Analysis of aroma-active compounds in three sweet osmanthus(Osmanthus fragrans) cultivars by GC-olfactometry and GC-MS

Objective：Aroma is the core factor in aromatherapy. Sensory evaluation of aromas differed among three sweet osmanthus （Osmanthus fragrans） cultivar groups. The purpose of this study was to investigate the aroma-active compounds responsible for these differences. Methods： Gas chromatography-olfactometry （GC-O） and GC-mass spectrometry （GC-MS） were used to analyze the aroma-active compounds and volatiles of creamy-white （‘Houban Yingui’, HBYG）, yellow （‘Liuye Jingui’, LYJG）, and orange （‘Gecheng Dangui’, GCDG） cultivars. Results：Seventeen aroma-active compounds were detected among 54 volatiles. trans-β-Ocimene, trans-β-ionone, and linalool, which were major volatiles, were identified as aroma-active, while cis-3-hexenyl butanoate,γ-terpinene, and hexyl butanoate were also aroma-active compounds, although their contents were low. Analysis of the odors was based on the sum of the modified frequency （MF） values of aroma-active compounds in different odor groups. HBYG contained more herb odors, contributed by cis-β-ocimene and trans-β-ocimene, while LYJG had more woody/violet/fruity odors released by trans-β-ionone, α-ionone, and hexyl butanoate. In GCDG, the more floral odors were the result of cis-linalool oxide, trans-linalool oxide, and linalool. Conclusions：Aroma-active compounds were not necessarily only the major volatiles：some volatiles with low content also contributed to aroma. The aroma differences among the three cultivars resulted from variation in the content of different odor groups and in the intensities of aroma-active compounds.

Aroma changes of black tea prepared from methyl jasmonate treated tea plants

Methyl jasmonate（MeJA） was widely applied in promoting food quality.Aroma is one of the key indicators in judging the quality of tea.This study examined the effect of exogenous MeJA treatment on tea aroma.The aroma components in black tea prepared from MeJA-treated fresh tea leaves were extracted using headspace solid-phase microextraction（HS-SPME） and were analyzed using gas chromatography-mass spectrometry（GC-MS） and GC-olfactometry（GC-O）.Forty-five volatile compounds were identified.The results revealed that the MeJA-treated black tea had higher levels of terpene alcohols and hexenyl esters than the untreated tea.Moreover,several newly components,including copaene,cubenol,and indole,were induced by the MeJA treatment.The activities of polyphenol oxidase and β-glucosidase in fresh tea leaves changed after the MeJA treatment.Quantitative real-time polymerase chain reaction（qRT-PCR） analysis indicated that the gene expression levels of polyphenol oxidase and β-primeverosidase were upregulated by two and three folds,respectively,by the MeJA treatment（P0.01）; however,the gene expression of β-glucosidase was downregulated to a half level.In general,the aroma quality of the MeJAtreated black tea was clearly improved.