Introduction

Synsepalum dulcificum is an evergreen shrub in the Sapotaceae family known by several names, including Miracle plant, Miracle berry plant, and red berry. The miraculous plant was initially found in West and Central Africa, specifically in Nigeria, Ghana, and the Democratic Republic of the Congo.¹ This plant can reach heights of up to 3 meters in cultivation and 6.1 meters in its natural environment. The length and width of the leaves range from 5 to 10 cm. When they mature, the cream-coloured flowers turn to dark red or brown. 

The blossoms are bisexual. There are four to five sepals in the calyx, four to five petals in the corolla, and five stamens in the androecium. The gynecium has an unimpressive stigma and is upright.² The ripe fruit has a red hue. Compared to other berry fruits like blueberries, blackberries, cranberries, and grapes, the miracle berry is less common. The berry is about 2 cm long and 1 cm wide, or about the size of a coffee bean. Its comparatively large seed is enclosed in a translucent pulp with a thin outer layer. The pulp contains the sweetening effect. Usually, the fruits are grouped together at the tips of the branches.³ 

Miracle fruit can be added to food and medicine, or used in its raw or processed form as an ingredient in cosmetic products. The plant's fruit has earned the moniker "miracle plant" in the past due to its special ability to change the taste of sour foods so that they become sweet in the mouth. This attribute has been attributed to a glycoprotein found in the fruit called miraculin. The brain's response to a sour taste is suppressed when miraculous in attaches itself to the tongue's sweet receptor cells. Because S. dulcificum turns carbonated water and sugar solutions orange-red, it has been regarded as an upcoming food colouring. The US Food and Drug Administration classified it as an additive.⁴

Nutritional profile of miracle fruit

Miracle fruit is a good source of antioxidants for use in functional food applications, in addition to flavour and colour. The berries are said to have an ample amount of essential vitamins that are necessary for a healthy lifestyle. These include vitamins A and C, which are crucial for healthy immune function, bone development, and vision, as well as for preventing infections. The others are vitamin K, which is essential for blood clotting and bone health, and vitamin E, which is involved in fertility, vision health, and preservation of cellular integrity. Additionally, the berries may be a good source of non-essential amino acids like glycine, proline, serine, and tyrosine as well as essential amino acids like lysine, leucine, isoleucine, phenylalanine, and threonine.⁵

The miracle berry flesh contains twelve different phenolics, with levels ranging from 0.3 for kaempferol to 17.8 mg/100 g FW for epicatechin. Additionally, lutein and α-tocopherol were measured at 0.4 and 5.8 mg/100 g FW, respectively. In comparison to the seeds, which had TP and TF contents of 306.7 GA and 3.8 mg QR mg Equiv/100 g FW, respectively, the flesh had TP and TF contents of 1448.3 GA and 9.9 QR mg Equiv/100 g FW. In the DPPH and ABTS tests, the flesh extract's percentages for reducing and scavenging free radicals were 32.5% and 96.3%, respectively. The flesh extract also exhibited a high FRAP of 22.9 mmol/100 g. Indeed, miracle berries, like blueberries, blackberries, cherries, and grapes, may also be a rich source of phytochemicals rich in antioxidants. It has been established that these antioxidant phytochemicals have health-promoting properties that help prevent a number of chronic illnesses, including diabetes, obesity, cardiovascular disease, and some types of cancer.⁶

The range of vitamins, proteins, fats, and dietary phytochemicals that Synsepalum dulcificum contains is indicative of its nutritional value and overall well-being. The vivid red colour of the fruit indicates the presence of flavonoids, particularly anthocyanins, which are beneficial antioxidants. Anthocyanins, one type of flavonoid, have been linked to anticancer and chemopreventive effects as well as potential uses in beverages. Eleicatechin, rutin, quercetin, myricetin, kaempferol, gallic, ferulic, syringic acid, delphinidin glucoside, cyanidin galactoside and malvidin galactoside, a-tocotrienol, a and c-tocopherol, and lutein are among the powerful antioxidative phytochemicals found in miracle fruit.⁷

While ten distinct fatty acids with a total unsaturated fatty acid content of 52.7% were found in the seed oil, He et al. reported that there was no fat in the flesh. Vitamins A, C, D, and K were also reported to be obtained from the fruit. This fruit has also been reported to contain a high concentration of vitamin C.

The proximate mineral analysis of the fruit pulp revealed that lead was absent and that the following elements were present: Ca (100 ppm), Fe (24.20 ppm), Zn (9.49 ppm), Cu (6.22 ppm), Cr (0.01 ppm), and Co (0.01).³

Miracle fruit is also said to contain a high concentration of flavonoids (57.01%). Tryptophan (8.06%), histidine (0.4%), isoleucine (0.7%), leucine (0.6%), lysine (0.6%), methionine (1.05%), phenylalanine (0.7%), threonine (1.1%), and valine (0.69%) were among the non-essential and essential amino acids that were also reported to be present. Sugars (glucosamine, mannose, fucose, xylose, and galactose), nitrogen, carbohydrates, and almost 191 amino acid residues made up the marker compound of the fruit "miraculin."⁸

Mechanisms of antioxidant action

Oxidative stress is prevented by antioxidants from harmful substances. Miracle berry pulps are rich in flavonoids, which are antioxidant phytochemicals. It also neutralises free radicals present in the body. A few studies assessed and validated the S. dulcificum methanol extracts of the flesh and seed for their in vitro antioxidant and radical scavenging properties. Among the techniques used were FRAP assays, ferric-reducing antioxidant power, DPPH (1,1-diphenyl-2-picrylhydrazyl) and ABTS (2,20-azino-bis (3-ethyl-49 benzothiazoline-6-sulfonic acid)) radical scavenging activities. It was found that the sample decreased fish oil's polyunsaturated fatty acid oxidation. As a result, the S.dulcificum plant may produce a fruit that is high in antioxidants and can improve health.

The flavonoids and phenols that have been extracted from fruits, leaves, and roots are responsible for the demonstrated antioxidant properties of S.dulcificum plant part extracts.⁹ Certain studies also revealed that the levels of hepatic malondialdehyde and serum total bilirubin were lower in the treated groups, while the glutathione-S-transferase activity of the liver was significantly (P < 0.05) higher. The results indicated that the extract could have hepatoprotective effects and strengthen the antioxidant defence at lower doses (<100 mg/kg).¹⁰

Health benefits of miracle fruit antioxidants

S. dulcificum has been shown to have various pharmacological activities, supporting its ethnomedicinal use. These pharmacological activities include antidiabetic, anticancer, antihyperuricemic, and anticonvulsant properties. Chen et al. studied the effect of miracle fruit (Synsepalum dulcificum) on insulin resistance induced by fructose-rich chow in male Wistar rats.¹¹ S. dulcificum contains two compounds, (þ)-syringaresinol and (þ)-epi-syringaresinol, which inhibit human skin cancer cells and have significant antioxidant activity in vitro. Compounds including (þ)-epi-syringaresinol, 4-acetonyl-3,5-dimethoxy-p-quinol, cis-p-Coumaric acid, trans-p-coumaric acid, p-hydroxybenzoic acid, vanillic acid, and N-cis-feruloyl-tyramine inhibited mushroom tyrosinase activity.

Tyrosinase inhibitors are used both medically to treat hyperpigmentation and in the cosmetic industry.¹² Shi et al. (2016) found that S. dulcificum fruit extract reduced hyperuricemia in RAW264.7 macrophages treated with xanthine oxidase and monosodiumurate. Xanthine oxidase is responsible for uric acid production. In mammals, uric acid produced by xanthine oxidase is catabolized to allantoin, so inhibiting xanthine oxidase directly inhibits uric acid formation.¹³ PTZ is a noncompetitive antagonist of the GABAA receptor that binds to the picrotoxin (PTX) site. In animals pre-administered with S. ducificum seed, there was 33.33% resistance to transience in PTZ- and strychnine-induced convulsion, as well as a significant reduction in the time to recovery from MES-induced seizure.¹⁴

The cholesterol-lowering activity of S. dulcificum was evaluated using a hamster model fed an experimental diet containing 2% ethanolic and water extracts of S. dulcificum seed, leaves, and dry pulp. Experimental diets with S. dulcificum seed extract reduced plasma total cholesterol, while lupeol acetate and β-amyrin acetate (triterpenoids isolated from the seed extract) decreased plasma total cholesterol by 15%-20% in hamsters. The ethanol extract of the seed was found to decrease plasma total cholesterol, possibly due to active triterpenoids.¹⁵

Summary

S. dulcificum is a remarkable shrub with exceptional medicinal and nutritional properties. Different parts of the plant are useful for both industrial and therapeutic purposes. The plant is recognised as one of the most commercially important African medicinal plants, with significant potential as a food and nutritional supplement. The miracle fruit plant has anticancer, antioxidant, anticonvulsant, antihyperuricemic, and cholesterol-lowering properties, among other things. Miraculin, in particular, has excellent nutritional and therapeutic properties as a low-calorie sweetener and anti-diabetic agent. Other significant components, which are yet to be discovered may be present in the plant. This requires further investigation. To increase the acceptability of plant products in more countries, known components should be standardised and proper safety evaluations performed. Plant-derived drugs for the treatment of diabetes and diabetic complications could be a viable area of focus. Furthermore, the synthesis of miraculin analogues with comparable or improved activity should be investigated in order to aid in the conservation of this species. The miracle plant contains numerous bioactive compounds, and its pharmacological properties are expected to expand in the future.