Effect of drying temperatures on the volatile substances of Tilia miqueliana flower
[Objective]To provide a theoretical basis for the development of Tilia miqueliana's medicinal value.[Method]This article used the blooming flowers of T.miqueliana as the experimental material to study the effects of hot air drying(35,40,45℃)and vacuum freeze-drying on the volatile substances of T.miqueliana flowers.Gas chromatography-mass spectrometry(GC-MS)was used to identify volatile compounds in the samples,and the composition and content of volatile compounds in T.miqueliana fresh flowers and four dried flowers were compared.The differences were analyzed using partial least squares discriminant analysis(PLS-DA).[Result]A total of 23 volatile components were identified in T.miqueliana flowers,mainly consisting of olefins,alcohols,and aldehydes,and containing a large amount of volatile substances with medicinal value.There were differences in composition and relative content of volatile compounds between fresh flowers and different dried flowers.D-limonene,γ-terpenes,nonanal,and phenylethanol were substances commonly found in fresh flowers and different dried flowers,and their relative content was significantly higher.T.miqueliana flowers contain volatile substances with medicinal value,such as α-pinene,D-limonene,γ-terpenes,α-farnesene,nonanal,decanal,1-hexanol,and phenylethanol.The content of D-limonene,γ-terpinene,and α-farnesene reached the highest level in fresh flowers,at 104.34,23.62,and 104.16 ng/g,respectively.After drying,the relative content of these substances significantly decreased in flowers of T.miqueliana(P＜0.05);After drying,the relative content of nonanal in the T.miqueliana flowers significantly increased(P＜0.05),with the highest concentration found in the vacuum freeze-dried samples at 40.17 ng/g,followed by the samples dried at 45℃with hot air at 34.81 ng/g;Decanal had the highest content in vacuum freeze-dried samples(4.66 ng/g),followed by 45℃hot air dried samples(4.63 ng/g);1-hexanol was only detected in samples dried with hot air at 35℃,samples dried with hot air at 45℃,and samples dried with vacuum freeze-drying,with the highest content of 10.56 ng/g in samples dried with vacuum freeze-drying;Except for the 45℃hot air dried samples,the relative content of phenylethanol in dried flowers increased compared to fresh flowers,with the highest relative content of 42.87 ng/g in the 40℃hot air dried samples.The similarity rate of volatile compounds between fresh flowers and dried flowers in different treatments ranges from 0.24 to 0.93.There were differences in the aroma components of fresh flowers and dried flowers under different temperatures.Six key differentially volatile compounds were selected based on the criteria of P＜0.05 and variable importance in the projection(VIP)＞1,with grass fragrance being the main characteristic of the key differentially volatile compounds.[Conclusion]Different treatments for volatile substances have their own advantages and disadvantages.Vacuum freeze-drying takes a long time and consumes a lot of energy,which is not conducive to drying a large number of samples.Hot air drying is convenient,economical,and still has beneficial volatile substances.In practical applications,suitable temperatures can be selected to produce T.miqueliana dried flowers based on the medicinal value and economic situation of beneficial volatile substances.
Tilia miquelianaflowerhot air dryingvacuum freeze dryingvolatile substances
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