Triglycerides in coffee

The lipid content of green arabica averages some 15% on a dry basis, whilst robusta contains much less around 10%. Most of the lipids the coffee oil, are located in the endosperm of the coffee bean while only a small amount, the coffee wax is in the outer layer.

Coffee oil is composed mainly of triglycerides with fatty acids in proportions similar to those found on common edible vegetable oils.

Arabica coffees contain 11.1 to 13.6% oil, whereas Robusta coffees contain only 4.4 to 4.8% oil. Apparently, there is even an increase of up to 20 percent in their levels in the roasted coffee. Triglycerides account for 70-80 percent of coffee oil’s content.

The relatively large unsaponifiable fraction is rich in diterpenes of the kaurane family, mainly cafestol, kahweol and 16.0 methylcafestol, which have received increasing attention in recent years because of their physiological effects.

For most part, the fatty acids are present as glycerol esters in the triglycerides, some 20% are esterified with diterpenes and a small proportion as sterol esters.
Triglycerides in coffee

Chlorogenic acid in coffee

The chlorogenic acids are ubiquitous in the plant kingdom. Although chlorogenic acids are common in vegetables foodstuffs, the relatively large quantity present in coffee make it an important dietary sources.

Chlorogenic acid and its isomers represent major coffee constituents of phenolic acid. They are family esters of quinic acid with several hydroxycinnamic acids, particularly caffeic, ferulic, p-coumaric acids.

coffee berries

In coffee they are essentially mono- and diesters and by far the prevailing acids. Other esters may occur but generally only in small amounts.

The quality of coffee depends in part on the relative proportion of mono and dichlorogenic acids, The ratio between these two acids is slightly less in robusta than in arabica. An excess of dichlorogenic acids might result in a metallic after-taste in the beverage.

Oral ingestion by man of 200 mg of chlorogenic acid was found to stimulate stomach secretion with enhancement of hydrochloric acid production. Caffeic acid had the same effect, and quinic acid, XII was inactive.
Chlorogenic acid in coffee

Coffee aroma chemicals

Each variety of coffee has its own flavor and other characteristics. Generally, marketed coffee is a blend of different varieties of coffee beans.

The blends are controlled for flavor, aroma, color and strength or body of the beverage from the roasted bean.

It has been established, primarily from gas chromatography evidence, that there are nearly 1000 different more or less volatile compounds present in roasted coffee.

Most results from the thermal decomposition of carbohydrates and phenols, especially chlorogenic acids that are present at significant concentrations in green beans during roasting.

Some compounds are located in the carbohydrate matrix of the roasted bean whereas others are located in the coffee oil distributed within the bean.

Heterocyclic aroma chemicals, which are major constituents of a brewed coffee extract possessed considerable antioxidants activities.

The flavor and aroma of coffee are best when it is freshly roasted. Many of the aromatic components of roasted coffee, and particularly of coffee oil itself, are extremely susceptible to deterioration by the action of moisture and oxygen.

The staleness of coffee exposed to air is due to the oxidative changes that take place with certain coffee constituents.

The major factor affecting coffee quality is the length of storage, as volatile aroma compounds are lost, especially from ground coffee, with methanethiol and 2,3-pnentanedione being used as indicators of coffee freshness, because they are rapidly lost on storage, especially the 2,3-pentanedione.
Coffee aroma chemicals

Chemical composition coffee beans

Coffee is a drink brewed from coffee beans that comes from the tropical shrub of the genus Coffea, botanically family Rubiaceae.

The quality of the coffee beans used to make coffee is directly related to their chemical composition. The constituents of coffee that are important in making a good beverage are the flavor substances, the bitter substance and caffeine which is responsible for the stimulating effects.

Compared with robusta green beans, arabica green beans have substantially higher lipid, sucrose and trigonelline contents but lower caffeine and chlorogenic acid (CGA) contents.

Caffeine is present in the coffee bean in both the free and combined states. Its content in the bean varies in different species – C. arabica contains 1.0 – 1.2; C. robusta 1.5 – 2.5 and C. liberica 1.4 – 1.6 per cent.

Caffeine, in addition to stimulation, also contributes to the bitterness of the coffee.

Several organic acids are present in the aqueous extract from green coffee beans, the predominant being chlorogenic acid and the least acetic acid.

Coffee beans contains between 8% and 18% (dry basis) fat depending on a variety and species. Green robusta beans generally have lower lipid contents than arabica coffee beans.

Around 75% of coffee oil is in a triglyceride form, with linolenic and palmitic acids being the main fatty acids.

The composition of roasted coffee will vary according to the raw material, roasting degree and roasting parameters such as time, temperature and speed in which the process occurs.
Chemical composition coffee beans

Cafestol and kahweol in coffee

Cafestol and kahweol are fat soluble compounds knows as diterpenes, which have been found to raise serum lipid levels (causing a rise in total cholesterol, low-density-lipoprotein (LDL) cholesterol, and triglycerides) and affect liver.

The structure of cafestol and kahweol is nearly identical, differing in only in the degree of saturation of one conjugated bond to the furan ring.

The diterpenes occur largely as fatty acids esters, esterified at the primary hydroxyl group.  Some cafestol and kahweol are extracted from ground coffee during brewing, but are largely removed from coffee by paper filters.

Diterpenes exhibit good stability at high temperatures, but they can form dehydro-derivative (dehydro-cafestol and dehydro-kahweol) in small amounts when roasting temperatures are raised.

Because coffee beans are high in cafestol and kahweol, ingestion of coffee beans or grounds on regular basis may also raise serum and LDL cholesterol.

Scandinavian-style boiled coffee and Turkish-style coffee contained the highest amounts, equivalent to 7.2 and 5.3 mg cafestol per cup and 7.2 and 5.4 mg kahweol per cup, respectively.
Cafestol and kahweol in coffee