Quality of Selected Fruits and Vegetables of North America - American

11 Volatile Constituents of Pumpkins THOMAS H. PARLIMENT, MICHAEL G. KOLOR, DONALD J. RIZZO, and DENISE HERZING-GIORDANO

Downloaded by UNIV OF ARIZONA on January 15, 2013 | http://pubs.acs.org Publication Date: November 11, 1981 | doi: 10.1021/bk-1981-0170.ch011

General Foods Corporation, Technical Center, 250 North Street, White Plains, NY

Pumpkins (Cucurbita pepo) are a member of the family Cucurbitaceae which includes squashes, melons, pumpkins and cucumbers. Pumpkins are of New World origin and are believed to have been important in the diet of aboriginal Americans. The flavor composition of the Cucurbits has received little attention though other members of the Cucurbitaceae have been investigated. For example, the carbonyl compounds of fresh cucumbers (Cucumis sativus) were studied almost 20 years ago (1). More recently, the total volatile composition of d i s t i l l e d cucumbers was investigated by a number of groups (2,3). The steam volatile compounds of muskmelons (Cucumis melo) have also received attention (4,5,6) as have those of watermelons (Citrullus vulgaris) (7). The most striking feature in the volatile components of a l l these fruits is the variety and magnitude of the ninecarbon compounds. These compounds include nonanol, nonanal, various nonenols, nonadienols, nonenals and nonadienals. The purpose of this study is to identify the major volatile components of freshly cooked pumpkins and to compare these to the volatiles of commercially canned pumpkins.

0097-6156/81/0170-0129$05.00/0 © 1981 American Chemical Society In Quality of Selected Fruits and Vegetables of North America; Teranishi, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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Sample P r e p a r a t i o n In a t y p i c a l experiment, 4 k g o f f r e s h , l o c a l l y grown pumpkins ( v a r i e t y : Connecticut f i e l d ) were homogenized w i t h 2 L o f water and t h i s s l u r r y was p l a c e d i n a 12 L t h r e e - n e c k e d flask. The sample was h e a t e d a t r e f l u x f o r 3 hours using a modified Likens-Nickerson d i s t i l l a t i o n head (.8) . The d i s t i l l a t i o n was performed a t a t m o s p h e r i c p r e s s u r e and d i e t h y l e t h e r was used as the e x t r a c t i n g s o l v e n t . The e t h e r e a l concen t r a t e was d r i e d o v e r anhydrous sodium s u l f a t e , f i l t e r e d and c o n c e n t r a t e d u s i n g a low h o l d - u p d i s t i l l a t i o n column by the u s u a l p r o c e d u r e . F o r our s t u d i e s o f canned pumpkin, 1.2 kg o f c o m m e r c i a l l y canned pumpkin ( i n g r e d i e n t l i n e r e a d s : pumpkin, water) were combined w i t h 800 ml water and the s l u r r y was worked up i n the same f a s h i o n as was the f r e s h pumpkin. S e p a r a t i o n and

Identification

S e p a r a t i o n o f the m i x t u r e was a c c o m p l i s h e d by g a s - l i q u i d chromatography (GLC) i n a P e r k i n - E l m e r Model Sigma I I ( P e r k i n - E l m e r C o r p o r a t i o n , South Norwalk, C o n n e c t i c u t ) u s i n g a c a p i l l a r y column. The chromatograph had an a l l g l a s s l i n e a r s p l i t t e r ( s p l i t 80:1) and a h e l i u m l i n e a r v e l o c i t y o f 23 cm/sec. A P e r k i n - E l m e r f u s e d s i l i c a column was used which measured 0.235 mm i d , χ 25 m l o n g and w h i c h was c o a t e d w i t h OV-101 (methyl s i l i c o n e ) l i q u i d phase. The column was h e l d 4 min a t 45°C then programmed a t 3°C/min t o 120°C. Mass s p e c t r a were o b t a i n e d u s i n g tandem gas chromatography/mass spectrometry. The column e f f l u e n t was p a s s e d i n t o the i o n s o u r c e o f a DuPont Model 21-491 mass s p e c t r o m e t e r (DuPont Instrument D i v i s i o n , W i l m i n g ton, D e l a w a r e ) . Mass s p e c t r a were o b t a i n e d a t 70 eV and a s o u r c e temperature o f 200°C.

In Quality of Selected Fruits and Vegetables of North America; Teranishi, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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Volatile Constituents of Pumpkins

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Component i d e n t i f i c a t i o n was a c c o m p l i s h e d b y comparison o f mass s p e c t r a and gas c h r o m a t o g r a p h i c r e t e n t i o n times o f t h e i s o l a t e d m a t e r i a l s t o t h a t o f known s t a n d a r d s which were c o m m e r c i a l l y a v a i l a b l e o r i n our reference l i b r a r y . Retention indices r e l a t i v e t o e t h y l e s t e r s (9) were c a l c u l a t e d f o r a l l peaks and compared t o t h o s e o f a u t h e n t i c compounds o r t o t h e values l i s t e d i n our f i l e s . Sample q u a n t i t a t i o n was p e r f o r m e d on a P e r k i n - E l m e r Sigma 10 d a t a system. P e r c e n t o f each component (on a s o l v e n t f r e e b a s i s ) was c a l c u l a t e d , u s i n g r e s p o n s e f a c t o r s o f 1. RESULTS AND DISCUSSION I d e n t i f i c a t i o n o f t h e major components o f cooked pumpkins i s p r e s e n t e d i n T a b l e I and t h e gas chromatogram i s shown i n F i g u r e 1. TABLE I VOLATILE COMPONENTS OF FRESHLY COOKED PUMPKINS PEAK % COMNUMBER^ POSITION IDENTITY 6.2 1 Diacetyl 2 0.9 Ethyl Acetate 2.6 3 E t h y l Furan 4 1.3 3-Pentanone 5 2.7 Pyridine 6 1.5 2-Pentenal 7 1.8 1-Pentanol 8 n-Hexanal 11.1 1.5 9 Furfural 0.4 10 2-Methyl-2-Pentenal 17.8 2-Hexenal 11 12 20.6 cis-3-Hexenol 13 21.6 n-Hexanol 14 0.5 Methional 0.2 15 2-Heptanone 0.4 16 2-Heptenal 0.4 17 Benzaldehyde 0.5 18 l-Octene-3-ol 19 0.8 P e n t y l Furan 0.6 20 Phenyl Acetaldehyde 0.6 21 M e t h y l Thiophene Carboxyaldehyde 22 0.7 Phenyl Ethanol (1) As I n d i c a t e d i n F i g u r e 1



TIME, MIN.

10

18 19

12

τ

20

21

14

16

Τ

Figure 1. Gas chromatogram of volatile components offreshlycooked pumpkins

6

8

4

16 17

2

1415

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22

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E TA L .

The s u r p r i s i n g f e a t u r e o f t h i s f r u i t i s t h e q u a n t i t y o f s i x - c a r b o n a l c o h o l s and a l d e h y d e s . Taken as a group, t h e s e compounds c o n s t i t u t e o v e r 70% o f t h e total volatiles. We had f u l l y e x p e c t e d t o f i n d a v a r i e t y o f n i n e - c a r b o n compounds i n o u r essence and we s p e c i f i c a l l y l o o k e d f o r them s i n c e they a r e t h e major v o l a t i l e s i n o t h e r C u c u r b i t a c e a e . F o r example, n o n a n a l , 2-nonenal, 6-nonenal and 2 , 6 - n o n a d i e n a l a r e some o f the major components o f cucumber (3_) and 6nonenol i s the major compound i n f r o z e n muskmelon (5_) . None o f t h e s e compounds were found; i f p r e s e n t , t h e y a r e below t h e 1% l e v e l . The i d e n t i t i e s o f the major v o l a t i l e components o f commercial canned pumpkin a r e p r e s e n t e d i n T a b l e I I and t h e gas chromatogram i s shown i n F i g u r e 2. TABLE I I

PEAK NUMBER(2) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

VOLATILE COMPONENTS OF COMMERCIALLY CANNED PUMPKINS

IDENTITY Diacetyl Ethyl Acetate iso Valeraldehyde 2-Methyl B u t a n a l 2,3-Pentanedione Pyridine Toluene 2-Methyl T e t r a h y d r o f u r a n - 3 - o n e Furfural 2-Methyl-2-Pentenal c i s-3-Hexeno1 M e t h y l F u r y l Ketone 2,5-Dimethyl P y r a z i n e Dimethyl T r i s u l f i d e Phenyl Acetaldehyde (2)

% COMPOSITION 8.7 2.0 4.1 16.7 2.4 15.1 1.1 1.6 15.0 3.2 3.5 0.5 0.9 0.9 2.2

As I n d i c a t e d i n F i g u r e 2.

The compounds h e r e a r e d r a m a t i c a l l y d i f f e r e n t from t h o s e i n f r e s h cooked pumpkin. T h i s i s b e s t shown i n T a b l e I I I where t h e 10 major compounds o f each sample a r e compared.


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TABLE I I I


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COMPARISON OF COMPONENTS IN PUMPKINS

RANK 1 2 3 4 5 6 7 8 9 10

FRESH COOKED IDENTITY n-Hexanol cis-3-Hexenol 2-Hexenal n-Hexanal Diacetyl Pyridine E t h y l Furan Furfural 3-Pentanone Ethyl Acetate

% COMPOSITION 21.2 20.6 17.8 11.1 6.2 2.7 2.6 1.5 1.3 0.9

RANK 1 2 3 4 5 6 7 8 9 10

CANNED IDENTITY 2-Methyl B u t a n a l Pyridine Furfural Diacetyl i s o Valeraldehyde 2-Methyl-2-Pentenal cis-3-Hexenol 2,3-Pentanedione Phenyl Acetaldehyde Ethyl Acetate

% COMPOSITION 16.7 15.1 15.0 8.7 4.1 3.2 3.5 2.4 2.2 2.0

V i r t u a l l y a l l o f t h e s i x - c a r b o n a l d e h y d e s and a l c o h o l s found i n f r e s h l y cooked pumpkin have been l o s t . Furf u r a l h a s i n c r e a s e d s i g n i f i c a n t l y and 2-methyl t e t r a h y d r o f u r a n - 3 - o n e h a s appeared. These changes a r e l i k e l y due t o t h e s e v e r e t h e r m a l p r o c e s s i n g canned pumpkins must r e c e i v e . Pumpkins a r e a low a c i d food w h i c h h e a t p r i m a r i l y b y c o n d u c t i o n and as such r e q u i r e extended p r o c e s s i n g times a t 250°F o r h i g h e r . F u r f u r a l i s a w e l l known c o n s t i t u e n t o f t h e r m a l l y decomposed c a r b o h y d r a t e s , and t h e furanone as w e l l as t h e f u r y l - k e t o n e have been r e p o r t e d i n numerous cooked food p r o d u c t s (10). 2-Methyl b u t a n a l and i s o v a l e r a l d e h y d e a r e a l s o common c o n s t i t u e n t s o f p r o -



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c e s s e d foods w h i c h c a n a r i s e from t h e s t r e c k e r D e g r a d a t i o n o f i s o l e u c i n e and l e u c i n e , r e s p e c t i v e l y . S i m i l a r l y , model system s t u d i e s have shown t h a t d i m e t h y l p y r a z i n e s r e s u l t from h e a t i n g sugar and amino a c i d s t o g e t h e r . Thermal p r o c e s s i n g d o u b t l e s s r e s u l t s i n t h e o t h e r q u a l i t a t i v e and q u a n t i t a t i v e d i f f e r e n c e s w h i c h a r e e v i d e n t when f r e s h l y cooked and canned pumpkins a r e compared. A n o t h e r i n t e r e s t i n g f e a t u r e o f b o t h f r e s h l y cooked and canned pumpkins i s t h e v i r t u a l absence o f e s t e r s . This i s u n u s u a l s i n c e t h e v o l a t i l e f l a v o r components o f most f r u i t s a r e r i c h i n e s t e r s , y e t a l l we found were q u i t e low l e v e l s o f e t h y l a c e t a t e .

LITERATURE CITED 1.

Forss, D.A., Dunstone, E . A . , Ramshaw, E . H . , Stark, W., J. Food Sci. 1962, 27 90. 2. Hatanaka, Α . , Kajiwara, T . , Harada, T . , Phytochemistry 1975, 14 2589. 3. Kemp, T.R., Knavel, D . E . , Stoltz, L . P . , J. Agr. Food Chem. 1974, 22 717. 4. Kemp, T.R., Stoltz, L . P . , Knavel, D . E . , J. Agr. Food Chem. 1972, 20 196. 5. Kemp, T.R., Knavel, D . E . , Stoltz, L . P . , Phytochemistry 1973, 12 2921. 6. Yabumoto, K . , Jennings, W.G., J. Food Sci. 1977, 42 32. 7. Kemp, T.R., Knavel, D . E . , Stoltz, L . P . , Lundin, R . E . , Phytochemistry 1974 , 13 1167. 8. Schultz, T . H . , Flath, R.A., Mon, T.R., Eggling, S.B., Teranishi, R., J . Agr. Food Chem. 1977, 25 446. 9. van den Dool, H . , Kratz, P., J . Chrom. 1963, 11 463. 10. van Straten, S., Volatile Compounds in Food. 4th. Edition, including Supplement 1 and 2. Central Institute for Nutrition and Food Research, Zeist, Netherlands, 1978. RECEIVED

April 3, 1981.


Quality of Selected Fruits and Vegetables of North America - American

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