16 Quality of Selected Fruits and Vegetables of North America Downloaded from pubs.acs.org by UNIV OF CALIFORNIA SAN DIEGO on 03/30/16. For personal use only.
Lipid Oxidation in Fruits and Vegetables ROLAND TRESSL, DAOUD BAHRI, and KARL-HEINZ ENGEL Technische Universität Berlin, Seestrasse 13, D-1000 Berlin 65, West Germany
The enzymic formation of aldehydes, ketones, a l c o hols, and oxoacids (from l i n o l e i c and l i n o l e n i c acids) on d i s r u p t i o n of plant tissues i s an important b i o synthetic pathway by which f r u i t and vegetable volatiles are formed. Some examples are: (E)-2-hexenal ("leaf aldehyde") and (Z)-3-hexenol ("leaf alcohol") i n tea; (E)-2-hexenal in apples; (Ε,Ζ)-2,6-nonadienal ("violet leaf aldehyde") and (E)-2-nonenal in cucumber; (Z)-6-nonenal in musk melon; (Ζ,Ζ)-3,6-nonadienol i n water melon, and 1-octen-3-ol ("mushroom alcohol") i n c e r t a i n edible mushrooms and Fungi. The enzyme system i s highly substrate s p e c i f i c to a (Ζ,Z)1,4-pentadiene system ( l i k e lipoxygenase) s p l i t t i n g the >C = C< double bond at the W - 6 and/or W - 9 p o s i t i o n . There fore l i n o l e i c - , l i n o l e n i c - , and arachidonic acids are natural substrates. I t seems to be a common p r i n c i p l e i n leaves, f r u i t s , vegetables, and basidiomycetes. Some of the v o l a t i l e s formed are known as important aroma components, pheromonones or wound hormones. In 1966 our experiments with f r u i t homogenates showed that l i n o l e n i c acid i s transformed into (Z)3hexenal, (E)-2-hexenal and the corresponding alcohols. By means of radio l a b e l i n g experiments with r i p e bananas we could demonstrate that the precursor i s converted into (E)2-hexenal and 12-oxo-(E)-10-dodecenoic acid. Green bananas decomposed ( U - C ) l i n o l e n i c acid into (Ε,Z)-2,6-nonadienal and 9-oxononanoic acid (1,2). 14
F i g u r e 1 shows Cg-, C 9 - , C 3 - , C-|o~/ ^ 12" components which a r e formed from l i n o l e n i c a c i d i n c e r t a i n p l a n t s , f r u i t s , v e g e t a b l e s , and mushrooms. There a r e n o r m a l l y f o u r enzymes i n v o l v e d which seem t o be membrane bonded and l o c a t e d i n t h e c h l o r o p l a s t s . I n 1970 we t r i e d t o i s o l a t e and c h a r a c t e r i z e t h e s e e n zymes and c o u l d demonstrate t h a t l i p o x y g e n a s e ( E l ) , an a n c
0097-6156/81/0170-0213$05.00/0 © 1981 American Chemical Society
c
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QUALITY
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FRUITS
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a l c o h o l o x i d o r e d u c t a s e (E4) , and a (Z) -3 / ( E ) - 2 - i s o merase (E3) a r e o p e r a t i v e i n r i p e and g r e e n bananas and a p p l e s . We f a i l e d t o i s o l a t e an a c t i v e enzyme E2 c o n v e r t i n g the 13-L00H i n t o h e x e n a l (and C-j 2~°xoacid) o r 13-LnOOH i n t o (ZJ-3-hexenal and ( E ) - 2 - h e x e n a l . T h i s was p r e t t y f r u s t r a t i n g because t h e enzyme E2 showed a v e r y h i g h a c t i v i t y i n homogenates and t i s s u e s l i c e s b u t no a c t i v i t y a t a l l i n the i s o l a t e s . We s t o p p e d our e x p e r i m e n t s and c a l l e d E2 = "aldehyde l y a s e " . In 1976 V i c k and Zimmerman (_3) demonstrated a " h y d r o p e r o x i d e l y a s e " a c t i v i t y i n water melon s e e d l i n g s and i n 1977 1978 G a l l i a r d and coworkers (_4, 5, 6) c h a r a c t e r i z e d a " h y d r o p e r o x i d e c l e a v i n g enzyme" from f r u i t s o f cucum b e r s and tomatoes. The c l e a v i n g enzyme E2 was l o c a t e d i n the c h l o r o p l a s t s and o t h e r s u b c e l l u l a r membranes and l o s t i t s a c t i v i t y d u r i n g p u r i f i c a t i o n . 13- and 9-L00H were good s u b s t r a t e s b u t n o t the c o r r e s p o n d i n g hydroxy a c i d s o r k e t o l s . On t h e o t h e r hand Hatanaka and coworkers (]_) i n v e s t i g a t e d an enzyme system i n Thea s i n e n s i s c h l o r o p l a s t s which c o n v e r t e d ( U - 1 4 c ) l i n o l e n i c a c i d i n t o {Z)-3-hexenal, (E) -2-hexenal, and 12- oxo-(^Z)-9-, and 1 2-oxo- (E)-10-dodecenoic acids. (Ζ,Ζ)-3,6-nonadienoic a c i d was a l s o c o n v e r t e d i n t o (Z)-3-hexenal. Therefore E i n Thea c h l o r o p l a s t s seems t o be no l i p o x y g e n a s e system. Many p l a n t s (and f r u i t s ) p o s s e s s l i p o x y g e n a s e but no c l e a v i n g enzymes E2. The hydroperoxides are converted i n t o carbonyls, a l c o h o l s , and o x o a c i d s by c h e m i c a l r e a c t i o n s (examples: cooked asparagus, p o t a t o e s , m a l t ) . The p r o d u c t s i n t h e s e systems a r e comparable t o t h o s e o f the a u t o x i d a t i o n o f fatty acids. 2
F o r m a t i o n o f C a r b o n y l s and Oxoacids Reactions
by
Chemical
Thermal o x i d a t i o n , a u t o x i d a t i o n , and l i g h t i n d u c e d o x i d a t i o n w i t h o u t s e n s i t i z e r produce 9- and 13-L00H from l i n o l e i c a c i d , which a r e decomposed t o h e x a n a l , 13- O X O - 9 , 1 1 - t r i d e c a d i e n o i c a c i d , 9-oxononanoic a c i d , c a p r y l i c a c i d , and 2 , 4 - d e c a d i e n a l s as major components. T h i s i s demonstrated i n F i g u r e 2 and T a b l e I . M e t h y l l i n o l e a t e was d i s s o l v e d i n e t h a n o l / w a t e r and i r r a d i a t e d w i t h l i g h t a t 25°C i n t h e p r e s e n c e o f oxygen du r i n g 5 t o 20 h r . The v o l a t i l e s were i s o l a t e d and i n v e s t i g a t e d by c a p i l l a r y gas chromatography-mass s p e c t r o m e t r y , and p r e p a r a t i v e gas c h r o m a t o g r a p h y - i n f r a r e d s p e c t r o s c o p y . The r e s u l t s and methods used w i l l be p u b l i s h e d i n d e t a i l ( B a h r i and T r e s s l , 1981) . S i m i l a r r e s u l t s were r e c e n t l y p r e s e n t e d by Chan e t a l . (_8) who i n j e c t e d 13- and 9-L00H i n the i n j e c t i o n p a r t o f a
16.
Lipid Oxidation in Fruits and Vegetables
TRESSL E T A L .
215
12-0X0-(Z)-9-D0DECEN0IC ACID [Î0-0X0- (E) -8jDECE_N0IC _AÇIDJ 9-0X0N0NAN0IC ACID LINOLENIC ACID CH-,CH CH=CH-CH -CH=CH-;CH -CH=CH- (CH ) -CCX)H
Quality of Selected Fruits and Vegetables of North America Downloaded from pubs.acs.org by UNIV OF CALIFORNIA SAN DIEGO on 03/30/16. For personal use only.
0
0
0
2
?
I (Z)-3-HEXENAL (Ε)-2-HEXENAL : ( Ζ,Z)-3,6-NONADIENAL. ;: (Ε,Z)-2,6-NONADIENAL: I 1,5-0CTADIEN-3-0NE| I 1 5-0CTADIEN-3-0L _ J I 2,5-0CTADIEN-1-OL /
Figure 1.
Figure 2.
Various components formed from linolenic acid in certain plants, fruits, and vegetables
Thermal oxidation, autoxidation, and light-induced oxidation without sensitizer
216
QUALITY
Table I
OF SELECTED
FRUITS A N D V E G E T A B L E S
F o r m a t i o n o f V o l a t i l e s by L i g h t Induced O x i d a t i o n o f M e t h y l L i n o l e a t e (ML) I CW2QM ML+( 0 ) MLH- OO2) Precursor (OV 101) ug/mg ML ug/mg ML MLOOH 3
K
Quality of Selected Fruits and Vegetables of North America Downloaded from pubs.acs.org by UNIV OF CALIFORNIA SAN DIEGO on 03/30/16. For personal use only.
Component
2
1
Hexanal
1060
3,8
5,4
13-ML00H
2
2-Pentylfuran
1205
0,73
1,6
1O-ML0OH
3
1-0cten-3-on
1286
-
0,4
1O-ML0OH
4
(E)-2-Heptenal
1296
1,38
13,8
12HVIL00H 9-MLOOH
5 Methyl caprylate
1372
9,6
13,8
1-0cten-3-ol
1394
0,4
1,3
10-ML00H
7 2-Octenal 3- Nonenal
1404 1414
0,2
2,3 0,7
10-MDOOH 1O-ML00H
8 2-Nonenal
1510
0,08
0,48
1CHVIL00H
6
9
(E,Z) -2,4-Decadienal
1743
2,8
4,0
9-^L00H
10
(E,E)-2,4-Decadienal
1781
5,9
7,6
9-ML00H
Methyl 8-oxooctanoate 1925
0,7
0,95
9-MLOOH
4,5
5,7
9-MLOOH
0,08
0,25
11
12 Methyl 9-oxononanoate 2010 13
Methyl 8-(2'-furyl) - 2097 octanoate
14 Methyl 10-oxo-(E)-8decenoate
2278
0,78
12-ML0ŒÎ 13-ML00H
11,4
1O-ML0OH
15
Methyl 11-oxo-9undecenoate
(1780)
0,8
2,8
1O-ML0OH 12-ML00H
16
Methyl 12-oxo-10dodecenoate
(1982)
0,2
0,9
12-MLOOH 13-ML00H
17 Methyl 13-oxo-(9 11)- (2175) tridecadienoate
1,2
2,6
13-ML00H
/
a)
Methyl linoleate solution was irradiated with light, presence of oxygen, without sensitizer (autoxidation)
b)
Methyl linoleate irradiated under same conditions, with methylene blue as sensitizer (photo-oxidation)
Quality of Selected Fruits and Vegetables of North America Downloaded from pubs.acs.org by UNIV OF CALIFORNIA SAN DIEGO on 03/30/16. For personal use only.
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ET AL.
Lipid Oxidation in Fruits and Vegetables
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GC-system. The r e s u l t s o f t h e analogous p h o t o - o x i d a t i o n w i t h methylene b l u e as s e n s i t i z e r a r e p r e s e n t e d i n F i g u r e 2 and T a b l e I . D u r i n g t h i s r e a c t i o n oxygen i s t r a n s f o r m e d i n t o t h e s i n g l e t s t a t e , which may attack C = C MS Rt/ MS, IR R f MS, IR R f MS R f MS, IR R f MS
Quality of Selected Fruits and Vegetables of North America Downloaded from pubs.acs.org by UNIV OF CALIFORNIA SAN DIEGO on 03/30/16. For personal use only.
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AL.
Lipid Oxidation in Fruits and Vegetables
229
A l l oxo- and hydroxy a c i d s were c h a r a c t e r i z e d f o r the f i r s t time as enzymic d e g r a d a t i o n p r o d u c t s from l i n o l e i c a c i d . The major components 1 - o c t e n - 3 - o l and 1 , 5 - o c t a d i e n - 3 - o l were o p t i c a l l y a c t i v e . T h i s was proved by f o r m a t i o n o f an e s t e r w i t h an o p t i c a l l y a c t i v e a c i d and c a p i l l a r y s e p a r a t i o n . The methods used w i l l be p u b l i s h e d i n the near f u t u r e ( T r e s s l and Engels 1981). These r e s u l t s i n d i c a t e a h i g h l y s p e c i f i c enzy me-system i n A g a r i c u s c a m p e s t r i s c a t a l y z i n g the con v e r s i o n o f l i n o l e i c a c i d i n t o ( - ) - 1 - o c t e n - 3 - o l and 10-hydroxydecanoic a c i d r e s p . i n t o (JZ) -2-octen-1 - o l and 9-hydroxydecanoic a c i d . As demonstrated i n T a b l e V I l i n o l e n i c a c i d i s t r a n s f o r m e d i n t o the c o r r e s p o n d i n g Cs-components c o n t a i n i n g two C = C
