A Review of Pharmacognostical Studies on Moringa oleifera Lam. flowers

Moringa oleifera Lam. of the family Moringaceae, popularly called ‘miracle tree’ is a native of sub Himalayan tracts of Northern India and is widely cultivated in tropical and subtropical regions. Research on Moringa mainly pivoted around its leaves and seeds because of their immense nutraceutical potential but recently there is a greater interest in flowers too, mostly inspired by the positive outcomes of several pharmacognostical studies on flowers. Moringa flower is a rich reservoir of bioactive phytochemicals and crude flower extracts showed promising antibacterial, antifungal, anti larval, antioxidant, anti inflammatory and anticancer properties. This review concisely presents the various phytochemicals identified and isolated as well as the various bioassays employed to validate the therapeutic potential of flower. It is prepared after a detailed search on Google scholar. Reports on Moringa oleifera flower were sorted and tabulated based on the bioassays performed and solvents used for extraction. A grading pattern is adopted for comparing efficiency of different extracts in eliciting bioactivities. Many of these studies are at the preliminary stage but two of them present advanced mechanisms. First is the presence of a proteinaceous larvicidal compound ‘MoFTI’ in the flower capable of inhibiting larval trypsin of Aedes aegypti. The second describes flower extract’s anti inflammatory mechanism effecting via NF-KB pathway and consequent suppression of inflammatory mediators’ activation, but short of identifying lead compound/compounds behind this effect. Thus authors suggest further studies to elucidate the detailed mechanisms, identify and isolate the active compound or compounds of synergism behind the many therapeutic potential of the Moringa flower extracts.

pizza pakoras etc or eaten raw as salads, or used for making tea and honey. 4Bhavaprakasa of Bhava Misra, an important treatise on Ayurveda depicts Shigru flowers (Moringa flowers) as Drusti Pathya meaning wholesome food for eyes. 5Anwar et al made a concise presentation of common medicinal uses of different parts of Moringa oleifera with an impressive list assigned to flower alone that include its high medicinal value as a stimulant, aphrodisiac, abortifacient and cholagogue.This study starts with a short description on morphology and anatomy of the flowers, major phytochemicals present, and compounds identified and isolated.Bioassays of flowers conducted in different extracts are then presented in a tabular form so as to make an easy assessment on the pharmacognostical prospects of the flower.Review was prepared based on a detailed search on google scholar for Moringa oleifera related reports.Reports were sorted based on the bioassays performed.Those activities are tabulated against solvents used in the extraction of phytochemicals from flowers.A grading pattern is adopted for comparing efficiency of these extracts in eliciting bioactivities.Abbreviations Pharmacognosy Journal, Vol 9, Issue 1, Jan-Feb, 2017 H, M, L and N were used for noting the High, Medium, Low and Nil activity of extracts.These comparisons are true on results obtained from a single assay, but not necessarily between different assays.Nevertheless they are helpful in understanding the efficiency of solvents in eliciting a particular bioactivity.

Morphology and anatomy
Flowers are fragrant yellowish white, bisexual born in 10 to 25 cm long axillary, compound inflorescence called panicles.Individual flowers slightly zygomorphic have dimensions of about 1 cm length by 2 cm breadth set in a basal cup of thalamus namely hypanthium.Sepals and petals are five in numbers, free, unequal, reflexed and spathulate.Stamens five, dorsifixed filaments of different lengths with posterior ones longest with yellow one celled anthers bending downwards There are five staminodes alternating with the stamens forming an outer whorl.The gynoecium is tricarpellary syncarpous borne on a small gynophore.The ovary continues into a long style which protrude out of anthers and end in creamy white and pitted stigma.Reports suggest a pollen presentation mechanism for behind the overall logistics [6][7][8][9] There are two peaks of flowering October-November rainy season and April-May summer season. 10ytochemistry Proximate analysis found that percentage of dry weight of proteins in flowers is 18.92, ash 9.68, lipids 2.91, dietary fibre 32.45 and non structural carbohydrate 36.04 which suggest a comparable nutritional profile for leaves and flowers. 11Total Antioxidant Content of flower is also found higher than other plant parts. 12Flower contains all the 20 amino acids and the percentage of essential to nonessential amino acids is almost equal. 13The vitamin C content in flowers was found to be in highest 77.502 to 224.672 mg/100 g when compared to other parts. 146][17][18][19][20][21] Most of them air dried fresh flowers, powdered and macerated with occasional soxhlation and employed distilled water, methanol, acetone, ethyl acetate, chloroform or hexane etc for extraction.The yield for various solvents is found to be in the order of Aqueous> Methanol> Ethanol> Acetone> Ethyl acetate> Hexane.Preferred solvent is methanol as it found to contain the most bioactive fractions.Generally the phytochemical composition depends on the geographical location and age of the plant and extraction protocols. 3

Major compounds identified
Modern analytical tools were employed to profile the phytochemical composition of Moringa flowers.Gas Chromatography Mass spectrometry (GCMS) done on methanol extract of flowers identified 26 compounds in which ethyl oleate, quinic acid and cis -9-hexadecenal are the major constituents with reported anticancer, anti inflammatory, antioxidant properties. 22Simultaneous distillation-extraction and capillary gas chromatography/mass spectrometry of flower volatile compounds identified Seventy-four molecules in which the major compounds are (E)-nerolidol (13.33%) α-terpineol (7.8%) and benzyl isothiocyanate (6.4%). 23When freeze-dried samples were used for extraction and analysis by HPLC-DAD-electrospray mass spectrometry showed presence of 22 compounds that include Glucosinolates such as benzyl glucosinolate,  24 When hydroethanolic crude flower extracts is subjected to HPLC-DAD-ESI MS/MS analysis the list of tentative compounds include Quinic acid, 4-p coumaryolquinic acid, Quercetin 3 O acetyl glucoside, Kaempferol-3-O acetyl hexoside, Octadecenoic acid, Heneicosanoic acid, Behenic ( docosanoic) acid. 25resence of a proteinaceous Trypsin inhibitor or MoFTI in aqueous flower preparations was reported. 21Backed by this impressive biochemical profile, attempts begin to isolate purify and characterize these compounds but so far the list include only a few -rhamnetin 3-O-(2``galloyl)-β-D-galactopyranosyl-4`-β-D-xylopyranoside, 26 Kaempferol-7-O-β-D-alloside, 27 quercetin 3-O-α-L rhamnosyl (1→ 6) β D-glucoside, 28 and a proteinaceous MoFTI. 29On the other hand crude flower extracts has been put into all sort of pharmacognostical studies with several promising outcomes in the way.The scope of such studies can be easily accessed from the Table 1.

Pharmacognostical studies
Most of pharmacognostical studies on Moringa flowers are reported recently.These studies are summarized in the Table 1 in which bioassays performed, solvent extracts employed, results obtained and significance of each study are shown.To compare the efficiency of extract in eliciting a particular bioactivity, four abbreviations 'H' , 'M' , 'L' and 'N' are used where H stands for high activity, M for medium, L for low and N for nil activity.The numbers accompanying each of this letters denote the corresponding reference.

DISCUSSSION
It is evident that Moringa flower is under extensive phytochemical and pharmacological studies for the last couple of years.There are several studies supporting the therapeutic potential of moringa flower.They employed different extracts and covered diverse assays such as antibacterial, antifungal, anti protozoan, larvicidal, antioxidant, anti inflammatory, hepatoprotective, anticancer, osteo protective, uterotonic, antisickling, biofortification, bioremediation and nanoparticle synthesising properties.To make comparison of solvent efficiency easier, abbreviations H, M L and N were used, corresponding to the high, medium, low and nil activities.Within a report these comparisons are true and indicate their relative efficiency but not necessarily for different reports.Antibacterial studies against of 15 species by either disc or agar well diffusion found methanol and ethanol extracts producing high inhibition zones.Dichloromethane a non polar solvent is also reported to possess antibacterial activity.Antifungal properties were reported for chloroform extracts while ethyl acetate extract is active against protozoan Leishmania donovani.Mosquito larvicidal activity of flower extract is studied elaborately and a proteinaceous Trypsin inhibitor Factor isolated from flower is held responsible for the property.Interestingly larvicidal effect is noted for methanol and ethyl acetate extract too.There are several notable studies on the antioxidant properties of aqueous, methanol, ethanol and acetone extracts of flower.Antioxidant assays such as DPPH, FRAP and TEAC proved that flower has highest total antioxidant content than other plant parts.Though anti inflammatory studies were few, positive results were observed for several parameters such as activation of anti inflammatory mediators and suppression of pro inflammatory mediators.Hepato protective nature of flower extract is essentially an extension of its anti inflammatory and antioxidant potential and they produced good results in vivo with mice models.Bone protective potential of the methanol and ethanol extracts tested osteoblast stimulating potential and overall effect is promising.Uterotonic and anti sickling potential of flower yielded positive results Non-traditional application of flower extracts especially in dairying, bioremediation, biofortification and nanoparticle synthesis  were also attempted successfully.But we need more studies to arrive at a general conclusion on any such properties of the flower.
Table 1 shows that majority of the studies especially antimicrobial, antioxidant, anti inflammatory assays came up with awesome results indicating the huge therapeutic potential M. oleifera flower, but these studies still remain in the preliminary stage of investigations.It is can be conclusively said that most of the biologically active secondary metabolites responsible for above said properties can be extracted with polar solvents such as methanol ethanol or acetone.Though there are slight discrepancies between reports on the potentiality of different extracts, it may be due to unavoidable variations in protocol followed for sample collection and preparation.There is huge gap in the number of biologically active phytochemicals identified v/s isolated.In fact all reports suggest further investigations to elaborate up on the bioactivity of the extracts as well as to identify any 'ace compound' in them.Consider the antioxidant, antiinflammatory and hepatoprotective studies in which the same extract give positive results for several related assays.A detailed study well done on the anti inflammatory potential of ethanol extract demonstrates multiple actions such as the Inhibition of NO and pro inflammatory interleukins ( IL-6, IL-1 β, TNF-α, and PGE2) and at the same time helping formation of anti inflammatory IL-10 and IκB-α expressions-all these acting in unison to ameliorate inflammatory damage via NF-kB pathway in macrophages.Here the authors are yet to specify any compound for this pharmocological effect.In the anticancer study, in silico investigation predicted ligand binding of several compounds such as Quinic acid, alpha-Tocopherol-beta-D-mannoside, (4-Hydroxyphenyl) acetonitrile, Ethyl Oleatemade from GC MS analysis of methanol flower extract, more effectively to different drug targets than control drugs in PC3 cell lines.Incorporating such novel assays will lend more light on the specific action of novel phytochemicals.Similarly their synergism in effecting a desirable outcome is also a good possibility and the probable reason behind many of the traditional therapeutic uses.Elucidating these synergistic pathways or tracing the ace compound is a huge challenge for researchers but worth the time and energy as it will lay a strong foundation for evidence based application of traditional medicine systems and development of numerous potential plant extracts into novel drugs.

CONCLUSION
Flowers of Moringa oleifera, hitherto unexplored part of otherwise hugely investigated Moringa oleifera plant is a storehouse of valuable bioactive phytochemicals.Preliminary investigations into the antibacterial, antifungal, antiviral, antioxidant anti inflammatory and anticancer investigations of various solvent extracts are highly promising.There is scope for detailed studies to elucidate the mechanism behind this high therapeutic potential of Moringa flower as well as to isolate purify and characterize the bioactive phytochemicals.

Table 1a : Bioassays on Moringa flower extracts No Bioactivity Test cell /organism/ materials Parameters tested Activity of extracts
Pharmacognosy Journal, Vol 9, Issue 1, Jan-Feb, 2017