Abstract
Aldehydes occur in rice wines and most of them arise in fermentation, which can be varied by raw material, species of yeasts, fermentation stages, and different processes. Aldehydes exhibit adverse health effects to human beings. Therefore, it is important to improve the quality of rice wine by monitoring the concentrations of aldehydes in the production line. In this method, aldehydes in rice wines were derivatized with 2,4-dinitrophenylhydrazine (DNPH) and analyzed by HPLC with UV detector. The effect of alcohol content on the derivatization reaction was studied by varying concentrations of HCl and DNPH. The derivatization reactions were investigated to obtain the rate constants and equilibrium constants. In order to exclude the possible formation of acetaldehyde from derivatization, acetaldehyde concentration in 40% alcohol by mixing two different alcohol sources was investigated. The results confirmed that the derivatization reaction would not oxidize alcohol to acetaldehyde and the existence of alcohol would only affect the derivatization rate. This method has been successfully applied to determine the concentration of acetaldehyde in rice wines. Concentrations of acetaldehyde in rice wines were in the range of 360-2304 uM. Amino acids in rice wine and wine lees were also investigated in the study. In our analysis, the amounts of amino acids in wine lees were approximately 2 to 4 order of magnitude more than those in rice wines.