Phytochemical Studies of Selected Medicinal and Aromatic Plants of Nepal and Effect of γ-Irradiation on Volatile Organic Compounds of Glycyrrhiza uralensis F.

Abstract

This study was performed to enumerate the phytochemicals alkaloids, anthocyanosides, cardiac glycosides, carotenoids, coumarins, glycosides, flavonoids, saponins, tannins, triterpenoids and essential oils from medicinal and aromatic plants (MAP's) of Nepal. The screening tests were carried out on aqueous and alcoholic extracts using standard procedures. The essential oils were extracted using simultaneous steam distillation and extraction (SDE) and the volatile organic compounds (VOC's) were analyzed by gas chromatography/mass spectrometry (GC/MS). Effect of γ-irradiation on VOC's of Glycyrrhiza uralensis F. was studied to ascertain its threshold limit and acceptability. Effect of different plant extracts on spontaneously induced rat uterine smooth muscle cell contractility was also evaluated. Phytochemical screening of forty-seven MAP's of Nepal belonging to 45 genera and 39 families revealed the presence of plant secondary metabolites in all species with the various concentrations. Glycosides, tannins, terpenoids, flavonoids, alkaloids and saponins were the major secondary metabolites present in most of the plants while cardiac glycosides and carotenoids were rarely detected. Amongst the investigated plants, 81% plant species contained glycosides, 70% showed the presence of tannins, 66% terpenoids, 62% alkaloids, 60% flavonoids, 57% saponins, 45% volatile oils, 43% coumarins, 30% anthocyanosides, 17% cardiac glycosides and 15% carotenoids. Flowers and roots were rich in alkaloids, flavonoids, tannins and saponins. Most of the plants can be seen as a potential source of useful drugs particular reference to glycosides, flavonoids, saponins, tannins, and terpenoids. However total 8 species Asparagus racemosus, Bergenia ciliata, Daphne bholua, Rhododendron arboretum, Schima wallichii, Terminalia chebula, Tinospora cordifolia and Woodfordia fructiosa, out of 47 species containing high concentrations of diverse phytochemicals are confirmed the potential species of medical value. Study on the essentials oils of 8 MAP's of Nepal revealed that all the plants have the existence of essential oils but their concentration varies. The yields of essential oils obtained from Acorus calamus, Asparagus racemosus, Bergenia ciliata, Centella asiatica, Dipsacus mitis, Swertia chirata, Terminalia chebula and Woodfordia fruticisa were 0.7, 0.005, 0.006, 0.1, 0.006, 0.024, 0.004 and 0.019% respectively. Similarly, numbers of VOC's tentatively identified in essential oil of above species were 53, 49, 44, 53, 53, 77, 53 and 81 respectively. Aldehyde was detected as a dominant group in T. chebula and W. fruticosa. Similarly ketone and alcohol were dominant in A. calamus, B. ciliata, S. chirata, A. racemosus and D. mitis respectively and hydrocarbon group was dominant in C. asiatica. Compounds β-asarone, borneol, 5,6-dihydro-2-pyranone, [Z]-β-farnesene, 2-butenal and undecanoic acid, were detected as a major compounds in A. calamus, A. racemosus, B. ciliata, C. asiatica, D. mitis and S. chirata, respectively while furfural was commonly dominant in both T. chebula and W. fruticisa. Some of the compounds such as linalool, farnesol, -terpeniol were common among many species. Majority of compounds detected in those species were monoterpenes. More than 9 monoterpene hydrocarbons viz: [Z]-ocimene, -phellandrene, -myrcene, -pinene, -pinene, camphene, thujene, limonene, 3-carene were prevalent constituents of species A. calamus, A. racemosus and C. asiatica. Sesquiterpene hydrocarbons such as -copaene, -elemene, junipene, [E]-caryophyllene, -humulene, -farnesene etc were highly distributed in A. calamus, and C. asiatica. Some of them were detected in S. chirata and very few were detected in T. chebula and A. racemosus. Oxygenated terpenes were higher in S. chirata and W. fructicisa. Essential oils obtained from C. asiatica. A. calamus, A. racemosus and S. chirata can offer good source for terpenoids, much wanted aromatic chemicals in perfume, flavour and pharmaceutical industries. However, due to low concentrations of essential oils in plants D. mitis, B. ciliate, A. racemosus and T. chebula, can not be recommend for further studies in course of extraction and separation of essential oils. Species W. fruticisa and S. chirata, offer new interest whereas essential oil content of C. asiatica and A. calamus, were verified. Study on the effect of -irradiation on the VOC's of licorice (Glycyrrhiza uralensis F.) showed that low irradiation doses did not affect the yield and number of compounds. Sixty-one volatile organic compounds of the essential oil were tentatively identified in licorice. Above the dose of 1 kGy, one more compound of aldehyde group detected and a few kinds of compounds detected upto 10 kGy irradiated samples were disappeared at 20 kGy irradiated sample. Though the 10 kGy dose of irradiation induced the maximum yield of essential oil of licorice by 12.12%, the maximum dose given at 20 kGy inhibited the total yield by 6.11%. Highest numbers of the compounds highly enhanced at 10 kGy doses resulted that the total yield of volatile oil was found maximumly increased at this dose. Though the content of several VOC's increased after irradiation, the content of major compounds 4-terpineol, myrtenal, tetramethylpyrazine, hexanoic acid, azulene and p-cymene were decreased by the process. Alcohol group was detected as major volatile chemical class (44.12~51.71%) of irradiated samples like in non-irradiated sample. The relative content of total alcohol compounds from volatile oil of irradiated licorice was increased by 5.47~11.44% from 1~10 kGy but decreased by 4.91% at 20 kGy dose of irradiation. The contents of functional groups identified from volatile oil of licorice were changed after irradiations but their proportions were variable in dose dependent manner. We conclude that γ-irradiation upto 20 kGy causes only slight differences in the content and composition of VOC's of licorice. Therefore, the application of irradiation is feasible as it did not undergo major qualitative and quantitative loss of VOC's when subjected to such irradiation doses. Biological activity of different plant extracts on the smooth muscle cell contraction was also evaluated. Uterine smooth muscle tissues were obtained from non-pregnant rats (n=21). Dramatic muscular relaxation on spontaneous contractility was obtained by methanol extract of Dipsacus mitis at concentration of 6500 g/ml and slight relaxation on spontaneous contractility was obtained upto concentration of 20000 g/ml of Woodfordia fructicosa. These results appear to justify their traditional uses.