e p r o d u c i b i l i t y ; i i ) by d e g r a d i n g the column used and i n t e r f e r i n g i n t o the d e t e c t i o n p r o c e s s by e x t i n g u i s h i n g the FID. T h i s problem was p a r t i c u l a r l y i m p o r t a n t i n the case o f a n a l y s i s o f aqueous samples. So i n the case o f the a n a l y s i s o f the t r u f f l e juice, experimental f a c t o r s which i n f l u e n c e d d e s o r p t i o n o f volatile compounds from the sample and t h e i r a d s o r p t i o n on the t r a p , t h a t i s t o say t r a p c o o l i n g t e m p e r a t u r e , amount o f sample, a s h i n g bottle h e a t i n g t e m p e r a t u r e , purge gas f l o w , p u r g i n g time and t r a p r e h e a t i n g t e m p e r a t u r e , had t o be o p t i m i z e d i n o r d e r t o a v o i d b o t h water t r a p p i n g and b r e a k t h r o u g h from the Tenax, i . e . e l u t i o n o f v o l a t i l e s p a r t i a l l y t h r o u g h the t r a p d u r i n g the a d s o r p t i o n phase. The t r a d i t i o n n a l " f a c t o r by f a c t o r " methodology c o n s i s t i n g i n t r e a t i n g each f a c t o r s e p a r a t e l y (by changing j u s t the l e v e l o f one parameter, m a i n t e n i n g o t h e r ones c o n t a n t ) was v e r y time consuming. Furthemore, i f several factors played a r o l e , t h e i r interaction c o u l d not be d i s c e r n a b l e even i f they were dominant because f a c t o r s were o f t e n i n t e r d e p e n d e n t ( 7 - 9 ) . On the o p p o s i t e , the "factorial methodology" a l s o c a l l e d E x p e r i m e n t a l Designs method, makes i t p o s s i b l e t o o b t a i n the maximum i n f o r m a t i o n w i t h minimum t e s t s ( f o r each f a c t o r , d i f f e r e n t l e v e l s were f i x e d and combined w i t h one another according to a f a c t o r i a l experimental design). This methodology was s u c e s s f u l l y applied i n other f i e l d s of a n a l y t i c a l c h e m i s t r y e.g., atomic and plasma e m i s s i o n spectometry (10-14 ).


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A f r a c t i o n a l f a c t o r i a l d e s i g n was s e l e c t e d f o r the s t u d y of the f i v e e x p e r i m e n t a l f a c t o r s r e t a i n e d . The responses measured were the t o t a l peaks a r e a and the number o f p e a k s , o b t a i n e d w i t h an ENICA 10 i n t e g r a t o r ( D e l s i I n s t r u m e n t s , P a r i s , F r a n c e ) . The c o m p u t e r i z e d t r e a t m e n t o f the r e s u l t s (15) a l l o w e d us t o q u a n t i f y the main e f f e c t and i n t e r a c t i o n e f f e c t s o f the f i v e f a c t o r s under s t u d y and s u b s e q u e n t l y t o determine the optimum c o n d i t i o n s o f a n a l y s i s ( T a l o u , T. Chromatographia, i n p r e s s . ) . Under our o p t i m i z e d s a m p l i n g c o n d i t i o n s , no b l o c k i n g o f the trap ( v i s u a l l y v e r i f i e d a t the manometer o f the s c a v e n g i n g gas c i r c u i t ) and no l o s s e s o f v o l a t i l e s d u r i n g the a d s o r p t i o n phase ( s e n s o r i a l l y v e r i f i e d a t the odor p o r t ) were observed. The v o l a t i l e i s o l a t e desorbed and s e n s o r i a l l y a s s e s s e d a t our odor p o r t was d e s c r i b e d as t y p i c a l o f p r o c e s s e d black truffle, showing t h a t the Tenax had adsorbed and desorbed v o l a t i l e components r e s p o n s i b l e f o r canned b l a c k t r u f f l e aroma. I d e n t i f i c a t i o n o f v o l a t i l e s compounds. Separate gas chromatographic - mass s p e c t r o m e t r i c a n a l y s i s were made on f i v e d i f f e r e n t canned t r u f f l e s p r o c e s s e d d u r i n g the January - March I987 p e r i o d . The chromatographic p r o f i l e s o f headspace v o l a t i l e s from canned f l e s h and j u i c e were s i m i l a r , but more i n t e n s e i n the case o f the juice. A t y p i c a l t o t a l i o n c u r r e n t chromatogram o f the Tenax trapped canned b l a c k t r u f f l e (Tuber Melanosporum) j u i c e v o l a t i l e s i s shown i n F i g u r e 2. The compounds i d e n t i f i e d by GC-MS are l i s t e d i n T a b l e I i n the o r d e r o f e l u t i o n from the GC column w i t h t h e i r c h a r a c t e r i s t i c mass s p e c t r a l d a t a . The i d e n t i f i c a t i o n o f these compounds was based on comparison o f the mass s p e c t r a o b t a i n e d w i t h those s t o r e d i n the NIH/EPA library and a l s o w i t h those o f a u t h e n t i c compounds. Moreover, an a d d i t i o n a l s e a r c h o f p u b l i s h e d s t a n d a r d mass s p e c t r a t o confirm the identity of unknowns was undertaken (16). The major v o l a t i l e components i d e n t i f i e d i n canned b l a c k t r u f f l e s were a l c o h o l s and carbonyls, including acetaldehyde, acetone, 2-butanone, 2 - m e t h y l - l - p r o p a n o l and the two methyl-1b u t a n o l s . A l s o i n r e l a t i v e l y l a r g e amount was d i m e t h y l s u l f i d e . Found i n p r o c e s s e d t r u f f l e s but absent i n f r e s h t r u f f l e s were two f u r a n s (compound 4 and 7) and a p y r a z i n e (compound 2 4 ) . Furans are w e l l known t o r e s u l t from the t h e r m a l degradation of carbohydrates w h i l e a l k y l p y r a z i n e s r e s u l t from the r e a c t i o n o f amino a c i d s and a l p h a - d i k e t o n e s . A number o f methyl ketones were a l s o observed i n the canned p r o d u c t which were absent i n the f r e s h product. Methyl ketones are known t o r e s u l t from the thermal decomposition of beta-keto a c i d s (17-19). M o d i f i c a t i o n o f F l a v o r Due t o Thermal P r o c e s s i n g . Despite the s i m i l a r i t y o f the chromatographic p r o f i l e s o f headspace v o l a t i l e s o f canned and f r e s h t r u f f l e s , a s e n s o r y a n a l y s i s c a r r i e d out by a p a n e l o f e x p e r t s r e p o r t e d a marked d i f f e r e n c e between the two aromas. Aroma i s o l a t e s o f p r o c e s s e d and unprocessed t r u f f l e s which were assessed a t our odor p o r t were d e s c r i b e d as t y p i c a l o f the r e s p e c t i v e aromas. S i n c e the most s t i k i n g d i f f e r e n c e between canned and fresh truffle aroma was the presence o f some minor c o n s t i t u e n t s , t h i s


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12

19

22+23

16 15 18 il?

200

600

20

1000

32

1

21

1400

1800

3 3

2200

3

5

2600

3000

SCAN NUMBER

Figure 2 . Reconstructed c a p i l l a r y GC-total i o n current chromatogram o f headspace v o l a t i l e s o f canned b l a c k t r u f f l e (Tuber Melanosporum) j u i c e .



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Table I .


Peak Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

V o l a t i l e compounds i d e n t i f i e d i n canned B l a c k T r u f f l e (Tuber Melanosporum)

Compound

Mass S p e c t r a l Data 0

acetaldehyde dimethyl s u l f i d e propanal furan acetone 2-methylpropanal 2-methyl f u r a n ethyl acetate 2-butanone 2-methylbutanal 3-methylbutanal ethanol 2-pentanone chloroform 2-butanol 1-propanol dimethyl d i s u l f i d e 2-methyl-2-butenal 2-methyl-1-propanol 1-butanol 2-heptanone 2-methyl-1-butanol 3-methyl-1-butanol 2-methyl p y r a z i n e 1-pentanol 3-octanone 2-octanone anisole 1-hexanol 3-octanol methyl a n i s o l e l-octen-3-ol acetic acid 2-ethyl-1-hexanol benzaldehyde 2-formyl thiophene

29,44,43,42 42,62,45,46 29,28,27,58 39,68,29,38 43,58,42,39 43,41,72,27 82,53,39,81 43,29,61,45 43,72,29,27 41,57,29,58 44,41,43,29 31,45,46,29 43,86,27,29 83,85,47,48 45,31,59,29 31,29,42,27 94,45,79,46 55,84,29,27 43,33,42,41 31,56,41,43 43,58,41,71 41,29,57,56 41,29,42,55 94,28,67,40 42,55,31,70 43,57,29,99 43,58,71,41 108,78,65,39 56,43,55,42 59,55,41,83 122,91,107,77 57,43,29,72 45,43,60,28 57,43,55,56 105,106,77,51 111,112,39,45

Ident. Present i n GC,MS canned f r e s h GC,MS GC,MS GC,MS MS GC,MS GC,MS MS MS GC,MS GC,MS GC,MS GC,MS MS MS GC,MS GC,MS MS MS GC,MS MS MS GC,MS GC,MS MS MS MS MS GC,MS MS MS MS MS GC,MS MS GC,MS MS

+

+

+

+

+

+

+

-

+

+

+

+

+

-

+

+

+

+

+

+

+

+

+

+

+

-

+

+

+

+

+

+

+

+

+

-

+

+

+ +

-

+

+

+

+

+

-

+ + +

-

-

+

+

+

+

-

+

+

+

-

+

+

+

+

+ +

Rel. % i n canned 3 6 0.2 0.3 10 6 tr 0.2 5 5 tr 30 tr tr 0.5 1 tr 0,1 17 tr tr 15 tr tr tr tr tr 0.5 tr tr 0.1 tr tr tr 0.1 tr

a) The peak numbers c o r r e s p o n d t o numbers i n F i g u r e 2; b) The f o u r most i n t e n s e peaks a r e r e p o r t e d ; c ) key: + = p r e s e n t ; - = n o t d e t e c t e d ; d) key : t r =

Thermal Generation of Aromas - American Chemical Society

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