Food Chemistry

21.1 Coffee and Coffee Substitutes 943

Table 21.5.Lipid composition of roasted coffee beans
(coffee oil)

Constituent Content Constituent Content
(%) (%)

Triacylglycerols 78. 8 Triterpenes
Diterpene esters 15. 0 (sterols) 0. 34
Diterpenes 0 .12 Unidentified
Triterpene esters 1. 8 compounds 4. 0

weol (II). Cafestol and kahweol are degraded by
the roasting process.
Since 16-O-methylcafestol is found only in Ro-
busta coffee (0.6–1.8g/kg of dry weight, green
coffee), it is a suitable indicator for the detection
of the blending of Arabica with Robusta coffee,
even in instant coffee.

(21.1)

A diterpene glycoside is atractyloside and its
aglycon, atractyligenin:

(21.2)

Sitosterol and stigmasterol are major compounds
of the sterol fraction.

21.1.3.3.4 Acids

Formic and acetic acids predominate among the
volatile acids, while nonvolatile acids are lac-

Table 21.6.Chlorogenic acid content as a function of

the degree of roasting

Raw/degree of roasting Arabica Robusta

Raw 6 .9% 8 .8%

Light 2 .7% 3 .5%

Medium 2 .2% 2 .1%

Dark 0 .2% 0 .2%

tic, tartaric, pyruvic and citric. Higher fatty acids

and malonic, succinic, glutaric and malic acids

are only minor constituents. Itaconic (I), citra-

conic (II) and mesaconic acids (III) are degra-

dation products of citric acid, while fumaric and

maleic acids are degradation products of malic

acid:

(21.3)

Chlorogenic acids are the most abundant acids

of coffee (Tables 21.2 and 21.3). The content of

these acids drops on roasting as shown in Ta-

ble 21.6.

21.1.3.3.5 Caffeine

The best known N-compound is caffeine (1,3,7-

trimethylxanthine) because of its physiological

effects (stimulation of the central nervous system,

increased blood circulation and respiration). It is

mildly bitter in taste (threshold value in water is

0 .8–1.2 mmole/l), crystallizes with one molecule

of water into silky, white needles, which melt

at 236. 5 ◦C and sublime without decomposition

at 178◦C. The caffeine content of raw Arabica

coffee is 0.9–1.4%, while in the Robusta variety,

it is 1.5–2.6%. In contrast there are caffeine-free

Coffea varieties. Santos, an Arabica coffee, is

on the low side, while Robusta from Angola

is at the top of the range given for caffeine

content. Other purine alkaloids are theobromine

(Arabica: 36–40 mg/kg, Robusta: 26–82 mg/kg)