Influence of manufacturing conditions and crop season on the formation of 4-mercapto-4-methyl-2-pentanone in Japanese green tea (sen-cha)

4-Mercapto-4-methyl-2-pentanone is one of the most strongly contributing odorants in the volatile fraction of a Japanese green tea (sen-cha) infusion, and on the basis of the results of an aroma extract dilution analysis, the contribution of this compound to the flavor of the sen-cha infusion varied according to the degree of heating of the tea leaves during the roasting process. The concentration of this odorant in the sen-cha infusion, as with other roasty odorants, increased with the increasing roasting temperature. However, the slope of the increase curve differed with the odor compound, and even if roasting was done at a low temperature, at which the other roasty odorants hardly increased, 4-mercapto-4-methyl-2-pentanone still increased and reached a maximum at 112 degrees C. On the other hand, the amount of 4-mercapto-4-methyl-2-pentanone in sen-cha was a maximum in the first crop, then decreasing in the order of the second and third crops. These results suggested that the amount of 4-mercapto-4-methyl-2-pentanone was closely involved with the quality of sen-cha and that the concentration was dependent on the roasting conditions for the green tea leaves, which might be accompanied by an enzymatic reaction.