Effects of lactic acid on the perception of volatile pyrazine aroma substances in Laimao Baijiu and its molecular interaction mechanisms

Abstract

Lactic acid (LA) is commonly presented in Baijiu, but its influence on flavor is ambiguous. The volatile pyrazines and LA content in Laimao Baijiu were investigated by comprehensive two-dimensional gas chromatography–mass spectrometry (GC × GC-qMS) and ultra-performance liquid chromatography-tandem hybrid quadrupole-Orbitrap mass spectrometry (UPLC-Q-Exactive Orbitrap MS). The results demonstrated that 5 kinds of pyrazine with odor activity values ≥1 were identified as important odorants, and the content of LA was 857.72–1807.79 mg/L. Through sensory experiments, the perceptual interaction of LA with five types of pyrazines in a Baijiu matrix was evaluated. The results showed that after adding LA, the olfactory thresholds of tetramethylpyrazine (TMP) and 2,3,5-trimethylpyrazine (TP) significantly decreased, while the olfactory thresholds of 2,6-dimethylpyrazine (DP), 2-ethyl-3,5-dimethylpyrazine (EDP), and 2-ethyl-6-methylpyrazine (EM) increased. Ultraviolet spectrum analysis and molecular dynamics simulation results indicated that with the addition of LA, the intermolecular attraction related to TMP/TP decreases, while the intermolecular attraction related to DP/EDP/EM increases. LA and pyrazines were mainly affected by van der Waals interaction, electrostatic interaction and hydrophobic interaction. Theoretical calculation results further confirmed that the absolute binding energy of LA-DP, LA-EDP, and LA-EM was greater than that of LA-TMP, and LA-TP. The binding trend of DP, EDP, and EM with LA was more obvious. Overall, LA alters the intermolecular forces between pyrazine molecules, thereby changing the sensory perception of Baijiu flavor. It will provide theoretical guidance for enhancing the aroma quality of soy sauce aroma type Baijiu and promote a more in-depth study of Baijiu.