Comparison of Potent Odorants in Raw and Ripened Pu-erh Tea Infusion Based on Odor Activity Value Calculation and Multivariate Analysis: Understanding the Role of Pile Fermentation.

Infusions prepared from raw pu-erh tea (RAPT) and ripened pu-erh tea (RIPT) showed remarkable aroma differences. Predominant odorants in RAPT and RIPT infusions were identified and compared by the combined use of gas chromatography-olfactometry (GCO), aroma extract dilution analysis (AEDA), odor activity values (OAV) and multivariate analysis. A total of 35 and 19 odorants (OAV>1) were detected in RIPT and RAPT, respectively. Odorants in RAPT and RIPT are significantly different in both odor properties and aroma compound intensities. Overall, RAPT contained a complex variety of chemical classes with diverse odors and moderate odor intensities, while RIPT are dominated by structurally and organoleptically similar compounds with high potency. Specifically, stale and musty smelling methoxybenzenes contributed the most to RIPT, while floral, sweet and woody smelling terpene alcohols, terpene ketones and phenolic compounds were the predominant odorants in RAPT. Orthogonal partial least squares discriminant analysis (OPLS-DA) revealed that linalool, α-ionone, 1,2,4-trimethoxybenzene, 1,2,3-trimethoxy-5-methylbenzene, 1,2,3,4-tetramethoxybenzene and 1,2,3-trimethoxybenzene underwent remarkable changes during pile-fermentation and could be used as potential odor-active markers for RIPT and RAPT discrimination. The comprehensive aroma characterization of pu-erh teas and determination of the effect of pile-fermentation on odorant alteration herein will provide guidance for pu-erh tea flavor quality control and evaluation.