Tandem Solid-Phase Extraction Columns for Simultaneous Aroma Extraction and Fractionation of Wuliangye and Other Baijiu

Abstract

Wuliangye baijiu is one of the most famous baijiu in China, with a rich, harmonic aroma profile highly appreciated by consumers. Thousands of volatiles have been identified for the unique aroma profile. Among them, fatty acid esters have been identified as the main contributors to the aroma profile. In addition, many non-ester minor compounds, many of which are more polar than the esters, have been identified to contribute to the characteristic aroma unique to Wuliangye baijiu. The analysis of these minor compounds has been challenging due to the dominance of esters in the sample. Thus, it is desirable to fractionate the aroma extract into subgroups based on functional group or polarity to simplify the analysis. This study attempts a new approach to achieve simultaneous volatile extraction and fractionation using tandem LiChrolut EN and silica gel solid-phase extraction (SPE) columns. A baijiu sample (10 mL, diluted in 40 mL of water) was first passed through the LiChrolut EN (1.0 g) column. The loaded LiChrolut EN column was then dried with air and coupled with a silica gel (5.0 g) SPE column with anhydrous Na2SO4 (10.0 g) in between. The volatile compounds were eluted from the LiChrolut EN column and simultaneously fractionated on the silica gel column based on polarity. The simultaneous extraction and fractionation technique enabled the fractionations of all fatty acid esters into less polar fractions. Fatty acids, alcohols, pyrazines, furans, phenols, hydroxy esters, and other polar compounds were collected in more polar fractions. This technique was used to study the volatile compounds in Wuliangye, Moutai, and Fengjiu baijiu. In addition to fatty acid esters, many minor polar compounds, including 2,6-dimethylpyrazine, 2-ethyl-6-methylpyrazine, 2-ethyl-3,5-dimethylpyrazine, p-cresol, and 2-acetylpyrrole, were unequivocally identified in the samples. The procedure is fast and straightforward, with low solvent consumption.

Volatile Phenols: Direct Analysis Using Large-Volume Injection-Online Trapping-Gas Chromatography-Tandem Mass Spectrometry (LVI-GC-MS/MS) and Aroma Contribution to Different Aroma-Type of Baijiu

“…Chinese Baijiu is a unique distilled spirit from solid fermentation and solid distillation. It is rich in aroma compounds, such as fatty acid esters, fatty acids, volatile phenolic compounds, and other compounds. ,,, According to the China National Standard (GB/T 15109-2021 Terminology of Baijiu Industry), traditional Baijiu can only be from the fermentation of grains with starters, and alcohol, aroma, or flavor-producing substances cannot be added directly or indirectly . Since Baijiu is a distilled product aged in porcelain jars, it is possible to develop a green analytic approach based on direct large-volume injection-online trapping GC-MS/MS for sensitive quantitation of volatile phenolic compounds in Baijiu.…”

“…The Plackett−Burman design was conducted to obtain the factors that had the most significant influence on the responses of volatile phenols of the LVI method, and each variable was tested at two experimental levels, a high level (+) and a low level (−). 41 According to preliminary results, eight instrumentation factors (Table 2), including (1) initial temperature (40 and 60 °C), (2) vent flow (50 and 150 mL/min), (3) vent time (0.2 and 0.6 min), (4) final temperature (220 and 280 °C), (5) vent pressure (20.68 and 48.26 kPa (3 and 7 psi)), (6) desorption time (0.5 and 3.5 min), (7) desorption flow (1 and 3 mL/min), and (8) purge flow (200 and 300 mL/min), were selected for further optimization for the LVI-GC-MS/MS method. Additionally, to find the systematic error or unknown variables affecting the model, three "dummy" factors were also added to the design, including (1) heating rate, (2) gas saver flow, and (3) flow of the postrun.…”

“…In addition, the extraction and concentration procedures are tedious and time-consuming. Solid phase extraction (SPE) with suitable absorbent can selectively extract the analytes and significantly reduce solvent consumption. ,, The technique still needs some organic solvents and is cumbersome. In addition, the SPE packing and solvent systems must be carefully selected to recover the analytes.…”

Comparison of two data processing approaches for aroma marker identification in different distilled liquors using comprehensive two‐dimensional gas chromatography‐time‐of‐flight mass spectrometry dataset

“…The LiChrolut EN‐based SPE technique has high capacity and sensitivity, ease of automation, and reduced solvent consumption (Weldegergis et al., 2011). The technique has been proven efficient for extracting most aroma compounds (Wang, Gao et al., 2020; He et al., 2021; Zheng et al., 2022), including distilled liquors, such as baijiu (Wang, Gao et al., 2020), whisky (Wisniewska et al., 2015), and brandy(Barnaba et al., 2015).…”

Identification of Chinese baijiu from the same brand based on a graphene quantum dots fluorescence sensing array

“…Today, thousands of trace components have been detected in liquors, 7 such as esters, which add aroma, acids, which soften the taste, aldehydes, which improve the stale taste, and alcohol, which brings out the aroma of the esters. 8 These organic substances complement each other and work together to create baijiu with an incomparable taste. 9 Baijiu has increased in popularity all over the world as the market demand has increased.…”