Research on the Aroma Components and Antioxidant Activity of Dendrobium officinale Flowers
Dendrobium Sw., as the second largest genus in the Orchidaceae family, after the genus Cymbidium, has about 1000 species worldwide, with 76 species in China. It is mainly distributed in provinces south of the Qinling Mountains, especially in Yunnan. The aroma of Dendrobium flowers is diverse, and most of them have very distinct characteristics. Dendrobium bensoniae Rchb.f is an epiphytic plant of the Orchidaceae family, native to northeastern India and Myanmar. Due to its elegant and unique design as well as pleasant aroma, it is deeply loved by consumers and has become an important ornamental horticultural flower. It is widely planted worldwide and has enormous commercial value.

For horticultural ornamental flowers, floral fragrance is one of the most important factors determining consumers’ sensory experience and the market value of fresh flowers. However, there is currently little research on the volatile compounds of Dendrobium flowers. Among the reported literature, headspace solid phase micro extraction (HS-SPME) is the only widely used method for extracting the aroma of Dendrobium flowers. There have been studies on the volatile compounds of Dendrobium flowers, such as D. fimbriatum Hook., D. officinale Kimura et Migo, and D. chrysotoxum Lindl. However, there are still some urgent issues that need to be addressed. Firstly, the different types of adsorption columns used in HS-SPME exhibit selective bias in the enrichment of floral aroma compounds, which cannot fully extract and reflect the entire aroma profile of the original sample; Secondly, previous studies have mainly focused on the study of volatile compounds in Dendrobium flowers, lacking analysis of their aroma properties.

In addition, Dendrobium flowers contain various active ingredients such as Dendrobium polysaccharides, Dendrobine, flavonoids, amino acids, etc., which have antioxidant, hepatoprotective, hypoglycemic, and antihypertensive effects. The study of the antioxidant activity of Dendrobium officinale flowers is currently one of the hotspots and an important factor in determining their development and utilization value. Represented by Dendrobium officinale, Dendrobium chrysotoxum, Dendrobium fimbriatum, Dendrobium nobile Lindl., and Dendrobium huoshanense C.Z.Tang et S.J.Cheng, which are included in the Pharmacopoeia of the People’s Republic of China, 31 species of Dendrobium have been reported by scholars at home and abroad to have antioxidant activity, but research on the antioxidant activity of Dendrobium officinale flowers is still blank. Therefore, this article combines floral analysis with antioxidant research to jointly explore the development value and utilization prospects of Dendrobium officinale flowers.

This article adopts the solvent assisted flavor evaporation (SAFE) method to separate the aroma compounds extracted from Dendrobium officinale. This method uses various solvents to assist samples in distillation under low temperature and high vacuum conditions, achieving efficient separation of volatile and non-volatile compounds. Low temperature distillation can greatly reduce the loss of volatile components. Compared with HS-SPME, SAFE produces aroma extracts that are closer to the aroma entity and have better experimental reproducibility. Subsequently, gas chromatography-mass spectrometry was used to analyze the aroma compounds, and the relative percentage content of each component was calculated using peak area normalization method. Furthermore, the odor activity value (OAV) of the aroma compounds was calculated to analyze the aroma composition of Dendrobium officinale flowers. Meanwhile, the antioxidant activity of Dendrobium officinale fresh flower extract was evaluated using hydroxyl radical scavenging assay, DPPH radical scavenging assay, ABTS radical scavenging assay, and SOD enzyme activity repair assay in human immortalized cortical cells (HaCaT).

This article is the first to use solvent assisted flavor distillation combined with gas chromatography-mass spectrometry technology to extract, analyze, and identify the volatile components of Dendrobium officinale fresh flowers. 51 volatile compounds were identified, mainly aldehydes and alcohols. Based on the peak area normalization method and the calculation of the odor activity values of compounds, 16 key aroma compounds contained in the volatile compounds of fresh flowers were preliminarily confirmed. The main aroma types were green grass aroma, sweet aroma, and floral aroma, which are consistent with the fresh and pleasant aroma characteristics of Dendrobium officinale fresh flowers with sweet and honey aroma; The main aroma types of six modified aroma compounds and three potential aroma compounds are lipid aroma, sweet aroma, and amine aroma with unpleasant odor, which constitute the main aroma profile of Dendrobium officinale flowers. The above research elucidates the chemical basis of the main aroma profile of Dendrobium officinale flowers, and the analysis results can more accurately reflect the olfactory characteristics of its flowers. But in addition to the characteristic aroma compounds such as “floral fragrance”, “sweet fragrance”, and “grassy fragrance”, some compounds with “fat fragrance” and “amine fragrance” have also been found to exist in its entire aroma profile. When smelled, in addition to the above floral characteristics, it may also feel slightly greasy and pungent.

In the study of antioxidant activity of extracts from Dendrobium officinale flowers, three in vitro free radical scavenging models, namely hydroxyl radical scavenging model, DPPH free radical scavenging model, and ABTS free radical scavenging model, were used to evaluate the antioxidant activity of the three extracts of Dendrobium officinale flowers, combined with the human immortalized cortex cell SOD enzyme repair model. The results showed that the 95% ethanol extract of Dendrobium officinale flowers exhibited antioxidant activity in all four models, especially in the last three models, where strong antioxidant activity was observed; The 60% ethanol extract showed weak antioxidant activity in the other three models, except for not showing antioxidant activity in DPPH radical scavenging rate; Petroleum ether extract only has a certain hydroxyl radical scavenging activity.

This study elucidated the aroma profile of Dendrobium officinale flowers and preliminarily identified their key aroma components; Studies on antioxidant activity have shown that flower extracts, especially high concentration ethanol extracts, have good antioxidant activity. The related research provides a scientific basis for the research and development of the flower scented daily chemical essence of Dendrobium bence and the development of potential antioxidant substances.