Abstract:

The volatile components of Michelia crassipes tepals at the flower bud stage，the first-open stage and fully-bloom stage were analyzed using by HS-SPME-GC-Orbitrap-HRMS. A total of 641 volatiles，which could be further classified into 14 groups（mainly terpenes and esters），were identified. Among them，434 volatiles were found in the tepals at the fully-bloom stage，392 volatiles at the first-open stage，and 352 volatiles at the flower bud stage. Also 96，80 and 118 unique volatiles were detected in each stage. At the fully-bloom stage，3 unique alkaloids were detected and they were tetrahydrologanine，tropinone and pilocarpine. The total amount of volatile compounds at fully-open stage was the highest of 668.993 μg · kg^-1，followed by the first-open stage at 628.111 μg ·kg^-1，and the lowest at the bud stage of 522.590 μg · kg^-1. α-guaiene，germacrene B，cis-muurola-4(15), 5-diene，β-caryophyllene，bicyclosesqui- phellandrene，cis-β-ocimene，β-humulene，bicyclogermacrene，γ-muurolene and α-copaene were the major volatiles（content over 13.000 µg · kg^-1）. The analysis of OAV concluded that the characteristic aroma components of M. crassipes tepals included methyl benzoate and α-pinene and the modified aroma components included cis-β-ocimene，β-caryophyllene，linalool and nerolidol. Herbal，floral and woody odor types were the main aroma characteristics. Β-ionone with a low aroma threshold made the tepals in the first-open stage much more floral odor type than that in the bud stage. Benzyl acetate was an unique volatile compound of tepals in fully-open stage，which contributed its strong sweet odor type. The results of principal component analysis indicated that the aroma characteristics of tepals of M. crassipes were not dominated by high-content volatiles，but by the interaction and mutual influence of multiple volatiles. In conclusion，the composition of volatile components in the tepals of M. crassipes is rich，but there are certain differences in different flowering stages. The differences in the types，contents and aroma thresholds of volatile components affected the aroma characteristics of tepals at different flowering stages，making them exhibit diverse fragrance.

Key words: Michelia crassipes, flower volatile substances, GC-Orbitrap-HRMS, terpenes, characteristic aroma components