Flavor Quality: Objective Measurement

6 Measurement of Flavor Quality i n Apples, A p p l e Juices, and Fermented Ciders

Downloaded by AUBURN UNIV on December 26, 2017 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0051.ch006

A. A. WILLIAMS, A. G. H. LEA, and C. F. TIMBERLAKE University of Bristol, Research Station, Long Ashton, Bristol, ΒS18 9AF, England

Quality may be understood as merely a measure of desira bility in a product and, as such, must be closely related to consumer acceptance, something which is important to any producer, whether of fruit products or foods in general, because without it he will soon be out of business. The consumer, whether he buys directly or has his opinion reflected in the eyes of a buyer for a processing industry, is therefore the final key to what constitutes quality. One function of the scientist interested in flavour is to translate this consumer opinion into tangible information, such as the chemical and physical composition of the product, so that eventually he has a better understanding of what the consumer considers as constituting quality and can then devise logical scientific methods for its improvement. When considering the produce of the apple industry, although it is the sensory responses evoked in the consumer and the pleasure and satisfaction they give, that have the greatest influence on quality, other factors are also important. The keeping quality of the fruit or beverage, its nutritional value, the variety of uses to which it can be put in the home, the ease and convenience of eating and, of course, the price, are some of the more tangible attributes which are also important to the consumer. The fact that man made fertilisers and insecticides may have been used during the growing of the fruit, the image created by the varietal name, advertising and preconceived ideas of the product also have subtle effects on the acceptability of a fruit. Such phrases as an apple a day keeps the doctor away have l i t t l e scientific backing but may well subconsciously influence the housewife when she shops for apples and apple products. Other factors besides the sensory quality of the fruit are also important to the apple producer and processor. Crop yields, resistance of the tree to disease, length and uniformity of harvest, ability to transport and storage potential play a major role in the growers choice of orchard practices and selection of varieties. For apples destined for juice and cider production, f

1

1

71 Scanlan; Flavor Quality: Objective Measurement ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

72

FLAVOR QUALITY:

OBJECTIVE

MEASUREMENT


a b i l i t y to r e a d i l y produce a h i g h y i e l d of j u i c e i s another factor i n defining quality. During the l a s t twenty years i t i s s u c h c o n s i d e r a t i o n s as t h e s e w h i c h have a l m o s t e n t i r e l y g o v e r n e d the type of f r u i t produced. T h i s h a s b e e n p a r t i c u l a r l y so i n the case of e a t i n g a p p l e s , where the o n l y t a n g i b l e c r i t e r i a b e i n g i m p o s e d b y t h e r e t a i l e r a p p e a r t o be t h o s e o f c o l o u r , s i z e , shape and l a c k o f d i s o r d e r s . When t r a d i t i o n a l m e t h o d s w e r e b e i n g u s e d to grow and market f r u i t such c r i t e r i a p o s s i b l y proved q u i t e adequate. However, as a r e s u l t of modern t e c h n o l o g y , greater y i e l d s o f a p p l e s a n d a l o n g e r s t o r a g e l i f e a r e now p o s s i b l e a n d c r i t e r i a , s u c h as f l a v o u r , w h i c h a r e not d i r e c t l y a s s e s s e d , are beginning to suffer. I n t h e a p p l e j u i c e and c i d e r i n d u s t r i e s i n c r e a s e d c l e a n l i n e s s , the use of a s c o r b i c a c i d , s u l p h u r d i o x i d e and pure y e a s t c u l t u r e s have g i v e n t h e m a n u f a c t u r e r s more c o n t r o l o v e r t h e i r p r o d u c t s . T h i s has meant t h a t t h e o c c u r r e n c e o f completely unacceptable beverages i s becoming l e s s frequent and, here again, t h e m a n u f a c t u r e r i s b e c o m i n g more c o n c e r n e d w i t h m a i n t a i n i n g those f l a v o u r aspects of h i s product which the customer considers t o be d e s i r a b l e . Measurement

of

Flavour

Quality

S e v e r a l a t t e m p t s h a v e b e e n made t o f o r m u l a t e sensory, p h y s i c a l and a n a l y t i c a l c r i t e r i a by which q u a l i t y o f b o t h a p p l e s a n d t h e i r p r o d u c t s c a n be a s s e s s e d a n d c o m p a r e d . Sensory assessments are mainly of the type i n which general attributes s u c h as c l a r i t y , aroma and f l a v o u r a r e s c o r e d and combined, w i t h e i t h e r the r e s u l t s of simple chemical analyses, or estimabes of c o m m e r c i a l v a l u e t o g i v e a n i n d i c a t i o n o f q u a l i t y (.1,2.). Over r e c e n t y e a r s , h o w e v e r , a number o f more o b j e c t i v e approaches have been developed i n c o n n e c t i o n w i t h s p e c i f i c r e s e a r c h p r o grammes 6), b u t , a p a r t from the v o c a b u l a r y u s e d by V G n S y d o w e t a l . (5) a n d M o s k o w i t z a n d V a n S y d o w (6) to describe apple j u i c e s , these are s t i l l of a r a t h e r general n a t u r e . From the p o i n t o f v i e w of p h y s i c a l measurements r e l a t i o n s h i p s a r e c l a i m e d t o e x i s t b e t w e e n b o t h t h e c o l o u r CZ.,8,.2.) a n d l i g h t t r a n s m i t t a n c e ( 1_0,ll) o f a p p l e s a n d t h e i r e a t i n g q u a l i t y a n d u s e h a s b e e n made o f t h e s e i n d e v e l o p i n g i n s t r u m e n t s f o r g r a d i n g p u r p o s e s ( U l g _ , Y%_, H ) . A n a l y t i c a l l y , measurements of the sugar and a c i d c o n t e n t s have been u s e d f o r e s t i m a t i n g q u a l i t y o f a p p l e s (± V2. 16) a n d j u i c e s (2., Vj), although i n the case of the l a t t e r i t i s claimed that the polyphenol content should also f a l l w i t h i n s p e c i f i c l i m i t s (ijO . I n England i t has l o n g been t h e custom to c l a s s i f y c i d e r s , c i d e r a p p l e s and t h e i r j u i c e s o n t h e i r a c i d and p o l y p h e n o l c o n t e n t as a means o f i n d i c a t i n g t h e i r f l a v o u r p r o p e r t i e s and s u i t a b i l i t y f o r c i d e r m a k i n g . Whether i t i s an apple, j u i c e or c i d e r , s i m p l e , a n a l y t i c a l and p h y s i c a l measurements o f t h i s n a t u r e are o n l y v e r y crude i n d i c a t o r s of q u a l i t y , g i v i n g very l i t t l e i n d i c a t i o n of the true 9

9

Scanlan; Flavor Quality: Objective Measurement ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6.

WILLIAMS ET

AL.

Apples,

Apple

Juices,

and

Fermented

73

Ciders

f l a v o u r e f f e c t s of i n d i v i d u a l compounds. For example, s c i e n t i s t s are unable to t e l l from the r e s u l t s of permanganate t i t r a t i o n s whether the polyphenols are c o n t r i b u t i n g to b i t t e r ness or a s t r i n g e n c y or whether they are soapy or hard . Also, e x c e p t b y a s s o c i a t i o n , s u c h m e a s u r e m e n t s do n o t t a k e i n t o a c c o u n t t h e more s u b t l e e f f e c t s o f t h e v o l a t i l e components on aroma and f l a v o u r , the i n t e r a c t i o n of b o t h v o l a t i l e and n o n - v o l a t i l e f l a v o u r components and the e f f e c t o f f r u i t s t r u c t u r e on the r e l e a s e of the f l a v o u r i m p a r t i n g compounds.


1

1

!

f

Modern a n a l y t i c a l techniques have, of course, been a p p l i e d t o most a s p e c t s of a p p l e p r o d u c t s . F o r example, gas c h r o m a t o g r a p h y h a s e n a b l e d o v e r 2 5 0 v o l a t i l e c o m p o n e n t s ( 1 8 , 1 9 , 2 θ ) t o be i d e n t i f i e d and o t h e r c h r o m a t o g r a p h i c t e c h n i q u e s have g i v e n i n f o r m a t i o n on the n o n - v o l a t i l e s . Some o f t h e s e obviously c o n t r i b u t e more t o t h e f l a v o u r t h a n o t h e r s ( 2 1 , 2 2 ) , but u n t i l one c a n s t a t e w h i c h a r e t h e i m p o r t a n t compounds and c h a r a c t e r i s t i c s , s u c h i n f o r m a t i o n c a n n o t be u s e d as a g u i d e t o q u a l i t y . As s t a t e d e a r l i e r , t h e c u s t o m e r i s t h e f i n a l k e y t o u n d e r standing quality. H o w e v e r , a l t h o u g h t h e a v e r a g e c o n s u m e r , when p r e s e n t e d w i t h a number o f p r o d u c t s , c a n r e a d i l y t e l l you w h i c h he p r e f e r s , he i s o f t e n much l e s s p r e c i s e i n s a y i n g why he l i k e s t h e one he h a s c h o s e n . I n e v a l u a t i n g f l a v o u r q u a l i t y i t was t h e r e f o r e c o n s i d e r e d u n w i s e t o t r y , e i t h e r t o get t o o much i n f o r m a t i o n from the consumer or to i n t e r p r e t h i s p r e f e r e n c e i n f o r m a t i o n d i r e c t l y , p a r t i c u l a r l y i n terms of a n a l y t i c a l d a t a . The a p p r o a c h a d o p t e d t h e r e f o r e was t o u s e a t r a i n e d p a n e l a n d w e l l defined terminology to assess o b j e c t i v e l y the c h a r a c t e r i s t i c s p r e s e n t i n the p r o d u c t , t h u s o b t a i n i n g a d e t a i l e d measiire b o t h q u a l i t a t i v e l y and q u a n t i t a t i v e l y , of t h e v a r i o u s s e n s o r y c h a r a c t e r i s t i c s c o n t r i b u t i n g to the o v e r a l l a p p r e c i a t i o n of the f r u i t , juice or c i d e r . C o r r e l a t i n g t h i s i n f o r m a t i o n on t h e one hand w i t h the consumer s assessment or p r e f e r e n c e r a t i n g s would give an i n d i c a t i o n of the r e l a t i v e importance of the c h a r a c t e r i s t i c s f o r a c c e p t a n c e and q u a l i t y , w h i l s t c o m p a r i n g i t w i t h t h e c h e m i c a l and p h y s i c a l d a t a w o u l d e n a b l e the a n a l y t i c a l parameters which give r i s e to these various a t t r i b u t e s t o be d e t e r m i n e d . 1

This three d i r e c t i o n a l approach i n v o l v i n g preference r a t i n g s , o b j e c t i v e s e n s o r y assessment and a n a l y t i c a l d a t a has formed t h e b a s i s of our t h i n k i n g w i t h r e g a r d t o q u a l i t y and f l a v o u r e v a l u a t i o n o v e r t h e p a s t two y e a r s and two e x a m p l e s i l l u s t r a t i n g a s p e c t s o f t h i s a p p r o a c h , one i n v o l v i n g t h e aroma c o m p o n e n t s of a p p l e s a n d a n o t h e r t h e p h e n o l i c s o f f e r m e n t e d c i d e r w i l l now b e discussed. Annies From the p o i n t o f v i e w of e a t i n g q u a l i t y , the c u l t i v a r C o x s Orange P i p p i n , i s c o n s i d e r e d by the 1

apple majority


of

74

FLAVOR QUALITY:

OBJECTIVE

MEASUREMENT

E n g l i s h g r o w e r s , r e t a i l e r s a n d c o n s u m e r s t o be a m o n g s t t h e m o s t d e s i r a b l e o f a p p l e s , p a r t i c u l a r l y when c o n s i d e r i n g c u l t i v a r s w h i c h c a n be k e p t f o r any l e n g t h o f t i m e a f t e r h a r v e s t i n g . Preference r a t i n g s , comparing i t with three other v a r i e t i e s , Red D e l i c i o u s , S p a r t a n and I d a r e d ( T a b l e i ) , even t h o u g h t a k e n i n A p r i l when t h e C o x was n e a r i n g t h e end o f i t s s t o r a g e life, serve to i l l u s t r a t e the overwhelming s u p e r i o r i t y of t h i s cultivar. For economical reasons i t i s becoming d e s i r a b l e to TABLE


Mean r a n k i n g o f

four

I varieties

of

apples

* Cultivar

C o x s Orange P i p p i n Spartan Idared Red D e l i c i o u s 1

* 1 β most

preferred

E x t e r n a l aroma (total score)

* Overall (total score)

2

1.25

2.6

3 2.5

2.3 2.6

4 =

2.9 least preferred

s t o r e Cox f o r l o n g p e r i o d s b e f o r e m a r k e t i n g . Although these l a t e s t o r e d Cox a p p l e s are f r e e o f d i s o r d e r s and have excellent t e x t u r e and a p p e a r a n c e , t h e i r f l a v o u r i s not a t t r a c t i v e and t h e consumer i s b e g i n n i n g to c o m p l a i n . The i n d u s t r y i s n a t u r a l l y w o r r i e d b e c a u s e i t b e l i e v e s t h a t much o f t h e s a l e s o f t h i s c u l t i v a r depends on f l a v o u r . The t h r e e d i r e c t i o n a l a p p r o a c h d e s c r i b e d i s b e i n g a d o p t e d t o t r y a n d d i s c o v e r w h a t i s s o d e s i r a b l e i n t h e C o x a p p l e a n d how t h e i m p o r t a n t a t t r i b u t e s from t h e s e n s o r y and a n a l y t i c a l p o i n t o f v i e w change b o t h d u r i n g C o n t r o l l e d Atmosphere s t o r a g e and i t s shelf l i f e afterwards. The development of an o b j e c t i v e language for d e s c r i b i n g the v a r i o u s sensory a t t r i b u t e s of the f r u i t was t h e f i r s t s t e p i n t h e p r o g r a m m e . To a c c o m p l i s h t h i s , t e r m s a n d i d e a s w e r e c o l l e c t e d f r o m a p a n e l o f 21 t a s t e r s who a s s e s s e d a p p l e s d u r i n g t h e 1 9 7 3 - 7 4 s e a s o n b o t h a s t h e y came f r o m the t r e e and a f t e r r e m o v a l from s t o r a g e . A p p r o x i m a t e l y 200 a d j e c t i v e s and p h r a s e s were s u g g e s t e d f o r d e s c r i b i n g the v a r i o u s a s p e c t s o f Cox f l a v o u r . The most f r e q u e n t l y u s e d , t o g e t h e r w i t h a number of the o t h e r terms w h i c h the p a n e l c o n s i d e r e d s i g n i f i c a n t , were d i s c u s s e d and, where p o s s i b l e , s t a n d a r d s i n the form of essences, c h e m i c a l s and n a t u r a l m a t e r i a l s , p r o d u c e d . The t e r m s d e r i v e d were g r o u p e d i n t o v a r i o u s c l a s s e s w h i c h u l t i m a t e l y formed the b a s i s of an assessment sheet f o r s c o r i n g


WILLIAMS ET

AL.

Apples,

Apple

Juices,

and

Fermented

75

Ciders

v a r i a t i o n s i n t h e f l a v o u r c h a r a c t e r s f r o m one b a t c h o f a p p l e s t o another. The sheet c o n s i s t e d o f e i g h t s e c t i o n s d e a l i n g w i t h the e x t e r n a l and i n t e r n a l appearance o f the a p p l e , i t s f e e l to the hand, i t s e x t e r n a l and i n t e r n a l aroma, t a s t e and t e x t u r e and finally its aftertaste (Table II). Each s e c t i o n contained the TABLE


Segregation

of

flavour

II

attributes

1.

Appearance

2. 3.

Feel Aroma

4. 5. 6.

Taste Texture Aftertaste

for

sensory

G ι) 0 D)

external internal

0 i) 0 D)

external internal

evaluation

a p p r o p r i a t e d e r i v e d a d j e c t i v e s a n d p h r a s e s and was s c o r e d o n t h e amount o f a p a r t i c u l a r a t t r i b u t e p r e s e n t i n t h e a p p l e u s i n g a 0-5 s c a l e . I n s c o r i n g these a t t r i b u t e s p a n e l i s t s were i n s t r u c t e d t o be o b j e c t i v e a n d n o t t o be i n f l u e n c e d b y p e r s o n a l preferences, these being i n d i c a t e d separately. In order to reduce e r r o r s apples were assessed i n a p r e - s e t manner. Examination of c o r r e l a t i o n co-efficients between o v e r a l l r a t i n g s and the v a r i o u s i n d i v i d u a l s e c t i o n r a t i n g s (Table III) based on t w e l v e months t a s t i n g s i n d i c a t e d t h a t the t a s t e and texture sensations r e f l e c t e d the o v e r a l l r a t i n g s best, i n t e r n a l aroma and e x t e r n a l aroma as s u c h o n l y g i v i n g r e l a t i v e l y low correlation co-efficients. The r e s u l t s o f m u l t i p l e r e g r e s s i o n 1

TABLE Correlation

of

III

individual section

rating with

overall

Correlation co-efficients with overall rating

External External Internal Internal External External Internal Taste Texture

appearance colour appearance colour feel aroma aroma

0.80 0.43 0.74 0.77 0.75 0.56 0.69 0.87 0.84


rating


76

FLAVOR QUALITY:

OBJECTIVE

MEASUREMENT

a n a l y s i s , however, i n d i c a t e d t h a t the r a t i n g f o r t a s t e c o u l d not be i n t e r p r e t e d e n t i r e l y i n t e r m s o f s w e e t n e s s , s o u r n e s s and b i t t e r n e s s , b u t , as e x p e c t e d , was a f f e c t e d b y o t h e r factors s u c h as t h e m i n o r c h a r a c t e r i m p a r t i n g , v o l a t i l e f l a v o u r components not d i r e c t l y defined i n t h i s s e c t i o n . A n a l y t i c a l m e t h o d s w e r e d e v e l o p e d a t t h e same t i m e t o g i v e i n f o r m a t i o n on t h e c h e m i c a l components i n the a p p l e . In connection with t h i s i t i s worth noting that differing q u a l i t a t i v e and q u a n t i t a t i v e p i c t u r e s were o b t a i n e d from the v o l a t i l e s d e p e n d i n g on t h e c o l l e c t i o n method u s e d and the d e g r e e o f enzyme a c t i o n a l l o w e d t o t a k e p l a c e d u r i n g p r e p a r a t i o n . As t h e a i m o f t h e w o r k was t o i n t e r p r e t r e s u l t s i n t e r m s o f a s e n s o r y e f f e c t the problem e x i s t s as to w h i c h method gave r e s u l t s c l o s e s t t o t h e c o m p o s i t i o n o f t h e aroma when t h e f r u i t was b e i n g c h e w e d w h e n , a f t e r a l l , some enzyme a c t i o n a n d o x i d a t i o n must o c c u r . A f t e r a number o f i n v e s t i g a t i o n s (23)it was f i n a l l y d e c i d e d t o a d o p t two p r o c e d u r e s f o r collecting volatiles. Headspace c o l l e c t i o n from i n t a c t f r u i t u s i n g a s i m p l e s y r i n g e t e c h n i q u e , supplemented by c o l l e c t i o n on P o r a p a k Q, w a s u s e d t o o b t a i n i n f o r m a t i o n f o r c o m p a r i s o n w i t h the e x t e r n a l aroma comments. To c o r r e l a t e w i t h t h e altogether different i n t e r n a l a r o m a a n d t a s t e s c o r e s i n f o r m a t i o n was o b t a i n e d by an e x t r a c t i o n p r o c e d u r e , based on c h i p p i n g t h e f r u i t f o l l o w e d by m e t h a n o l i n h i b i t i o n o f enzymes a f t e r 10-15 s e c . E x a m i n a t i o n of the aroma p r o f i l e s o f the Cox a p p l e s ( F i g u r e 1) s h o w e d t h a t t h e p a n e l i s t s h a d s e l e c t e d a n d w e r e s c o r i n g c h a r a c t e r s w h i c h were not the normal f r u i t y , e s t e r y ones usually associated with apples. Two o f t h e s e w e r e t h e d r i e d l e a f and s p i c y aromas, t h e former of w h i c h o f t e n d o m i n a t e d t h e e x t e r n a l aroma p a t t e r n . As y e t t h e c a u s e o f t h e d r i e d l e a f c h a r a c t e r has not been determined, but e x a m i n a t i o n of other a p p l e c u l t i v a r s showed t h a t t h e s p i c e - l i k e c h a r a c t e r was p r e s e n t i n a number o f t h e s e ( F i g u r e 1 ) , i n p a r t i c u l a r one known as E l l i s o n s O r a n g e , w h e r e i t was b e i n g d e s c r i b e d n o t j u s t as s p i c e l i k e b u t b y some t a s t e r s a s s p e c i f i c a l l y aniseed-like. 1

C o l l e c t i o n of the v o l a t i l e s from t h i s v a r i e t y u s i n g the P o r a p a k t e c h n i q u e (22) f o l l o w e d by gas c h r o m a t o g r a p h i c e x a m i n a t i o n n a t u r a l l y gave a v e r y complex p a t t e r n ( F i g u r e 2 ) . Odour e v a l u a t i o n of t h e s e p a r a t e d components i n d i c a t e d most o f them t o have f r u i t y and e s t e r y o d o u r s . One h i g h b o i l i n g p e a k h o w e v e r had a s s o c i a t e d w i t h i t the s p i c y aniseed aroma. Gas c h r o m a t o graphy-mass s p e c t r o m e t r y , p r e p a r a t i v e gas l i q u i d chromatography and i n f r a r e d s p e c t r o s c o p y gave i n f o r m a t i o n w h i c h e n a b l e d t h i s compound t o be i d e n t i f i e d as 4 - m e t h o x y a l l y l b e n z e n e , a compound with a d i s t i n c t aniseed smell. E x a m i n a t i o n of v o l a t i l e components from o t h e r c u l t i v a r s by t h i s and o t h e r methods showed 4 - m e t h o x y a l l y l b e n z e n e t o be p r e s e n t i n a l l c u l t i v a r s examined, t h e amounts d e t e c t e d , however, corresponding approximately to the l e v e l of s c o r i n g of the s p i c y c h a r a c t e r by the p a n e l ( F i g u r e 3)·


6.

Apples,

WILLIAMS E T A L .

Apple

Juices,


ADJECTIVE SCORE 1

Dried leaves

2

Green

and Fermented

d

(i)Cox

3

Sharp Alcoholic/Winey

5

Scented

6

Estery

7

Banana like

8

Sugary

9

Spicy

10

Estery (wax like)

11

Fatty/Greasy

12

Rancid

(iii) Ellison's Orange

At

M

4

77

Ciders

4

_9.

(iv)Bramley

(ii)Egremont Russett

10 5_

O

^ 1 0

mmn ADJECTIVE Figure

1.

External

Sugary Pineapple

Peardrops

aroma profiles of apples

Cooked apple

F r u i t

η ,

π

E

Apple l p e e

v/ ,

\ I ,stery I / Fruity ^ r r y \ » Apple I ^ Sharp! / Α

0

E

β

tiim Μ

-

in

/

η

χ

T /* V

\

μ

2r

/

οι Aniseed

î

Mv

Green

Green apple

\

VjU Time/ Momp

„

Column :150m * 0 76mm Carbowax Figure

2.

Chromatogram

mins °C

50 165

30 105

20M; programmed from 65*-210*C at 2-4'C/min

of vohtiles Aroma

from apples comments.

(Cultivar

Ellisons


Orange)

78

FLAVOR QUALITY:

OBJECTIVE

MEASUREMENT

T h r e s h o l d measurements i n aqueous s o l u t i o n based on t r i a n g u l a r assessments i n wine glasses i n d i c a t e d 4 - m e t h o x y a l l y l b e n z e n e t o h a v e a t h r e s h o l d o f 0.035 ppm ( s i g n i f i c a n t P=0.01) w h i c h p u t s i t on a p a r w i t h compounds l i k e h e x y l a c e t a t e and hexyl 2-methylbutyrate ( 2 4 * 2 5 ) , two compounds o f i m p o r t a n c e i n apples (Table IV). I t i s h o w e v e r a f a c t o r o f 100higher t h a n ethyl 2-methylbutyrate, t h e s i g n i f i c a n t compound i n A m e r i c a n Delicious apples (24). TABLE Threshold

values

(ppm)


compounds Our

in

IV of

significant

figures

Flath

et

(24) Hexanal 2-Hexenal Ethyl 2-methyl butyrate Hexyl 2-methyl butyrate Hexyl acetate 4-methoxyallylbenzene

aroma

apples a l . Jakob

et

al.

(2£)

0.005 0.017 0.0001 0.08

0.002

0.00008 0.06 0.085

0.035

D i s t r i b u t i o n measurements between an aqueous s o l u t i o n of 4m e t h o x y a l l y l b e n z e n e and i t s v a p o u r i n d i c a t e t h a t an aqueous c o n c e n t r a t i o n o f 0.035 ppm g i v e s r i s e t o a v a p o u r c o n c e n t r a t i o n o f 2.1 χ 10"-^ ppm. Q u a n t i t a t i v e f i g u r e s from the c o l l e c t i o n of a p p l e v o l a t i l e s on Porapak Q i n d i c a t e d t h a t the gas stream from E l l i s o n s O r a n g e c o n t a i n e d i n t h e r e g i o n o f 1 χ 10~4 ppm o f 4methoxyallylbenzene, approximately f i v e times greater than t h i s threshold concentration. 1

Fermented

Cider

Odour e v a l u a t i o n of the gas c h r o m a t o g r a p h i c e f f l u e n t (26). t h e u s e o f t h r e s h o l d v a l u e s a n d o d o u r u n i t s (20) and c o r r e l a t i o n of gas chromatographic d a t a w i t h s e n s o r y d e s c r i p t i o n of the a r o m a (27»28) h a s y i e l d e d m u c h u s e f u l i n f o r m a t i o n o n t h e c o n t r i b u t i o n i n d i v i d u a l v o l a t i l e c o m p o n e n t s make t o t h e a r o m a o f ciders. Although important to the o v e r a l l f l a v o u r of the b e v e r a g e t h e s e compounds w i l l n o t be d i s c u s s e d f u r t h e r i n t h i s paper. In the E n g l i s h c i d e r i n d u s t r y the p r a c t i c e of fermenting c o m p l e t e l y and a d j u s t i n g t h e s u g a r and a c i d c o n t e n t b e f o r e b o t t l i n g has meant t h a t t h e a b i l i t y o f t h e o r i g i n a l j u i c e t o i m p a r t sweetness and a c i d i t y i s becoming l e s s and l e s s i m p o r t a n t . T h i s i s not so w i t h t h e compounds r e s p o n s i b l e f o r b i t t e r n e s s and a s t r i n g e n c y , two e s s e n t i a l f l a v o u r c h a r a c t e r i s t i c s o f E n g l i s h c i d e r s w h i c h c a n o n l y be d e r i v e d f r o m t h e f r u i t . Unfortunately, there i s a c o n t i n u i n g shortage of apples which can impart these



6.

WILLIAMS ET AL.

Apples,

Apple

Juices,

and

Fermented

Ciders

79

c h a r a c t e r s , p a r t i c u l a r l y i n r e l a t i o n t o demands t o increase cider production. T h e i n d u s t r y c a n make u p some o f i t s f r u i t d e f i c i e n c i e s by u s i n g s u r p l u s d e s s e r t a p p l e s , but t h i s can o n l y go so f a r , a s c i d e r made e n t i r e l y f r o m t h e s e v a r i e t i e s l a c k s t h e true cider flavour. B e f o r e s a l e s u c h c i d e r s must be b l e n d e d w i t h a c e r t a i n amount o f m a t e r i a l made f r o m b i t t e r s w e e t or bittersharp cider fruit. From the p o i n t o f v i e w o f the i n d u s t r y a n d c o n s u m e r s i t i s t h e r e f o r e i m p o r t a n t t h a t we o b t a i n m o r e knowledge on t h e compounds r e s p o n s i b l e f o r t h i s d e s i r a b l e b i t t e r n e s s and a s t r i n g e n c y and d i s c o v e r means o f i n c r e a s i n g them b o t h i n t h e c i d e r a p p l e s a n d t h e c i d e r s made f r o m t h e m . The i n v o l v e m e n t o f p h e n o l i c m a t e r i a l i n t h e b i t t e r n e s s a n d a s t r i n g e n c y o f E n g l i s h c i d e r s and p e r r i e s has been recognised s i n c e 1801 ( 2 9 ) . b u t n o t u n t i l c o m p a r a t i v e l y r e c e n t l y h a s i t been p o s s i b l e t o s e p a r a t e and examine t h e compounds o f t h e g e n e r a l ' t a n n i n ' m i x t u r e , and t o d i s c o v e r w h i c h o f them c o n t r i b u t e t o t h e c h a r a c t e r s o f b i t t e r n e s s and a s t r i n g e n c y so d e s i r a b l e i n true English cider. In the mid 1950 s paper chromatography r e v e a l e d t h a t t h e p h e n o l i c s o f c i d e r c o u l d be b r o k e n down i n t o a number o f g r o u p s ( F i g u r e 4). C i r c u m s t a n t i a l evidence d e r i v e d from t a s t i n g pure commercial c o m p o u n d s i n d i c a t e d t h a t i t was o n l y t h e p r o c y a n i d i n s w h i c h made any d i r e c t c o n t r i b u t i o n to b i t t e r n e s s and a s t r i n g e n c y . C o n f i r m a t i o n o f t h i s w a s o b t a i n e d w h e n new p r e p a r a t i v e scale s e p a r a t i o n t e c h n i q u e s , u s i n g Sephadex g e l as an a d s o r p t i o n medium,allowed l a r g e enough q u a n t i t i e s of the p h e n o l i c fractions t o be i s o l a t e d f r o m c i d e r f o r t a s t i n g t r i a l s t o be c a r r i e d o u t . !

Although a t o t a l p r o c y a n i d i n f r a c t i o n , free from other p h e n o l i c s , c o u l d e a s i l y be i s o l a t e d o n S e p h a d e x , t h e p r o b l e m o f s e p a r a t i n g i n d i v i d u a l p r o c y a n i d i n s p e c i e s f r o m one a n o t h e r s t i l l remained. The r e a d i n e s s o f t h e s e compounds t o b o t h h y d r o g e n bond w i t h or to H a n almost any s u r f a c e or c h r o m a t o g r a p h i c s u p p o r t , a n d t o be c o n v e r t e d t o a m o r p h o u s b r o w n p o l y m e r s u n d e r t h e i n f l u e n c e o f h e a t , l i g h t a n d o x y g e n made t h i s v e r y d i f f i c u l t . 1

The t e c h n i q u e w h i c h p r o v e d more s u c c e s s f u l t h a n any o t h e r i n s e p a r a t i n g b u l k q u a n t i t i e s o f p r o c y a n i d i n s was t h a t o f c o u n t e r - c u r r e n t d i s t r i b u t i o n between e t h y l a c e t a t e and w a t e r . By u s i n g a m o d e r n a u t o m a t e d m a c h i n e w h i c h moved b o t h t o p and b o t t o m p h a s e s i n o p p o s i t e d i r e c t i o n s , i t was p o s s i b l e t o s e p a r a t e t h e p r o c y a n i d i n s o f c i d e r i n t o s i x f r a c t i o n s ( T a b l e V), gram q u a n t i t i e s s u f f i c i e n t f o r b o t h s e n s o r y and s t r u c t u r a l studies thereby easily being obtained.


80

FLAVOR QUALITY:

OBJECTIVE

MEASUREMENT

1 St.Edmund's Russett 4-Methoxy allyl benzene

2 Idared 3 Discovery 4 Cox's Orange Pippin 5 Beauty of 6 Golden

Bath

Delicious

7 Bramley 8 Worcester Pearmain 9 Egremont


10 Laxton's

Russett Superb

11 Kidd's Late Orange 12 Ellison's

Orange

.

. Spicy score

Figure

3.

Rehtionship

of spicy scores to amounts

of

4-methoxyallylbenzene

H O ^

phenolic acids eg

Chlorogenic acid

H=CHCOO

/H\COOH J/OH

HO\|

phloretin derivatives eg

Phloridzin H

V \

0

H

^ y ^ C O C H ^ H ^ OGI

Vc \ = /

simple catechins

procyanidins eg H°

Figure

4. Paper chromatographic ration of cider phenolics

sepa-


6.

WILLIAMS ET

AL.

Apples, Apple Juices, and Fermented Ciders

TABLE Counter

current

Component

V

separation


procyanidins

Tetrameric procyanidins Trimeric procyanidins Dimeric procyanidins Epi-catechin

of

cider

Partition co-efficient (Ethyl acetate/ water)

P o l y m e r i c and o x i d i s e d procyanidins Pentameric

81

phenolics Taste

) 0 0.05

-

0.10

0.18

i

Most

astringent

Most

bitter

)

0.37 0.67 4.0

S t r u c t u r a l s t u d i e s , based on techniques developed by Weinges e t a l . i n H e i d e l b e r g (^0.) a n d H a s l a m e t a l . i n S h e f f i e l d (31 ), i n v o l v e d p u r i f i c a t i o n o f t h e p r o c y a n i d i n s on Sephadex g e l s , mass s p e c t r o m e t r y o f t h e m e t h y l e t h e r s t o o b t a i n m o l e c u l a r w e i g h t s and n u c l e a r magnetic resonance s p e c t r o s c o p y of b o t h the n a t i v e and a c e t y l a t e d compounds t o g i v e s t e r e o c h e m i c a l information. Cleavage of the procyanidins w i t h a c i d t o l u e n e t h i o l followed by paper chromatography and n u c l e a r magnetic r e s o n a n c e spectroscopy o f the fragments a l s o gave v a l u a b l e i n f o r m a t i o n on the c o n s t i t u t i o n o f u n i t s m a k i n g up the p r o c y a n i d i n s . By p r e s e n t i n g the i s o l a t e d f r a c t i o n s i n aqueous s o l u t i o n to a t a s t i n g p a n e l , i t was p o s s i b l e t o d e m o n s t r a t e t h a t o n l y t h e materials of p a r t i t i o n co-efficient

Flavor Quality: Objective Measurement

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