2009_Book_FoodChemistry

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 composition
of roasted coffee. This varies greatly, depending
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 content
of the hydrolysate drops by about 30% because
of considerable degradation.
Arginine, aspartic acid, cystine, histidine, lysine,
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 degree
of roasting)
Component
Arabica
Content (%) a
Robusta
Caffeine 1.3 2.4
Lipids 17.0 11.0
Protein b 10.0 10.0
Carbohydrates 38.0 41.5
Trigonelline, niacin 1.0 0.7
Aliphatic acids 2.4 2.5
Chlorogenic acids 2.7 3.1
Volatile compounds 0.1 0.1
Minerals 4.5 4.7
Melanoidins c 23.0 23.0
a Based on solids. Water content varies between 1 and
5%.
b Calculated as the sum of the amino acids after acid
hydrolysis.
c Calculated as the difference.
Table 21.4. Amino acid composition of the acid hydrolysate
of Colombia coffee beans prior to and after
roasting
Amino acid Green coffee Roasted coffee a
(%) (%)
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
a A loss due to roasting amounts to 17.6%.
21.1.3.3.2 Carbohydrates
Most of the carbohydrates present, such as cellulose
and polysaccharides consisting of mannose,
galactose and arabinose, are insoluble. During
roasting a proportion of the polysaccharides are
degraded into fragments which are soluble. Sucrose
(cf. Table 21.2) present in raw coffee is decomposed
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, followed
by palmitic acid. The raw coffee waxes,
together with hydroxytryptamide esters of various
fatty acids (arachidic, behenic and lignoceric)
originate from the fruit epicarp. These compounds
are 0.06–0.1% of normally roasted coffee.
The diterpenes present are cafestol (I, R =
H), 16-O-methylcafestol (I, R = CH 3 ), and kah-