Nutritional composition and cytotoxicity studies of black monkey (<i>Strychnos madagascariensis</i>) ripe fruit

Abstract

Strychnos madagascariensis also known as black monkey orange is found in tropical and subtropical Africa including South Africa, Lesotho, Zimbabwe, and Swaziland. The fruit is consumed traditionally as food in the northern coastal region of Kwazulu-Natal in South Africa and the Southern part of Zimbabwe. This study investigated the nutritional, anti-nutritional composition, and cytotoxicity of S. madagascariensis ripe fruit. Fruits were randomly selected, and the parameters of each experiment were measured in triplicates. The seed coat and fruit pulp were analysed for proximate, mineral and anti-nutrients (phytic and oxalic acid) composition using standard protocols. The cytotoxic effect of methanolic extracts from the fruit parts of S. madagascariensis was tested on human embryonic kidney (HEK293) and cervical cancer (HeLa) cell lines using the MTT [3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide] cell proliferation assay. The fruit pulp’s moisture (6%), ash (11%), protein (5%), fat (1%), fibre (12%), and carbohydrate (12%) contents were significantly different (P<0.05) from the compositions of the fruit pulp (5% moisture, 5% ash, 4% protein, 33% fat, 8% fibre and 11% carbohydrate). The minerals analysed were significantly (P<0.05) higher in the fruit pulp compared to the seed coat (testa). The fruit's seed coat and fruit pulp's methanolic extracts did not show any significant toxicity in the HEK293 cell line. The seed coat's methanolic extract exhibited moderate toxicity in the HeLa cell line. The methanolic extracts from both fruit parts showed a dose-dependent effect in HEK293 and HeLa cell lines. The results of the cytotoxicity analysis revealed the safe nature of the fruit pulp while caution needs to be taken when consuming the seed coat. The seed coat contained 1.39±0.01% phytic acid, but oxalic acid and phytic acid were not detected in the fruit pulp. This study suggests that the fruit parts could serve as a source of potassium, magnesium, and nitrogen, but poor sources of protein, carbohydrates, and fat (pulp).