Lipid content in coffee.

Of the two commerically important species of coffe, arabica generally contains more lipids than robusta coffee averaging 15-17% and 10-11.5%, respectively. Only a small percentage of the lipid oil is actually contained in the waxy portion covering the bean, with the majority distributed throughout the endosperm ^1,2. Table 1 below summarizes the lipid fraction composition generall found in green coffee.

Table 1: Lipids in Green Coffee^a
Component	% Lipids
Triglycerides	75.2
Esters of diterpene alcohols & fatty acids	18.5
Diterpene alcohols	0.40
Esters of sterol & fatty acids	3.2
Sterol	2.2
Tocopherols	0.04-0.06
Phosphatides	0.1-0.5
Tryptamine derivatives	0.6-1.0
^a: Illy, A. Espresso Coffee. 2nd

In terms of quality, arabica coffee contains almost 60% more lipids than robusta which may play an important role in aroma elucidation - since many important aromatic compounds are oil soluble. A study of Central American coffees demonstrated a correlation betweeen lipid content and beverage quality by a panel of cupping experts.

Studies on coffee storage has shown that fatty acid concentrations increase when coffee is stored for an extended period of time at subtropical temperatures. The increase is the result of enzymatic activity which sometimes leads to the formation of off flavors¹.

During roasting lipids and caffeine remain virtually unchanged, while sugars and proteins decrease significantly³. Its also interesting to note that the majority of the coffee oil found in coffee is composed of triglycerides and fatty acids in proportions similiar to edible vegetable oil.

References:
1. Illy, A. Espresso Coffee. 1st Ed.
2. Illy, A. Espreso Coffee. 2nd Ed.
3. Petracco, M. J. Chem. Ed., vol. 82, No. 8, Aug 2005.
4. E. Alpizar, et al. Fat Content: A Quality Indicator for Central American Coffee. CIRAD, ASI.