Effects of regulation of sugars and amino acids on aroma components of coffee before roasting

The main purpose of this experiment was to investigate the effect of soaking coffee bean aroma precursor sugar and amino acid on the formation of coffee aroma components. The aroma of coffee beans is greatly affected by roasting time. In this part of the experiment, roasting at different times and functional evaluation analysis showed that the most popular roasting time of coffee beans at 219 ℃ was 16.5min. In the part of soaking sucrose, in terms of the total amount of aroma compounds, the content of aroma compounds collected from roasted coffee beans soaked in 5% sucrose solution was the most, and with the increase of sucrose concentration, the total amount of aroma compounds decreased gradually.

Among the aroma components of coffee beans, Furans, Nitrogen-containing and Ketones compounds are more abundant. The content of these aroma compounds also decreased with the increase of the concentration of soaked sucrose. Therefore, soaking in high concentration of sucrose did not increase the content of aroma components in roasted coffee beans, which was due to the loss of amines which catalyzed the cyclization of sugars to produce aroma compounds in roasted coffee beans. In the part of soaking amino acid, the content of volatile compounds in roasted coffee beans soaked in different concentrations of Serine and Threonine solution increased with the increase of soaking concentration. After soaking in different concentrations of Cysteine solution, the content of volatile compounds in roasted coffee beans did not show a regular trend.

Overall, there was no significant difference in the total amount of aroma compounds in roasted coffee beans soaked in different concentrations of Serine and Threonine. Among the aroma compounds obtained after soaking, roasted coffee beans soaked in Serine and Threonine produced more Pyrazine compounds, while roasted coffee beans soaked in Cysteine produced more Thiazole and Thiophene sulfur compounds. In terms of the percentage composition of aroma compounds, the percentage composition of Nitrogen-containing compounds increased with the increase of soaking amino acid concentration, while the percentage composition of Furans and Ketones compounds decreased with the increase of soaking concentration, so there was a significant correlation between the concentration of soaking amino acid solution and the aroma composition of roasted coffee beans.

In terms of the optimum conditions, the optimum condition obtained by reaction surface experimental design (RSM) is that the soaking concentration is 21.80% and the baking time is 16.61min;Serine. The best condition is that the soaking concentration is 3.22% and the baking time is 16.17min;Threonine. The best condition is that the soaking concentration is 2.69% and the baking time is 16.53min. The best condition of Cysteine is that the soaking concentration is 0.59% and the roasting time is 17.90 min. In the experiment of discussing the optimum soaking conditions and whether the preference of coffee roasted by the optimal roasting time is increased, it is known that the preference of coffee beans soaked in sucrose tends to increase, while the preference of coffee soaked in Serine, Threonine and mixed concentration does not significantly increase or change, but the preference of soaking Cysteine to coffee decreases.