Kinetic study of vicinal diketones in brewing, II: theoretical aspect for the formation of total vicinal diketones.

Nakatani, K., Takahashi, T., Nagami, K. and Kumada, J.

Abstract
The roles of valine and isoleucine in the formation of total vicinal diketones (VDK) are clarified. The assimilation of seventeen amino acids in wort during fermentation is presented illustrating that both valine and isoleucine are assimilated after a lag time of one to two days under the conditions of this experiment. The production of total VDK occurs in two patterns which depend upon the free amino nitrogen (FAN) content of the wort. Additionally, there is a hyperbolic relationship between the maximum value of total VDK and minimum FAN content. The results of this study show that when valine is assimilated by yeast, the formation of total diacetyl is strongly suppressed and similarly, the assimilation of isoleucine suppresses total 2,3 pentanedione formation. Furthermore, valine showed significant suppressive effect on 2,3 pentanedione formation while isoleucine did not have any direct effect on diacetyl formation. The minimum FAN level is suggested to be a useful index towards the formation of total VDK in the later stages of fermentation.
Keywords: amino acid brewing diacetyl fermentation vicinal diketones