Effects of amino acids on the release of acidic odor compounds in Langjiu and its potential mechanisms

Non-volatile amino acids could influence the overall aroma volatility and perception of Chinese liquor (Baijiu), yet the underlying mechanisms remain unclear. In this study, stir bar sorptive extraction-gas chromatography-mass spectrometry (SBSE-GC-MS) and amino acid analyzer were used to identify the odor compounds and free amino acids in Langjiu. Six acidic odor compounds with an odor activity value (OAV) ≥ 1 and the flavor amino acid L-phenylalanine (L-phe) were selected for analysis. Partition coefficient and olfactory threshold analyses were conducted to investigate the effect of L-phe on the release of these odor compounds. The results indicated that L-phe promoted the release of 3-methylbutanoic acid and pentanoic acid, while it inhibited the release of 2-methylpropanoic acid, butanoic acid, hexanoic acid, and octanoic acid. However, at high concentrations (257 mg/L), L-phe attenuated both the promotive and inhibitory effects. Fluorescence spectroscopy and isothermal titration calorimetry analyses demonstrated that the six acidic odor compounds effectively quenched the intrinsic fluorescence of L-phe through a static quenching mechanism, forming ground-state complexes. The primary interactions between L-phe and 3-methylbutanoic acid and pentanoic acid were attributed to hydrophobic interactions, while the interactions with 2-methylpropanoic acid, butanoic acid, hexanoic acid, and octanoic acid were mainly due to electrostatic interactions. This study provides new insights into the flavor regulation of Baijiu.