Optimization and Validation of a Method for Analysis of Non-Volatile Organic Acids in Baijiu by Derivatization and its Application in Three Flavor-Types of Baijiu

Organic acids have essential effects on the flavor of Baijiu. Except for some small molecular organic acids, which are volatile, most of other organic acids are non-volatile. And due to their low contents in Baijiu, the detection of non-volatile organic acids (NVOAs) in Baijiu is a challenging work. In this study, an optimized derivatization method was developed to detect the NVOAs in Baijiu. Optimization on the derivatization reagent, reaction time and temperature revealed that 10 mL of Baijiu was concentrated to dryness, followed by adding 100 μL BSTFA and 50 μL pyridine and subsequent derivatization over 3 h at 80 °C was suitable. Under the optimal conditions, excellent linearity for all NVOAs was obtained with determination coefficients of R2 > 0.99, inter-day and intra-day precision were below 7.30% and 6.90%, respectively, and recovery rates were in the range of 80.64–113.46%. The LODs were between 0.05 and 11.75 μg/L, which were one-fifth to one ten-thousandth of those detected by HPLC and HPLC–MS. Thirty-six NVOAs in soy sauce (SS), strong (ST), and Laobaigan (LBG) flavor-types of Baijiu were identified. The concentration of lactic acid among the three types of Baijiu was the highest, whose contents were (1069.16 ± 58.74, 7330.11 ± 47.67, 2054.02 ± 54.15) mg/L in LBG, SS, and ST, respectively. Besides, the NVOAs in these three Baijiu were quite different according to principal component analysis and hierarchical cluster analysis. This study provides an effective method for the analysis of NVOAs in complex matrix foods.