Protein in coffee beans

The nitrogen (N2) content of the coffee sample was determined on a Kjeldahl Digestion System. Protein content was calculated as nitrogen x 6.25.

The average protein content of coffee beans is 10%. The free amino acid content of green coffee beans shows a wide range, from 0.001% for methionine in Robusta to 0.1% for glutamic acid in Arabica.

Proteins are composed of different amino acids which are the main compounds contributing to the formation of the typical aroma during roasting, and previous studies have reported that alanine is the amino acid with the highest content (1.2 mg/g) in Robusta coffee beans, followed by asparagine (0.68 mg/g).

During roasting, volatile aromatic compounds and polymeric brown pigments are formed in the beans, while water and carbon dioxide are released. The principal thermally reactive constituents of the raw bean are the monosaccharides and sucrose, free amino acids, chlorogenic acids and trigonelline, and the newly formed precursors of degraded carbohydrates and denaturated proteins.
Protein in coffee beans

Coffee flavor

Coffee aroma and flavor determine about 80% of the quality of a roasts coffee beverage. Green coffee beans from the tree and after processing, do not yet have the color and coffee flavor or aroma of roast beans. They are formed during the roasting process – normally at 210 °C for 6-10 mins.

Reichstein and Staudinger made an outstanding contribution by characterizing more than 70 flavor compounds in roasted coffee. Since 1960 the list of constituent increased to 300 in green coffee, and to 850 in roasted coffee, respectively.

Many natural flavor compounds were first identified in roasted coffee and were later characterized as key compounds in certain processed foods. The pleasant aroma arising from roasted coffee beans during grinding is as attractive as the aroma of fresh brewed coffee for coffee flavored prepared foods.

However, because these pleasant aromas are especially highly volatile and unstable compounds, these are easily lost during the industrialized processing and storage of coffee products such as beverages.

The protein content in green coffee was reported as 8.7% - 12.2%. More importantly, there exists a considerable amount of amino acids in the forms of peptides and free amino acids, which is essential to generation of characteristics roasted coffee flavor. Free amino acids in green coffee play central roles in formation of roasted coffee flavors although their contents are generally at a level of 0.15% - 0.25% in green coffee bean.
Coffee flavor

Protein content in coffee

The nonvolatile fraction of green coffee is composed primarily of water carbohydrates and fiber, proteins and free amino acids, lipids, minerals, organic acids, chlorogenic acids, trigonelline and caffeine. The coffee bean contains a large percent of protein – fourteen percent.

Protein content in roasted coffee amount to about 10% when estimated by acid hydrolysis. The protein composition of coffee appears to vary little between the varieties of the bean, but a variation exists in the total protein content between green and roasted coffee, as protein content decreases and the physiochemical properties of the proteins are altered as a result of denaturation.

During roasting, some protein nitrogen is lost as a result of browning reactions between proteins and carbohydrates producing heterocyclic aroma volatiles.

The total amino acids content of the hydrolysates drops by about 30% because of considerable degradation.

The most important of the amino acids are glutamic acid, leucine, valine, aspartic acid, proline, glycine, phenylalanine, alanine, isoleucine and tyrosine.
 Protein content in coffee