Based on joint research led by Professor Hiroyuki Wariishi of the Faculty of Arts and Science, Kyushu University and Doctor Chifumi Nagai of the Hawaii Agriculture Research Center (HARC), Suntory Global Innovation Center Limited (President: Masato Arishiro, Minato-ku, Tokyo) ascertained for the first time in the world that tryptophan1, an essential amino acid in Coffea arabica green beans, is a specific marker of maturity level in coffee cherries.2 Suntory has now clarified that the tryptophan products generated through roasting impact the flavor and aroma of the resultant coffee beverage, and it presented this finding at the 25th International Conference on Coffee Science (held from September 8th to September 13th 2014 in Armenia, Columbia.
||One of a number of essential amino acids. Tryptophan is chemical compound understood to be a precursor of plant growth hormones such as auxin. (see Figure 1.)
||Presented in the science journal PLoS ONE 8 (8):70098 (August 2013.)
▼ Presentation Title
Tryptophan in Coffea arabica green beans decides the coffee flavor quality.
IWASA Keiko*, SETOYAMA Daiki**, SETA Harumichi*, SHIMIZU Hiroaki*, FUJIMURA Yoshinori**, MIURA Daisuke**, WARIISHI Hiroyuki**, NAGAI Chifumi***, NAKAHARA Koichi*.
*Suntory Global Innovation Center Co. Ltd, Osaka, JP. ** Innovation Center for Medical Redox Navigation, Kyushu University, Fukuoka, JP. *** Hawaii Agriculture Research Center (HARC), Hawaii, USA.
< Background >
The flavor and aroma of a coffee beverage is determined by a number of factors including roasting and extraction, but the most important factor is the quality of the coffee beans themselves. It is well known that the flavor of coffee is related to the maturity of the coffee cherries at harvest time. Previously, Suntory analyzed metabolites contained in their thousands in Coffea arabica green beans using metabolomics*3 technology, and uncovered for the first time in the world that tryptophan, a type of amino acid, is strongly correlated with the maturity level of coffee cherries. Continuing research along this line, Suntory recently conducted experiments to clarify the actual impact that tryptophan exerts upon the flavor and aroma of coffee through roasting.
< Experiments >
||Using a pyrolyzer (thermal decomposition unit), the reagent tryptophan was heated for ten minutes at a temperature of 230 °C (the roasting temperature of coffee beans) to instigate a pyrolysis reaction, and the resultant chemical composition was analyzed using the GC-MS method.*4
||Coffee cherries at four distinct stages of maturity (immature, semi-mature, ripe, and overripe) were harvested from an experimental field owned by HARC, and samples of Coffea Arabica green beans and roasted beans were prepared from this harvest. LC-MS analysis*5 was performed on the Coffea Arabica green beans, and GC-MS analysis was performed on the roasted beans. The levels of tryptophan in the Coffea Arabica green beans and the levels of tryptophan pyrolysis products in the roasted beans were then comparatively analyzed.
||Tryptophan pyrolysis products were added to coffee extract (at concentrations of 10 ppb and 100ppb, respectively.) The coffee extract was then organoleptically evaluated by a panel of six experts to clarify the impact of such products on the coffee beverage quality.
||Metabolomics refers to the comprehensive and objective analysis of metabolites. Metabolites are chemical compounds produced by the biological activity of plant and animal cells. Metabolomics comprehensively analyzes trace amounts of such chemical compounds.
||GC-MS is an abbreviation of Gas Chromatography-Mass Spectrometry. Gas Chromatography-Mass Spectrometry is a method for qualitatively and quantitatively analyzing a sample of compounds. It involves vaporizing the compounds and separating them using a chromatogram, and then detecting the separated compounds using a mass spectrometer.
||Liquid Chromatography-Mass Spectrometry is a method for qualitatively and quantitatively analyzing a sample of compounds. It involves separating the compounds based on their different degrees of compatibility with the stationary phase and the mobile phase, and then detecting the separated compounds using a mass spectrometer.
< Results >
In Experiment 1, the pyrolysis products of tryptophan were revealed to be indole*6 and 3-methylindole*6 (skatole). See Figure 2.
In Experiment 2, it was found that immature beans had higher levels of tryptophan and that, likewise, immature roasted beans had higher levels of indole and 3-methylindole, thus confirming a strong correlation between the two. See Figure 3.
In Experiment 3, the organoleptic evaluation of the coffee extracts prepared with 100 ppb of indole and 10 ppb of 3-methylindole verified that these tryptophan pyrolysis products increase bad odor and bad flavor. See Figure 4.
||Both indole and 3-methylindole are known to be causative agents of bad odors in intestinal gas. Such odors are produced when bacteria break down tryptophan products in the digestive tract. At extremely low concentrations, they produce a jasmine-like scent.
< Conclusion and Future Prospects >
It is widely known in the coffee industry that the maturity level of coffee cherries impacts the flavor of coffee. Generally speaking, coffee beans taken from immature cherries are referred to as immature beans, and they are known to be a type of defective bean, a slight mixture of which can spoil a cup of coffee by producing a foreign smell and foreign taste. Through this series of research, Suntory found for the first time in the world that the amount of tryptophan in Coffea arabica green beans is an effective marker for predicting the maturity level of coffee cherries, and subsequently clarified that tryptophan pyrolysis products are the direct cause of the foreign taste and foreign smell produced by immature beans. It is hoped that these findings will lead to the improvement in the quality of coffee beverages, specifically by prompting the development of technology that uses tryptophan as a specific marker in order to prevent contamination from immature beans, and technology that removes indole and its derivatives, the causal agents of bad odor.
Suntory Beverage & Food Limited Group Companies will continue collaboration with Suntory Global Innovation Center with a view to utilizing these research results for the creation of added value in the beverage and food manufacture and retail sector.
Suntory Global Innovation Center Limited website : http://www.suntory.co.jp/sic/
Suntory Beverage & Food Limited website : https://www.suntory.com/sbf/