Sensory quantitative descriptive analysis (SQDA) was used to analyze the flavor structure of nine samples of three aroma types (Nongxiangxing, Jiang-flavor and Zhima-flavor) of Shanzhuang Laojiu, and the results showed that there were significant differences in flavor and taste attributes among the aroma types. Liquid-liquid extraction coupled with gas chromatography-mass spectrometry (LLE-GC-MS) was used to analyze the composition of volatile compounds in these samples, and a total of 74 volatile flavor compounds were identified at high concentrations, manly including esters, alcohols and acids. Based on their aroma activity values (OAVs), 10 characteristic compounds contributing to the aroma of Shanzhuang Laojiu were identified. Partial least squares (PLS) analysis and correlation analysis were used to study the correlation between the sensory attributes and the characteristic aroma compounds, and the results showed that the Jiang, Qu and empty-cup aromas all had good correlation with acetic acid; ethyl butyrate, ethyl caproate, ethyl octanoate, butyric acid and capric acid were the main flavor compounds responsible for the alcoholic, ester, grain-like, sweet and fruity aromas; and the caramel-like and burnt aromas were highly correlated with ethyl myristate, ethyl oleate, ethyl linoleate and 2,3-butanediol. This study may lay the foundation for future research of the flavor formation mechanism of the three aroma types of baijiu.

In order to improve the thermal stability of cutinase AFLACUT-2, the mutants were predicted and screened based on the change of free energy (ΔΔG) for protein folding, and the enzymatic properties of the selected mutant were characterized. The results showed that the thermal stability of mutant Q163M was significantly improved without affecting the enzymatic activity, which retained 86.09% of its activity when incubated at 40 ℃ for 168 h, compared with that of the wild-type strain. At 60 ℃, the half-life of the mutant was 1.68 times higher than that of the wild-type strain. In addition, compared with the wild-type strain, mutant Q163M showed better tolerance to an acidic environment. The mechanism for improved thermal stability of mutant Q163M was elucidated by intermolecular forces and molecular dynamic simulation. These results provide a basis for rationally modifying the thermal stability of cutinase and improving its capacity for the aqueous-phase synthesis of flavor ester at high temperature.