Optical Isomers of Linalool and Linalool Oxides in Tea Aroma

Abstract

The main aroma components of oolong and black tea, linalool and four diastereomers of linalool oxides (LOs), were enantioselectively isolated by capillary gas chromatography, using a column coated with an optically active liquid phase, permethylated fJ-cyclodextrin.The RIS ratio varied among linalool and LOs, and among the different types of tea, the ratio for a particular compound also being different. However, the complete patterns of RIS ratio were similar in the semi-fermented and fermented teas, respectively.Using a specific cultivar of black tea, the RIS ratio for each of the five compounds was compared in the free state in black tea with that of an aglycone of the glycoside in fresh tea leaves or in black tea. While the e.e. values of the compounds varied, those for a specific compound were similar, except for linalool, regardless of their free or combined state.These results show that LOs are not directly transformed from linalool, but are formed enzymatically from glycoside precursors.The mono terpene alcohols play an important role in semi-fermented tea (oolong tea) and in fermented tea (black tea) aroma, among which linalool and its oxides (LOs) are the main components, which in some varieties of black tea account for over 50% of the tea volatiles.1 ) Both linalool and LOs have asymmetric carbon, as shown in Fig. 1. It is known that some optical isomers have a different aroma character,2) and identification of the chirality of aroma components existing in tea is important for clarifying the formation mechanism for tea aroma in plants and during tea fermentation.A few chiral aroma compounds in tea volatiles have already been studied in our laboratory by the classical chemical approach. 3) However, the most important tea aroma components, linalool and LOs, were not included. High-resolution gas chromatography (HRGC), using an open tubular capillary column coated with a cyclodextrinbased chiral stationary phase, has recently been developed to conduct an effective enantioselective analysis of various ~", . . . O<- The optical separation and structural elucidation of linalool by using such a column coated with heptakis (2,3,6-tri-O-methyl)-fJ-cyclodextrin (CD column) have been reported by Konig et al., (R)-linalool being eluted earlier than (S)-linalool. 7) The elution order for the diastereomers of furanoid and pyranoid LOs in the CD column has been ascertained, and direct stereodifferentiation of the furanoid LOs in the CD column and their chromatographic behavior has also been clarified by Askari and Mosandl. 8) We tried to compare the ratio of the optical isomers of linalool and LOs in different varieties of tea, and the ratio of the optical isomers of free and glycosidically bound linalool and LOs to evaluate their enzymatic or non-enzymatic formation process, as well as the separation conditions for the optical isomers. Materials and MethodsMaterials. Two varieties of commercial oolong tea (Huang Jin Gui and Tie Guan Yin) were imported from China in 1993. Two varieties of black tea (Clone 2025 and Cl...

Volatile compounds and sensory characteristics of various instant teas produced from black tea

“…Linalool and its metabolites, linalool oxides isomers, have previously been reported in various tea samples (Du et al, 2014;Qin, Pang, Chen, Cheng, Hu, & Wu, 2013;Schuh & Shieberle, 2006). It is known that linalool and linalool oxides develop remarkably during enzymatic hydrolysis of green tea leaves (Wang, Ando, Morita, Kubota, & Kobayashi, 1994). Linalool was recognized as one of the key odorants in several studies of black tea leaves and tea infusions (Schuh & Shieberle, 2006), green tea (Kumazawa & Masuda, 2002), and presented as contributor to citrus and floral odour notes of teas (Schuh & Shieberle, 2006;Wang et al, 1994;Wang et al, 2008).…”

“…It is known that linalool and linalool oxides develop remarkably during enzymatic hydrolysis of green tea leaves (Wang, Ando, Morita, Kubota, & Kobayashi, 1994). Linalool was recognized as one of the key odorants in several studies of black tea leaves and tea infusions (Schuh & Shieberle, 2006), green tea (Kumazawa & Masuda, 2002), and presented as contributor to citrus and floral odour notes of teas (Schuh & Shieberle, 2006;Wang et al, 1994;Wang et al, 2008). There were no terpenes detected in DCIT, and may have possibly been lost during the extraction of caffeine.…”

Aroma Character Impact Compounds in Kinokuni Mandarin Orange (Citrus kinokuni) Compared with Satsuma Mandarin Orange (Citrus unshiu)

“…The enantiomeric distribution of linalool in mandarins is summarized in Table 5. Previous studies [55][56][57] have judged the odor quality and threshold value for each enantiomer of linalool to be different. Specifically, (R)-linalool had woody, lavender-like, strong green floral notes (an odor threshold of 0.8 ppb), while (S)-linalool had sweet, floral, petitgrain-like, oily, heavy green notes (an odor threshold of 7.4 ppb).…”

Differences in the Volatile Components and Their Odor Characteristics of Green and Ripe Fruits and Dried Pericarp of Japanese Pepper (Xanthoxylum piperitum DC.)

“…(R)-Linalool was 44, 74, and 20% ee in the green fruit, ripe fruit, and dried pericarp, respectively. The absolute configuration of linalool has often been investigated in lavender, jasmine flower, and tea leaves (20)(21)(22), and it has also been clarified that the absolute configuration greatly affected the overall odor of jasmine tea (23). The odor threshold value of (R)-linalool (0.035-0.040 ppm), with a strong, green floral note, is 3-4 times lower than that of (S)-linalool, with an oily, heavy, green note (24).…”