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Abstract
Coffee oil contains pentacyclic diterpenes as typical lipid constituents which have not been detected in any other foods. Major representatives are 16-O-methylcafestol, cafestol, and kahweol. Cafestol is contained in Arabica as well as in Robusta coffee. 16-O-Methylcafestol is found only in Robusta coffee. Larger quantities of kahweol were detected in Arabica coffee, but only trace amounts are present in Robusta.
In coffee oil, the diterpenes are hardly present in free form. They are largely esterified with fatty acids. Up to 14 fatty acid esters of 16-O-methylcafestol and cafestol have been identified. Palmitate followed by linoleate, oleate, stearate, arachidate, and behenate comprise almost 98% of the acid moieties. In Robusta coffee, the total amount of these six 16-O-methylcafestol esters are between 1.0 and 3.0 g/kg d.m. The contents of the corresponding cafestol esters vary between 2.0 and 8.0 g/kg d.m. in Robusta coffee and 9.0 and 22.0 g/kg d.m. in Arabica coffee.
Roasting has little influence on the percentage compositions of the diterpene ester fractions. Accordingly, the percentage distribution of diterpene esters in coffee powder is reflected in the resulting coffee brew. The absolute amounts depend on the type of preparation. In Scandinavian-type coffee, about 23% of the diterpene esters present in the powder can be found in the beverage. The lowest amount (0.3% of the initial quantity) is found in filtered coffee. An intermediate position is taken by espresso coffee with up to 2.5% of the initial concentration.
ACKNOWLEDGMENT
The authors would like to thank the Deutsche Forschungsgemeinschaft for financial support.