Thermal Generation of Aromas - American Chemical Society

Chapter 31

Downloaded by UNIV OF MICHIGAN ANN ARBOR on February 18, 2015 | http://pubs.acs.org Publication Date: October 3, 1989 | doi: 10.1021/bk-1989-0409.ch031

Thermally Degraded Flavors in Citrus Juice Products 1

2

S. Nagy , R. L. Rouseff , and H. S. Lee 1

1

Citrus Research and Education Center, Florida Department of Citrus, 700 Experiment Station Road, Lake Alfred, F L 33850 Citrus Research and Education Center, University of Florida, 700 Experiment Station Road, Lake Alfred, F L 33850 2

Undesirable flavors in citrus juice products are produced by thermal processing and prolonged product storage. Substrates responsible for thermally degraded flavors are essential oils, phenolic acids, sugars, lipids, ascorbic acid and sulfur-containing compounds. Identified detrimental flavor compounds originating from these substrates include 4-vinyl guaiacol, α-terpineol, 1,4-cineole, p-cymene, p-cymen-8-ol, α,p-dimethylstyrene, 2,5-dimethyl-4-hydroxy-3(2H)furanone, dimethyl sulfide and trans, trans-2,4decadienal. Heated and cardboard (oxidized) flavors have been recognized in single-strength and concentrated juices, but the causative agents have not been identified.

F l a v o r d e g r a d a t i o n i s t h e s i n g l e most i m p o r t a n t f a c t o r i n q u a l i t y l o s s o f c i t r u s j u i c e p r o d u c t s . The o v e r a l l f l a v o r d e g r a d a t i o n i s a complex s e r i e s o f c h e m i c a l r e a c t i o n s i n v o l v i n g d i f f e r e n t s u b s t r a t e s , r e a c t i o n r a t e s , ζ-values and pH. Changes o c c u r r i n g i n c i t r u s j u i c e d u r i n g t h e r m a l p r o c e s s i n g and s t o r a g e may be c o n s i d e r e d a s l o s s o f o r i g i n a l f l a v o r and development o f f l a v o r s f o r e i g n t o f r e s h l y e x p r e s s e d j u i c e ( 1 ) . D u r i n g t h e p a s t 40 y e a r s , s e v e r a l t h e o r i e s have been proposed t o e x p l a i n o r i g i n s and causes o f t h e r m a l l y degraded f l a v o r s i n c i t r u s j u i c e s : ( a ) changes i n e s s e n t i a l o i l c o n s t i t u e n t s , (b) changes i n l i p i d c o n s t i t u e n t s , ( c ) f o r m a t i o n o f p h e n o l i c and s u l f u r - c o n t a i n i n g compounds, and ( d ) b y - p r o d u c t s o f nonenzymic browning from s u g a r s , a s c o r b i c a c i d and amino a c i d s ( 2 ) . A d d i t i o n a l l y , c a r d b o a r d o f f - f l a v o r (COF) and N O T E : This chapter is journal paper number 1 0 6 4 8 of the Missouri Agricultural Experiment Station. 0097-6156/89/0409-0331$06.00/0

© 1 9 8 9 American Chemical Society

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

332

THERMAL GENERATION OF AROMAS h e a t e d o f f - f l a v o r have been r e c o g n i z e d f o r many y e a r s ; however, the compounds r e s p o n s i b l e f o r these o f f - f l a v o r s remain t o be identified.


Substrate Categories Producing Off-flavors E s s e n t i a l O i l s . Boyd and P e t e r s o n (1) s t a t e d t h a t the presence o f v o l a t i l e o i l s i n orange j u i c e i m p a r t e d a p l e a s a n t aroma and c o n t r i b u t e d t o f l a v o r . However, under c e r t a i n c o n d i t i o n s , the presence of s m a l l amounts o f o i l y i e l d e d o b j e c t i o n a b l e o f f - f l a v o r s during prolonged storage. B l a i r e t a l . (3) suggested t h a t the a c i d o f the j u i c e promoted a s e r i e s o f hydration-dehydration r e a c t i o n s w i t h peel o i l terpenes. d-Limonene, the p r i n c i p a l component o f p e e l o i l , was thought t o undergo t h e s e r e a c t i o n s t o produce h y d r o c a r b o n s , a l c o h o l s , e t h e r s , p o l y h y d r o x y compounds and other products. The c o n s t i t u e n t oxygen o f t h e s e newly formed o x y g e n - c o n t a i n i n g compounds was d e r i v e d from w a t e r by c h e m i c a l a d d i t i o n , and not from d i s s o l v e d oxygen by o x i d a t i o n . T a b l e I i s a summary o f t h e r m a l l y degraded compounds d e r i v e d from e s s e n t i a l o i l c o n s t i t u e n t s . O f f - f l a v o r n o t e s d e r i v e d from some o f the compounds have g e n e r a l l y been d e s c r i b e d as " t e r e b i n t h i n e " ( t e r p e n t i n e - l i k e ) or " t e r p e n e y . " When A s k a r e t a l . (8,9) added limonene and l i n a l o o l t o a model j u i c e , d e c r e a s e s o f b o t h t h e s e compounds were temperature dependent. Both compounds degraded t o α-terpineol and c i s - 1 , 8 - p - m e n t h a n e d i o l , w h i l e l i n a l o o l a l s o degraded t o n e r o l and g e r a n i o l (Table I ) . A l t h o u g h j u i c e c o n t a i n s much l e s s l i n a l o o l r e l a t i v e t o limonene, the l i n a l o o l m o l e c u l e i s more r e a c t i v e and produces most o f the α-terpineol. Taturn and coworkers (4) showed t h a t 2.5 ppm α-terpineol i m p a r t e d a s t a l e , musty or p i n e y note when added t o f r e s h l y squeezed orange j u i c e . C i s - 1 , 8 - p - m e n t h a n e d i o l forms from α-terpineol by a c i d - c a t a l y z e d h y d r a t i o n ( 4 ) ; i t , i n t u r n , undergoes f u r t h e r t r a n s f o r m a t i o n s t o form 1 , 8 - c i n e o l e and 1,4-cineole. B l a i r e t a l . (3) a t t r i b u t e d the t e r e b i n t h i n e odor t o the c i n e o l e s and s e c o n d a r i l y t o t e r p e n e hydrocarbons i s o m e r i c w i t h limonene. S i n c e 1 , 4 - c i n e o l e i s produced a t h i g h a c i d i t y and i n c r e a s e d . s t o r a g e t e m p e r a t u r e s , i t i s thought t o be r e s p o n s i b l e f o r the t y p i c a l pungent, camphoraceous o f f - f l a v o r o f s t o r a g e - a b u s e d orange j u i c e s . C i t r a l ( m i x t u r e of n e r a l and g e r a n i a l ) i n lemon and l i m e j u i c e beverages undergoes a s e r i e s of a c i d - c a t a l y z e d h y d r a t i o n - d e h y d r a t i o n r e a c t i o n s l e a d i n g t o the f o r m a t i o n o f an i s o m e r i c m i x t u r e of p-mentha-1,5-dien-8-ol (6,7^) and p - m e n t h a - l ( 7 ) , 2 - d i e n - 8 - o l . These two compounds f u r t h e r degrade by rearrangement and d e h y d r a t i o n t o t h r e e malodorous compounds, namely, p-cymen-8-ol, p-cymene and a , p - d i m e t h y l s t y r e n e ( 7 ) . A d d i t i o n a l l y , Ikeda e t a l . (10) and Shaw (11) found t h a t i n l i m e and lemon o i l , γ-terpinene i s c o n v e r t e d t o the o f f - f l a v o r compound p-cymene. S t r u c t u r e s o f s e l e c t e d o f f - f l a v o r n o t e s are p r e s e n t e d i n F i g u r e 1. L i p i d c o n s t i t u e n t s . E a r l y s t u d i e s on o f f - f l a v o r development i n c i t r u s p r o d u c t s suggested t h a t o f f - f l a v o r s might be r e l a t e d t o the d e g r a d a t i o n o f l i p i d s (12-14). C u r l (15) compared the f l a v o r s b e f o r e and a f t e r s t o r a g e o f whole t a n g e r i n e j u i c e and t a n g e r i n e


31.

NAGYETAL.

Thermally Degraded Flavors in Citrus Juice Products

Table I. T h e r m a l l y Degraded Compounds D e r i v e d from E s s e n t i a l O i l Constituents

Precursor

D e r i v e d Compounds


d-Limonene

α -terpineol

Linalool

α -terpineol

a-Terpineol

Cis-1,8-p-menthanediol

F l a v o r Response

Reference

stale,musty, piney

3,4

stale,musty, piney

5,8,9

nerol

sweet,rose fruity

geraniol

sweet,floral rose

cis-1,8-p-menthanediol sweet, camphoraceous

3,5

a

1,8-cineole

pungent, camphoraceous

1,4-cineole Citral^

p-mentha-1,5-dien-8-ol not c h a r a c t e r i z e d

6,7

p-mentha-l(7),2-dien-8-ol not c h a r a c t e r i z e d cis-p-mentha-2,8-dien-l-ol not c h a r a c t e r i z e d trans-p-mentha-2,8-dien-l-ol not c h a r a c t e r i z e d p-Mentha-1,5-dien-8-ol + p-cymen-8-ol p-Mentha-l(7),2-dien-8-ol p-cymene

nonspecified off-flavor terpeney o f f - f l a v o r

α -ρ-dimethylstyrene

γ-Terpinene

p-cymene

6,7

terpeney off-flavor

t e r p e n e y o f f - f l a v o r 10,11

A l s o known as c i s t e r p i n o l I s o m e r i c m i x t u r e o f n e r a l and g e r a n i a l


333


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THERMAL GENERATION OF AROMAS

D

E

F

G

H

I

F i g u r e 1. Chemical s t r u c t u r e s o f s e l e c t e d o f f - f l a v o r n o t e s of c i t r u s j u i c e p r o d u c t s . (A) 4 - v i n y l g u a i a c o l , (B) α-terpineol, (C) 1 , 8 - c i n e o l e , (D) 1 , 4 - c i n e o l e , (E) 2,5-dimethyl-4-hydroxy-3(2H)-furanone, ( F ) p-cymen-8-ol (G) α,p-dimethylstyrene, (H) p-cymene, ( I ) trans,trans-2,4-decadienal.


31.

NAGYETAL.

Thermally Degraded Flavors in Citrus Juice Products


j u i c e from w h i c h the suspended m a t t e r , w h i c h i n c l u d e s the l i p i d s , had been removed. He c o n c l u d e d t h a t the suspended m a t t e r was r e s p o n s i b l e f o r much of the c h a r a c t e r i s t i c f l a v o r but a l s o c o n t a i n e d p r e c u r s o r s o f the s t o r a g e - d e v e l o p e d o f f - f l a v o r s . Nagy and Nordby (16) s t u d i e d the e f f e c t s o f s t o r a g e temperatures and d u r a t i o n on the d i f f e r e n t l i p i d c l a s s e s o f s i n g l e - s t r e n g t h orange j u i c e , and found e x t e n s i v e d e g r a d a t i o n o f p h o s p h o l i p i d s . E x a m i n a t i o n o f TLC p r o f i l e s o f the p h o s p h o l i p i d f r a c t i o n d i d not show f o r m a t i o n o f any l y s o - d e r i v a t i v e . They c o n c l u d e d , t h e r e f o r e , t h a t b o t h f a t t y a c i d s a s s o c i a t i o n w i t h the p h o s p h o l i p i d m o l e c u l e were s p l i t o f f .

Table I I .

Time (mo. )

0 3 5 11 15 16

Weight o f Free F a t t y A c i d s as a F u n c t i o n o f Storage Time and Temperature

. 16:

1..3 2,.0 2..3 3,.3 3..5 4,.0

Weight (mg/15 g d r i e d c i t r u s 4C 16: :0 18: :1 18: :3 18: :2

1,.3 1,.9 2,.0 2 .7 3..4 3,.3

1..1 1,.7 2..0 2,.7 3..0 3..4

Number of carbons i n c h a i n : Source (16)

0, 6 0,.9 1..1 1,.4 1..6 1,.8

1..3 4,.5 5..7 8,.7 9..1 9,.1

j u i c e powder) 29 C 18: :1 18: :2

18: :3

1..1 4,.3 5..7 9,.1 10. ,1 10, .2

0..6 2..4 3..3 4,.5 5..6 5,.8

1..3 4,.1 5..3 7,.6 8..8 8..8

number o f double bonds

T a b l e I I l i s t s the i n c r e a s e s f o r the f o u r major f a t t y a c i d s i n the free f a t t y a c i d f r a c t i o n . C o l l e c t i v e l y , p a l m i t i c (CJ^.Q)» o l e i c ( C ^ g . ) , l i n o l e i c (C-^g^) * l i n o l e n i c (C^g.^) comprise g r e a t e r than'88% of a l l f a t t y a c i d s i n orange j u i c e ( 1 7 ) . For 4°C s t o r e d j u i c e , the f o u r a c i d s i n c r e a s e d about t h r e e - f o l d . I n j u i c e s t o r e d a t 29 C, f r e e p a l m i t i c and o l e i c a c i d s i n c r e a s e d about s e v e n - f o l d , whereas l i n o l e i c and l i n o l e n i c i n c r e a s e d about n i n e - f o l d . F a t t y a c i d s from the p h o s p h o l i p i d f r a c t i o n a r e not o f f - f l a v o r e d as such but a r e thought t o c o n s t i t u t e an u n s t a b l e system w h i c h u l t i m a t e l y l e a d s t o the p r o d u c t i o n o f s u b s t a n c e s i m p a r t i n g a r a n c i d note t o juice flavor. F r e e , l o n g - c h a i n u n s a t u r a t e d f a t t y a c i d s , as found i n s t o r e d c i t r u s j u i c e , are i m p o r t a n t p r e c u r s o r s of many v o l a t i l e o f f - f l a v o r compounds, namely, a l k - 2 , 4 - d i e n a l s , 2 - o c t e n a l and n-hexanal ( 1 8 ) . A s k a r and co-workers (8) showed t h a t s t o r a g e o f orange j u i c e r e s u l t e d i n an i n c r e a s e i n n - h e x e n a l , n - h e x a n a l , n - o c t a n a l and n - d e c a n a l . Moshonas and Shaw (19) i s o l a t e d t r a n s , t r a n s - 2 , 4 - d e c a d i e n a l i n c i t r u s o i l s and suggested t h a t i t might have been produced by o x i d a t i v e breakdown o f l o n g c h a i n , u n s a t u r a t e d f a t t y a c i d s . A l t h o u g h some p r o d u c t s o f l i p i d a n c


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THERMAL GENERATION OF AROMAS


o x i d a t i o n c o n t r i b u t e t o f l a v o r d e t e r i o r a t i o n , Nagy (20) c o n c l u d e d t h a t these compounds were not the major o f f - f l a v o r components formed d u r i n g s h o r t - t e r m , h i g h temperature s t o r a g e o f c i t r u s j u i c e products. P h e n o l i c compounds. Thermal d e g r a d a t i o n o f v a r i o u s types o f p h e n o l i c compounds has been shown t o produce u n d e s i r a b l e o f f - f l a v o r compounds. Tatum e t a l . (4) i d e n t i f i e d 4 - v i n y l g u a i a c o l as the most d e t r i m e n t a l o f f - f l a v o r compound i n aged orange j u i c e . When added t o f r e s h l y e x p r e s s e d orange j u i c e a t a l e v e l o f 0.075 ppm, i t i m p a r t e d an o l d f r u i t o r r o t t e n f l a v o r . S u b s t a n t i a l amounts of 4 - v i n y l g u a i a c o l , from 0.6 t o 1.6 ppm, were found i n orange j u i c e s t o r e d f o r 12 weeks a t 35°C by Tatum e t a l .

Thermal Generation of Aromas - American Chemical Society

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