Identification of age-markers based on profiling of Baijiu volatiles over a two-year maturation period: Case study of Lu-flavor Baijiu

Baijiu is a highly-valued traditional Chinese distilled alcoholic liquor and maturation markedly improves its sensory qualities and market value. Identification of age-markers is challenging because of the complexity of the endogenous chemical profile and the absence of exogenous components added during maturation. Here, freshly-distilled raw Lu-flavor Baijiu samples were stored for two years and non-targeted screening for age-markers based on the volatile profile characterized by solid-phase micro-extraction assisted GC-MS. The resulting volatile datasets were analyzed by partial least-squares discriminant analysis, Spearman's correlation and Random-forest decision-tree, to identify potential age-markers. The contents of long chain fatty acid ethyl esters varied the most during maturation, mostly being absent in freshly-distilled Baijiu, but appearing at different times. Similar behavior was observed in bottled samples matured up to four years. In addition, a slight increase in short/medium chain fatty acid ester content was observed. Unsupervised PCA analysis, applied only to the fatty acid ethyl ester dataset, was able to distinguish between bottled Baijiu samples matured for one, two, three, or four years. These age-markers may help establish a reliable model for verifying the maturation time of Lu-flavor Baijiu. This screening approach should be adaptable to other alcoholic liquors, for quality assessment and authenticity testing.