Interactions between Major Acids and Esters in Nongxiangxing Baijiu and Underlying Mechanisms

To ascertain the interactions between the major acids and esters in nongxiangxing Baijiu and the underlying mechanisms, the effects of different types and concentrations of acids on the aroma release of Baijiu model systems containing ethanol (52%, V/V), four acids (acetic acid, lactic acid, butyric acid, an hexanoic acid) and four esters (ethyl hexanoate, ethyl lactate, ethyl acetate, and ethyl butyrate). Electronic nose and sensory evaluation showed that the response intensity and aroma profile of Baijiu model systems varied with different concentrations of acetic acid, lactic acid, butyric acid and hexanoic acid, being most pronouncedly affected by lactic acid. Furthermore, we studied the effect of lactic acid concentration on the volatility and ultraviolet (UV) absorption of Baijiu model systems. The results showed that the volatility was reduced by adding lactic acid. UV spectra demonstrated that there was an interaction between lactic acid and other substances in Baijiu model systems. The volatilization curves of binary systems of lactic acid and esters showed that lactic acid could promote the release of ethyl acetate and ethyl lactate but inhibited the release of ethyl hexanoate and ethyl butyrate. UV spectroscopy showed that the characteristic absorption peaks of the binary system varied with increasing concentration of lactic acid. The thermodynamic parameters showed that the interactions between lactic acid and four esters were spontaneous; the primary interaction force with ethyl hexanoate was hydrophobic interaction, while the interaction forces with the other three esters were hydrogen bond and van der Waals force. This study provides a theoretical basis for the flavor regulation of nongxiangxing Baijiu.