Solanum macrocarpon (igbagba in Yoruba) is a tropical perennial plant of West African origin. The leaves are alternate, lobed with wavy margins; they bear stellate hairs. The flowers are solitary, pale-purple. The stamens are arranged around the androecium but are not connivent. The fruits are round turning from green to yellowish-brown as they ripen. The fruit is boiled and spiced with pepper, onion and oil as sauce for eating meals like yam, cocoyam, plantain, etc.
Solanum nigrum (odu in Yoruba) is an annual or biennial herb which can be as tall as one metre. The plant can be prostrate, ascending or erect; the stem is smooth or sparsely hairy. The leaves are alternate, ovate, smooth-margined or minimally-lobed; they are smooth or bear fine hairs. The inflorescences develop from stalks that arise directly from the stem between the leaves. The flower bears white petals and yellow anthers which are connivent (wrapped tightly) around the style. The inflorescence is an umbel-like cyme clustered on axillary peduncles.
Solanum scabrum (ogunmo in Yoruba) can be an annual or short-lived perennial; it is cultivated as vegetable in some African cultures. It is a small, erect plant reaching a height of 100-150 cm. The rhomboid, ovate-lanceolate leaves are arranged spirally; the leaves are cuneate at the base and decurrent along the petiole. The flowers are like those of S. nigrum with white petals and yellow anthers clasping the female flower. Let us now consider the pharmacological importance of the species.
Solanum macrocarpon: It is squeezed like bitterleaf before boiling. My favourite way of eating this is by adding melon (egusi) and lots of locust beans (iru). It has laxative and hypotensive properties. In Sierra Leone, the leaves are heated and then chewed to ease throat pain. In Kenya, the roots are boiled and the juice is then consumed to kill hookworm in the stomach. The root is also used for bronchitis, body aches, asthma and it speeds up the process of healing wounds.
- macrocarpon contains glycoalkaloids and the levels found in the fruit are five to 10 times higher than what is considered safe and so may not be safe for humans to eat. It is recommended that all these are consumed sparingly, as consuming them in large frequencies may potentially be poisonous to the body.
Solanum nigrum: Studies have reported the potential health benefits of different parts of this vegetable. Its juice extract has been reportedly used in folklore for the treatment of the Parkinson’s disease, memory impairment, angina, cancerous tumour and inflammation among others.
Its leaves have also been reportedly used in traditional medicine for the management of several diseases, including seizure and epilepsy, pain, ulcer, inflammation and diarrhoea, some eye infections and jaundice. S. nigrum is a widely used plant in oriental medicine where it is considered to be antitumorigenic, antioxidant, anti-inflammatory, hepatoprotective, diuretic, and antipyretic.
Some experiments indicate that the plant inhibits growth of cervical carcinoma in mice. The active ingredient of the plant, solanine, inhibits the proliferation of different cancer cells, such as breast cancer and pancreatic cancer in vitro. Its anti-tumor mechanism is mainly through the induction of different cell and molecular pathways, leading to apoptosis and autophagy of cells and molecules thereby inhibiting tumor metastasis.
It is also used in the treatment of gastric ulcer. Through experiments on mice gastric ulcer model and control group. The results showed that the powder and methanol extract could significantly affect the secretion of gastric acid and protease in mice, thus significantly reducing the gastric ulcer index of mice.
Researchers have identified Solanum nigrum as a vegetable that pregnant women can eat to lower miscarriage risks. The study in the May 2017 edition of the Ethiopian Journal of Health Science involved Freddy O. Agoreyo, Rita Ohimai and Magdalene I. Omigie. Water extract of S. nigrum was found to significantly inhibit acetylcholine-induced uterine contractions. Acetylcholine is a conventional drug that aids contraction of the womb during childbirth. The researchers suggested that the extract of Solanum nigrum can thus be synthesized and analysed therapeutically to establish a safe dose for the management of pre-term contraction in pregnant women.
Solanum scabrum: The leaves of Solanum scabrum are rich in nutrients, especially proteins, iron, ascorbic acid and riboflavin.
A variety of health-promoting, bioactive phytochemicals such as phenolic compounds, carotenoids and chlorophylls have been identified in S. scabrum.
The green, unripe fruits contain comparatively high amounts of the glycoalkaloid solanine and the less poisonous solanidine. The initial effect of solanine poisoning includes diarrhoea and vomiting, and frequent consumption of this compound may lead to accumulation in the liver, causing dizziness, mental confusion and loss of speech; and it can even result in blindness. Only the fully ripe fruits should be used, the unripe fruits contain the toxin solanine.
The leaves contain appreciable amounts of methionine. It contains only low levels of these alkaloids, which are probably associated with its bitter taste. Unfortunately, heating or frying will not reduce the toxic effects of solanine and solanidine.
The whole plant is antiperiodic, antiphlogistic (anti-inflammatory), diaphoretic (induces perspiration), diuretic, emollient, febrifuge, narcotic, purgative and sedative. The leaves, stems and roots are used in the treatment of cancerous sores, leucoderma and wounds.
Extracts of the plant are analgesic, antispasmodic, anti-inflammatory and vasodilatory. The plant has been used in the manufacture of local analgesic ointments and the juice of the fruit has been used as an analgesic for toothaches. Both the leaves and fruits are a source of dye. The anthocyanin pigments in the purple to black fruits are used as a dye or as a kind of ink.
A research aimed at determining the influence of cultivation and processing on the health- promoting capacity of Solanum scabrum by Grace Akinyi Odongo et. al. concluded that, irrespective of the processing method, consumption of the leaves from S. scabrum might help in cancer prevention strategies, based on their present in vitro findings.
Processing clearly affected the content of phytochemicals but this did not result in a diminished chemopreventive effect. However, other endpoints relevant for cancer prevention may perhaps be influenced by this change in phytochemicals, in a negative or positive way.
All Solanum species contain spirosolane alkaloids, including solanine and solanidine. These are bitter-tasting and potentially poisonous when consumed frequently. The leaves of Solanum species are more consumed than the fruits since these can contain high amounts of anti-nutrients such as solanaceous glycoalkaloids like solasodine. For the leaves, this is normally less. Some scientists have pointed out that the toxicity of S. nigrum can be determined by the species and regions where it grows. Despite toxicity issues with some forms, the ripe berries and boiled leaves of edible strains are eaten.
Credit: Olufunke, Punch