Citrus Nutrition and Quality - American Chemical Society

11 Citrus Juice Processing as Related to Quality and Nutrition CHARLES VARSEL Downloaded by UNIV OF AUCKLAND on October 17, 2014 | http://pubs.acs.org Publication Date: December 15, 1980 | doi: 10.1021/bk-1980-0143.ch011

The Coca-Cola Company Foods Division, 7105 Katy Road, Houston, TX 77024

There is much that can be said in favor of the consumption of fresh fruits and vegetables in the daily diet. In much of the world, citrus is consumed primarily as the fresh fruit, but in the United States processed products are consumed as the major source of citrus in the diet. The main staple of processed citrus juices in the U.S. is frozen concentrated orange juice (FCOJ). Were it not for the processing of citrus fruits, this rich source of nutritious food, in the forms of juices and drinks, would be available to us for only limited periods of time throughout the course of any year. Processing techniques practiced today in the citrus industry ensure the availability of a continuous supply of citrus juices and their allied products to people in a l l regions of the United States and, indeed, in many parts of the world. Our increased knowledge of nutrients in the food supply and how they are affected by processing has led to an increased awareness on the p a r t of processors about the n u t r i t i o n a l aspects and q u a l i t i e s of t h e i r products, and f o r a greater d e s i r e to improve p r o c e s s i n g techniques so that the consumer can derive maximum b e n e f i t s from those n u t r i e n t s . There has been an increased r e c o g n i t i o n i n the food i n d u s t r y that we have some r e s p o n s i b i l i t y for the n u t r i t i o n a l q u a l i t y of our food supply. This awareness of r e s p o n s i b i l i t y has led to increased safeguards i n processing so that not only the n u t r i t i o n a l q u a l i t y , but also the f l a v o r a c c e p t a b i l i t y i s b e t t e r r e t a i n e d i n the processing of n a t u r a l foods. The increased awareness on the part of consumers about nut r i t i o n has l e d to an increased demand f o r c i t r u s j u i c e s and p r o d u c t s , a demand that i s greater today than i t has ever been. This has l e d to a tremendous growth w i t h i n the c i t r u s i n d u s t r y , and developing nations of the world that have climates s u i t a b l e f o r the production of c i t r u s f r u i t s have b e n e f i t t e d tremendously from t h i s consumer demand. B r a z i l i s a prime example. The growth of the c i t r u s i n d u s t r y i n B r a z i l has been a great economic f a c t o r i n

0-8412-0595-7/80/47-143-225$l 1.75/0 © 1980 American Chemical Society In Citrus Nutrition and Quality; Nagy, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

Downloaded by UNIV OF AUCKLAND on October 17, 2014 | http://pubs.acs.org Publication Date: December 15, 1980 | doi: 10.1021/bk-1980-0143.ch011

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the w e l f a r e of i t s people. B r a z i l today i s a major f a c t o r i n the worldwide supply of c i t r u s products and i s second only to the U.S. i n the p r o d u c t i o n of c i t r u s . T h i s i s evidenced i n Table I, which presents data on c i t r u s f r u i t production by s p e c i f i e d c o u n t r i e s (j.) . The o v e r a l l growth of the c i t r u s i n d u s t r y i s , o f course, f o s t e r e d by improved economic c o n d i t i o n s i n many count r i e s and e v o l v i n g technologies that permit the production, storage, and shipment of c i t r u s products over long d i s t a n c e s . R e f r i g e r a t i o n , new d i s t r i b u t i o n methods, and new packaging techniques represent developments without which many people i n the world could not enjoy the f u l l f l a v o r and n u t r i t i o n of c i t r u s products. The unique and d i s t i n c t i v e f l a v o r s o f the c i t r u s f r u i t s and the general a c c e p t a b i l i t y of these f l a v o r s by peoples throughout the world have a l s o been f a c t o r s c o n t r i b u t i n g to the growth of the c i t r u s i n d u s t r y . Orange f l a v o r i s probably the most widely recognized and accepted f l a v o r i n the food and beverage i n d u s t r y worldwide. Because of i t s d i s t i n c t i v e f l a v o r and aroma i t i s used to f l a v o r many foods and beverages and to aromatize many household products. G r a p e f r u i t i s l e s s popular than the orange but perhaps more popular than the lemon r e l a t i v e t o consumption of the j u i c e . P o p u l a r i t y of g r a p e f r u i t j u i c e i s i n c r e a s i n g i n many p a r t s of the world, p a r t i c u l a r l y i n the United States and i n Japan. How much i t s c h i m e r i c a l image as a d i e t e t i c food has c o n t r i b u t e d tc t h i s i n c r e a s i n g p o p u l a r i t y i s not known, but i t undoubtedly has been a f a c t o r . C h i l l e d and b o t t l e d g r a p e f r u i t j u i c e s are growing i n p o p u l a r i t y whereas the usage of frozen concentrated g r a p e f r u i t j u i c e continues to grow, but at a s l i g h t l y slower r a t e . Lemon j u i c e has many uses i n the food i n d u s t r y that other j u i c e s do not have because of i t s uniquely d i f f e r e n t composition i n r e l a t i o n to other j u i c e s , except perhaps lime. Large q u a n t i t i e s of lemon j u i c e are used to enhance food f l a v o r s and to develop and balance the f l a v o r s of many food items, seafood being an outstanding example. P o s s i b l y only sugar and s a l t are used more e x t e n s i v e l y i n the development and enhancement of food f l a v o r s . Lemon j u i c e has a l s o gained i n p o p u l a r i t y because o f t e c h n o l o g i c a l advances that now permit the manufacture of concentrated j u i c e s and the p r o d u c t i o n of a frozen concentrate f o r lemonade. The f l a v o r of lemon, c o n t r i b u t e d by the p e e l o i l , i s probably second only to orange f l a v o r i n o v e r a l l p o p u l a r i t y . The growth i n market f c r the powdered s o f t d r i n k mixes and the f r u i t d r i n k mixes, p a r t i c u l a r l y f o r lemon-flavored products, has i n creased the demand f o r lemon o i l . Added to t h i s i s the i n c r e a s ing demand f o r lemon o i l s f o r use i n the carbonated and noncarbonated s o f t d r i n k s that are i n c r e a s i n g i n p o p u l a r i t y worldwide.

In Citrus Nutrition and Quality; Nagy, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

11.

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Citrus Juice

227

Processing

TABLE I Citrus Fruit: P r o d u c t i o n , by Selected C o u n t r i e s , of P r i n c i p a l Types, Crop Years 1976-77 through 1918-19(1)

Country

i

1 1976-77

j

Crop Years 1977-78

1978-79 2J

1,000 M e t r i c Tons 11


Orange s and Tangerines United S t a t e s Brazil Japan Spain Italy Morocco Israel Argentina Mexico Egypt Turkey Greece South A f r i c a Australia Cyprus Chile TOTAL

10,144 6,087 3,575 2,466 2,258 784 968 990 1,283 840 671 533 463 384 100 45

9,256 8,205 4,119 2,514 1,942 1,055 949 925 750 747 735 455 591 393 109 47

8,725 7,256 3,663 2,473 1,699 992 975 926 783 780 780 629 583 395 113 48

31,591

32,792

30,820

Lemons United States Italy Brazil Argentina Turkey Spain Greece TOTAL

1/ 2J

896 792 371 320 278 220 190

900 800 363 280 280 313 194

758 600 367 267 250 239 175

3,067

3,130

2,656

One m e t r i c ton i s equivalent to 2204.6 pounds P r e l i m i n ary. The Florida Crop and Livestock Reporting Service


228


TABLE I I


U.S.

Crop Y e a r

P r o d u c t i o n o f Oranges Y e a r s 1 9 7 3 - 7 8 ÇL)

U t i l i z a t i o n of Production 1000 M e t r i c Tons

Fresh

Processed

% Tons Processed

Total

1973-74

1613

6900

8514

81.0

1974-75

1951

7339

9290

79.0

1975-76

1803

7717

9519

81.1

1976-77

1680

7886

9567

82.4

1977-78

1598

7059

8657

81.5

1978-79*

1451

6854

8306

82.5

1683

7292

8976

81.2

AVERAGE

^Estimate The Florida Crop and Livestock Reporting Service


11.


1

VARSEL

Citrus Juice

229

Processing

Processing

T e c h n o l o g i c a l developments i n high vacuum evaporation techniques have been r e s p o n s i b l e f o r the r a p i d growth o f the domestic c i t r u s i n d u s t r y . These techniques were developed and r e f i n e d , f o r the most p a r t , during World War I I and they made p o s s i b l e the manufacture and production o f many p e r i s h a b l e foods and medicines. Most n o t a b l e f o r the domestic c i t r u s i n d u s t r y was the development of f r o z e n concentrated c i t r u s j u i c e s which was made p o s s i b l e by the development of these high vacuum evaporators Frozen concentrated orange j u i c e began to capture a r e a l segment of the c i t r u s market i n 1948, and s i n c e then, i t s presence has been a dominant c o n t r i b u t i n g f a c t o r to the i n c r e a s i n g per c a p i t a consumption of c i t r u s j u i c e s worldwide. Processed orange products accounted f o r the usage of about 81% of the domestic orange crop between the years 1973 and 1978, as can be seen i n Table I I . Frozen concentrated orange j u i c e i n that p e r i o d was by f a r the major product of the U.S. c i t r u s i n d u s t r y , which i s concentrated i n 4 s t a t e s ; F l o r i d a , C a l i f o r n i a , Texas, and A r i z o n a , w i t h F l o r i d a being the dominant f a c t o r i n the i n d u s t r y . About 94% of the F l o r i d a orange crop went i n t o the product i o n o f orange j u i c e products during the 6-year p e r i o d , 1973-1978, and f r o z e n concentrated orange j u i c e accounted f o r approximately 81% of that usage. About h a l f o f the orange crcp of Texas and about 40% o f the A r i z o n a crop were u t i l i z e d i n processed products, but only about o n e - t h i r d of the C a l i f o r n i a crop was so u t i l i z e d . The major p o r t i o n o f the l a t t e r crop went to the f r e s h f r u i t market. These data are summarized i n Table I I I . TABLE I I I U.S.

Production of Oranges by Region 6-Year Average 1973-1978 (1)

1000 State Florida California Texas Arizona TOTAL

M e t r i c Tons

Processed

T o t a l Production

6614 500 129 49 7292

7069 1550 235 122 8976

% Processed 93.6 32.3 54.9 40.2 81.2

The Florida Crop and Livestock Reporting Service

S i m i l a r trends to those noted above e x i s t i n the domestic



230

TABLE IV


U.S. Production of G r a p e f r u i t Years 1973-1978 (1)

Crop Year

U t i l i z a t i o n of Production 1000 M e t r i c Tons

Fresh

Processed

% Tons Processed

Total

1973-74

1023

1416

2439

58.1

1974-75

1038

1231

2270

54.2

1975-76

1193

1390

2583

53.8

1976-77

1034

1716

2750

62.4

1977-78

1101

1646

2747

59.9

1978-79*

1038

1452

2490

58.3

1071

1475

2547

57.9

AVERAGE

*Estimate The Florida Crop and Livestock Reporting Service


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Citrus Juice

Processing

231

g r a p e f r u i t market, but that t o t a l market i s only about 30% as l a r g e as that f o r oranges as seen i n Table IV, Almost two-thirds of the F l o r i d a g r a p e f r u i t crop goes to the production of processed products with frozen concentrated g r a p e f r u i t j u i c e accounting f o r about 35% of the processed j u i c e . C h i l l e d g r a p e f r u i t j u i c e accounts f o r about 12% of the processed j u i c e , and that market segment i s growing along w i t h the b o t t l e d g r a p e f r u i t j u i c e market. Of the g r a p e f r u i t produced i n the other U.S. growing r e g i o n s , C a l i f o r n i a , Texas, and A r i z o n a , more than h a l f go to the f r e s h f r u i t markets. About 46% i s processed. These data are shown i n Table V.


TABLE V U.S. Production of G r a p e f r u i t by Region 6-Year Average 1973-1978 (1)

1000 M e t r i c Tons State Florida California Texas Arizona TOTAL

Processed

Total

% Processed

1173 93 167 42

1894 200 375 78

61.9 46.5 44.5 53.8

1475

2547

57.9

The Florida Crop and Livestock Reporting Service

Table VI shows the average amounts of the F l o r i d a orange and g r a p e f r u i t crops that went i n t o processed products during the f i v e - y e a r p e r i o d from 1973-1977. Frozen concentrates accounted f o r the major p o r t i o n of the processed orange j u i c e and about one-third of the processed g r a p e f r u i t j u i c e . C h i l l e d orange j u i c e i n b o t t l e s and i n d a i r y cartons accounted f o r a s i g n i f i c a n t p o r t i o n of the processed F l o r i d a orange crop and t h i s i s presently the f a s t e s t growing segment of the market. C h i l l e d g r a p e f r u i t j u i c e i s a growing market, but b o t t l e d , s h e l f - s t a b l e g r a p e f r u i t j u i c e i s a l s o e x p e r i e n c i n g major growth at the present time. C h i l l e d g r a p e f r u i t j u i c e accounted f o r about one-eighth of the processed j u i c e ; but, canned and b o t t l e d g r a p e f r u i t j u i c e s accounted f o r a major p o r t i o n of the processed g r a p e f r u i t j u i c e as can be seen i n Table VI.



232 TABLE VI

Processed F l o r i d a C i t r u s Products 6-Year Average 1973-1978 (JL)

Product Category

Gallons Produced (000 s)

Fruit Utilization (1000 M e t r i c Tons)

% Of Processed Oranges

5644 405

81.0

978 144

14.0

40,393 66,328 68 5,861

278 588

4.0

64 7,639 465

21 38

0.3


T

% Of Processed Grapefruit

Frozen Concentrated Juice (Reconst. B a s i s ) Orange Grapefruit Tangerine Blended

Chilled

684,419 40,912 4,700 28

34.5

Juice

Orange* Grapefruit

125,517 16,244 (est.)

12.3

Canned J u i c e Orange* Grapefruit Tangerine Blended

50.0

F r u i t Sections Orange Grapefruit Blended

3.2

*Includes Temples, Tangelos, and Honey Tangerines The Florida Crop and Livestock Reporting Service


11.


1.1

VARSEL

Citrus Juice

Processing

233

Juice Extraction

Citrus f r u i t i s delivered to a processing plant i n truckload q u a n t i t i e s of 20,410 t o 21,430kg or 20.4 to 21.4 m e t r i c tons. The f r u i t i s unloaded, inspected f o r maturity and graded to remove unwholesome and damaged f r u i t , a f t e r which i t i s conveyed to f r u i t b i n s f o r storage. F r u i t from the b i n s i s washed w i t h a detergent i n a r o t a r y brush washer, r i n s e d , then inspected and graded a second time to remove unwholesome f r u i t . J u i c e e x t r a c t o r s d i f f e r i n design, but a l l a r e f a s t , rugged, easy t o c l e a n , and a d j u s t a b l e to accomodate f r u i t o f d i f f e r e n t sizes. P r i o r to the i n v e n t i o n of automatic e x t r a c t o r s , the r o t a r y j u i c e press was i n common use, and i s s t i l l used commercially i n many p a r t s of the world, p r i n c i p a l l y I t a l y , Spain, & South America. The FMC In-Line E x t r a c t o r i s widely used i n the domestic i n dustry, most p a r t i c u l a r l y i n F l o r i d a , because i t can e f f e c t s i multaneous recovery o f both j u i c e and o i l . A five-headed e x t r a c tor can process from 325 to 500 f r u i t / m i n u t e . The e x t r a c t o r cons i s t s of a bottom cup, i n t o which the f r u i t i s f e d , and an upper cup that meshes w i t h the bottom as c i r c u l a r plugs are cut from the top and bottom o f the f r u i t . The f r u i t i n the bottom cup i s compressed as the upper cup descends and j u i c e and other f r u i t components are f o r c e d through the bottom plug i n t o a s t r a i n e r tube. The contents o f the s t r a i n e r tube, rag, seeds, and c e l l sacs, are squeezed between the top and bottom plugs r e s u l t i n g i n almost complete e x t r a c t i o n o f j u i c e and, i n essence, a f i r s t - f i n i s h i n g o p e r a t i o n s i n c e t h e plug (seeds, pulp, and peel) i s separated from t h e j u i c e . As the f r u i t i s squeezed i n the cup, p e e l o i l expressed from the flavedo and s m a l l p i e c e s of p e e l are washed i n t o a conveyer by a water spray that surrounds the e x t r a c t o r cup. The v a l u a b l e o i l i s recovered from the o i l / w a t e r slurry. S e v e r a l types o f Brown e x t r a c t o r s a r e used i n the c i t r u s i n dustry throughout the world. The Model 400 produces a j u i c e that i s low i n p e e l o i l content and h i g h i n j u i c e q u a l i t y . The f r u i t i s halved and the j u i c e removed by a r o t a t i n g reamer that exerts pressure t o e f f e c t e x t r a c t i o n . The Brown Model 700 E x t r a c t o r operates i n a manner s i m i l a r to the Model 400 and produces j u i c e o f the same h i g h q u a l i t y with low o i l content. I t expresses the j u i c e from about 700 f r u i t / m i n . compared t o the 350 f r u i t / m i n . that can be processed by the Model 400. A more s o p h i s t i c a t e d e x t r a c t o r , the Brown Model 1100, accepts three p a r a l l e l l i n e s of s i n g l e - f i l e f r u i t , and has a p r o c e s s i n g c a p a c i t y of almost 11 metric tons of f r u i t per hour. I t produces maximum j u i c e y i e l d s . F r u i t e n t e r i n g the e x t r a c t o r i s halved by a s t a i n l e s s - s t e e l k n i f e and each h a l f passes between a s t a i n l e s s s t e e l g r i d and a r o t a t i n g d i s c . The j u i c e i s expressed i n two stages e q u i v a l e n t to a l i g h t e x t r a c t i o n (low pulp/low o i l ) and a hard e x t r a c t i o n (higher o i l / h i g h e r pulp), t h e n flows t o the bottom of the c o l l e c t o r where i t can be d i v i d e d i n t o two f r a c t i o n s .


234


The s t a i n l e s s - s t e e l g r i d provides a coarse f i r s t - s t a g e f i n i s h i n g o p e r a t i o n simultaneously w i t h the e x t r a c t i o n . The j u i c e flows through o u t l e t s at the bottom of the c o l l e c t o r s and i s conveyed to f i n i s h e r s .


1.2

Finishing

Operations

In the f i n i s h i n g o p e r a t i o n , seeds are removed from the j u i c e and the pulp content i s lowered. As w i t h e x t r a c t o r s , f i n i s h e r s vary i n design. The two types most commonly used are the screwtype and the paddle-type. In both designs, s e p a r a t i o n i s accomp l i s h e d by a c y l i n d r i c a l p e r f o r a t e d screen. J u i c e and a cont r o l l e d amount of i n s o l u b l e s o l i d s or f i n e pulp pass through the screen w h i l e the remainder of the s o l i d s i s discharged at the end of the f i n i s h e r . The s i z e of the screen p e r f o r a t i o n s d e t e r mines the s i z e of the s o l i d p a r t i c l e s that remain with the j u i c e . The j u i c e e x t r a c t o r and f i n i s h e r are employed i n tandem to control the c h a r a c t e r i s t i c s of the processed j u i c e , but they a l s o a f f e c t the j u i c e y i e l d and q u a l i t y . The j u i c e c h a r a c t e r i s t i c s controlled by these operations i n c l u d e the pulp content and s i z e , and o i l content. The f i n i s h e d j u i c e i s conveyed to blend tanks at which time the a c i d i t y and s o l u b l e s o l i d s l e v e l may be determined. I f necessary, the j u i c e can be deaerated and d e o i l e d , dependent upon the product to be produced. 1.3

Evaporation

According to Cook ( 2 ) , the f i r s t commercial orange concent r a t e was produced i n F l o r i d a i n 1938 on a low-temperature (20°25°C) evaporator w i t h 13 stages that operated under h i g h vacuum. Most of the evaporators used i n the s t a t e of F l o r i d a p r i o r to 1947 u t i l i z e d h i g h temperatures and long residence times. These evaporators operated somewhere between 48.9° and 82.2°C (120°-180°F). F r u i t s o l i d s remained i n these evaporators f o r a minimum of 30 minutes; hence, the products produced on such evaporators were of poor q u a l i t y and e x h i b i t e d a s t r o n g heat processed f l a v o r . In 1946, the f i r s t commercial f r o z e n concentrated orange j u i c e was produced i n a f a l l i n g - f i l m type evaporator operated at low temperature and high vacuum. T h i s evaporator, i n s t a l l e d by the Minute Maid Company (now The Coca-Cola Company Foods Division) employed a l a r g e steam j e t pumping system to remove water vapor at h i g h enough vacuum to maintain an o p e r a t i n g temperature of about 18.3°C (65°F). The j u i c e stayed i n the evaporator f o r a long p e r i o d of time, but the concentrate produced was f a r superior to t h a t produced i n high-temperature evaporators. Low-temperature evaporators of the f a l l i n g - f i l m type were h e a v i l y u t i l i z e d i n the c i t r u s i n d u s t r y through the 1950 s and f


11.

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Citrus Juice

Processing


f

235

and e a r l y 6 0 s . The f i r s t high-temperature short-time evaporator was i n s t a l l e d i n F l o r i d a i n 1959. T h i s was a d o u b l e - e f f e c t twostage u n i t that employed some r e c i r c u l a t i o n of steam. T h i s r e search i n t o evaporation p r i n c i p l e s l e d to the development of the present u n i t s that are used almost e x c l u s i v e l y today i n the domestic c i t r u s i n d u s t r y . These u n i t s are known as TASTE (thermallya c c e l e r a t e d short-time evaporation) evaporators. Most of these u n i t s employ a s i n g l e pass of j u i c e , and they are composed of four to s i x e f f e c t s w i t h s i x or seven s t a g e s . The water removal c a p a c i t y i s normally 18,000 to 23,000 l i t e r s per hour, but some of the new u n i t s being c o n s t r u c t e d have water removal c a p a c i t i e s of n e a r l y 41,000 l i t e r s / h o u r . F i g u r e 1 i l l u s t r a t e s the o p e r a t i n g p r i n c i p l e s of a TASTEtype evaporator (2). J u i c e passes through the preheaters and i s heated to the temperature of s t a b i l i z a t i o n , about 205°-210°F (96.l°-98.9°C), to destroy enzyme a c t i v i t y . After stabilization, the j u i c e passes through the n o z z l e at the top of the f i r s t stage where i t f l a s h e s to a lower temperature, one that c o r r e sponds to the pressure at that p o i n t . The r e s u l t i n g mixture of j u i c e and vapor i s p r o j e c t e d i n t o the tube bundle i n the f i r s t stage where f u r t h e r evaporation of water occurs as the j u i c e passes down through the tubes. T h i s i s not a f a l l i n g - f i l m evaporator because the l i q u i d ( j u i c e ) i s mostly suspended i n the vapor, and heat t r a n s f e r i s to the turbulent mixture. The e x i t v e l o c i t y of the j u i c e from the tubes i s on the order of 20 to 100 meters per second (2). As i t e x i t s from the tubes, the l i q u i d and vapor mixture t r a v e l s i n t o a c e n t r i f u g a l - t y p e vapor s e p a r a t o r , and the l i q u i d then flows down the s u c t i o n l i n e to a heavy-duty pump. On b e i n g pumped to the next stage, the l i q u i d f l a s h e s through the n o z z l e and the mixture t r a v e l s down the tube bundle as i t d i d i n the f i r s t stage. Vapor from the f i r s t - e f f e c t s e p a r a t o r prov i d e s the heat f o r evaporation i n the second stage. The j u i c e passes through a d d i t i o n a l stages, normally about seven i n a l l , and a f t e r the l a s t stage, the j u i c e enters a chamber where i t i s f l a s h cooled to about 10°C (50°F). A f t e r f l a s h c o o l ing, the concentrate, which w i l l be at 65°-68°Brix, i s pumped i n to drums or to a h o l d i n g tank i n one of the newly constructed tank farms that are becoming more p r e v a l e n t i n the domestic citrus industry. In a f o u r - e f f e c t evaporator steam i s put i n t o the f i r s t e f f e c t , where an e f f e c t r e l a t e s to vapor flow, and the heat from t h a t steam i s used four times b e f o r e condensation occurs i n a barometric condenser. In theory, a f o u r - e f f e c t evaporator w i l l remove four l i t e r s of water per k i l o g r a m of steam usage, but i n a c t u a l p r a c t i c e that water removal i s about 3.4 1 per kg of steam. Heat losses and the change i n the heat of v a p o r i z a t i o n w i t h tempe r a t u r e account f o r the d i f f e r e n c e . A t y p i c a l TASTE evaporator i n use i n a c i t r u s p l a n t i s shown i n F i g u r e 2. The Coca-Cola Company Foods D i v i s i o n operates three




236

Institute of Food Technologists

Figure 1.

Figure 2.

Flow diagram for TASTE

TASTE

evaporator (2)

evaporator (courtesy of George Craddock)


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c i t r u s p r o c e s s i n g p l a n t s i n the s t a t e of F l o r i d a , and i n these p l a n t s are e i g h t TASTE evaporators dedicated to the p r o d u c t i o n of orange j u i c e concentrate. A d d i t i o n a l evaporators of the same type are a l s o used f o r by-product p r o d u c t i o n , e.g., c i t r u s molasses and washed pulp s o l i d s . The e i g h t evaporators used f o r the p r o d u c t i o n of orange j u i c e concentrate have a t o t a l r a t e d c a p a c i t y f o r water removal of 170,000 1 per hour. The l a r g e s t of these evaporators i s r a t e d at 36,400 1 per hour of water removal. Berry and Veldhuis (3) r e c e n t l y presented a comprehensive treatment of evaporators, and the reader i s r e f e r r e d to that art i c l e f o r a more in-depth review.


1.4

Ion-Exchange Processing-

A c i d removal from c i t r u s j u i c e s was f i r s t reported by K i l burn and Drager (4) i n the e a r l y 1960 s. They employed e l e c t r o d i a l y s i s to remove c i t r a t e i o n from c i t r u s j u i c e s . L a t e r , Berry and Wagner (5) used calcium hydroxide f o r p r e c i p i t a t i o n of c i t r a t e in citrus juices. A more recent process, i . e . , a c i d r e d u c t i o n by a n i o n i c ion exchange, was developed at the Research and Development Laborat o r i e s of The Coca-Cola Company Foods D i v i s i o n i n Plymouth, F l o r ida. Removal of c i t r a t e i o n by an a n i o n i c ion-exchange process can be accomplished by exchange w i t h hydroxy1 i o n and the subsequent formation of water, which i s a component of j u i c e and which can be removed by evaporation; hence, i t should be pref e r a b l e to a method that r e l i e s on the a d d i t i o n of a n e u t r a l i z i n g substance to a c i t r u s j u i c e . The ion-exchange process i s i l l u s t r a t e d i n the f o l l o w i n g equation: T

3

+

3

3 R+ ' OH" + C H 5 0 7 ~ ^ ( R ) · C H 0 - + 30H", where R equates to a p o s i t i v e l y charged u n i t of the r e s i n s t r u c t u r e . 6

3

6

5

7

+

The ion-exchange r e s i n employed i n the a c i d r e d u c t i o n process i s weakly b a s i c and i s approved f o r food use as p r e s c r i b e d i n the food a d d i t i v e r e g u l a t i o n 173.25(a)(14) i n T i t l e 21, Code of Fede r a l Regulations (21CFR) (6). Because the a n i o n i c r e s i n i s weakly b a s i c , the r e t e n t i o n of stronger acids i s favored. As a r e s u l t , when p r o c e s s i n g orange j u i c e , the r e t e n t i o n of c i t r i c a c i d i s favored with r e s p e c t to the weaker organic a c i d s , a s c o r b i c and f o l i c , which a r e w e l l recognized n u t r i e n t s i n orange j u i c e . A l s o , mass a c t i o n favors the removal of c i t r i c a c i d . The process permits the treatment of e i t h e r b u l k concentrate or f r e s h l y e x t r a c t e d j u i c e . Freshly extracted j u i c e i s f i r s t s t a b i l i z e d at 175°-180°F (79.4°-82.2°C) then c e n t r i f u g e d i n a h i g h speed c e n t r i f u g e to e f f e c t a pulp r e d u c t i o n to 2% to i n h i b i t development of e x c e s s i v e back pressures i n the column due to plug-



238


ging. T h i s pulp can be re-added to the j u i c e stream f o l l o w i n g a c i d r e d u c t i o n i n the ion-exchange column. Bulk concentrate must f i r s t be d i l u t e d to about 15°Brix a f t e r which pulp r e d u c t i o n i s accomplished by c e n t r i f u g a t i o n . S t a b i l i z a t i o n of the d i l u t e concentrate i s not necessary because of i t s p r i o r s t a b i l i z a t i o n during concentration. A c i d r e d u c t i o n of orange j u i c e i s e f f e c t e d by downflow passage through the r e s i n . J u i c e i s passed through the column u n t i l the e l u a t e (reduced-acid j u i c e ) drops te a pH below 4.6 as monitored by a pH meter. T h i s method assures minimal l o s s of ascorbic acid. The column e l u a t e i s discharged i n t o an evaporator feed tank where i t s pH i s adjusted to a maximum of 4.6 through the a d d i t i o n of f r e s h l y e x t r a c t e d , but u n t r e a t e d , j u i c e or concentrated orange juice. At t h i s time the pulp removed i n c e n t r i f u g a t i o n can a l s o be re-added. T h i s adjustment of pH ensures that no growth of pathogenic organisms can occur, and s t u d i e s by independent l a b o r a t o r i e s have confirmed t h i s f i n d i n g . F o l l o w i n g pH adjustment of the acid-reduced j u i c e , i t i s concentrated to 65°Brix i n a TASTE evaporator. 1.5

P a s t e u r i z a t i o n and Packaging

The purpose of p a s t e u r i z a t i o n , as i t i s p r a c t i c e d i n the domestic i n d u s t r y today, i s to destroy s p o i l a g e organisms, i n a c t i vate enzymes, or both. Heating to temperatures of only 150°F (65.6°C) w i l l destroy most s p o i l a g e organisms but some heat r e s i s t a n t molds may r e q u i r e p a s t e u r i z a t i o n temperatures as h i g h as 210°F (98.9°C) f o r c o n t r o l . C i t r u s j u i c e s that are p a s t e u r i z e d at the lower temperatures, 65-66°C, can undergo c l a r i f i c a t i o n , i . e . , a process of s e p a r a t i o n that r e s u l t s i n a lower l a y e r of l i q u i d and sediment and an upper l a y e r of c l e a r l i q u i d . T h i s process i s brought about by the n a t u r a l enzyme, p e c t i n e s t e r a s e , that occurs i n c i t r u s f r u i t s . Studies have shown that p r o c e s s i n g of the j u i c e at temperatures of 170-210°F (76.7-99°C) f o r a f r a c t i o n of a second to 40 seconds w i l l destroy the p e c t i n e s t e r a s e a c t i v i t y i n c i t r u s j u i c e s (7-10). The temperature necessary to s t a b i l i z e the j u i c e i s pH dependent. J u i c e s at higher pH r e q u i r e h i g h e r temperatures f o r s t a b i l i z a t i o n . With the new high-temperature short-time techniques and equipment, s t a b i l i z a t i o n can u s u a l l y be e f f e c t e d i n a f r a c t i o n of a second. F l a s h p a s t e u r i z a t i o n can be accomplished i n e i t h e r a p l a t e - t y p e or a tube-type heat exchanger. C h i l l e d j u i c e s , both orange and g r a p e f r u i t , are i n c r e a s i n g i n p o p u l a r i t y and, indeed, t h i s market segment i s p r e s e n t l y the f a s t e s t growing i n the i n d u s t r y . These products are p a s t e u r i z e d , cooled, and f i l l e d i n t o paper cartons l i n e d w i t h a p l a s t i c or a l u minum f o i l laminated w i t h a p l a s t i c . The c h i l l e d j u i c e market experienced much of i t s i n i t i a l growth through d a i r y p r o c e s s i n g and d e l i v e r y systems, but today



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much o f the product i s processed i n p l a n t s owned by companies i n v o l v e d i n the c i t r u s i n d u s t r y , even though the technology employed i s based on that developed f o r the d a i r y i n d u s t r y . The products are p a s t e u r i z e d by the HTST (high-temperature s h o r t time) process i n which the j u i c e i s heated to a high temperature, on the order of 175°-180°F (79.4°-82.2°C) f o r a very short time, about 0.5 second. I t i s then cooled and f i l l e d i n t o cartons a t about 32°-40°F (0°-4.4°C). Such a process i s not damaging to the f l a v o r and t e x t u r e of the j u i c e and the r e s u l t i n g product has a very acceptable f l a v o r and aroma. C h i l l e d products, which have s h e l f l i v e s i n the order of f i v e to s i x weeks, a r e s o l d a t r e f r i g e r a t e d temperatures (4.4°7.2°C)in r e t a i l o u t l e t s . Open code d a t i n g of these products en-*sures a supply o f f r e s h product f o r the consumer at r e t a i l . Some c h i l l e d products a r e packaged i n g l a s s c o n t a i n e r s , 32f l . oz. and 6 4 - f l . oz., but the d a i r y - t y p e cartons account f o r the major segment o f t h i s market. Berry e t a l . (11) reported that t h e q u a l i t y of these products remained high f o r long periods of time i f maintained a t 50°F (10°C) o r lower, and products i n g l a s s e x h i b i t e d b e t t e r a s c o r b i c a c i d and f l a v o r s t a b i l i t y than those i n paper o r p l a s t i c cartons. Higher temperatures l e d t o more,rapid d e t e r i o r a t i o n o f a s c o r b i c a c i d and f l a v o r . Canned and b o t t l e d j u i c e s a r e p a s t e u r i z e d at r e l a t i v e l y h i g h temperatures (76. 7°-90.6° C) and the containers a r e f i l l e d hot. The hot f i l l serves to s t e r i l i z e the c o n t a i n e r and, i n the case o f a can, i t i s i n v e r t e d f o r 60-90 seconds a f t e r seaming to s t e r i l i z e the l i d . The cans a r e then cooled to about 105°F (40.6°C) i n a s p i n c o o l e r o r a spray c o o l e r before b e i n g l a b e l e d and cased. B o t t l e s are f i l l e d i n the same manner, but the caps are s t e r i l i z e d w i t h steam or a chemical s t e r i l a n t b e f o r e being app l i e d t o the b o t t l e . The f i l l e d containers are then cooled gradu a l l y i n a spray c o o l e r . When f r e s h l y e x t r a c t e d j u i c e i s b e i n g f i l l e d i n t o cans o r b o t t l e s , the temperature of p a s t e u r i z a t i o n must be s u f f i c i e n t t o i n a c t i v a t e the n a t u r a l enzymes, p a r t i c u l a r l y p e c t i n e s t e r a s e . F o r orange j u i c e , t h i s temperature i s somewhere between 185° and 195°F (85°-90.6°C) and i s , to a degree, dependent upon the pH of the juice. G r a p e f r u i t j u i c e , g e n e r a l l y , need not be subjected to temperatures as high as a r e necessary to orange j u i c e i n order to achieve s t a b i l i z a t i o n . The temperatures r e q u i r e d f o r g r a p e f r u i t j u i c e are between 170°-189°F (76.7°-87.2°C). J o s l y n and Sedky (7) showed that the heat i n a c t i v a t i o n o f enzymes r e s p o n s i b l e f o r cloud i n s t a b i l i t y i n g r a p e f r u i t j u i c e was more r a p i d a t pH 2.5 than a t pH 4.0. Rouse and A t k i n s (9) and P r a t t and Powers (12) corroborated these f i n d i n g s . Of course, w i t h any j u i c e the i n a c t i v a t i o n of enzymes i s dependent upon both time and temperature. As the temperature of p a s t e u r i z a t i o n i s i n c r e a s e d , the length of time i n the p a s t e u r i z e r can be decreased.



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1.5.1

A s e p t i c Packaging

Canned and b o t t l e d c i t r u s j u i c e s are examples of products that are packed a s e p t i c a l l y , and these processes have been used i n the i n d u s t r y f o r many years. One of the newer processes f o r a s e p t i c packaging employs a paperboard package that i s s t e r i l i z e d with hydrogen peroxide p r i o r to the form, f i l l , and s e a l operation. This process, developed by T e t r a Pak Ab of Lund, Sweden, i s i n use i n many p a r t s of the world, but i t has not yet been approved by the U.S. Food and Drug A d m i n i s t r a t i o n f o r domestic use. The new packaging system developed by T e t r a Pak i s known as the T e t r a B r i k ® , and i s g e n e r a l l y a v a i l a b l e i n 1-1, 200-ml, and 250-ml s i z e s . The system i s considered to be an a l t e r n a t i v e to metal and g l a s s c o n t a i n e r s . The packaging m a t e r i a l comes i n r o l l stock form and i s a 6-or 7-layer laminate. Polyethylene and aluminum f o i l o f f e r the major b a r r i e r p r o p e r t i e s to the package. The system enables heat s e n s i t i v e products to be processed with minimal heat i n p u t . The processing temperatures employed are s i m i l a r to those employed f o r the dairy-type paper cartons. The package i n t e g r i t y , when p r o p e r l y s t e r i l i z e d and maintained, i s such that m i c r o b i a l r e i n f e c t i o n i s i n h i b i t e d . Because oxygen can permeate the package along the l o n g i t u d i n a l and l a t e r a l seams, i t i s not t r u l y hermetic even though i t does provide a s e p s i s . One major advantage of the package i s that i t contains no headspace because the top s e a l i s a c t u a l l y formed through a column of s t e r i l e product. T h i s l a c k of headspace o f f e r s some p r o t e c t i o n , at l e a s t i n i t i a l l y , to oxygen-sensitive products. In many of the developing c o u n t r i e s of the world, the T e t r a B r i k ® system o f f e r s the only economical and p r a c t i c a l package f o r j u i c e s and j u i c e products ( a l s o m i l k ) . The major disadvantages of the T e t r a B r i k ® process are the slow l i n e speeds (70 u n i t s per minute) and the l i m i t e d mechanical and p h y s i c a l s t r e n g t h of the package. The l a t t e r makes c a r e f u l handling and adequate secondary packaging q u i t e e s s e n t i a l . 2

N u t r i t i o n a l Q u a l i t y of C i t r u s J u i c e s

2.1

Vitamin

C

C i t r u s f r u i t s have long been noted as e x c e l l e n t sources of a s c o r b i c a c i d (Vitamin C), which i s the most abundant v i t a m i n i n the c i t r u s f r u i t s . C i t r u s f r u i t s are a l s o q u i t e r i c h i n the mine r a l element, potassium, and are o f t e n recommended f o r p a t i e n t s who must use d i u r e t i c drugs. Healthy a d u l t s r e q u i r e 60mg per day of Vitamin C and about 2.5g per day of potassium (13) . A t k i n s et a l . (14) reported that most of the a s c o r b i c a c i d that occurs i n the orange i s present as a c o n s t i t u e n t of the peel. Based on the weight of whole f r u i t , the j u i c e contains about 25% of the t o t a l a s c o r b i c a c i d content. The j u i c e of the g r a p e f r u i t contains only about 17% of the t o t a l a s c o r b i c a c i d content on the same b a s i s .



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The a s c o r b i c a c i d content of the j u i c e of d i f f e r e n t c i t r u s f r u i t s v a r i e s c o n s i d e r a b l y , and the content w i l l vary with stage of f r u i t maturity, f r u i t v a r i e t y , and climate. Soil conditions and f e r t i l i z i n g p r a c t i c e s have only minimal e f f e c t s i f any at a l l (15). According to Ting and Attaway (16), oranges g e n e r a l l y cont a i n from 40-70mg/100ml of j u i c e , whereas g r a p e f r u i t , tangerine, and lemon j u i c e contain between 20 and 50mg/100ml of j u i c e . The a s c o r b i c a c i d c o n c e n t r a t i o n i s high i n immature f r u i t , and i t decreases as the f r u i t r i p e n and increase i n s i z e , according to Harding e t a l . (17). As w i t h oranges, g r a p e f r u i t e x h i b i t an i n v e r s e r e l a t i o n s h i p between a s c o r b i c a c i d content and m a t u r i t y . M e t c a l f e e t a l . (1_8) examined f i v e v a r i e t i e s of g r a p e f r u i t grown i n s i x l o c a t i o n s i n the Rio Grand V a l l e y of Texas and concluded that, although there were only small d i f f e r e n c e s among the v a r i e t i e s , there were great v a r i a t i o n s i n a s c o r b i c a c i d content of the f r u i t from any given tree. These workers a l s o reported a s i g n i f i c a n t decrease i n asc o r b i c a c i d content due to m a t u r i t y . Ross (19) reported v a r i a t i o n s i n a s c o r b i c a c i d content of g r a p e f r u i t from trees i n d i f f e r e n t areas, as w e l l as from trees i n the same grove. He c o r r e l a t e d the a s c o r b i c a c i d content with a c i d i t y and reported that i t increased w i t h a c i d i t y . A number of workers examined the e f f e c t of l i g h t exposure on a s c o r b i c a c i d content and the general conclusion i s that d i r e c t s u n l i g h t has a p o s i t i v e e f f e c t on i t s content; i . e . , exposure to d i r e c t s u n l i g h t tends to i n c r e a s e the a s c o r b i c a c i d content of fruit. Long et a l . (20) found that the a s c o r b i c a c i d content of g r a p e f r u i t was i n v e r s e l y r e l a t e d to t h e i r s i z e . In V a l e n c i a oranges, S i t e s and R e i t z (21) found a p o s i t i v e c o r r e l a t i o n between a s c o r b i c a c i d and the s o l u b l e s o l i d s of f r u i t from the same tree. As might w e l l be expected, other c i t r u s f r u i t s e x h i b i t the same type of seasonal d e c l i n e i n a s c o r b i c a c i d content of the j u i c e w i t h maturity. Harding and Sunday (22) reported that the a s c o r b i c a c i d content of tangerines may be 35mg/100ml of j u i c e i n the e a r l y season and as low as 10-15mg per 100ml i f the f r u i t i s allowed to overmature. 2.2

Other N u t r i e n t s of D i e t a r y

Significance

Other n u t r i e n t s i n orange j u i c e that are of d i e t a r y s i g n i f i cance, according to standards s e t by the U.S. Food and Drug Adm i n i s t r a t i o n , i . e . , they are present at a l e v e l of 10% or more of the U.S. RDA (Recommended D a i l y Allowance) per s e r v i n g , are f o l i c a c i d and thiamine (Vitamin B-^). The f a c t o r of s i g n i f i c a n c e (10% of the U.S. RDA per serving) i s s e t f o r t h i n 21CFR 101.9(c) (7)(v)(6). A s e r v i n g s i z e f o r orange j u i c e i s g e n e r a l l y regarded as s i x f l u i d ounces or 177ml.



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Ting (23) reported values f o r thiamine i n orange j u i c e between 0.75 and 0.85mcg per gram of j u i c e , and a survey of the l i t e r a t u r e i n d i c a t e s that other c i t r u s j u i c e s c o n t a i n l e s s e r amounts. Analyses of orange concentrate by an i n d u s t r i a l l a b o r a tory f o r our C i t r u s R&D L a b o r a t o r i e s r e s u l t e d i n a value of 75mcg per 100g of r e c o n s t i t u t e d orange j u i c e , i n good agreement with the values reported by T i n g (23). Adams (24) r e p o r t s 91mcg/100g f o r r e c o n s t i t u t e d orange j u i c e . In the compilation of Adams (24) , r e c o n s t i t u t e d g r a p e f r u i t j u i c e i s reported to d e l i v e r about 38mcg of thiamine per 100g and tangerine j u i c e ( r e c o n s t i t u t e d ) about 59mcg/100g. Per s e r v i n g of 177ml, these values would be 170, 70, and lOOmcg, respect i v e l y , f o r orange, g r a p e f r u i t , and tangerine. With a U.S. RDA of 1.5mg, the percentage of the U.S. RDA of thiamine d e l i v e r e d by these j u i c e s would be 11%, 5%, and 7%, r e s p e c t i v e l y . F o l i c a c i d , g e n e r i c a l l y d e s c r i b e d as f o l a c i n , i s chemically known as pteroylmonoglutamic a c i d . There are s e v e r a l compounds that e x h i b i t f o l i c a c i d a c t i v i t y and they d i f f e r only i n the number of glutamic a c i d residues they c o n t a i n . These polyglutamates, as they are known, must be acted upon by the enzyme, conjugase, to r e l e a s e the f o l i c a c i d f o r metabolic a c t i v i t y . A deficiency of t h i s v i t a m i n leads to m e g a l o b l a s t i c anemia (25) . Most e v i dence p l a c e s the d a i l y requirement f o r f o l i c a c i d at about 50mcg per day of c r y s t a l l i n e f o l i c a c i d (26,27) ; however, the U.S. RDA f o r t o t a l food f o l a c i n i s set at 400mcg f o r the adolescent, f o r a d u l t males, and f o r non-pregnant, n o n - l a c t a t i n g females. The higher RDA i s s p e c i f i e d to allow f o r a b s o r p t i o n of only 25% of f o l i c a c i d a c t i v i t y i n a manner comparable to the c r y s t a l l i n e f o l i c a c i d and to allow f o r a wide range of a v a i l a b i l i t y of the polyglutamate form (13). E a r l y work p l a c e d the f o l a c i n content of orange j u i c e at between three and s i x micrograms/100ml (28). L a t e r , Hurdle et a l . (29) r e v i s e d t h i s to 20-45mcg/100g f o r orange products, and they a l s o reported that canned g r a p e f r u i t products contained about llmcg/lOOg. More recent work by S t r e i f f (30) i n d i c a t e d a f o l a c i n value o f from 50-100mcg with i n g e s t i o n of 100-125ml of orange juice. G r a p e f r u i t j u i c e and tangerine j u i c e were reported to have lower l e v e l s . Dong and Oace (31) reported a f o l a c i n value of 50mcg/100ml f o r orange j u i c e , and a somewhat lower l e v e r f o r grapefruit juice. Ting et a l . (32) reported an average f o l a c i n value f o r recons t i t u t e d F l o r i d a orange j u i c e of about 45mcg/100ml. In our own s t u d i e s , with analyses conducted by independent a n a l y t i c a l l a b o r a t o r i e s , we have not seen values of that magnitude, but r a t h e r have observed values on the order of 26-33mcg/100ml of j u i c e . These values would be on the order of 12%-15% of the U.S. RDA. T i n g (23) has a l s o reported that wide v a r i a t i o n i n the f o l i c a c i d content occurs throughout the growing season and that the concent r a t i o n i n c r e a s e s as the season progresses.


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Other N u t r i e n t s

A number of n u t r i e n t s of l e s s e r d i e t a r y s i g n i f i c a n c e are present i n orange j u i c e and other c i t r u s j u i c e s . Measurable l e v e l s of Vitamin A, r i b o f l a v i n (Vitamin I ^ ) , n i a c i n , p y r i d o x i n e ( V i t a min B 5 ) and pantothenic a c i d have been reported i n orange j u i c e . The l e v e l s of these n u t r i e n t s are g e n e r a l l y i n the range of 2-3% of t h e i r r e s p e c t i v e U.S. RDA's. For a more extensive review of these n u t r i e n t s , one should consult T i n g (23) and Araujo (33)· In a d d i t i o n to the vitamins mentioned above, c i t r u s j u i c e s are a r i c h source of potassium. Even though potassium i s an e s s e n t i a l m i n e r a l i n human n u t r i t i o n , the U.S. Food and Drug Adm i n i s t r a t i o n does not i n c l u d e i t i n i t s n u t r i t i o n a l l a b e l i n g program because i t i s w i d e l y d i s t r i b u t e d i n foods. The Food and N u t r i t i o n Board of the N a t i o n a l Academy of Sciences (13) has determined that healthy a d u l t s r e q u i r e about 2.5g of potassium per day. Based on the data of McHard et a l . (34) a 6-oz. s e r v i n g (177ml) of orange j u i c e would provide about 0.29g of potassium. Values produced i n our own l a b o r a t o r i e s would approximate a potassium content of about 0.4g per 177ml of orange j u i c e . T i n g (23) r e p o r t s a potassium content of 0.30-0.4g per 177ml f o r orange j u i c e . Other m i n e r a l elements are present i n c i t r u s j u i c e s i n measurable q u a n t i t i e s . McHard et a l . (34) reported on the t r a c e element contents of F l o r i d a and B r a z i l i a n orange j u i c e . They c i t e d c o n c e n t r a t i o n ranges f o r 25 elements. T i n g (23) reported that calcium, i r o n , phosphorus, magnesium, z i n c , and copper are present i n r e c o n s t i t u t e d FCOJ at l e v e l s e q u i v a l e n t to about 1% to 5% of t h e i r r e s p e c t i v e U.S. RDA's. Phosphorus r e p o r t e d l y occurs i n orange j u i c e at l e v e l s of about 10-30mg/100g of j u i c e (24,34,35), e q u i v a l e n t to 1.9-5.6% of the U.S. RDA; magnesium was reported at l e v e l s between 8-15mg/100 ml of j u i c e by B i r d s a l l et a l . (36), whereas Ingwalson et a l . (37) reported l e v e l s i n r e c o n s t i t u t e d orange j u i c e of 12-14mg/100g. McHard et a l . (34) reported s i m i l a r v a l u e s . The maxiumum would be about 6.5% of the U.S. RDA per 177ml of orange j u i c e . Orange j u i c e was reported tc c o n t a i n from 50 to 160mcg of copper per 100ml by B i r d s a l l e t a l . (36) , whereas others reported values i n the range of 30-50mcg/100g (34,37), a maximum of 1.7% of the U.S. RDA, but p o s s i b l y as low as 0.3% of the U.S. RDA. Calcium has been reported at 6.5-15.4mg/100g of r e c o n s t i t u ted orange j u i c e (34,35,37). T h i s l e v e l , which i s 1.2% to 2.7% of the U.S. RDA, i s not of any great s i g n i f i c a n c e . Likewise, i r o n , which has been reported at l e v e l s of 0.08 to 0.7mg/100g of orange j u i c e (34,37) i s not of any great n u t r i t i o n a l s i g n i f i cance because the l e v e l i s only 0.8% to 7% of the U.S. RDA. 3

E f f e c t s of P r o c e s s i n g on N u t r i t i o n a l Q u a l i t y

P r o c e s s i n g as i t i s p r a c t i c e d i n the i n d u s t r y r e q u i r e s the input of heat to e f f e c t p a s t e u r i z a t i o n , enzyme s t a b i l i z a t i o n , and/



244


or c o n c e n t r a t i o n . Heat p r o c e s s i n g to achieve one of these three r e s u l t s would not be expected to have any d e t r i m e n t a l e f f e c t on the mineral composition of c i t r u s j u i c e s . These m i c r o n u t r i e n t s should not be l o s t during p r o c e s s i n g ; n e i t h e r should they be degraded. The same cannot be s a i d f o r the organic m i c r o n u t r i e n t s , the v i t a m i n s , and the s o - c a l l e d macronutrients, carbohydrates, p r o t e i n s , and f a t s , which supply energy as w e l l as n u t r i t i o n to the human body. C i t r u s f r u i t s are not regarded as good n u t r i t i o n a l sources of f a t based on 21CFR 101.9(c)(6) that the d e l i v e r y of l e s s than one gram of f a t per s e r v i n g i s not of d i e t a r y s i g n i f i c a n c e (6). According to Adams (24) , r e c o n s t i t u t e d FCOJ d e l i v e r s about 0.2g of f a t per 177ml; r e c o n s t i t u t e d f r o z e n concentrated g r a p e f r u i t j u i c e about 0.2g/177ml. Tangerine j u i c e may be s l i g h t l y higher i n f a t content. According to Nagy (38), the l i p i d s that occur i n c i t r u s j u i c e c o n t a i n high unsaturated/saturated f a t t y a c i d r a t i o s (>4). The c o n t r i b u t i o n of l i p i d o x i d a t i v e products to o f f - f l a v o r development has been s t u d i e d by many workers, and a review of these s t u d i e s has been presented by Nagy (38). I t i s g e n e r a l l y agreed that the c o n t r i b u t i o n of the l i p i d o x i d a t i v e products to the f l a v o r d e t e r i o r a t i o n of processed c i t r u s products i s r e l a t i v e l y minor when compared to the c o n t r i b u t i o n s by the products formed by the a c i d - c a t a l y z e d h y d r o l y s i s of f l a v o r i n g o i l s and the products of M a i l l a r d browning (39,40). C i t r u s j u i c e s and t h e i r products cannot be considered s i g n i f i c a n t d i e t a r y sources of p r o t e i n because the p r o t e i n e f f i c i e n c y r a t i o (PER) of c i t r u s p r o t e i n i s l e s s than 20% that of c a s e i n (23, 41). According to the r e g u l a t i o n s set f o r t h i n 21CFR 101.9(c) ( 7 ) ( i i ) ( b ) , p r o t e i n w i t h a PER l e s s than 20% that of c a s e i n i s not of d i e t a r y s i g n i f i c a n c e (6). The p r o t e i n i n c i t r u s is"~generally a s s o c i a t e d w i t h the s o l i d p o r t i o n s of the f r u i t , i . e . , the seeds, f l a v e d o , albedo, chromatophores, and pulp. Some of these components f i n d t h e i r way i n t o the j u i c e along with the a v a i l a b l e f r e e amino acids during extract i o n and p r o c e s s i n g and storage. Studies conducted i n our l a b o r a t o r i e s (42,43,44) and by others (45) have shown that reductions i n the pulp content of j u i c e slow the rate of browning. According to Ting (23,41), a s e r v i n g (177ml) of reconstituted FCOJ d e l i v e r s about 19g of carbohydrate and 84 c a l o r i e s c o n t r i b u ted p r i m a r i l y by the sugars, sucrose, glucose, and f r u c t o s e . Adams (24) , i n d i c a t e s that a s e r v i n g of r e c o n s t i t u t e d FCOJ d e l i v e r s 92 c a l o r i e s , whereas g r a p e f r u i t and tangerine, j u i c e del i v e r 76 and 68 c a l o r i e s per 177ml, r e s p e c t i v e l y . C i t r u s j u i c e s c o n t a i n both nonreducing (sucrose) and reduc i n g ( f r u c t o s e and glucose) sugars. Mature oranges c o n t a i n almost equal amounts of the two types and the reducing sugar content i s composed of almost equal amounts of f r u c t o s e and glucose. Grapef r u i t tend to have n e a r l y e q u i v a l e n t amounts of reducing and non-



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reducing sugars, but at times, the reducing sugars tend to be s l i g h t l y more dominant (16). In tangerines, the nonreducing sugar dominates except i n immature f r u i t ; i n j u i c e from mature f r u i t , sucrose may account f o r 60-65% of the t o t a l sugar content. In lemon j u i c e , the reducing sugars dominate (46) and may account for about 90% of the t o t a l sugars. The sugars, which c o n t r i b u t e much to the a c c e p t a b i l i t y of c i t r u s j u i c e s , under adverse c o n d i t i o n s can play a major r o l e i n the formation of o f f f l a v o r s that reduce the a c c e p t a b i l i t y of the c i t r u s j u i c e s and t h e i r products. The sugars, p r i m a r i l y the hexoses, can p a r t i c i p a t e i n "browning" r e a c t i o n s that cause darkening of the j u i c e and these r e a c t i o n s g i v e r i s e to components that are d e s c r i b e d g e n e r a l l y as a p r i c o t - l i k e or p i n e a p p l e - l i k e i n flavor. In general, the more processed f l a v o r that a c i t r u s product e x h i b i t s , the l e s s acceptable i t becomes to the consumer. Some authors have i n d i c a t e d that the sugar-amino a c i d react i o n s of the M a i l l a r d type are of minor importance i n c i t r u s j u i c e s because of the high a c i d i t i e s i n v o l v e d . Studies i n our l a b o r a t o r i e s (42-44) would tend to i n d i c a t e that, to the contrary, the amino acids and sugars are of more than j u s t minor importance i n the darkening of c i t r u s j u i c e s . Huffman (42) t r e a t e d c i t r u s j u i c e s w i t h c a t i o n i c ion-exchange r e s i n s to remove amino a c i d s , p r o t e i n s , and the mineral c a t i o n s , then r e s t o r e d the c a t i o n s . The j u i c e s from which the f r e e amino a c i d s were removed were l e s s s u b j e c t to darkening and o f f - f l a v o r development than were t h e i r r e s p e c t i v e c o n t r o l s a f t e r heating f o r long periods of time to temperatures near 100°C, then s t o r i n g at room temperature. J u i c e s were a l s o dehydrated i n a vacuum s h e l f dryer and on a chain b e l t dryer with l e s s v i s i b l e darkening than c o n t r o l samples. The ion-exchange t r e a t e d j u i c e s were judged by sensory panels to be much more acceptable than untreated c o n t r o l s when presented as p a s t e u r i z e d j u i c e or as dehydrated j u i c e . Addit i o n a l s t u d i e s conducted i n our l a b o r a t o r i e s (43) corroborated the f i n d i n g s of Huffman. In a d d i t i o n , lowering the pulp content of j u i c e p r i o r to dehydration decreased the tendency f o r j u i c e to darken during the d r y i n g process. Seaver and Kertesz (47) reported that D-galacturonic and D-glucuronic a c i d s , when heated alone or i n the presence of amino a c i d s , formed c o l o r e d compounds at a r a t e exceeding that found with common sugars. They f u r t h e r r e ported that L - a s c o r b i c a c i d formed c o l o r e d compounds more r a p i d l y than the sugars, but s t i l l at a slower r a t e than the u r o n i c acids. C u r l (48), i n a study conducted with a s y n t h e t i c orange j u i c e , reported that the l o s s of a s c o r b i c a c i d occurred i n the presence of c i t r i c a c i d and potassium c i t r a t e b u f f e r alone, but that the l o s s e s were i n c r e a s e d by the a d d i t i o n of the sugars, lévulose, sucrose, and dextrose, i n that order. He found that darkening of the s y n t h e t i c j u i c e occurred p r i n c i p a l l y when both amino a c i d s and sugars were present; and, the e f f e c t was even more pronounced by the presence of a s c o r b i c a c i d . P r u t h i and L a i (49), i n a study of d i f f e r e n t methods f o r


246


p r e s e r v i n g and s t o r i n g c i t r u s j u i c e s , reported that the a d d i t i o n of 5% cane sugar to the j u i c e s a c c e l e r a t e d the darkening and d i d not a i d i n a s c o r b i c a c i d r e t e n t i o n . Kato and Sakurai (50) studi e d the e f f e c t s of a s c o r b i c a c i d , organic a c i d s , amino a c i d s , and i n o r g a n i c ions on browning i n a model system. They determined that 3-deoxyglucosone and 5-hydroxymethylfurfural were formed by the a c t i o n o f organic a c i d on f r u c t o s e (formed by i n v e r s i o n of sucrose). Browning, they reported, was a f f e c t e d by organic acids, amino a c i d s , o x i d i z e d a s c o r b i c a c i d , and the i n o r g a n i c i o n s , S n \ F e 3 , S n , and A l . These i n v e s t i g a t o r s reported that 3-deoxyglucosone and 5-hydroxymethylfurfural were intermediates i n the browning of concentrated lemon j u i c e that occurred when the concentrate was d i l u t e d to s i n g l e - s t r e n g t h j u i c e with a sucrose s o l u t i o n . They concluded that amino acids had a r o l e i n the browning (51).


+

+

+ 2

+ 3

Wolfrom e t a l . (52) s t u d i e d the nonenzymic browning of dehydrated orange j u i c e and concluded that 4-aminobutyric a c i d was of p a r t i c u l a r s i g n i f i c a n c e i n the formation o f c o l o r e d products. The i n i t i a l phase of the browning r e a c t i o n l e d to a l o s s o f D-glucose and 4-aminobutyric a c i d . Kampen (53) s t o r e d f r e e z e d r i e d orange j u i c e c r y s t a l s and a s y n t h e t i c mixture f o r 40 days at 50°C and monitored l o s s e s of t o t a l amino acids (73%), a s c o r b i c a c i d (100%), c i t r i c a c i d (5.1%), and sucrose (4.4%). The orange j u i c e c r y s t a l s were d i s c o l o r e d from M a i l l a r d browning, and severa l carbonyl compounds and f u r f u r a l d e r i v a t i v e s were i d e n t i f i e d as products o f the r e a c t i o n s . Berry e t a l . (54) s t u d i e d foammat d r i e d i n s t a n t orange j u i c e s t o r e d a t 70°F and a t 85°F and reported that the s t a b i l i t y of the product was improved by the use o f more a c i d i c j u i c e s , but adding a c i d , or removing sugar. They reported an i n v e r s e r e l a t i o n s h i p between s t a b i l i t y of the i n s t a n t orange j u i c e and the pH of the orange concentrate dried. Although the importance o f the sugars i n the browning of c i t r u s j u i c e s has been debated by many i n v e s t i g a t o r s , v i r t u a l l y a l l agree on the importance of a s c o r b i c a c i d i n t h i s r e a c t i o n . J o s l y n (55) reported that a s c o r b i c a c i d was the most r e a c t i v e of the system, a s c o r b i c acid-amino acid-sugar, that occurs i n orange juice. Sugars, he reported, e x e r c i s e a p r o t e c t i v e e f f e c t on the enzymic and nonenzymic o x i d a t i o n of a s c o r b i c a c i d ; hence, both glucose and f r u c t o s e are i n h i b i t o r y to browning. The amino acids were reported t o have an i n h i b i t o r y e f f e c t i n the e a r l y stages o f the browning r e a c t i o n , but i n l a t e r stages, these components increased the r a t e o f browning. Moore et a l . (56) reported that the decomposition of ascorb i c a c i d i n orange j u i c e was d i r e c t l y a s s o c i a t e d w i t h darkening. According to C u r l (57), the development of o f f f l a v o r s i n orange j u i c e s a t 13-71% s o l u b l e s o l i d s was c l o s e l y p a r a l l e l e d by the l o s s of a s c o r b i c a c i d and by darkening. In mandarin j u i c e , Aiba et a l . (58) found t h a t the r a t e of browning was r e l a t e d to the decomposition of a s c o r b i c a c i d . Studies with the j u i c e of natsu-



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d a i d a i (a Chinese c i t r o n ) by Imai et a l . (59) and others a l s o i m p l i c a t e d a s c o r b i c a c i d as a major reactant r e s p o n s i b l e f o r browning. Imai e t a l . (59) reported that the f r e e amino a c i d s played an important r o l e i n the browning o f the j u i c e . Clegg (60) s t u d i e d the nonenzymic browning of lemon j u i c e and reported that the phenomenon was a t t r i b u t a b l e to a s c o r b i c a c i d r a t h e r than sugar-amino a c i d condensations. She reported that f u r f u r a l was produced during the. development of browning, but d i d not consider that i t played an important r o l e i n the a e r o b i c a l l y - p r o d u c e d browning. In model systems that simulated lemon j u i c e , she reported that amino a c i d s i n a s c o r b i c systems were major c o n t r i b u t o r s to browning (61). I t has been reported and i s g e n e r a l l y agreed that a s c o r b i c a c i d i n c i t r u s j u i c e s can be degraded through a e r o b i c and anaerob i c pathways (53,62). The a c i d i s q u i t e s e n s i t i v e t o o x i d a t i o n and dehydroascorbic a c i d i s the primary o x i d a t i o n product, though r e l a t i v e l y unstable. I t undergoes conversion to 2,3-diketoguloni c a c i d . In a d d i t i o n to these o x i d a t i o n products, f u r f u r a l and h y d r o x y f u r f u r a l have been i d e n t i f i e d as products of the degradat i o n of a s c o r b i c a c i d (60,63,64,65). Bauernfeind and P i n k e r t (66) proposed pathways f o r both the aerobic and anaerobic pathways i n aqueous media. In these pathways, shown i n F i g u r e 3, f u r f u r a l can r e s u l t from e i t h e r mode o f a s c o r b i c a c i d d e s t r u c t i o n while h y d r o x y f u r f u r a l i s a product of the o x i d a t i v e system. In processed c i t r u s products, a s c o r b i c a c i d l o s s can occur through aerobic or anaerobic mechanisms. The o x i d a t i o n of ascorb i c a c i d i n orange j u i c e was s t u d i e d by Evenden and Marsh (67) and was reported to be a f i r s t order r e a c t i o n whose r a t e was a f u n c t i o n o f temperature. In a very recent review, Nagy (65) reported that the degradation of a s c o r b i c a c i d was best explained by a f i r s t - o r d e r r e a c t i o n and that f o r g r a p e f r u i t j u i c e , the A r r henius p l o t showed a l i n e a r p r o f i l e f o r the temperature region 10-50°C. With orange j u i c e , h i s data suggested that two d i f f e r ent r e a c t i o n mechanisms were operative w i t h the k i n e t i c change o c c u r r i n g a t about 28°C. Between 10°and 27°C the r a t e of ascorb i c a c i d l o s s doubled f o r each 10°C r i s e ; from 27°to 37°C the r a t e quadrupled. The data of Nagy (65) a l s o confirmed e a r l i e r data by Ross (68) and Lamb (69) that i n d i c a t e d f o r s i m i l a r s t o r age temperatures the l o s s o f a s c o r b i c a c i d was greater f o r orange j u i c e than f o r g r a p e f r u i t j u i c e . 4

Processed C i t r u s Products

Of the 1978-79 domestic c i t r u s crop, some 6,855,000 metric tons o f oranges from a t o t a l o f 8,340,000 metric tons went to the production o f processed products. Of the 2,490,000 metric tons of g r a p e f r u i t that were harvested, 1,510,000 metric tons were u t i l i z e d i n processed products. A s i m i l a r p i c t u r e can be p a i n t e d f o r the other domestic c i t r u s crops. I t i s easy to see that the market f o r processed c i t r u s f r u i t i n the U.S. i s ex-

American Chemical Society Library 1155 16th St. N. W. Washington, D. C. 20036




248

ASCORBIC

ACID

DEHYDROASCORBIC ACID

DIKETQ6ULQNIC

-C-OH

C-H

ACID

+H2O

>K

ANAEROBIC

C-OH

I

II

CHOH

I

II

-C02

C-OH

I CHOH

I

C-OH

C-OH

CHOH

I CHOH

"

I

I

REARR.

Ç

H0H

CHOH

*

-3»2°

I CH2OH

CH OH

CHOH

2

I

\Λ 0

FURFURAL

CH20H

Figure 3.

Possible ascorbic acid degradation pathways


CHO

11.

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Citrus Juice

Processing

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tremely important to the c i t r u s i n d u s t r y . Almost 95% of the F l o r i d a orange crop i s u t i l i z e d by processors i n the production of j u i c e products. Since the d i e t s of domestic consumers contain processed products as t h e i r major source of c i t r u s , i t i s r e a sonable to look at these products and how they are a f f e c t e d nut r i t i o n a l l y by the p r o c e s s i n g techniques i n p r a c t i c e i n the industry. 4.1

Frozen Concentrated J u i c e s

Frozen concentrated orange j u i c e (FCOJ) i s by f a r the most widely d i s t r i b u t e d of the processed c i t r u s products. First marketed i n the mid-1940 s, i t has grown i n consumer acceptance u n t i l the present day, and to the p o i n t where i t s volume consumption exceeds the combined t o t a l f o r a l l other processed c i t r u s products. FCOJ and other frozen concentrated c i t r u s j u i c e s are produced by the process o u t l i n e d i n F i g u r e 4. P r i o r to evaporation the process i n c l u d e s e x t r a c t i o n , f i n i s h i n g , and b l e n d i n g . In the evaporator, the j u i c e may be concentrated to 45°Brix (% s o l u b l e s o l i d s ) or higher; and, as a matter of r o u t i n e p r a c t i c e , most of the evaporator pumpout (concentrate) i s at 65-68°Brix. The concentrate can go to low-temperature s t c r a g e or d i r e c t l y to p r o c e s s i n g f o r FCOJ. During the f r u i t p r o c e s s i n g season, cutback j u i c e may be used to d i l u t e the concentrate to 45°Brix. At other times, essence and water are used to prepare FCOJ. Berry and Veldhuis (3) reviewed t h i s process i n great d e t a i l . The l o s s of a s c o r b i c a c i d during e x t r a c t i o n , f i n i s h i n g , and b l e n d i n g i s minimal. Based on the data of Sale (70) and Hayes et a l . (71), the l o s s should be no g r e a t e r than 2%. Hayes et a l . (71) prepared orange j u i c e concentrates having 50-60% s o l i d s and reported a mean r e t e n t i o n of 96.6% of a s c o r b i c a c i d . T i n g et a l . (32) c o l l e c t e d samples of FCOJ from 23 manufact u r i n g p l a n t s i n F l o r i d a during 1973 and 1974 and analyzed them f o r s e l e c t e d n u t r i e n t s , those s p e c i f i e d by the U.S. Food and Drug A d m i n i s t r a t i o n as being e s s e n t i a l to human n u t r i t i o n . The average n u t r i e n t content of FCOJ r e c o n s t i t u t e d to 12.8°Brix expressed as percent of the U.S. RDA i s shown i n Table VII along with the U.S. RDA s as s p e c i f i e d by the Food and Drug A d m i n i s t r a t i o n (6). Based on these data, i t can be seen that FCOJ i s of d i e t a r y s i g n i f i c a n c e with respect to Vitamin C ( a s c o r b i c a c i d ) , f o l i c a c i d , and thiamine, i . e . , i t provides 10% or more of the r e s p e c t i v e U.S. RDA per 177ml s e r v i n g . Much has been w r i t t e n about the e f f e c t s of p r o c e s s i n g , tempe r a t u r e , and storage c o n d i t i o n s on the s t a b i l i t y of a s c o r b i c acid i n citrus juices. On the other hand, l i t t l e i s known about the s t a b i l i t y of f o l i c a c i d under s i m i l a r c o n d i t i o n s . Chen and Cooper (72) s t u d i e d the e f f e c t s of temperature and oxygen and a s c o r b i c a c i d on the thermal degradation of f o l i c a c i d , and they reported that a s c o r b i c a c i d i n c r e a s e d the s t a b i l i t y of the tetra-


f

T



250


A * IT corns OUT next Figure 4.

^

L

Flow diagram for frozen concentrated orange juice production (courtesy Adney Reed)


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Processing

TABLE V I I Average N u t r i e n t D e l i v e r y p e r Serving o f R e c o n s t i t u t e d FCOJ (12.8°Brix) i n R e l a t i o n to U.S. RDA 77^ U.S. KDk K±J


Nutrient Vitamin A

5000

IU

Vitamin C

60

mg

Average % U.S. RDA/ j(2) 1

7

7

m

l

F C O

1.4 131

Thiamine

1.5mg

9.8

Riboflavin

1.7mg

2.4

mg

2.0

20

Niacin

1.0g

Calcium

1.8

18

mg

1.1

2

mg

4.9

Folic Acid

0.4mg

20.3

Phosphorus

1.0g

3.3

Iron Vitamin B

6

400

mg

4.9

15

mg

0.7

2

mg

4.4

10

mg

3.3

Vitamin D

400

IU

Vitamin Ε

30

IU

Magnesium Zinc Copper Pantothenic A c i d

Vitamin

B^

Iodine

meg

150

meg

0. 3 mg

Biotin

Source:

6

1) 2)

U.S. Food and Drug A d m i n i s t r a t i o n ( 6 ) . Ting et a l . (32).



252


hydro- and 5 - m e t h y l f o l i c a c i d at 1 0 0 ° C T h e i r data i n d i c a t e d t h a t the degradation of these f o l a t e s at high temperature was due to an o x i d a t i v e process that r e q u i r e d the presence of molecular oxygen. Floyd and Rogers (73) analyzed authentic samples of F l o r i d a orange j u i c e s and concentrates to determine the e f f e c t s of conc e n t r a t i o n on chemical composition. They reported no s i g n i f i c a n t e f f e c t s of concentration on the chemical composition of orange j u i c e concentrate as compared to s i n g l e - s t r e n g t h j u i c e . S e t t y et a l . (74) reported that the n u t r i e n t content of mandarin orange j u i c e when concentrated to 62°Brix and higher was very l i t t l e affected. Horton and Dickman (75) reported that the p h y s i o l o g i c a l l y a v a i l a b l e a s c o r b i c a c i d ( a s c o r b i c a c i d and dehydroascorbic acid) i n r e c o n s t i t u t e d orange j u i c e was s t a b l e over a two-week p e r i o d , both at 4°C and at room temperature. A e r a t i o n caused by blendori z i n g at high speed f o r two minutes had no e f f e c t on a s c o r b i c acid s t a b i l i t y . B i s s e t t and Berry (76) reported on the a s c o r b i c a c i d r e t e n t i o n i n orange j u i c e as a f u n c t i o n of container type. They stored FCOJ i n f o i l - l i n e d cardboard, r e c t a n g u l a r cartons and i n polyethylene ( P E ) - l i n e d f i b e r c y l i n d r i c a l cans f o r a year at -20.5°, -6.7°, and 1.1°C. At -20.5°C, the a s c o r b i c a c i d r e t e n t i o n was 93.5% i n the f o i l - l i n e d cartons and 91.5% i n the PEl i n e d cans. Neither c o n t a i n e r proved e f f e c t i v e above f r e e z i n g due to m i c r o b i a l s p o i l a g e . The f o i l - l i n e d carton was s u p e r i o r at 1.1°C, i n that 89% of the a s c o r b i c a c i d was r e t a i n e d a f t e r three months. In the P E - l i n e d can, the r e t e n t i o n was 44% a f t e r three months at 1.1°C. G a r c i a (77) s t u d i e d the e f f e c t of storage on 45°Brix and 54°Brix orange j u i c e concentrates packaged i n 6-oz. f o i l - l i n e d , spiral-wound cans and i n 2 0 0 - m l f o i l - l i n e d , r e c t a n g u l a r cartons ( T e t r a B r i k ® ). The l a t t e r were both c o l d f i l l e d and a s e p t i c a l l y f i l l e d v i a high-temperature short-time p a s t e u r i z a t i o n . These products were stored f o r one year at -17.8°, 7.2°, and 23.9°C. The a s e p t i c a l l y - p r o c e s s e d concentrates r e t a i n e d s t e r i l i t y throughout the course of the study and were s t o r e d at 7.2° and 23.9°C. The samples i n 6-oz. f o i l - l i n e d composite cans and those c o l d f i l l e d i n t o the 200-ml r e c t a n g u l a r packages were stored only at -17.8°C because they were not a s e p t i c a l l y packed and were subject to m i c r o b i a l s p o i l a g e . Figures 5 and 6 show the a s c o r b i c a c i d r e t e n t i o n i n the 200-ml packages as a f u n c t i o n of time. The data f o r the 6-oz. composite can are not shown because the a s c o r b i c a c i d r e t e n t i o n i n these packages was s i m i l a r to but j u s t m a r g i n a l l y poorer than was the r e t e n t i o n i n the 200-ml packages at -17.8°C. This marg i n a l d i f f e r e n c e was a t t r i b u t e d to the presence of some headspace oxygen i n the 6-oz. cans which r e s u l t e d i n the l o s s of s l i g h t l y more a s c o r b i c a c i d . At -17.8°C, the r e t e n t i o n of a s c o r b i c a c i d over 12 months


VARSEL

Citrus Juice

100 0,,


'±

g

η

ο

253

Processing

°-

1

1.5

4.5

3.C

6.0

7.5

12 0

9.0

MONTHS Figure 5. Ascorbic acid retention in 54° Brix concentrated orange juice as a function of storage temperature ((O) -17.8°C; Ο 7.2°C; (A) 23.9°C)

Τ

ΔΔ

—"—α......

Δ"- .

1.5

3.0

a..

^

4.5

6.0

7.5

9.0

10.5

12.0

MONTHS

Figure 6. Ascorbic acid retention in 45° Brix concentrated orange juice as a function of storage temperature ((O) -17.8°C; Ο 7.2°C; (A) 23.9°C)



254


exceeded 97% i n the 200-ml packages and 94% i n the 6-oz. compos i t e cans. The a s c o r b i c a c i d r e t e n t i o n i n both the 45°Brix and 54°Brix concentrates s t o r e d at 7.2°C were very s i m i l a r over 12 months. The l o s s of a s c o r b i c a c i d amounted to about 8% to 10% over the storage p e r i o d . At 23.9°C, the 45°Brix concentrate i n i t i a l l y e x h i b i t e d a more r a p i d l o s s of a s c o r b i c a c i d than d i d the 54°Brix concentrate, but at the end of e i g h t months both had l o s t about 25% of t h e i r s t a r t i n g ascorbic acid. The more r a p i d l o s s of a s c o r b i c a c i d may have been caused by the amount of d i s s o l v e d oxygen i n the 45°Brix concentrate i n i t i a l l y . I t may have been the r e s u l t of more r a p i d d i f f u s i o n of oxygen i n t o the lower °Brix concentrate once i t entered the package along the l o n g i t u d i n a l seam and at the corners. N e i t h e r f a c t o r was measured. As might have been expected, f l a v o r d e t e r i o r a t i o n followed the same p a t t e r n as d i d the degradation of a s c o r b i c a c i d , i . e . , the concentrates at 23.9°C d e t e r i o r a t e d i n f l a v o r a c c e p t a b i l i t y more r a p i d l y than d i d those at 7.2°C; those at 7.2°C d e t e r i o r a t e d at a f a s t e r rate than d i d those s t o r e d f r o z e n . The products stored at 23.9°C remained acceptable i n f l a v o r f o r about s i x months; those at 7.2°C remained acceptable f o r e i g h t to ten months. At -17.8°C, the products were s t i l l acceptable a f t e r a year of storage. Packages of the type used i n t h i s study by G a r c i a are pres e n t l y used i n many p a r t s of the world f o r the packaging of m i l k , j u i c e s , and j u i c e products. B r i k Pak, Inc., a s u b s i d i a r y of T e t r a Pak Ab has p e t i t i o n e d the £ood and Drug A d m i n i s t r a t i o n for approval to use the T e t r a B r i k © package i n the U.S., but a f i n a l d e c i s i o n regarding t h e i r p e t i t i o n i s s t i l l pending. Frozen concentrated g r a p e f r u i t j u i c e i s produced i n essent i a l l y the same manner as FCOJ. P r i o r to evaporation, the j u i c e i s s t a b i l i z e d at 66° to 88°C to prevent g e l a t i o n and clarificat i o n during storage. As i s done i n the manufacture of FCOJ, coldpressed g r a p e f r u i t p e e l o i l i s added to the g r a p e f r u i t conc e n t r a t e to enhance i t s f l a v o r . Essence, the v o l a t i l e water s o l uble f l a v o r from the f r u i t , may be added during the manufacture of a g r a p e f r u i t concentrate, but t h i s system of f l a v o r s does not seem e s s e n t i a l to h i g h f l a v o r q u a l i t y . T h i s i s contrary to what i s g e n e r a l l y found w i t h FCOJ where essences do enhance f l a v o r q u a l i t y (78). 4.2

Reduced-Acid Frozen Concentrated

Orange J u i c e

I n t e r e s t i n reduced-acid c i t r u s j u i c e s o r i g i n a t e d i n the e a r l y I960's when K i l b u r n and Drager (4) employed e l e c t o d i a l y s i s tc remove c i t r a t e ions from j u i c e . The F l o r i d a Department of C i t r u s t e s t e d the reduced-acid concept w i t h consumers at the New York World's F a i r i n 1965, and followed t h i s t e s t with a n a t i o n a l consumer survey i n 1972. The Coca-Cola Company Foods D i v i s i o n



11.

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conducted an independent consumer survey i n 1973, and a l l of the s t u d i e s i n d i c a t e d s u b s t a n t i a l consumer i n t e r e s t i n reduceda c i d c i t r u s j u i c e s . A f t e r f u r t h e r t e s t i n g with consumers i n which products were t e s t e d i n homes, the Foods D i v i s i o n was granted a permit from the U.S. Food and Drug A d m i n i s t r a t i o n and the F l o r i d a Department of C i t r u s to manufacture the product and to d i s t r i b u t e i t i n i n t e r s t a t e commerce. L a t e r the FDA was p e t i t i o n e d to e s t a b l i s h a new standard of i d e n t i t y f o r reduceda c i d f r o z e n concentrated orange j u i c e . The issuance of that standard i s s t i l l pending. A reduced-acid frozen concentrated orange j u i c e i s presently being t e s t marketed by The Coca-Cola Company Foods D i v i s i o n . This product i s produced by blending r e g u l a r concentrated orange j u i c e with acid-reduced concentrate i n p r o p o r t i o n s that w i l l r e s u l t i n a f i n a l f r o z e n concentrated orange j u i c e with a B r i x / a c i d r a t i o between 21 and 26 to 1; the p r e c i s e blend being dependent on the B r i x / a c i d r a t i o s of the two concentrates employed. A f t e r b l e n d i n g , the concentrate i s adjusted to 45°Brix through the a d d i t i o n of water and essence. Coldpressed orange o i l i s added f o r good f l a v o r q u a l i t y . The product i s then canned and s t o r e d at -17.8°C. The f a t e s of the n u t r i e n t s of orange j u i c e were n a t u r a l l y of concern i n the process of producing an acid-reduced orange conc e n t r a t e , so many s t u d i e s were conducted to a s c e r t a i n the l e v e l s of the major n u t r i e n t s before and a f t e r p r o c e s s i n g . The major concerns were i n regard to a s c o r b i c and f o l i c a c i d s , s i n c e these components might w e l l be removed during the ion-exchange process to remove c i t r a t e i o n . Since the a n i o n i c r e s i n employed i s weakly b a s i c , the retent i o n of stronger a c i d s i s favored with respect to the weaker a c i d s , a s c o r b i c and f o l i c . A l s o , because of the law of mass a c t i o n , the removal of c i t r a t e ion i s favored over ascorbate and f o l a t e . The change i n the a s c o r b i c a c i d c o n c e n t r a t i o n of j u i c e during a c i d r e d u c t i o n p r o c e s s i n g i s i l l u s t r a t e d i n F i g u r e 7. Some a s c o r b i c a c i d i s i n i t i a l l y r e t a i n e d by the r e s i n but i t i s l a t e r r e p l a c e d by the stronger a c i d , c i t r i c , as the exchange c a p a c i t y of the r e s i n i s depleted. T h i s i n i t i a l r e d u c t i o n i n a s c o r b i c a c i d i s on the order of 15%, but as the column i s exhausted t h i s a c i d i s r e p l a c e d by c i t r i c and i t i s e l u t e d i n the j u i c e stream. Near the end of treatment, the a s c o r b i c a c i d l e v e l r i s e s tc i t s i n i t i a l l e v e l and even exceeds i t as that which was i n i t i a l l y h e l d by the column i s r e p l a c e d by c i t r a t e . I t can be seen i n F i g u r e 7 that some a s c o r b i c a c i d can be l o s t i f the ion-exchange r e s i n i s not completely exhausted during p r o c e s s i n g . When the column i s exhausted t h i s l o s s of a s c o r b i c a c i d i s minimized. A s c o r b i c a c i d l o s s i n acid-reduced j u i c e s never exceeded 10% except i n cases where the ion-exchange r e s i n was not comp l e t e l y exhausted and g e n e r a l l y i t was i n the range of 3% to



256


50

pH4.2

A 3.9

40

si

Citrus Nutrition and Quality - American Chemical Society

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