Food Chemistry

942 21 Coffee, Tea, Cocoa

changes involved in aroma and flavor damage.
The changes are retarded by storing coffee at
low temperatures, excluding oxygen and water
vapor.

21.1.3.3 Composition of Roasted Coffee

Table 21.3 provides information about the com-
position of roasted coffee. This varies greatly, de-
pending on variety and extent of roasting.

21.1.3.3.1 Proteins

Protein is subjected to extensive changes when
heated in the presence of carbohydrates. There is
a shift of the amino acid composition of coffee
protein acid hydrolysates before and after bean
roasting (Table 21.4). The total amino acid con-
tent of the hydrolysate drops by about 30% be-
cause of considerable degradation.
Arginine, aspartic acid, cystine, histidine, ly-
sine, serine, threonine and methionine, being
especially reactive amino acids, are somewhat
decreased in roasted coffee, while the stable
amino acids, particularly alanine, glutamic acid
and leucine, are relatively increased. Free amino
acids occur only in traces in roasted coffee.

Table 21.3.Composition of roasted coffee (medium de-
gree of roasting)

Component Content (%)a

Arabica Robusta

Caffeine 1. 32. 4
Lipids 17. 011. 0
Proteinb 10. 010. 0
Carbohydrates 38. 041. 5
Trigonelline, niacin 1. 00. 7
Aliphatic acids 2. 42. 5
Chlorogenic acids 2. 73. 1
Volatile compounds 0. 10. 1
Minerals 4. 54. 7
Melanoidinsc 23. 023. 0

aBased on solids. Water content varies between 1 and

5%.
bCalculated as the sum of the amino acids after acid

hydrolysis.
cCalculated as the difference.

Table 21.4.Amino acid composition of the acid hy-

drolysate of Colombia coffee beans prior to and after

roasting

Amino acid Green coffee Roasted coffeea

(%) (%)

Alanine 4. 75 5. 52

Arginine 3. 61 0

Aspartic acid 10. 63 7. 13

Cystine 2. 89 0. 69

Glutamic acid 19. 80 23. 22

Glycine 6. 40 6. 78

Histidine 2. 79 1. 61

Isoleucine 4. 64 4. 60

Leucine 8. 77 10. 34

Lysine 6. 81 2. 76

Methionine 1. 44 1. 26

Phenylalanine 5. 78 6. 32

Proline 6. 60 7. 01

Serine 5. 88 0. 80

Threonine 3. 82 1. 38

Tyrosine 3. 61 4. 35

Valine 8. 05 8. 05

aA loss due to roasting amounts to 17.6%.

21.1.3.3.2 Carbohydrates

Most of the carbohydrates present, such as cellu-

lose and polysaccharides consisting of mannose,

galactose and arabinose, are insoluble. During

roasting a proportion of the polysaccharides are

degraded into fragments which are soluble. Su-

crose (cf. Table 21.2) present in raw coffee is de-

composed in roasted coffee up to concentrations

of 0.4–2.8%. Monosaccharides also hardly occur.

21.1.3.3.3 Lipids

The lipid fraction appears to be very stable and

survives the roasting process with only minor

changes. Its composition is given in Table 21.5.

Linoleic acid is the predominant fatty acid, fol-

lowed by palmitic acid. The raw coffee waxes,

together with hydroxytryptamide esters of var-

ious fatty acids (arachidic, behenic and ligno-

ceric) originate from the fruit epicarp. These com-

pounds are 0.06–0.1% of normally roasted cof-

fee. The diterpenes present are cafestol (I, R =

H), 16-O-methylcafestol (I, R = CH 3 ), and kah-