Coffee Enzymes and Coffee Quality

3 Coffee Enzymes and Coffee Quality

Downloaded by NORTH CAROLINA STATE UNIV on December 17, 2012 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0047.ch003

HENRIQUE V. AMORIM and VERA L. AMORIM Department of Chemistry, Sector of Biochemistry, Esc. Sup. Agric, "Luiz de Queiroz," University of São Paulo, 13400 Piracicaba, Sp, Brazil

Coffee beverage is the i n f u s i o n of the roasted coffee seed. I t is the most consumed stimulant beverage i n the world and is second i n i n t e r n a t i o n a l t r a d e . The coffee tree i s a perennial plant and grows in t r o p i c a l and s u b - t r o p i c a l r e g i o n s . The p r i c e of coffee beans (bean, i s a worldwide used name, but the correct form should be coffee seed) depends on the q u a l i t y . I t i s almost impossible to define q u a l i t y because what i s a good coffee f o r one, could be a bad coffee f o r o t h e r s . However, it is important to take i n t o c o n s i d e r a t i o n the acceptance of the product by the majority of the consumers. I t will be considered i n t h i s paper that the best coffee q u a l i t y i s the one that i s accepted as being high q u a l i t y by the majority of people involved in the coffee i n d u s t r y . Coffea a r a b i c a L. f o r example, i s considered the most f l a v o r f u l and i s a l s o the most expensive. I t accounts f o r 3/4 of the world consumption. Following t h i s comes C . Canephora, P i e r r e ex Froehner, known i n the i n t e r n a t i o n a l trade by Robusta, and accounts f o r 1/4. A small percentage comes from C . L i b e r i c a , H i e r n . Within each s p e c i e , coffee i s a l s o c l a s s i f i e d by its q u a l i t y , which includes p h y s i c a l aspects of raw bean ( c o l o r , s i z e , shape and i m p u r i t i e s ) and the f l a v o r q u a l i t y of the beverage ( a c i d i t y , body and aroma) a f t e r r o a s t i n g . The q u a l i t y of the coffee w i t h i n a given specie i s d i c t a t e d by the region where the plant i s grown, by the c u l t u r a l p r a c t i c e s and by h a r v e s t i n g , processing and storage c o n d i t i o n s . In s p i t e of the importance of c o f f e e q u a l i t y to the p r i c e of the commercial bean, little has been done on the chemical and enzymological aspects as coffee seed. Tea i s probably the most studied stimulant beverage. The f l a v o r precursors of black tea and s e v e r a l of the chemical components i n the 27 In Enzymes in Food and Beverage Processing; Ory, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.


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E N Z Y M E S IN FOOD A N D B E V E R A G E PROCESSING

Figure 1. Cross section of a ripe coffee fruit

In Enzymes in Food and Beverage Processing; Ory, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.


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AMORiM AND AMORiM

Coffee and Coffee Quality

29

f i n i s h e d i n f u s i o n are w e l l known and t h e i r e f f e c t on q u a l i t y are f a i r l y w e l l e s t a b l i s h e d (1* 8) studied the e f f e c t of d r y i n g temperature on the a c t i v i t y of polyphenol oxidase and on the q u a l i t y of the beverage. The best temperatures f o r a c i d i t y , body and aroma were found to be 40, 5 0 and 80°C. Temperatures of 5 0 , 60 and 70°C gave a poor beverage, with respect to these three organoleptic c h a r a c t e r i s t i c s . The a c t i v i t y of polyphenol oxidase g e n e r a l l y decreased when temperature increased, with one exception at 40°C. The enzyme a c t i v i t y at 40°C was lower than that at 3 0 and 50°C. From the data presented, i t would appear that there i s s t i l l no d i r e c t r e l a t i o n s h i p between q u a l i t y , temperature and enzymatic activities. In the s e c t i o n on r o a s t i n g the r e s i s t a n c e of some coffee enzymes to high temperatures, probably because of the dry state of the bean, w i l l be discussed. However, i t does seem that both enzymatic and nonenzym&tic r e a c t i o n might be involved i n changing the chemical composition during the d r y i n g process, but t h i s aspect needs f u r t h e r i n v e s t i g a t i o n .


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ENZYMES

I N FOOD A N D B E V E R A G E

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Role o f Enzymes During Coffee Storage Coffee storage i n humid and warm regions i s a serious problem, because the coffee bean becomes white, or yellow to brown, depending on the degree o f moisture i n the a i r and the time of storage. T h i s change i n c o l o r i s accompanied by a decrease i n flavor quality. MULTON and h i s group (60, 61, 62) have done a s e r i e s o f s t u d i e s on c o f f e e s t o r a g e T n d i f f e r e n t environment c o n d i t i o n s , analyzing microorganisms, water absorption, and enzymatic a c t i v i t i e s , and comparing them with the q u a l i t y o f the beverage. T h e i r major f i n d i n g s may be summarized as follows: above 75% r e l a t i v e humidity, the coffee bean absorbs a s i g n i f i c a n t amount of water and the increase i n moisture content i s p o s i t i v e l y c o r r e l a t e d to fungal growth, although the number of b a c t e r i a decreases. The q u a l i t y o f the beverage i s completely changed and a f t e r 3 0 days a t 9 5 % r e l a t i v e humidity, the c o f f e e beans are completely r o t t e n . At 9 5 % r e l a t i v e humidity there i s a l s o an increase of l i p a s e a c t i v i t y , with a concurrent increase i n free f a t t y a c i d s . In a d d i t i o n , ribonuclease and protease a c t i v i t i e s seem to increase under these c o n d i t i o n s . The dry weight l o s s may reach 2 5 % i n 2 0 0 days i f the r e l a t i v e humidity of the a i r i s above 9 0 % . In B r a z i l , JORDÂO et a l . (6£) a l s o found an increase i n f r e e f a t t y a c i d s during three years storage o f green c o f f e e . The peroxide value increased only a f t e r 2 years storage. In A f r i c a , ESTEVES (64) studying a c i d i t y i n the o i l of Robusta and Arabica c o f f e e s a l s o found an increase i n t i t r a t a b l e a c i d i t y with i n c r e a s i n g time of storage i n both types of c o f f e e s . PEREIRA (6£) i n Portugal was the f i r s t to report a decrease i n polyphenol oxidase a c t i v i t y i n green coffee with storage time. H i s r e s u l t s were confirmed l a t e r by OLIVEIRA ( 1 1 ) , VALENCIA ( 1 2 ) and AMORIM et al. (19). Figure 8 shows the polyphenol oxidase a c t i v i t i e s obtained by OLIVEIRA ( 1 1 ; with d i f f e r e n t coffee species a f t e r d i f f e r e n t times o f storage. The value f o r Arabicas represents the average o f four d i f f e r e n t v a r i e t i e s grown i n d i f f e r e n t regions; a l l gave similar patterns. Stored green c o f f e e s that give d i f f e r e n t q u a l i t i e s of beverage a l s o show decreases i n polyphenol oxidase a c t i v i t y and t o t a l carbonyls with time of storage (Table V I ) .



A M O R I M AND A M O R I M


Ε

Time (in months) of storage Figure 8.

Polyphenol oxidase activity during raw coffee bean storage (11)


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E N Z Y M E S IN FOOD AND

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TABLE VI. T o t a l carbonyls i n coffee o i l and polyphenol oxidase (PPO) a c t i v i t y of Arabica green coffee beans (each symbol i s the average


Coffee Sample Soft Rio Soft Rio

(stored (stored (stored (stored

1 1 2 2

yr) yr) yr) yr)

Total carbonyls umol/g o i l 113-7 a 88.8 b 93-0 b 87.6 b

PPO A c t i v i t y Abs. 10 min/g powder 1.72 a 0.72 b 0.97 c ρ-; ^ ^ Λ

Λ Λ

« 4 - zx>r

level. AKORIM et a l . (Γ9). The higher amount of t o t a l carbonyls found i n the best coffees agrees i n part with the work of CALLE ( 6 6 ) i n Colombia and GOPAL çt a l . ( 6 £ ) i n i n d i a , who found more aldehydes i n the best c o f f e e s . In a preliminary experiment with Arabica c o f f e e s , MELO and coworkers ( 6 8 ) and TEIXEIRA et a l . ( 6 9 ) observed that green coffee stored i n sealed cans or p l a s t i c bags f o r 21 months were s t i l l green, whereas coffee stored f o r the same period of time i n bags made of paper, cotton or vegetable f i b e r were white-yellow and y i e l d e d a poor beverage. These bleached beans showed concurrent lower d e n s i t i e s because of an increase i n s i z e (swelling) (Table VII). The a c t i v i t i e s of polyphenol oxidase and peroxidase were a l s o lower i n the s p o i l e d c o f f e e s . I t i s i n t e r e s t i n g to note that the beans kept i n cans and p l a s t i c had p r a c t i c a l l y a constant moisture content ( ~ 1 0 % ) , but coffee stored i n paper, cotton and vegetable f i b e r containers changed moisture contents from 9 to 13%* depending upon the season. I t i s well known t h a t , upon storage green coffee gradually becomes white. The d i s c o l o r a t i o n s t a r t s i n the outer l a y e r s of c e l l s and goes towards the center. The c o l o r of green coffee of a new crop, i f well processed, i s dark green or greenish-blue. With increased time of storage i t becomes l i g h t green and white. Depending upon the environmental conditions (humidity and temperature), the bean may change to yellow or brown. This change i n c o l o r of green coffee with storage was e x t e n s i v e l y studied by BACCHI ( 7 0 ) i n B r a z i l . By using two v a r i e t i e s of C. a r a b i c a , d i f f e r e n t methods of processing (wet and n a t u r a l ) , d i f f e r e n t pulping and h u l l i n g processes, and d i f f e r e n t storage c o n d i t i o n s , BACCHI concluded that


0 1

C*3 CD

§3

Q 8» 5· C* C O ·—• 2 ο =3 C5 ρ cr =3ρ : S 3


1.35

0.901

119.6 52

2

2

83

88

WELO e t . a l . (68).

cans.

yellowish

yellowish

0.28 0.05 1.9 • R e l a t i v e a c t i v i t y i n percentage r e l a t i v e to a c t i v i t y i n sealed ( s u b s t r a t e : PPO = DOPA; PER = o - d i a n i z i d i n e + H 0 ) .

l . s . d . 5%

Vegetable fiber

51

53

1.28

0.905

0.875

118.7 118.8

Cotton

yellowish

81

1.28

120.9

Plastic

Paper

green green

105

96

Color

1.32

PER0X.* Activity 100

1.118

PPO* Activity 100

1.46

1.124-

120.5

Can

Density

Dry wt. 1000 beans

Container type

Soluble Ν % d.wt.

Hard

Hard

Hard

Almost Soft

Almost Soft

Quality of beverage

TABLE VII· P h y s i c a l and chemical changes of green coffee stored i n d i f f e r e n t containers during 21 months ( a l l estimations were made with four replications).



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E N Z Y M E S IN FOOD A N D B E V E R A G E PROCESSING

the most important f a c t o r which causes the bean to become white i s mechanical i n j u r y , from harvesting to h u l l i n g , regardless of whether the coffee i s processed by the wet or the n a t u r a l method. The environmental f a c t o r which enhances most of the change i n c o l o r i s the moisture of the a i r . The chemical mechanism of coffee d i s c o l o r a t i o n has not y e t been establhished. However, from the data a v a i l a b l e i n the l i t e r a t u r e , and by comparison with d i s c o l o r a t i o n i n vegetables and f r u i t s (71), i t seems that green coffee bean d i s c o l o r a t i o n i s due to enzymatic o x i d a t i o n of phenolic compounds by polyphenol oxidase and peroxidase, with a concurrent oxidation o f ascorbic a c i d (£2). The ascorbic a c i d o x i d a t i o n might be coupled with the reduction of quinones produced by the a c t i o n of PPO and PER on phenolics (21)· general manner, d i s c o l o r a t i o n i n f r u i t s i s followed by a decrease i n phenolics, ascorbic a c i d and polyphenol oxidase a c t i v i t y (71% 2 2 ) . In c o f f e e , AMORIM*et a l . (26) found l e s s hydrolyzable phenolics i n Rio coffee than i n Soft c o f f e e , but the soluble chlorogenic acids (A.O.A.C. procedure (7^)) content i n the best coffee was s i g n i f i c a n t l y lower, i n comparison with the other q u a l i t i e s (26)· Chlorogenic a c i d determination i n green coffee should be r e i n v e s t i g a t e d because d i f f e r e n t types of coffee may give d i f f e r e n t r e s u l t s , depending upon the method used (75)· There i s a p o s s i b i l i t y that phenolics bound t o c e l l wall are responsible f o r the d i s c o l o r a t i o n r e a c t i o n s i n coffee. I t i s well documented i n the l i t e r a t u r e , that i n j u r y causes d i s c o l o r a t i o n or/and browning reactions i n plant t i s s u e s . Coffee beans seem t o be no exception. However, b e t t e r methods f o r a n a l y s i s should be devised i n order t o e x p l a i n many of the chemical and p h y s i c a l changes which occur i n coffee deterioration. a

Enzyme A c t i v i t i e s and P r o t e i n S o l u b i l i t y During the Roasting Process Coffee aroma and t a s t e develop only a f t e r the bean i s roasted. The r o a s t i n g temperature i s 24-0°C or higher and i t requires 3 t o 15 min., depending upon the temperature,load, machinery, e t c . Coffee aroma begins to form when the bean reaches 180-190°C (14, 76» 77)· The p r i n c i p a l precursor of coffee aroma seems t o be t r i g o n e l l i n e , sucrose, f r u c t o s e , glucose, f r e e amino a c i d s and peptides (£)· Carboxylic and



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AMORiM

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49

phenolic acids play an important r o l e i n the t a s t e o f the beverage (6, 77)· The a c t i v i t i e s of s e v e r a l enzymes i n the green bean must play an important r o l e i n modifying the q u a l i t y of the f i n a l beverage, as has been discussed i n t h i s paper. I n s e v e r a l processing steps there are occasions t o modify the chemical composition of the bean. I t i s not probable that enzyme a c t i v i t i e s , per se, play a major r o l e i n coffee f l a v o r during the r o a s t i n g process, because the coffee bean i s dehydrated and the high temperatures would i n a c t i v a t e a l l enzymes. However, due t o the f a c t that 20% o f the a c t i v i t y o f polyphenol oxidase could be retained a f t e r 5 hours exposure of green coffee beans t o 125°C (MELO and AMORIM, 1972, unpublished), i t was necessary to look a t the a c t i v i t y o f s e v e r a l h y d r o l y t i c ( β-galactosidase, β-glucosidase, acid phosphatase, ( 7 7 ) ) and oxidative (polyphenol oxidase, peroxidase) enzymes during the r o a s t i n g process. Figure 9 shows the r e l a t i v e a c t i v i t i e s of several enzymes plus the water-soluble p r o t e i n s (TCA p r e c i p i t a t a b l e ) during r o a s t i n g . As can be seen, the degree o f i n a c t i v a t i o n of the enzymes with i n c r e a s i n g temperature, d i f f e r s depending on the enzyme. At 5 min. ( 1 7 0 ° C ) , the powder has no coffee aroma. Instead, an odor reminiscent of roasted peanut aroma was observed. At 8 min. (187°C), a c l e a r l y defined coffee aroma was detected, which increases a t 12 and 15 min. of r o a s t i n g . The i n s o l u b i l i z a t i o n of p r o t e i n s coincides with the i n a c t i v a t i o n of enzymes and coffee aroma formation. Between the 5 t h t o 8th minute, the free amino a c i d s , peptides, t r i g o n e l l i n e and f r e e sugars should be r e a c t i n g to produce the coffee aroma· I f the f r e e amino acids and polypeptides are important i n coffee aroma formation (j?, 76), the r a t i o o f these amino a c i d s , as w e l l as t h e i r t o t a l amounts should be important to the f l a v o r o f the f i n a l beverage. A l s o , the amino a c i d composition o f the proteins and perhaps t h e i r t e r t i a r y s t r u c t u r e s also play a r o l e i n coffee f l a v o r . I t i s w e l l known that b a s i c and s u l f u r amino acids are destroyed by the r o a s t i n g process (22.* 81). Furthermore, POKORNY et a l . (81) observed that f r e e s u l f u r and b a s i c amino acids i n green coffee decrease with storage. I n B r a z i l , DOMONT et a l . (82), comparing the behavior o f amino acids during the r o a s t i n g of Soft and Rio c o f f e e s , observed that Rio coffees had 2 5 % more free amino acids than Soft c o f f e e s , and the speed of p y r o l y s i s of s e r i n e , threonine and c h i e f l y



50

E N Z Y M E S IN FOOD A N D B E V E R A G E

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O

O BETA GALACTOSIDASE

Δ

Δ POLYPHENOL OXIDASE

Figure 9. Water-soluble proteins and activity of β-galactosidase (p-nitrophenyl-βΌ-galactopyranoside), polyphenol oxidase (DOPA), peroxidase (pyrogallol + H 0 ), β-glucosidase (p-nitrophenyl-$-\)-g]LUCopyranoside), and acid phosphatase (p-nitrophenyl phosphate) during the roasting process. The temperature indicated is that of the air surrounding the bean. 2


2

3.

AMORiM AND AMORIM


51

a r g i n i n e , i s much f a s t l y i n Rio than i n Soft coffee samples. These r e s u l t s agree i n part with the observation that Rio coffee has more low molecular weight polypeptides than Soft c o f f e e s , as seen i n Figure 6· Thus, there i s a p o s s i b i l i t y that these polypeptides may a f f e c t the precursors of aroma formation.


Conclusion From a review of the l i t e r a t u r e and the data presented i n t h i s r e p o r t , there i s only one enzyme that i s c e r t a i n to depreciate coffee q u a l i t y . This i s the polyphenol oxidase of the pulp and mucilage (two enzymes detected), which o x i d i z e s chlorogenic a c i d and other phenolics to quinones. These quinones then form complexes with amino acids and polypeptides having a brown c o l o r , that bind to the center cut of the s i l v e r s k i n . This brown c o l o r of the center cut and s i l v e r s k i n depreciate the q u a l i t y of raw coffee and i t s appearance a f t e r r o a s t i n g . However, whether these pigments p o s i t i v e l y a f f e c t the q u a l i t y of the beverage, i s s t i l l disputed. Commercial p e c t i n o l y t i c enzymes may be used i n conjunction with reducing agents to speed up mucilage removal and avoid browning r e a c t i o n s . Although polyphenol oxidase and peroxidase a c t i v i t i e s i n many instances are c o r r e l a t e d with q u a l i t y of the beverage, proof of the mechanism and the compounds which take part i n these changes and a f f e c t cup q u a l i t y i s s t i l l l a c k i n g . Because of the f a c t that peroxidase i s located c h i e f l y i n the outer l a y e r s of the seed, i t seems probable that t h i s enzyme i s associated with coffee d i s c o l o r a t i o n upon storage. Considering a l l h y d r o l y t i c r e a c t i o n s catalysed by coffee seed enzymes, the l i p a s e s and other enzymes of l i p i d metabolism should be important, because o i l i s the aroma c a r r i e r . Also, the p r o t e i n hydrolases deserve a t t e n t i o n because they a f f e c t a known important coffee aroma precursor: the amino acids and polypeptides. By a f f e c t i n g the r a t i o of these aroma (and probably t a s t e ) precursors, i t i s reasonable to believe that both aroma and taste should be a l t e r e d . From the a v a i l a b l e l i t e r a t u r e on coffee chemistry i t seems that the c h a r a c t e r i s t i c f l a v o r of each coffee specie i s given c h i e f l y by the i n h e r i t e d chemical composition of the bean. However, the v a r i a t i o n i n q u a l i t y ( p h y s i c a l and organoleptic) whithin each specie, seems to be associated with


52

E N Z Y M E S IN FOOD AND

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v a r i a t i o n s i n chemical composition, caused "by the a c t i o n of h y d r o l y t i c and o x i d a t i v e enzymes of the bean and/or micr oorganisms. The d e l e t e r i o u s e f f e c t s of enzymes on the q u a l i t y of the r e s u l t i n g beverage may be prevented by using more s u i t a b l e methods f o r coffee processing and storage.


Acknowledgment Research was c a r r i e d out with grants from the I n s t i t u t o B r a s i l e i r o do Cafe, Conselho Nacional do Desenvolvimento C i e n t i f i c o e Tecnologico e Fundaçào de Amparo a Pesquisa do Estado de Sao Paulo. We are g r a t e f u l to Dr. A. A. T e i x e i r a and Dr. C. M. Franco f o r h e l p f u l d i s c u s s i o n s and to Dr. Robert L. Ory f o r reviewing the manuscript. Literature Cited

1. Sanderson, G.W. " S t r u c t u r a l and Functional Aspects of Phytochemistry". V. C. Runeckless and T. C. Τso E d i t o r s , v o l . 5, p. 24-7-316. Academic Press, New York and London, 1972. 2. Sanderson,G.W., Ranadive, A.S., Eisenberg, L.S., F a r r e l , F.J., Simons, R., Manley, C. H., Coggon, P., " P h e n o l i c , S u l f u r , and Nitrogen Compounds i n Food F l a v o r s " . ACS Symposium S e r i e s , 26, p. 14-46 (1976). 3. B i e h l , B., Ann. Technol. A g r i c . (1972) 21: 435-455. 4. Purr, Α., Ann. Technol. A g r i c . (1972) 21: 457-472. 5. Russwurm, H., 4ème Coll oque I n t e r n a t i o n a l sur, la Chemie du Cafè Vert, T o r r e f i e s and l e u r Derives. (ASIC), p. 103-109, Amsterdam, (1969). 6. Feldman, J.R., Ryder, W. S., Kung, J. T., J. Agr. Food Chem. (1969) 17: 733-739. 7. Vitzthum, O. G., "Kaffee und coffein". p. 1-77. Springer-Verlag, Berlin, Heildelberg, New York, 1975. 8. S i v e t z , M., H. E. Foote, "Coffee Processing Technology", v o l . I, p. 4 8 - 9 9 . The A 9. 10. Wilbaux, R., Repport annual. 2ème p a r t i e , p. 3-45. Congo, I n s t . Nat. E t . Agron. 1938. 11. O l i v e i r a , J.C., Relacão da a t i v i d a d e da p o l i f e n o l oxidase, peroxidase e catalase dos grãos de café e a qualidade da bebida. Doctor T h e s i s . Esc. Sup. Agr. "Luiz de Queiroz". U n i v e r s i t y of Sao Paulo. (1972), P i r a c i c a b a , SP, B r a z i l , 80 pages.


3.

AMORIM

12. 13. 14. 15.


16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31.

32. 33.

AND

AMORIM


53

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