Chemical profiling and α-glucosidase inhibitory activity of essential oils extracted with two methods from some North Western Himalayan aromatic crops

Abstract Solvent-free hydrodistillation adsorption apparatus (HDA) and normal clevenger hydrodistillation (NC) were applied to obtain Juniperus communis, Valeriana jatamansi and Hedychium spicatum essential oils (EOs). The yields, chemical compositions and α-glucosidase inhibitory activity of the EOs were investigated. Obtained EOs were analyzed using gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance (NMR) instruments. Recovery improvement was observed in HDA method (30.4%, 27.3% and 29.0% more recovery of EOs than NC method for V. jatamansi, H. spicatum and J. communis, respectively). Present results demonstrated NCV (V. jatamansi EO (essential oil) by NC method) had highest α-glucosidase inhibitory activity with half-maximal inhibitory concentration (IC50) values of 8.20 μg/mL. As a result, HDA method is considered to be the promising theme for producing EOs with high production recovery. Furthermore, current findings demonstrated that the selected EOs may be a good natural antidiabetic. Graphical Abstract


Introduction
Improvement of essential oils (EOs) recovery using different extraction techniques will straightly influence the demand of world essential oil (EO) market. Natural EOs are very important both economically and scientifically, having versatile compounds with diverse applications (Koundal and Agnihotri 2017;Almeida et al. 2018;Rezaei et al. 2019). Valeriana jatamansi Jones (family Valerianaceae) commonly known as muskbala, sugandhbala, tagar and Indian valerian (Maurya et al. 2021). The positive effects of this plant on human health have been attributed to its active class of metabolites, such as iridoids, valepotriates, lignans, flavonoids, sesquiterpenoids and phenolics (Maurya et al. 2020). Hedychium spicatum commonly known as kapur kachri, ginger lily and shati belonging to the Zingiberaceae family. Its rhizomes are used as an ingredient in several oriental medicine formulations (Koundal et al. 2014;Rawat et al. 2018). Juniperus communis (common Juniper) belongs to the Cupressaceae family and widely distributed in temperate Himalaya from Kashmir to Bhutan and western Tibet between 2500 and 4700 m altitude (Maurya et al. 2018). The EO is extensively used in cosmetics, perfumery, pharmaceutical and in food additive industries (Maurya et al. 2018). Several method have been reported previously for the extraction of EOs. However, these techniques have various disadvantages (Boukhatem et al. 2022). Therefore, it is necessary to find the most acceptable method for the improvement of EOs yield.
The present objective of our research was to improve the recovery of EOs, chemical profiling and assess their a-glucosidase inhibitory activity. Furthermore, current data of the EOs recovery will definitely give a positive impact on society by enhancing income of farmers cultivating these cash crops.

Essential oils yield and composition
In this study, comparative variation in EOs recovery (fresh basis and moisture free basis) for targeted plants were recorded (Table S1). Current findings revealed that recovery of EOs were improved when it was extracted by hydrodistillation adsorption apparatus (HDA) apparatus. The obtained EO from V. jatamansi in both methods (HDA and NC (normal clevenger hydrodistillation)) had showed the principal constituents such as isovaleric acid (27.6% in HDA and 14.2% in NC), 3-methyl valeric acid (19.9% in HDA and 14.2% in NC), patchouli alcohol (26.4% in HDA and 35.9% in NC) and maaliol (5.5% in HDA and 5.4% in NC) (Table S2 and Figure S1). Extracted EO from H. spicatum in both methods (HDA and NC) had showed the major metabolites such as 1,8cineole (37.4% in HDA and 53.9% in NC) along with 7-epi-a-eudesmol (14.7% in HDA and 10.5% in NC), s-muurolol (8.2% in HDA and 5.9% in NC) and elemol (5.6% in HDA and 4.3% in NC) (Table S2 and Figure S1). Separated EO from J. communis through both methods (HDA and NC) were dominated by sabinene (45.0% in HDA and 41.2% in NC) along with a-pinene (9.1% in HDA and 9.4% in NC), terpinen-4-ol (6.5% in HDA and 9.1% in NC) and b-myrcene (4.3% in HDA and 4.1% in NC) (Table S2 and Figure S1).
Current findings indicated that quantitative phytoconstituents of the targeted EOs were varied as 3-methyl valeric acid, isovaleric acid, patchouli alcohol and 1,8-cineole (Table S2). However, remaining metabolites had showed less variation by the application of NC and HDA extraction methods. These results are in agreement with the previously reported EO of Murraya koenigii (L) Spreng leaves part using NC and HDA extraction techniques (Koundal and Agnihotri 2017). Several researchers had investigated comparative EO recovery using various separation methods. Recently different hydrodistillation methods were applied in Oliveria decumbens Vent to improve the EO yield (Hossein et al. 2014).

Physicochemical properties of essential oils
Physicochemical characteristics of the EOs obtained using HDA and NC methods are given in Table S3. Values of the relative density, refractive index and optical rotation were clearly indicated the variation when extracted using HDA and NC methods.

Conclusion
The present study demonstrated EOs recovery for targeted aromatic and medicinal crops from Himalayan bioresources using NC and HDA methods. The quantitative components of the EOs varied according to the extraction methods. Current results showed that HDA method achieved more EO recovery as comparison to NC method in selected plants. Extracted EOs were effective against a-glucosidase activity and can be used for the treatment of type 2 diabetes mellitus and its complications. These findings indicated that the enhancement of EOs recovery using this approach may be suitable for both economically and scientifically in the area of crop growing industries and phytopharmaceutical applications.