Quality of Selected Fruits and Vegetables of North America - American

7 Establishing Criteria for Determining the Authenticity of Fruit Juice Concentrates 1

2

RONALD E. WROLSTAD , CHRISTOPHER J. CORNWELL , JEFFREY D. CULBERTSON , and FELIX G. R. REYES

Downloaded by SUFFOLK UNIV on January 19, 2018 | http://pubs.acs.org Publication Date: November 11, 1981 | doi: 10.1021/bk-1981-0170.ch007

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Department of Food Science and Technology, Oregon State University, Corvallis, OR 97331

Use of fruit juice concentrates in the manufacture of wines, j e l l i e s , and other foods and beverages i s increasing and fruit juice concentrate production has become a highly competitive growth industry in both domestic and foreign markets. Analytical methods for determining the authenticity of fruit juice concentrates are needed for quality assurance and ingredient specification as well as for regulatory activities. Consumers have become aware of possible adulteration problems through investigative journalism (l_, 2). By C /C analyses many apple products purchased from Boston and New York supermarkets were shown to be adulterated with corn syrup or cane sugar. This sophisticated analytical technique has proven very useful for detecting adulteration of honey with corn syrup and cane sugar. It cannot be used, however, for detecting addition of beet sugar or sugars derived from other plants that utilize the Calvin pathway for C0 fixation (3, 4). Fruit juice concentrates vary widely in price because of differences in raw product cost and processing yield. For example, wholesale 1978 prices for Pacific Northwest produced concentrates varied from $6.25 per gallon for apple and pear to $35» $75* and $110 per gallon for strawberry, blackberry, and black raspberry concentrates, respectively (5). The readily available, low priced concentrates are obvious potential adulterants for more expensive concentrates and methods are needed for their detection. Factors such as variety, maturity, climate, geographic origin, cultural practices, and the influences of stress and disease, can affect a plant's chemical composition. Changes in composition can occur during processing and storage and certain additives are 12

13

2

1

To whom correspondence shall be addressed Current address: Department of Food Science, Cornell University, Ithaca, NY 14853 Current address: Department of Food Science and Technology, Washington State University, Pullman, WA 99164 Current address: Faculdade de Engenharia de Alimentos e Agricola, UNICAMP, Campinas, S. P. Brazil 13100 2

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0097-6156/81/0170-0077$05.00/0 © 1981 American Chemical Society Teranishi and Barrera-Benitez; Quality of Selected Fruits and Vegetables of North America ACS Symposium Series; American Chemical Society: Washington, DC, 1981.


78

QUALITY

OF

SELECTED

FRUITS

AND

VEGETABLES

sometimes p e r m i t t e d as p r o c e s s i n g a i d s which confound the proof o f a u t h e n t i c i t y by c o m p o s i t i o n a l analyses. We attempted t o consider many o f these f a c t o r s i n a previous study (6) o f sugar and nonv o l a t i l e a c i d composition o f ih b l a c k b e r r y samples and w h i l e t h i s study was r e l a t i v e l y s m a l l i n scope i t s t i l l r e q u i r e d c o n s i d e r a b l e e f f o r t . We wanted t o o b t a i n reference c o m p o s i t i o n a l data f o r f r u i t s o f major economic importance t o the P a c i f i c Northwest grape, apple, pear, strawberry, plum, b l a c k b e r r y , c h e r r y , and r a s p b e r r y . A n a l y s i s o f an adequate number o f samples t o i n c l u d e v a r i e t a l , g e o g r a p h i c a l , seasonal, and m a t u r i t y d i f f e r e n c e s f o r these f r u i t s would ]pe a formidable t a s k . T a b u l a t i o n o f a u t h e n t i c data from the l i t e r a t u r e i s necessary t o i n d i c a t e p r i o r i t i e s f o r f u r t h e r c o m p o s i t i o n a l i n v e s t i g a t i o n s . Such a c o m p i l a t i o n should begin t o i n d i c a t e v a r i a b i l i t y due t o v a r i e t y and geographic o r i g i n and would a l s o i n c l u d e v a r i a t i o n caused by d i f f e r e n t methods o f a n a l y s i s . Free Sugars and S o r b i t o l A computer search f o r the g l u c o s e , f r u c t o s e , sucrose, and s o r b i t o l contents o f apple, pear, c h e r r y , plum, grape, b l a c k b e r r y , r a s p b e r r y , strawberry, and peach f r u i t was conducted and the data were compiled both as g/100 g f r e s h weight and as percent o f t o t a l sugars. T o t a l sugars and g l u c o s e : f r u c t o s e r a t i o s were c a l c u l a t e d and t h e range, mean, standard d e v i a t i o n , and percent c o e f f i c i e n t of v a r i a n c e determined f o r a l l e n t r i e s . T h i r t e e n t a b l e s r e s u l t i n g from t h i s c o m p i l a t i o n o f data were p u b l i s h e d as a separate paper (7.) which can be r e f e r r e d t o f o r s p e c i f i c i n f o r m a t i o n ; Tables I and I I are d e r i v e d from those 13 t a b l e s and r e v e a l the comparative sugar and s o r b i t o l p a t t e r n s f o r the d i f f e r e n t f r u i t s and t h e i r v a r i a b i l i t y . C o n s i d e r i n g the sample d i v e r s i t y and the d i f f e r e n t a n a l y t i c a l methods used, one might expect t o f i n d even g r e a t e r v a r i a t i o n i n the data than was obtained. The data sources f o r apple f r u i t , f o r example, represent s e v e r a l d i f f e r e n t v a r i e t i e s from Western and E a s t e r n USA, Canada, Germany, S w i t z e r l a n d , England, I t a l y , and New Zealand and a wide v a r i e t y o f a n a l y t i c a l methods gas l i q u i d chromatography (GLC), paper chromatography, i o n exchange chromatography, enzymic and wet chemical analyses. The percent coe f f i c i e n t o f v a r i a n c e {% C.V.) f o r f r u c t o s e expressed as percent of t o t a l sugars i s o n l y 8.8. The % C.V. f o r f r u c t o s e content expressed on a g/100 g b a s i s i s 9.8. The % C.V. f o r the i n d i v i d u a l sugars c a l c u l a t e d as percent o f t o t a l sugars i s lower than the % C.V. f o r the same sugars r e p o r t e d on a g/100 g f r e s h f r u i t b a s i s . T h i s holds t r u e f o r a l l f r u i t s and i s not s u r p r i s i n g s i n c e sugar d e t e r m i n a t i o n on a g/100 g f r e s h weight b a s i s w i l l r e f l e c t both v a r i a t i o n i n t o t a l s o l i d s and a n a l y t i c a l e r r o r s i n q u a n t i t a t i v e recovery o f t o t a l sugars. Dako et a l . (8J analyzed 10 t o 12 samples f o r each o f the f o l l o w i n g f r u i t s over a p e r i o d o f two years and r e p o r t e d the f o l l o w i n g ranges f o r t o t a l sugar content Cg/100 g ) : a p p l e , 6.03-15.25; pear, 5.77-9.7^; plum, 6.33-10.83; c h e r r y , 9-51-

Teranishi and Barrera-Benitez; Quality of Selected Fruits and Vegetables of North America ACS Symposium Series; American Chemical Society: Washington, DC, 1981.


10.Λ

1*6.8

1*8.0

12. k

6

8

Blackberry

Peach

a

11.9

17..9

1.30

1.00

91.5

1

17·*

9.3

33.2

D e r i v e d from c o m p i l a t i o n s from the l i t e r a t u r e (.7); sugar content l i s t e d as percent t o t a l sugars (T.S. % C.V. = percent c o e f f i c i e n t of v a r i a n c e ; η = number o f sources; g l u : f r u = glucose : f r u c t o s e r a t i o .

35.8

15.2

33.0

O.9U 31.-7

31.3

29.8

3h.6

6

Red r a s p b e r r y

61.2 1.16

22.,8

1*2.5

19.6

ko.k

9

Strawberry

1.03

16. 9

1*6.5

12. k

1*5.0

8

Grapes

20.6 1.22

5-,6

52.5

15.8

hk.o

5

Sour c h e r r y

30.5

1.17

15.,1*

52.3

16.0

1*6.1*

11

Sweet cherry

1.69

13..0

60.8

21.5

38.1

8

Processed plums

1+2.1*

1.9^

28..7

38.3

U9.1

23.0

13

Plum

72.7

0.U8

51. 9

23.9

29.0

5

57.9

Processed pear

3U.3

38.2

C.V.

37.8

%

0.26

3..8

16.8

65

16

13.0

Pear

0.37

66.3

13

20.,0

8.8

55.0 23.0

Glucose :Fructose glu:fru

19.1*

Processed apple

C.V.

0.37

Glucose % T.S. %

32.,2

13

Apple

Fructose % T.S. % C.V.

Average F r u c t o s e and Glucose Contents of F r u i t s '

21.0

η

Sample

Table I .



10.5 16.8 16.7 38.1+ 1.22

Processed apple

a

9 6 6 8

5 8

30.9 8.79 1+6.3 15.1 8.71

55.3

123 7.3

H+3 112 39.8 16.2

sugars

% t o t a l sugars +

% total

sorbitol

(1);

3 1 0 3 3

0

11.7 17.1+ li+.o

9 6 6 7

sources ; %

0

h

5 6

C.V. = percent of

7.17

16.9 0.6 0

5 8

26.3

2h.3

82.0

17.U 1+1.7

51.U 39.0

1+

22.5 29.8 25. h 19.6 19.6

5 12 8 8

18

13

U.l6 17.6 13.2 l6.0

59.8 11.8 81.2

13

C.V.

57.2 66.1 2U.8

%

8 8

h.lh

11+.8

12

η = number of

5-5 5.82 6.96 8.12

11.0 33.8 10.2

Sorbitol η

:% T.S.+S,.c

Contents of F r u i t s '

T o t a l Sugars % c.v. η

g/l00g

31.9 92.2 50.0

C.V.

1+9-5 18U l60

%

Derived from compilations from the l i t e r a t u r e c o e f f e c i e n t of v a r i a n c e

Peach

Blackberry

Red r a s p b e r r y

Strawberry

3.7 75.7

3.1+6 3.58 16.6 33.6

Sour c h e r r y

Grapes

1.0k

Sweet c h e r r y

Processed

Plum

Processed pear

19 5 13 8 11

13

2U.1

Apple

Pear

lh

%

b

Sucrose η T.S.

Average Sucrose, T o t a l Sugar, and S o r b i t o l

Sample

Table I I .



7.

WROLSTAD E T A L .

81

Authenticity of Fruit Juice Concentrates

16.Ο6; peach, k.65-8.58; grapes, 8.75-17-30; strawberry, 3.96-5-96; r a s p b e r r y , 3-66-9-30; b l a c k b e r r y , h.78-7-38. Patterns c h a r a c t e r i s t i c o f the i n d i v i d u a l f r u i t s are evident from Tables I and I I . Pear and apple c o n t a i n much more f r u c t o s e than glucose while r a s p b e r r y , b l a c k b e r r y , grape, strawberry, and c h e r r y have e s s e n t i a l l y i n v e r t sugar (glucose : f r u c t o s e = 1:1) p a t t e r n s . Conversely, peach and plum c o n t a i n more glucose than f r u c t o s e . The g l u c o s e : f r u c t o s e r a t i o i s u s e f u l , t h e r e f o r e , i n categorizing f r u i t s . I t w i l l be a l t e r e d , however, by sucrose i n v e r s i o n i n f r u i t s not having i n v e r t p a t t e r n s . Kliewer (9.) measured the g l u c o s e : f r u c t o s e r a t i o i n eight v a r i e t i e s o f grapes during r i p e n i n g and found t h a t the 1:1 r a t i o i n r i p e f r u i t changes t o 0.63 i n overripe f r u i t . Table I I shows t h a t sucrose l e v e l s are h i g h e s t i n peach f r u i t and very low i n b l a c k b e r r y , cherry, and grape. The % C.V. f o r sucrose content f o r many o f the f r u i t samples i s extremely h i g h , most l i k e l y because o f enzymic o r chemical h y d r o l y s i s . The average sucrose content o f plum f r u i t i s 38% o f t o t a l sugars, while pro cessed plums c o n t a i n only 1%. Presence o f l a r g e q u a n t i t i e s o f sucrose i n prune j u i c e has, i n f a c t , been used as an i n d i c a t i o n o f a d u l t e r a t i o n ( l O ) . C h e r r i e s and grapes c o n t a i n i n v e r t a s e ( l l , 12) which may account f o r sucrose not being detected i n some samples and may a l s o e x p l a i n the h i g h % C.V. f o r those f r u i t s . In examining apple j u i c e concentrates, we d i d not detect sucrose i n s e v e n - f o l d concentrates whereas we d i d i n f o u r - f o l d apple concentrates (7_) the time-temperature c o n d i t i o n s a l l o w i n g f o r complete h y d r o l y s i s i n the more concentrated product. S o r b i t o l content can be a u s e f u l index i n c l a s s i f y i n g f r u i t s . Pear, cherry, and plum f r u i t are highest i n s o r b i t o l and both peach and apple c o n t a i n s u b s t a n t i a l q u a n t i t i e s (Table I I ) . Trace amounts were found i n grapes (13.); no s o r b i t o l was r e p o r t e d f o r b l a c k b e r r y , r a s p b e r r y , and strawberry (Table I I I ) . The l a t t e r three f r u i t s are o f h i g h economic value and the presence o f s o r b i t o l i n t h e i r concentrates can be an i n d i c a t i o n o f a d u l t e r a t i o n with l e s s expen s i v e s o r b i t o l - c o n t a i n i n g f r u i t s . The % C.V. f o r s o r b i t o l content i s f a i r l y high f o r some f r u i t s . In some i n s t a n c e s , e.g. peach, the r e l a t i v e l y small sample s i z e may be a f a c t o r . Neubeller and S t o s s e r {lh) s t u d i e d the sugar and s o r b i t o l v a r i a t i o n o f 20 v a r i e t i e s o f sweet c h e r r i e s over three years and r e p o r t e d the s o r b i t o l content t o vary from 15-5 t o 2k.0 percent o f t o t a l sugars plus s o r b i t o l . Chan et a l (15) showed t h a t s o r b i t o l content o f apples can show c o n s i d e r a b l e v a r i a t i o n with v a r i e t y , storage c o n d i t i o n s , and season. We examined a number o f commercial blackbery j u i c e concen t r a t e s by GLC o f t h e i r t r i m e t h y l s i l y l (TMS) d e r i v a t i v e s . Three samples were found t o c o n t a i n from 2.8-21.5? o f t o t a l sugars as s o r b i t o l (l6) l e a d i n g us t o b e l i e v e t h a t those samples were a d u l t e r a t e d . P r e v i o u s l y , we had examined lh authentic samples o f b l a c k b e r r i e s by s i m i l a r a n a l y t i c a l procedures and no s o r b i t o l was de t e c t e d i n any of those samples (6). S o r b i t o l i s non-fermentative 5



82

QUALITY

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FRUITS

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and when we made wine from s o r b i t o l - c o n t a i n i n g b l a c k b e r r y j u i c e concentrate we r e a d i l y detected i t by high performance l i q u i d chromatography (HPLC). We looked at three commercial wines, and one which was l a b e l e d as being produced from imported European b l a c k b e r r i e s contained s o r b i t o l . Two other domestic wines may have contained t r a c e amounts of s o r b i t o l because a small peak with the same r e t e n t i o n time as s o r b i t o l was detected. Makinen and S o d e r l i n g (17) r e c e n t l y r e p o r t e d t h a t r i p e strawberry and r i p e red r a s p b e r r y c o n t a i n 320 and 85 yg s o r b i t o l / g f r e s h f r u i t , respect i v e l y . Previous workers have not found s o r b i t o l i n strawberries and r a s p b e r r i e s ; f u t u r e work using more s e n s i t i v e a n a l y t i c a l methods may show t h a t b l a c k b e r r i e s and other b e r r y f r u i t s a l s o cont a i n s o r b i t o l , i f only i n very small amounts. I f the raw product from which a j u i c e concentrate was made had been p a r t i a l l y f e r mented, t h i s c o u l d r e s u l t i n i n c r e a s e d concentration of any s o r b i t o l which might allow i t s d e t e c t i o n . A n a l y s i s of commercial apple j u i c e concentrates i n our l a b o r a t o r y r e v e a l e d that the s o r b i t o l content of one sample was f a r below the range f o r s o r b i t o l content r e p o r t e d i n the l i t e r a t u r e . That sample had a high g l u c o s e : f r u c t o s e r a t i o l e a d i n g t o the s u s p i c i o n t h a t i t may have been a d u l t e r a t e d with corn syrup. T h i s i l l u s t r a t e s how sugar a n a l y s i s can be a u s e f u l screening mechanism but the suspect sample should be subject e d t o f u r t h e r analyses f o r more d e f i n i t i v e proof. Nonvolatile Acids Table I I I l i s t s the m a l i c , c i t r i c , i s o c i t r i c , l a c t o i s o c i t r i c , t a r t a r i c , q u i n i c and t o t a l a c i d contents f o r apple, pear, plum, c h e r r y , grape, strawberry, raspberry, b l a c k b e r r y , peach, and cranberry f r u i t as reported i n s e l e c t e d l i t e r a t u r e r e f e r e n c e s . A wide range o f values f o r t o t a l a c i d s occurs both w i t h i n and between the d i f f e r e n t commodities, l i m i t i n g i t s u t i l i t y i n det e c t i n g a d u l t e r a t i o n . T h i s i s not s u r p r i s i n g because of the abrupt drop i n t o t a l a c i d i t y which w i l l occur with many f r u i t s when reaching the f u l l y r i p e stage, and the known i n f l u e n c e s of v a r i e t y and c l i m a t i c c o n d i t i o n s on a c i d i t y (l8.). There are s e v e r a l c o n t r a d i c t i o n s i n Table I I I as t o the q u a l i t a t i v e compos i t i o n o f a given f r u i t . For example, q u i n i c a c i d i s reported f o r some but not a l l samples of plum, apple, grape, strawberry, and peach f r u i t . Benk Ç19) reported t h a t strawberry j u i c e cont a i n s i s o c i t r i c as w e l l as c i t r i c a c i d and t h a t raspberry j u i c e contains more i s o c i t r i c than c i t r i c a c i d . Whiting C20) reported t h a t b l a c k b e r r i e s c o n t a i n i s o c i t r i c and not c i t r i c a c i d while Benk (19) r e p o r t e d t h a t b l a c k b e r r i e s contain both with i s o c i t r i c being present i n l a r g e r q u a n t i t i e s than c i t r i c a c i d . We were unable t o r e s o l v e c i t r i c and i s o c i t r i c a c i d i n our analyses of b l a c k b e r r y f r u i t by GLC (6). These two a c i d s are d i f f i c u l t t o r e s o l v e by GLC and c i t r i c a c i d content may be higher than the c o r r e c t value i n r e p o r t s f o r other f r u i t s because of presence of i s o c i t r i c a c i d . Fernandez-Flores et_ a l . (21) r e p o r t e d s y r i n g i c



7.

WROLSTAD E T A L .


83

a c i d t o be a major a c i d i n c h e r r r i e s and a l s o r e p o r t e d i t s presence i n plums, apples, and pears but t h i s has not been confirmed by other workers. Phosphoric a c i d apparently can be found i n small q u a n t i t i e s i n most f r u i t s when the a n a l y t i c a l methods permit i t s d e t e c t i o n . Ryan and Dupont (22) p o i n t e d out t h a t the GLC r e t e n t i o n time f o r t h e t r i m e t h y l s i l y l (TMS) d e r i v a t i v e o f phosphoric a c i d i s very s i m i l a r t o those f o r s u c c i n i c , fumaric, malonic, and maleic a c i d s on both SE-30 and OV-17 l i q u i d phases; these a c i d s as w e l l as g l y c o l i c , s h i k i m i c , and chlorogenic have p r e v i o u s l y been r e p o r t e d i n small q u a n t i t i e s i n many f r u i t s (l8_). They are not l i s t e d i n Table I I I because t h e i r d e t e c t i o n i n a f r u i t concent r a t e i s o f l i m i t e d value f o r a d u l t e r a t i o n analyses. With i n creased r e s o l u t i o n and s e n s i t i v i t y i n methods f o r n o n v o l a t i l e a c i d a n a l y s e s , i t i s l i k e l y t h a t they w i l l be detected i n authentic samples o f many f r u i t s i n small q u a n t i t i e s . There i s c o n s i d e r a b l e v a r i a t i o n i n the r e l a t i v e amounts o f the major a c i d s i n Table I I I f o r most o f the f r u i t s . F o r example, one r e f e r e n c e shows m a l i c a c i d t o be the major a c i d i n peaches while another shows c i t r i c t o be the p r i n c i p a l a c i d . In a n a l y z i n g t h e changes o f n o n v o l a t i l e a c i d s during t h e r i p e n i n g o f B a r t l e t t pears, we found m a l i c t o be t h e major a c i d i n underripe f r u i t and c i t r i c t o be present i n l a r g e s t q u a n t i t i e s i n r i p e f r u i t (.23). Cash et a l {2h) found m a l i c t o be present i n l a r g e r q u a n t i t i e s than t a r t a r i c i n l e s s mature Concord grapes, but t a r t a r i c was present i n r e l a t i v e l y l a r g e r amounts t h a t m a l i c i n t h e f u l l y r i p e f r u i t . Johnson and Nagel (25_) s i m i l a r l y found t a r t a r i c i n g r e a t e r q u a n t i t y than m a l i c a c i d i n f i v e v a r i e t i e s o f grapes when t h e f r u i t was f u l l y mature. We found a great d e a l o f q u a n t i t a t i v e v a r i a t i o n i n b l a c k b e r r y n o n v o l a t i l e a c i d s , i s o c i t r i c being the p r i n c i p l e a c i d i n some samples, malic being t h e predominant a c i d i n o t h e r s , and l a c t o i s o c i t r i c being t h e major a c i d i n a very underripe sample o f Evergreen b l a c k b e r r i e s (6_). Some a c i d s are c h a r a c t e r i s t i c o f i n d i v i d u a l f r u i t s and q u i t e u s e f u l i n a d u l t e r a t i o n i n v e s t i g a t i o n s . T a r t a r i c a c i d i s a major a c i d o f grapes and i s not found i n l a r g e q u a n t i t i e s i n t h e other fruits. However, removal o f t a r t a r i c a c i d through c r y s t a l l i z a t i o n and i o n exchange procedures can r e s u l t i n i t s being present i n only minor q u a n t i t i e s i n grape j u i c e and concentrates. Hence, i t may be present i n o n l y minor amounts i n a f r u i t concentrate a d u l t e r a t e d with grape j u i c e concentrate. L a c t o i s o c i t r i c a c i d has a l i m i t e d d i s t r i b u t i o n i n f r u i t s , but i s found i n b l a c k b e r r i e s . Our r e s u l t s showed t h a t i t i s not present i n a l l b l a c k b e r r y samples, however, and i t s absence i n b l a c k b e r r y j u i c e w i l l not deny i t s a u t h e n t i c i t y (6_). Quinic a c i d i s q u i t e widespread among f r u i t s and i s present i n q u i t e l a r g e concentrations i n plum and cranberry. We found h i g h l e v e l s o f q u i n i c a c i d i n an imported b l a c k b e r r y j u i c e concentrate which a l s o contained s o r b i t o l ; t h i s l e d us t o suspect t h a t t h e s o r b i t o l - c o n t a i n i n g a d u l t e r a n t may have been plum (l6). A c i d s such as c i t r i c and malic are permitted f o r use i n pH adjustment i n f r u i t j u i c e p r o c e s s i n g which may confound the i n t e r -



37-9

3*+. 5

51.6

5-7

37.6

concord

13.6

18.9

1.6

12.U

% T.A.

Tartaric

red

25.1

55-7

88.3 85.5

21.6

3.6

18.T

10.3

17.2

22.3

2.0

% T.A.

Lactoisocitric

51.5

h

2

Isocitric

1+5.7

juice

Grape

fruit

plum concentrate (10° B r i x ) Cherry

Italian

prune j u i c e

1

juice

Plum

5h.k 79.6

Bartlett

1

60.1

Winesap

91.3

35-7

Pear

Citric

Major N o n v o l a t i l e A c i d s i n F r u i t s

% T.A. % T.A. % T.A.

Malic

Delicious

a

69.3

6

n

Granny Smith

apple j u i c e

Apple

Sample

Table I I I .


T.A.^

h.d

9-8

30.7

10.0

l8.h

6.8

7.8

5.6

h.O

1759

1135

1029

2U3

515

2203 l8lU

791

210

535

1085

568

5^8

TOI

(21)

(21)

(39)

(21)

(Ul)

(21) (21)

(39)

(23)

(21)

(21)

(21)

(UO)

(39)

% T.A. mg/l00g Ref.

Quinic


Tr = t r a c e

= t o t a l acids

27.7

28.5

35.7

U8.9

U7.6

15.0

k.l

20.6

7.9

35.^

Malic % T.A.

η = i n d i c a t e d sample s i z e

27

juice

3

ik

1

k

1

"k T.A.

a

&

1

n

juice

Cranberry

fruit

fruit

Peach

fruit

M a i l i n g Promise Blackberry fruit

juice

Raspberry

fruit ( f u l l ripe)

fruit

Strawberry juice

Sample

Table I I I (continued)

13.7

17-9

tr°

0.7

1.3

2.8

3320

632

928

99U

1718

10U9

1968

25^7

1220

1098

975

(26)

(39)

(U3)

(21)

(20)

(6)

(20)

(39)

(U2)

(21)

(39)

Quinic T.A.^ ? T.A. mg/lOOg Ref.

39.8

3^.9

Tartaric % Τ.A.

32.5

d

Lactoisocitric % T.A.

39-5

17.5

59.9

Isocitric % T.A.

32.0

63.5

32.2

95-9

97. ^

73.6

85.6

59.5

Citric % T.A.


86

QUALITY

OF

SELECTED

FRUITS

AND

VEGETABLES

p r e t a t i o n of n o n v o l a t i l e a c i d p r o f i l e s of f r u i t j u i c e s and concentrates. Benzoic a c i d i s found n a t u r a l l y i n c r a n b e r r i e s (.0.6% o f t o t a l a c i d s ; (26)). In other f r u i t s i t s presence would i n d i c a t e a d d i t i o n o f sodium benzoate.


Free Amino A c i d s Table IV l i s t s the p r o l i n e , a r g i n i n e , a s p a r t i c a c i d , glutamic a c i d , aminobutyric a c i d , a l a n i n e and t o t a l amino a c i d contents of s e v e r a l f r u i t s as r e p o r t e d i n s e l e c t e d l i t e r a t u r e r e f e r e n c e s . A p a r t i c u l a r l y s a l i e n t r e f e r e n c e i s t h a t of Fernandez-Flores et_ a l (27) -who r e p o r t e d q u a n t i t i e s of 15 f r e e amino a c i d s f o r 22 d i f f e r ent f r u i t s . They suggested t h a t the 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 s t r i b u t i o n o f f r e e amino a c i d s c o u l d be c h a r a c t e r i s t i c of the i n d i v i d u a l f r u i t s . There were only small v a r i a t i o n s i n the p a t t e r n s f o r s i x d i f f e r e n t orange samples and seven strawberry samples. They concluded t h a t the 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 s t r i b u t i o n o f amino a c i d s c o u l d be a u s e f u l index f o r determining the authent i c i t y o f f r u i t products. A l s o , t o t a l amino a c i d content i t s e l f can be e f f e c t i v e l y used s i n c e apple and cranberry are very low i n t o t a l amino a c i d s while grape, b l a c k b e r r y , plum, and peach are r e l a t i v e l y high. C o l o r i m e t r i c determination of p r o l i n e content can be a u s e f u l q u a l i t y c o n t r o l measurement. Grapes are f a i r l y h i g h i n p r o l i n e , and apples are q u i t e low. The U.S.A. import duty f o r grape j u i c e concentrate i s $0.25 per g a l l o n on a s i n g l e s t r e n g t h b a s i s whereas apple and pear j u i c e concentrate are duty-free (28). Measurement of p r o l i n e content i s h e l p f u l i n determining e n t r y of grape j u i c e concentrate under an i l l e g a l c l a s s i f i c a t i o n . Swiss law permits a m e l i o r a t i o n of apple j u i c e with pear j u i c e t o a maximum o f 10 percent. Blumenthal and Hebling (29) used a combination o f p r o l i n e , c i t r i c a c i d , and s o r b i t o l analyses t o e s t a b l i s h b a s e - l i n e r e f e r e n c e data f o r determining whether the permitted 10 percent a m e l i o r a t i o n had been exceeded. They found t h a t one t h i r d of the commercial apple j u i c e s i n v e s t i g a t e d d i d not comply w i t h the l e g a l requirements. T h e i r approach t o s o l v i n g t h e i r d i f f i c u l t a n a l y t i c a l problem i l l u s t r a t e s the n e c e s s i t y of u s i n g a combination of parameters r a t h e r than r e l y i n g on measurement o f one p a r t i c u l a r c o n s t i t u e n t . Other amino a c i d determinat i o n s which may have u s e f u l a p p l i c a t i o n r e l a t e t o the high a l a n i n e content o f b l a c k b e r r i e s , the high aminobutyric a c i d content of grapes and b l a c k b e r r i e s , and the h i g h a s p a r t i c a c i d content of pears and plums. A t t e n t i o n needs t o be given t o changes i n f r e e amino a c i d content which occurs during p r o c e s s i n g and storage. Wucherpfennig Ç30) showed t h a t a marked r e d u c t i o n i n p r o l i n e and a r g i n i n e occurred i n p r o c e s s i n g grape j u i c e concentrate. Lowering amino a c i d content w i t h c a t i o n exchange r e s i n treatment i s permitted by US law i n non-standard!zed f r u i t j u i c e s and i s used t o reduce


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Proline

Η.5

1.1 0.6

n. a.

n. a.

n. a.

F r u i t (red) 16

F r u i t (black) 3

Fruit n. a.

n. a.

n. a.

n. a.

5.95

η.a.

η. a.

η. a.

η. a.

η. a.

η. a.

η. a.

n. a. n. a.

n. a.

n. a.

h.3

30Λ

n. a.

108

n. a.

n. a.

77

Fruit

3k

l+00-ΐδθΟ

tr

n. a.

tr

tr

0.8

39-1 30 125 13

η. a.

n. a.

n. a.

39.Τ

IT

J u i c e (red) 3k

Aspartic

6.5 8.9 2.1

n. a.

k.k

Fruit

Raspberry J u i c e (red)

Arginine

Glutamic

η.a.

η.a.

η. a.

η. a.

η. a.

n. a.

η. a.

η.a.

9.7 7.3

12.U

51

n. a.

n.a.

n.a.

n. a.

n.a.

n.a.

n. a.

n.a.

n. a.

n.a.

5.6

22

n. a.

η. a.

η.a.

η. a.

η.a.

η.a.

η.a.

η. a.

η.a.

5.7

5.8

35

η.a.

(1£)

(hi)

(21)

(U6)

(30)

(21)

(U8) 2.19° (39)

l.k2°

(U8)

(U£)

2.1U

(19) n.a.

(3£) n. a. C

1.05°

0.82° ( W )

n. a.

62.5 62.5 55.1

398

n. a.

172.8

22 Λ

n.a.

(21)

123.6

5.9 32.2

lU.7

(21)

135. k

35.0

mg/l00g 13. h

Total

mg/l00g Ref.

Alanine

19.1

mg/100 g

Aminobutyric

^3.6 36.6

mg/100 g mg/100 g mg/100 g mg/100 g

1.2

7 1 1

18

b η

Juice

Tioga

Hood

Strawberry fruit

Ripe f r u i t

Fruit

white

red

Grape black

Sample

Table IV. (continued)



Proline

I n d i c a t e d sample s i z e

° meq/100 g

Aspartic

Glutamic

η. a.

η. a.

6.2

105.6

n.a.

n.a.

56.2

2.1

1.6

n.a.

n.a.

17.ii

3.9

0.8

n.a.

n.a.

25.1

mg/100 g

Aminobutyric

tr

0.8

n.a.

n.a.

80.9

Alanine mg/lOOg

mg/100 g f r u i t or 100 ml j u i c e ; n.a. = not analyzed; t r = t r

tr

Cranberry fruit

Values are

tr

η. a.

Fruit

η. a.

η. a.

3

Peach freestone

a

Arginine

mg/100 g mg/100 g mg/100 g mg/100 g

juice

^

η. a.

η

5.2

Blackberry Fruit

Sample

Table IV. (continued)


Total

(27)

15.1

111.9

(27)

(21)

(19) 2.25° ( W ) n.a.

228.9

mg/l00g Ref.

90

QUALITY

OF

SELECTED

FRUITS

AND

VEGETABLES

c o l o r degradation through M a i l l a r d browning r e a c t i o n s i n manufacture o f pineapple j u i c e concentrate. T h i s s e v e r e l y r e s t r i c t s t h e u t i l i t y o f amino a c i d analyses i n c e r t a i n a d u l t e r a t i o n i n v e s t i g a t i o n s .


Anthocyanin Pigments and Other Secondary P l a n t M e t a b o l i t e s The anthocyanin pigment composition f o r many f r u i t s i s q u i t e d i s t i n c t i v e and i s u s e f u l i n c e r t a i n cases o f a d u l t e r a t i o n i n v e s t i g a t i o n . There are a number o f reviewers who have summarized t h e anthocyanin pigments which have been i d e n t i f i e d i n v a r i o u s f r u i t s (31, 32, 33). Paper chromatography of anthocyanin pigments has been used t o detect a d u l t e r a t i o n o f Concord grape j u i c e w i t h V i n i f e r a or h y b r i d v a r i e t i e s (3j+, 35.) and t o detect a d u l t e r a t i o n o f b l a c k b e r r y and cherry j u i c e concentrates w i t h e l d e r b e r r y or grape s k i n e x t r a c t (36). As mentioned b e f o r e , we suspected t h a t an imp o r t e d b l a c k b e r r y j u i c e concentrate sample was a d u l t e r a t e d w i t h plum j u i c e because o f i t s s o r b i t o l and q u i n i c a c i d content (l6). Plums c o n t a i n p e o n i d i n 3-glucoside and r u t i n o s i d e i n a d d i t i o n t o the c y a n i d i n - 3 - g l u c o s i d e and c y a n i d i n - 3 - r u t i n o s i d e , which have been i d e n t i f i e d t o be t h e pigments o f b l a c k b e r r i e s (37)· We f a i l e d t o f i n d any p e o n i d i n pigments i n t h a t imported b l a c k b e r r y concentrate sample. T h i s d i d not prove t h a t plums were not t h e a d u l t e r a n t because plums have r e l a t i v e l y low concentrations o f anthocyanins which are a l s o unstable and may have been degraded. Pigment a n a l yses o f some b l a c k b e r y concentrate and wine samples which we bel i e v e d t o be a u t h e n t i c , d i d r e v e a l t h e presence o f some pigments i n a d d i t i o n t o cyanidin-3-glucoside and c y a n i d i n - 3 - r u t i n o s i d e . These pigments may be minor compounds which have not been p r e v i o u s l y i d e n t i f i e d . I t has been our experience t h a t when we have f r a c t i o n a t e d l a r g e amounts o f pigments through p r e p a r a t i v e column chromatography we i n v a r i a b l y have found new pigments which had not been detected before (38). These pigments may p o s s i b l y be a r t i f a c t s of a n a l y s i s o r , i n t h e a n a l y s i s o f wines and j u i c e c o n c e n t r a t e s , may have been dégradâtive products formed during p r o c e s s i n g and storage. Therefore c a u t i o n must be used i n i n t e r p r e t i n g anthocyan i n data i n a d u l t e r a t i o n s t u d i e s . A n a l y s i s o f anthocyanins by HPLC should g i v e more meaningful q u a n t i t a t i v e data which would be e a s i e r t o i n t e r p r e t than t h e q u a l i t a t i v e p a t t e r n s obtained i n paper and t h i n - l a y e r chromatography. The s h o r t e r a n a l y s i s time u s i n g HPLC would a l s o be more amenable t o screening a l a r g e r number of samples. A n a l y s i s o f f l a v o n o i d s other than anthocyanins may prove u s e f u l s i n c e many o f these compounds are more s t a b l e than the l a b i l e anthocyanins. There i s a need f o r more d e f i n i t e i d e n t i f i c a t i o n work on the f l a v o n o i d composition o f many f r u i t s o f economic importance. In our i n v e s t i g a t i o n s t o date we have not used analyses o f f r u i t j u i c e concentrate v o l a t i l e s t o detect a d u l t e r a t i o n . The maj o r i t y o f the v o l a t i l e s are removed i n t h e c o n c e n t r a t i o n p r o c e s s , and t h e recovered essence may be added back t o t h e concentrate o r s o l d s e p a r a t e l y . Many o f t h e l e s s expensive concentrates are r e placements f o r sugar syrups and are v e r y bland i n f l a v o r ; they are


7.

WROLSTAD

E T A L .


91

the most l i k e l y candidates f o r use as a d u l t e r a n t s and would probably be d i f f i c u l t t o detect by v o l a t i l e a n a l y s i s . However, there may be cases where a n a l y s i s o f v o l a t i l e s would be u s e f u l i n i d e n t i f y i n g an a d u l t e r a n t .


Conclusions D e t e c t i o n o f a d u l t e r a t i o n i n f r u i t j u i c e concentrates i s a d i f f i c u l t problem because o f compositional v a r i a t i o n induced by v a r i e t a l , maturity, seasonal, and geographic f a c t o r s as w e l l as the changes which occur during p r o c e s s i n g and storage. A d d i t i o n o f a d d i t i v e s during p r o c e s s i n g and r e g u l a t o r y d i f f e r e n c e s between c o u n t r i e s add t o the complexity o f the problem. S t i l l , there are patterns i n the sugar, n o n v o l a t i l e a c i d , amino a c i d , and pigment composition which are c h a r a c t e r i s t i c o f the i n d i v i d u a l f r u i t s and can be used t o detect a d u l t e r a t i o n . I t i s undoubtedly t r u e t h a t our knowledge o f food composition l a g s behind our present a n a l y t i c a l c a p a b i l i t i e s . There i s a p a r t i c u l a r need t o f u r t h e r extend the knowledge o f changes i n food composition which occur during p r o c e s s i n g and storage. Acknowledgement s T e c h n i c a l Paper No. 5606 from the Oregon A g r i c u l t u r a l E x p e r i ment S t a t i o n . The work was supported i n part by grant No. 1079005*+ from the P a c i f i c Northwest Regional Commission.

Abstract The glucose, fructose, sorbitol, and sucrose contents of apple, pear, grape, cherry, plum, peach, strawberry, blackberry, red raspberry, and black raspberry fruit were compiled from the literature and analyzed statistically. The different fruits show characteristic sugar patterns with only moderate variation when considering the differences in geographic origin, variety, maturity, and method of analysis. Investigations in our laboratory utilizing GLC and HPLC reaffirm that sorbitol content and the glucose:fructose ratio are useful screening indices. Sucrose content shows considerable variation due to invertase activity and/or chemical hydrolysis, particularly in processed products. There is considerable quantitative variation in nonvolatile acid composition due to variety and maturity effects. Certain qualitative differences such as tartaric acid in grapes and lactoisocitric in blackberries are of practical use in detecting adulteration in certain cases. The free amino acid and anthocyanin pigment patterns are characteristic of individual fruits but changes in their composition which occur during processing and storage confound their utility in adulteration investigations.


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Quality of Selected Fruits and Vegetables of North America - American

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