Abstract: Monodora myristica (Gaertn.) Dunal is a useful but neglected tropical tree of the family Annonaceae distributed in many countries of the tropics and subtropics. It possesses an impressive range of medicinal and nutritional properties. Different parts of this plant such as seeds, bark and flowers contain important minerals and are a good source of protein, vitamins, β-carotene, amino acids and various phenolics. They also contain bioactive substances that exhibit health-beneficial effects, including stimulation of the cardiac and circulatory system, anti-inflammatory, antispasmodic, diuretic, antihypertensive, cholesterol lowering, antioxidant, anti-diabetic, hepatoprotective, antibacterial and antifungal activities. Crude extracts of the plant are being employed for the treatment of different ailments in the indigenous system of medicine, particularly in South Asia. This review focuses on the phytochemical composition, medicinal uses, as well as the pharmacological properties of different parts of Monodora myristica. Prospects for future exploitation of the plant were also discussed.
INTRODUCTION
Morphologically, Monodora myristica (M. myristica) is a perennial plant of the Annonaceae or custard apple family of flowering plants1,2. The tree grows naturally in the evergreen forests of the sub-Saharan African regions1 in West Africa: from Liberia to Nigeria, Cameroon and Ghana, as well as in Angola, Uganda and West Kenya3,4. Globally, the plant is widely distributed from Africa to Asia, Central and South America and Australia5,6. The tree can reach a height of 35 and 2 m in diameter3. Fruiting occurs from August-November5. The fruit of M. myristica is a berry of 20 cm in diameter, smooth, green and spherical and becomes woody at maturity. It is attached to a long stalk, which can be up to 60 cm long. Inside the fruit are the numerous oblong, pale brown seeds which are usually 1.5 cm long and are embedded in a white sweet-smelling pulp3,7. It has been observed that an average of 119-122 seeds can be found in one fruit1.
Monodora myristica is listed presently under Kew’s difficult seeds due to its inability to grow easily outside its natural habitat8. The plant is largely harvested from the wild and greatly affected by wild fires, urbanization, reckless and uncontrolled felling of trees for timber and firewood without replanting9. It is variously known as Iwor amongst the Itsekiris; Ikposa (Benin); Ehiri or Ehuru (Ibo); Gujiya dan miya (Hausa) and Ariwo, arigbo, Abo lakoshe or eyi naghose (Yoruba); Ehinawosin (Ikale), Uyengben (Edo), Fausse noix de muscade (French)10-13.
Study of Onyenibe et al.7 has shown that almost every part of the tree was important economically and a number of medicinal properties have been ascribed to various parts of this highly esteemed plant. The timber is hard, easy to work with and is used for carpentry, house fittings and joinery while the seeds are also made into necklaces14. The most economically important parts are the seeds. After harvesting, various unit operations, such as fermentation, washing, drying and cracking are performed before consumption or storage. The presence of bioactive compounds in the plant makes it possible for the seeds to be used in traditional medicines as well as a spice in local foods15. The aromatic seeds are antiemetic, aperient, stimulant, stomachic, tonic and they are added to medicines impart stimulating properties3,16,17.
So far, no comprehensive review has been compiled from the literature to show the huge socio-economic potential of the plant. This motivated us to bridge the information gap in this area and to write a comprehensive review on the medicinal, phytochemical and pharmacological properties and hence it’s high socio-economic value. It is expected that, in the medium to long terms, this review will contribute to increased utilisation of M. myristica and thus, an improvement in socio-economic and living standards of the communities living in the regions where it grows.
NUTRITIONAL COMPOSITION
Nutritional value of M. myristica centres on its usefulness as a seasoning because of its aromatic flavour18. Essential oil from the seed is used as a flavoring agent for food19,20. The oil provides a valuable flavor in meal preparations, soups, sauces and canned foods15,20,21. The oil could be used as a linolenic-rich salad oil or edible fat or margarine22. Its seeds are a popular spice used in cooking to flavour and thicken dishes23. It has been reported by many authors that oils containing unsaturated fatty acids especially linoleic and oleic acids can be used to lower plasma cholesterol24-26. The oil of M. myristica, because of its high level of unsaturated fatty acid is likely to reduce coronary heart disease if consumed27-29.
The whole seed together with its seed coat is either ground and used as a seasoning for West African soups or stews or is ground and used as a nutmeg-like flavouring in cakes and desserts30-32. There is wide variation in the proximate composition of M. myristica seeds reported in the literature as shown in Table 1.
Its moisture content is low33 making them suitable for long-term storage34 without deterioration in quality or microbial spoilage since microbial activity will be reduced to a minimum. This will be of benefit to rural communities which lack access to basic storage facilities and electricity as it will reduce the cost of handling and ensure long term storage35. Its ash content is moderately high (2.3-6.49%) implying that it has good mineral content and thus serves as a viable tool for nutritional evaluation36. Minerals are a group of essential nutrients which serve a variety of important metabolic functions and are parts of molecules such as haemoglobin, adenosine triphosphate (ATP) and deoxyribonucleic acid (DNA)37.
| Table 1: | Proximate compositions (% dry weight) of M. myristica seeds |
| Values are mean of triplicate determinations | |
Crude fat is high which indicates that it is a good source of flavour since it is rich in essential oil and also suggests possible sources of oil-soluble vitamins. Crude fibre content shows that when it is incorporated into food, it will help to prevent many metabolic or digestive disorders such as constipation and irritable bowels as this is the work of fibre in the body. Fibre has long been known to aid digestive health and can help one lose or maintain weight because eating fibre-dense wheat bread helps one feel full39. Recently, the hypoglycemic and hypocholesteremic effect of dietary fiber has been reported40. It is generally known that any plant food that provides more than 12% of their caloric value from protein is considered to be a good source of protein33. This signifies the healing properties of M. myristica as proteins are essential for the synthesis/repair of body tissues and as enzymes. Monodora myristica could be used as a good source of protein supplement in the human diet41. Its low carbohydrate content (8.96%) suggests low caloric value and is indicative of its low sugar concentration33.
Mineral composition: The seeds possess magnesium, calcium, potassium, phosphorus, manganese, iron, sodium, copper, aluminium and zinc31,1. Minerals are known to play important metabolic and physiological functions in living cells42. The calcium/phosphorus ratio is greater than 1, indicating that it would serve as good source of mineral for bone formation. The ratio of sodium to potassium in the body is of great concern for prevention of high blood pressure. Sodium/potassium ratio of less than 1 is recommended43. This is an indication that the inclusion of African nutmeg in the diet would probably reduce high blood pressure diseases since its sodium/potassium ratio is less than 131.
PHYTOCHEMISTRY
Feyisayo and Oluokun44 identified phenolics present in the seeds of Monodora myristica by gas chromatography (GC) coupled to flame ionization detector (FID). They estimated the total phenolic content as 1478.32 mg/100 g and concluded that M. myristica is a good source of phenolics. The seed is rich in Myristicin (42.60%), Caffeic acid (23.39%), Elemicin (3.82%) and Eugenol (1.02%)45 and contains 5.9% colourless essential oil46. Other reports on the phytochemical screening of the seeds of this plant revealed the presence of phenolic compounds, including flavonoids and tannins, cyanogenic glycosides, alkaloids, arocine, lactose, terpene, resins, fiberro-latic oils, anthraquinones, saponins, steroids, oxalates and phytates31,47,48.
Almond contains six non-essential amino acids (aspartate, glutamine, alanine, proline, arginine and glycine) and nine essential amino acids (histidine, valine, methionine, cysteine, isoleucine, leucine, phenylalanine, lysine, tyrosine)13. Based on this, it is qualified as a good source of protein because the quality of protein in food is determined by the content of amino acids especially the essential amino acids49. The amino acids phenylalanine (Phe), tyrosine (Tyr), arginine (Arg), glutamic acid (Glu) and asparagine (Asn) have been found to exhibit anti-sickling properties50-52. The crude aqueous extracts (CAE) of M. myristica exhibited anti-sickling potency due to the preponderance of these anti-sickling amino acids and other Vitamins like Vitamin C, E and sugars which are also identified in the extracts45,47.
The seeds also contain about 35-36% of a reddish brown fixed oil which is mainly linoleic acid (46.9%), oleic acid (35%), arachidic acid (9.52%), palmitic acid (8.78%) and butyric acid (3.74%)1,53-55. Linoleic acid helps to relieve flaky or rough skin and maintain smooth moist skin56.
The monoterpenoid content of M. myristica is mainly hydrocarbons comprising α-phellandrene (29.2%), p-cymene (11.2%), α-pinene (9.7%), cis-sabinol (6.9%), 0.10% camphene, geraniol 0.34%, eugenol 0.42%, 0.40% myrcene, thujene 0.22% and limonene (6.8%)57,21. Bakarnga-Via et al.58 reported that Monodora myristica seed oils from Chad and Cameroun contain mainly α-phellandrene at 52.7 and 67.1%, respectively. The essential oil is associated in the seeds with solid fat. The seeds have a pungent, peppery taste due to aromatic ketones such as gingerol and paradol48. This oil can be used as a counter-irritant and in the treatment of rheumatism and as carminative59. The essential oil that can be obtained from the leaves contains β-caryophyllene, α-humulene and α-pinene60. Structures of some active compounds of M. myristica are shown in Fig. 1.
Adewole et al.61 extracted the oil of M. myristica using Soxhlet extractor and petroleum ether as solvent and characterized the oil using gas chromatography-mass spectrophotometer. The compounds they identified are shown in Table 2.
Feyisayo and Oluokun44 estimated the total phenolic content of seeds of M. myristica as 1478.32 mg/100 g and used GC-FID (Gas Chromatography-Flame Ionization Detector) analysis to identify about fifty-three different types of phenolics.
| Fig. 1(a-g): | Structures of selected phytochemicals from M. myristica: (a) Myrcene, (b) 4-(2,2-Dimethyl-6-methylenecyclohexylidene)-3-methyl-2-butanon, (c) Limonene, (d) 1,3,3-Trimethyl-2-oxabicyclo[2,2,2] octan-6-ol, (e) Nonadecylic acid, (f) 1,3, 3-Trimethyl-2-oxabicyclo[2,2,2] oct-6-yl acetate and (g) Pinene |
| Table 2: | Properties of some identified compounds in the oil of Monodora myristica |
| CAS: Chemical abstracts service, Source: Adewole et al.61 | |
These are shown in Table 3. The GC-MS analytical report for the chloroform fraction of the seed showed the presence of o-Cymene, Trans-2-caren-4-ol, 4-methylene-1-(1-methylethyl)-, (1α, 3α, 5α), Thymol, Cyclohexene, Carbamic acid, phenyl ester, 2-Cyclohexen-1-one, 2-Cyclohexen-1-one, 4-(2,2-Dimethyl-6-methylenecyclohexylidene)-3-methyl-2-butanone, α-cadinol, 1, 4-Methanoazulen-3-ol, Quercetin, n-hexadecanoic acid, 9-Octadecamide, cis-9-hexadecenal, Acetic acid, Cis-vaccenic acid, Campestrol and Butyl-9-octadecenoate amongst others61.
MEDICINAL AND PHARMACOLOGICAL PROPERTIES AND APPLICATIONS
As stated earlier, M. myristica has several applications in traditional medicine, which is primarily based on indigenous knowledge systems (IKS). Some of the common traditional medicinal applications of M. myristica are shown in Table 4. Modern science research has revealed several medicinal and pharmacological properties of the plant. Most of these properties are likely to have been known a very long time ago through IKS and probably are the basis for the traditional medicinal applications of the plant. Several bioactive compounds have been identified and suggested to be responsible for the various medicinal and pharmacological properties of M. myristica. The next sections reviewed the reported medicinal and pharmacological properties of M. myristica.
Antimicrobial activities
Antibacterial and antifungal activities: The phenolic compounds in M. myristica are responsible for the anti-septic, antifungal or bactericide properties of the plant62.
| Table 3: | Phenolic compounds identified in Monodora myristica seeds by GC-FID |
Source: Feyisayo and Oluokun44 | |
The mechanism of inhibitory action of these alkaloids and phenolic compounds on micro-organisms may be due to impairment of variety of enzyme systems, including those involved in energy production, interference with the integrity of the cell membranes and structural component synthesis63-64.
These antimicrobial agents include different forms of alkaloids, sesquiterpenes, diterpenes, triterpenes saponins, triterpen aglycous, flavonoids, sterols, coumarin, quinines, monoterpenes, different proteins as well as lipids and tannins (Sofowora)74.
| Table 4: | Common traditional medicinal uses of the bark and seed of M. myristica |
Its phenolic content has been reported to be potent in killing Staphylococcus aureus, Bacillus subtilis and Canadidia albicans75,76. Also Oluwafemi and Taiwo77, reported on the reversal of toxigenic effects of aflatoxin by alcoholic extracts of Monodora myristica.
Nwaiwu and Imo78 screened M. myristica for the fungicity of their essential oils against mycelial growth of three foodborne fungi; Aspergillus fumigatus, Aspergillus nidulans and Mucor hiemalis. The essential oils from all the spices were fungi-toxic at varying degree to all the organisms. Ethanolic extract of M. myristica seed possesses antimicrobial activity against Klebsiella and Bacillus species79 and possess broad spectrum antibacterial activities against selected gram positive and negative bacteria80. It also inhibited Aspergillus niger in "Kunun" beverage81. This generally confirmed that this seed is highly potent to activities of many microorganisms.
Monodora myristica extracts inhibited the growth of mycelium, the formation of conidial spores and chlamydospores of Sclerotium rolfsii, thereby reducing the number of propagation units of this fungus in the medium64,82. Also, Enabulele et al.12 reported that the aqueous and ethanolic extracts of M. myristica seeds, were active against both gram negative and gram positive organisms-Staphylococcus aureus, Klebsiella pneumonia, Escherichia coli and Salmonella typhi. Its methanol and dichloromethane extract was active against mites and traditionally used against scabies83.
Ethanolic extracts of the leaves of the plant was tested against Escherichia coli, Staphylococcus aureus, Streptococcus pneumoniae, Proteus mirabilis, Pseudomonas aeruginosa and Klebsiella pneumoniae by the agar diffusion method84. They reported that this extract had the ability to inhibit the growth of the test pathogenic microorganisms and observed a corresponding increase in the rate of inhibition of the growth of the pathogens as the concentration of the extracts increased. Adewole et al.61 reported that the oil of Monodora myristica had strong antimicrobial properties and was very active against Escherichia coli, Bacillus substlus and Staphylococcus aureus.
Ukaegbu-Obi et al.85 reported that the seed extracts of M. myristica possess some antimicrobial activities which can be employed in the development of novel therapeutic agents against the test organisms. They assessed the antimicrobial activity of Monodora myristica seeds on four selected human pathogens, Escherichia coli, Staphylococcus aureus, Salmonella typhi and Pseudomonas aeruginosa using Disc diffusion technique for in vitro antibacterial screening. They observed that the most susceptible bacterium were E. coli, while the most resistant bacterium was P. aeruginosa and the minimum inhibitory concentration result showed that the seed extracts of M. myristica was bacteriostatic.
Antispasmodic, antiulcer and hepatoprotective activities: Lekana-Douki et al.86 tested dichloromethane and methanolic extracts of M. myristica plant for their antiplasmodial activity on two chloroquine-resistant strains of Plasmodium falciparum based on lactate dehydrogenase activity. Cytotoxicity was assessed with the MTT test on MRC-5 human diploid embryonic lung cells. They observed that the methanolic extract of Monodora myristica showed promising activity and low cytotoxicity and its dichloromethane extracts showed moderate activity against Plasmodium falciparum. In a similar experiment, crude extracts from the bark of M. myristica were assayed for in vitro antiplasmodial activity against the chloroquine-resistant strain of Plasmodium falciparum. It showed a good antiplasmodial activity with inhibition of 42.1% at 10 μg mL–187.
Oyinloye et al.88 investigated the protective effect of Monodora myristica (MM) on cadmium-induced liver damage in male Wistar albino rats. MM exhibited reversal potential on cadmium-toxicity at the tested doses. These results demonstrates that aqueous extracts of MM is effective in the amelioration of hepatic damages arising from cadmium-induced toxicity, indicating that the antioxidant bio-constituents of MM play an important role in the prevention of liver toxicity possibly by inhibiting bioaccumulation of free radicals in animal models. Also, M. myristica extracts exhibited anti-clastogenic, hepatoprotective activities and maintained semen viability in Wister rats89.
The aqueous seed extract of Monodora myristica was investigated for its antiulcer properties using the aspirin and alcohol-induced ulcer models in Wistar rats. The extract was seen to have a high percentage protective index, which compared favourably with the known anti-ulcer drugs in ulcer models. But it had a higher percentage protective index in the alcohol-induced model than the aspirin-induced model, which suggests that its mechanism of action may be coating and protecting the mucosal surface of the stomach90.
Anti-inflammatory and anticancer activities: Monodora myristica seeds are a natural source of anti-inflammatory agent. Flavonoid rich fraction of M. myristica seeds exhibited significant in vitro anti-inflammatory potentials by stabilizing red blood cell membrane exposed to hypotonic and heat induced lyses with maximum percentage stability of 88% in a biphasic mode of response that is comparable with Ibuprofen a standard anti-inflammatory drug. It also inhibited heat induced albumin denaturation with maximum inhibition of 75.38% in a concentration dependent manner that is comparable with aspirin and showed an anti-lipoxygenase activity range from 19-71% which is comparable to that produced by indomethacin70.
Ishola et al.91 carried out a study to investigate the antinociceptive and anti-inflammatory effects of the hydroethanolic seeds extract of Monodora myristca (HMM) in male albino rats. They reported that HMM possesses antinociceptive effect mediated through interaction with opioidergic, serotonergic and dopaminergic systems and an anti-inflammatory action through inhibition of inflammatory mediator's release. Their study established the scientific basis for its use in the management of pain and inflammatory conditions in traditional medicine.
Essential oils obtained by hydrodistillation of fruits of Monodora myristica exerted cytotoxic activity against cancer and normal cell lines with more pronounced effect on neoplastic cells in the majority of cases58.
Antihypertensive and cholesterol lowering activities: To evaluate the cholesterol lowering potential and protective ability of aqueous extract of Monodora myristica on experimental hypercholesterolemic rats, Onyenibe et al.7 induced hypercholesterolemia in the rats by administering cholesterol through the mouth. Results they obtained shows that treatment with M. myristica elicited a significant reduction (p = 0.05) in serum total cholesterol, triglycerides and low-density lipoprotein cholesterol levels while there was concomitant increase in high-density lipoprotein cholesterol of hypercholesterolemic rats. Elevations in serum aminotransferases activities and lipid peroxidation level were reversed and a significant amelioration was noticed in enzymatic and non-enzymatic antioxidants status in the liver and heart of hypercholesterolemic rats. Their study suggests that M. myristica possess cholesterol lowering potentials and protective ability in experimental hypercholesterolemia rat model.
Agomuo et al.92 reported that there was a significant (p<0.05) cholesterol reduction in male and female rats placed on 5% ground Monodora myristica seed and portable water; when compared with their control group placed on normal rat feed and portable water after 1 week. Furthermore, essential oil from M. myristica seed reduced Guinea pig blood pressure in a dose dependent manner66.
Antioxidant activities: Ogunmoyole et al.59 reported that ethanolic and water extract of M. myristica seed exhibited potent dose-dependent antioxidant properties such as ferric reducing, metal chelating, free radical scavenging and inhibition of both lipid and deoxyribose oxidation. In a similar experiment, Moukette et al.93 reported that the different extracts from M. myristica specifically the aqueous ethanol extract revealed several properties such as higher free radical scavenging properties, significant antioxidant capacities and protective potential effects on liver enzymes. Its dichloromethane and ethanol extracts exhibited free radical scavenging activity against 2,2-Diphenyl-1-Picrylhydrazyl (DPPH)94 and its antioxidant properties have been reported and attributed mainly to its phenolic and flavonoids composition23.
Womeni et al.95 investigated the efficacy of methanolic extracts and powders of M. myristica seed in stabilizing crude soyabean oil during accelerated storage and found them to be potent antioxidants for stabilization of crude soyabean oil.
Diabetes is known to involve oxidative stress and changes in lipid metabolism. Nwankwo96 evaluated the antihyperlipidaemic effect of methanolic extracts of M. myristica in comparison with vitamin E (a known antioxidant) in streptozotocin-induced diabetic rats and reported that oral administration of plant extracts of 200 mg kg–1 of the body weight daily for 3 weeks to both normal and diabetic rats resulted in significant (p<0.05) reduction in plasma and liver levels of total protein, total cholesterol, triacylglycerol, low density lipoprotein cholesterol and increase in the level of high density lipoprotein cholesterol and attributed it to the high level of flavonoids in M. myristica. The results of Nwankwo96 results clearly showed that the methanolic extracts of M. myristica may enhance protection against dyslipidaemia in streptozotocin-induced diabetic rats without possible damage to hepatic tissues. Aqueous extracts of M. myristca have equally been reported to possess anti-amylase activities which may be potentially useful in the treatment and management of diabetes mellitus and obesity97,98 due to the presence of phenolic compounds99.
Antioxidants protect the body against adverse effects of free radical or reactive oxygen species (ROS) generation100, which are characterized by their ability to cause oxidative damage to the body. Study by Erukainure et al.35 has shown that ROS are involved in various related physiological processes and diseases such as aging, cancer and atherosclerosis. Feyisayo and Oluokun11 evaluated the antioxidant activity of the flavonoid fraction of the seed extract of Monodora myristica. The flavonoid fraction exhibited potent and appreciable anti-oxidant potentials with maximum DPPH-radical scavenging activity (41.20%), hydroxyl radical scavenging activity (46.34%). It also exhibited a significant p<0.05 reduction of Fe3+ to Fe2+ (64.64%). It exhibited a dose dependent protective effect against free radical induced haemolysis of red blood cells with maximum protection and inhibition of lipid peroxidation and free radical generation in liver homogenate. They concluded that M. myristica seeds contained secondary metabolites with antioxidant activity which appeared to be significant in the reduction of free radicals in a dose dependent manner. Its phenolic compounds content could be a plausible explanation for the antioxidant activities exhibited by this spice. Therefore, its consumption could possibly boost the antioxidant defense system, thereby reducing the free radical status in humans101. Monodora myristica has been proven to have anti-sickling properties102.
INDUSTRIAL APPLICATIONS OF SOME OF THE ACTIVE COMPONENTS OF MONODORA MYRISTICA
Stearic acid (n-octadecanoic acid) can be used as a binding agent in food products, such as butter flavoring, vanilla flavoring, chewing gum, fruit waxes and butter61. O-cymene is used as a flavouring agent in the food industries60. Antioxidants play a major role in food quality preservation due to their ability to prevent oxidative deterioration of lipids103. Essential oils add flavour and aroma to baked products and also acts as food preservative61,104,105.
The α-phellandrene is a flavouring agent with a pleasant, fresh-citrusy and peppery-woody odor (No. 1328) and no safety concern-its estimated daily intake is below the threshold of concern (i.e., 1800 μg/person/day)106 and can be used to flavour food products such as yoghurt, baked foods etc. Because it is inexpensive, palmitic acid (n-Hexadecanoic acid) is used to add texture to processed convenience foods107.
The 1,3,3-Trimethyl-2-Oxabicyclo [2,2,2] octan-6- ol or eucalyptol a natural, organic compound which is a colorless liquid is used as an ingredient in many brands of mouthwash and cough suppressant60. Eucalyptol was found to control airway mucus hyper secretion and asthma, because it can suppress arachidonic acid metabolism and cytokine production in human monocytes108-109. Also, because of its pleasant spicy aroma and taste, eucalyptol is used in flavorings, fragrances and cosmetics110. This compound is also used as an insecticide and insect repellent111-112. The 1,3,3-Trimethyl-2-Oxabicyclo[2,2,2] oct-6-yl acetate and 4-(2,2-Dimethyl-6-methylenecyclohexylidene)-3-methyl-2-butanon are used as flavoring, fragrances and cosmetics110. Furthermore, n-Octadecanoic acid (stearic acid) can be used as a binding agent for products like lotions, soaps, deodorants and candles60. 9-Octadecenoic acid ethyl ester (oleic acid) inhibits collagen-stimulated platelet aggregation by approximately 90% when used at a concentration of 10 Aμg mL–1 113.
O-cymene is used as a fragrance in the fragrance industries61. Myrcene is an important intermediate used in the perfumery industry. It has a pleasant odor and analgesic, anti-inflammatory, antibiotic and antimutagenic properties. Thymol is used as an antiseptic, a herbal supplement and for the treatment of bronchitis. Pinene, camphene and dipentene in the essential oil are used to scent soaps and perfumes59. Alkaloids are widely used as cancer chemotherapeutic agents114. Limonene is common in cosmetic products115.
The seed oils can be used to scent soaps and perfumes116-117. They can be incorporated into cream as antimicrobial agent and as a perfume76. They can also be used in dental preparation32. Eicosanoic acid is used for the production of detergents, photographic materials and lubricants118.
FUTURE PROSPECTS
So far numerous studies have been conducted on different parts of M. myristica, but there is a dire need to isolate and identify new compounds from different parts of the tree, which have possible antitumor promoters as well as inhibitory properties. Further studies on the active components of its seeds should be conducted so as to maximize its medicinal and nutritional potential. The identified compounds could serve as important lead compounds in the synthesis of potent drugs and chemicals which can find use in the pharmaceutical and flavouring industries. Further purification of its crude extracts could produce activities comparable to that of standard antibiotics or even better as observed in most isolated active compounds from such sources. Its use in traditional medicine to treat various diseases deserves more in depth studies.
Many studies have found M. myristica to be a better candidate for treatment of both bacterial and fungal infections78,80,84. It can therefore be formulated in creams and ointments for the treatment of superficial infections and capsules for the treatment of gastrointestinal tract infections. It can also be exploited as an alternative antimicrobial drug for the treatment of diseases caused by these pathogens.
Anyika and Uwaegbute119 identified an increasing tendency among children and adults to move away from traditional eating pattern of three meals a day to eating snacks instead of meal. Snacks could be an excellent means to improve nutritional quality120. Therefore, addition of M. myristica-a natural food additive into snacks such as cookies could be an excellent means to improve nutritional quality, sensory properties and shelf life of snacks. Whereas, many synthetic additives can serve the same purpose, most consumers are allergic to them and they have too many side effects. Also, most of them are imported raising the need for a preservative that is cheap, inexpensive and readily available.
The antimicrobial activity of M. myristica can be tested on bread-a convenience baked food. Bread is an important stable food121. One of the main problems encountered by bread producers is its short shelf life. There is a need of innovation in bread making for attracting more people who are more reluctant for traditional products122. Anti-microbial activity of M. myristica against bacteria (Lactobacillus casei, Bacillus subtilis), yeast (Pichia burtonii) and moulds (Aspergillus flavus, Penicillium, Eurotium, Fusarium) responsible for spoilage of bread and other baked products123 has not been investigated.
Dietary fibre components can be incorporated into commercial food products to enrich their fibre content and/or serve as functional ingredients124. The term "Dietary fibre" is widely accepted to include the complex mixture of indigestible polysaccharides (e.g., cellulose, hemicelluloses, oligosaccharides, pectins, gums), waxes and lignin found in plants, mainly as plant cell wall material124. Dietary fibres promote beneficial physiological effects including laxation and/or blood cholesterol attenuation and/or blood glucose attenuation125. Although, data on crude fibre content of M. myristica exist in scientific literature, there is no published data on its dietary fibre characterisation. This data could be of great practical importance in developing dietary interventions aiming to achieve certain positive health effects, both in healthy individuals and patients with certain health problems. It is therefore important to characterise the dietary fibre content of M. myristica.
Information on the nutritive value and phytochemical profiles of this medicinal plant should be disseminated to pharmaceutical firms, which have been depending on the wild sources of medicinal plants for drug formulation. This plant offer wide-scope for utilization as raw material for food and pharmaceutical industries. The different parts especially the seeds should be processed and packaged in a convenient form for home and industrial use as other internationally recognised spices such as curry, rosemary, thyme etc.
The amino acid composition of protein cannot completely account for its nutritional quality. The measurement of the digestibility of the protein and its amino acids must be taken into account. The digestibility of proteins and individual amino acids in M. myristica should be determined by an in vitro assay. Furthermore, dietary anti-nutritional factors have been reported to adversely affect the digestibility of protein, bioavailability of amino acids and protein quality of foods126. Although, Nkafamiya et al.127 reported that the levels of anti-nutrients in M. myristica seeds are below the established toxic levels. High levels of antinutritional factors can significantly interfere with nutrient utilization and relationships between antinutritional factors and protein digestibility have been observed in Phaseolus vulgaris128. Therefore, it is imperative to investigate this relationship in M. myristica.
Further research is required to identify and isolate the bioactive component of M. myristica responsible for its hepatoprotective property and hence the exploration of the plant active substance in drug and nutraceutical formulation for liver toxicity. Although the antiplasmodial activities of the stem bark are promising, not much is known about the compounds responsible for this action. Additional research is warranted. In view of its multiple uses, M. myristica plant needs to be widely cultivated in most of the areas where climatic conditions favour its optimum growth. In this way, a maximum yield of its different useable parts could be achieved to derive the maximal amount of commodities of a multifarious nature for the welfare of human kind.
CONCLUSION
The antimicrobial strength, phytochemical compounds and the various organic compounds found in this plant is an eye opener for the discovery of novel bioactive compounds if the plant can be subjected to intensive research making use of various spectroscopic techniques like nuclear magnetic resonance (NMR), infra-red spectroscopy (IR), gas spectroscopy (GS) and mass spectroscopy (MS) to characterise the compounds to be isolated in order to discover known and new antibiotics and anti-parasitic agents. Extracts from Monodora myristica should be standardized and used in food processing industries to replace some of the artificial agents. Also, if it’s essential oil is isolated using various types of chromatographic techniques, well purified and modified, it will be of high value in pharmaceutical, food component and agrochemical industries. The plant could contribute significantly to the nutrition security, health and well-being of indigenous population groups in sub-Saharan Africa.
SIGNIFICANCE STATEMENTS
This review discovered the multipurpose nature of various parts of Monodora myristica and provided prospects that will help the researcher to maximise its medicinal and nutritional potential. Thus, new bio-actives, medicines and nutritional substances may be discovered from the plant.