A systematic approach for the characterization of the key aroma-active compounds in sun-dried Toona sinensis (SDTS) and vacuum-dried T. sinensis (VDTS) was performed by means of the molecular sensory science concept. A total of 64 aroma-active compounds were identified via gas chromatography−olfactometry (GC-O) and gas chromatography−mass spectrometry (GC-MS). Aroma extract dilution analysis (AEDA) and static headspace dilution analysis revealed 39 odorants in SDTS and 32 odorants in VDTS with flavor dilution (FD) factors from 8 to 4096, with the highest for vanillin and eugenol in both samples. Stable isotope dilution analysis (SIDA) and an internal standard method were applied to quantitate 42 odorants, revealing 35 compounds in concentrations above their respective odor thresholds in SDTS and 29 compounds in VDTS, respectively. Calculation of odor activity values (OAVs) indicated 2-isopropyl-3-methoxypyrazine, eugenol, and β-ionone with the highest OAVs in both samples. Recombination experiments of the overall aromas of SDTS and VDTS by mixing the odorants with OAVs ≥1 in their naturally occurring concentrations proved the successful identification and quantitation of the respective key odorants.
Tea is among the most consumed nonalcoholic beverages worldwide. Understanding tea flavor, in terms of both sensory aspects and chemical properties, is essential for manufacturers and consumers to maintain high quality of tea products and to correctly distinguish acceptable or unacceptable products. This article gives a comprehensive review on the aroma and off-flavor characteristics associated with 184 odorants. Although many efforts have been made toward the characterization of flavor compounds in different types of tea, modern flavor analytical techniques that affect the results of flavor analysis have not been compared and summarized systematically up to now. Thus, the overview mainly provides the instrumental flavor analytical techniques for both aroma and taste of tea (i.e., extraction and enrichment, qualitative, quantitative, and chemometric approaches) as well as descriptive sensory analytical methodologies for tea, which is helpful for tea flavor researchers. Flavor developments of tea evolved toward time-saving, portability, real-time monitoring, and visualization are also prospected to get a deeper insight into the influences of different processing techniques on the formation and changes of flavor compounds, especially desired flavor compounds and off-flavor substances present at (ultra)trace amounts in tea and tea products.
N-ethyl-2-pyrrolidinone-substituted flavan-3-ols (EPSFs) were prepared by an in vitro model reaction, and the taste thresholds of EPSFs and their dose-over-threshold factors in large-leaf yellow tea (LYT) were investigated. The effects of initial reactant ratios, reaction temperatures and time, pH values, and water addition on the yield of EPSFs were explored. The contents of EPSFs during roasting were determined by liquid chromatography quadrupole time-of-flight mass spectrometry (LC-Q-TOF-MS). When the initial ratio of (−)-epigallocatechin gallate (EGCG) to theanine was 1:2 and roasted under 120 °C for 120 min, the contents of EPSFs were the highest. The bitterness and astringency thresholds of four EPSF isomers were measured by the halftongue method, of which EPSF2 and EPSF3 had higher thresholds than EGCG. In LYT, four EPSFs had lower bitterness and astringency dose-over-threshold factors than EGCG. This study suggested that the reduction of bitterness and astringency of tea after roasting may be mainly due to the formation of EPSFs.
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