Characterization of terpenoids and norisoprenoids from base and retail Qingke Baijiu by GC × GC-TOFMS and multivariate statistical analysis

Qingke (highland barley) Baijiu is a special Chinese Baijiu which is mainly produced from Qinghai-Tibet Plateau. Since the pine board is used as the bottom of the fermentation pit, we deduced that the terpenoids and norisoprenoids in pine board might be introduced into Qingke Baijiu. Thus, the terpenoids and norisoprenoids in Qingke Baijiu were investigated by headspace solid phase microextraction (HS-SPME) combined with comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC × GC-TOFMS). The results showed that γ-terpinene (0.70–530.72 μg/L), α-phellandrene (0.34–256.66 μg/L), longicyclene (0–38.55 μg/L), α-pinene (1.21–35.54 μg/L) and limonene (0.93–23.69 μg/L) were the top 5 terpenoids/norisoprenoids in Qingke Baijiu. Pulegone was detected and reported for the first time in Baijiu, and the concentrations in Qingke Baijiu were 0.78 μg/L (fresh) and 3.90 μg/L (7 years old). According to the principal component analysis (PCA) plot, young, aged, and retail Qingke Baijiu could be differentiated clearly. Fold change (FC) and t-tests analysis indicated that β-pinene, γ-terpinene, and α-selinene were the most different terpenoids/norisoprenoids between young and aged Qingke Baijiu, and longifolene was the most different terpenoids/norisoprenoids between base and retail Qingke Baijiu. The terpenoids and norisoprenoids, such as (E)-β-ionone, isoborneol and β-cyclocitral, could be potential markers indicating the ageing process of Qingke Baijiu.