Production, Nutritional Value and Toxicity of Kawal, a Fermented Product from the Leaves of Cassia obtusifolia (L.): A Review

Cassia obtusifolia is a plant of the Fabaceae family. Its leaves are eaten as a vegetable in several African countries. In some African countries like Chad and Sudan, the leaves are processed by fermentation in a solid state, called in arabic kawal, which is eaten with cereal couscous. The present study is a literature review on the production of kawal and similar products. The production of kawal remains made by craftsmen. After crushing, the leaves are incubated in a buried jar for a period that varies from 14 to 30 days, sun-dried for 3 to 5 days and are ready for consumption. Kawal has several nutritional benefits. Fermentation of C. obtusifolia leaves increases protein, calcium, magnesium and iron content by 38, 98, 75 and 47% respectively, and reduces the levels of secondary metabolites like polyphenols, tannins and phytic acid by 20, 6 and 47% respectively. Fermentation of C. obtusifolia leaves reduces the levels of secondary metabolites like polyphenols, tannins and phytic acid by 20, 6 and 47% respectively. However, some studies on the effect of kawal on albino rats and chicken’s growth have revealed signs of toxicity manifested through high level of serum transaminases and histopathology of the liver and kidneys. These data show that the fermentation of C. obtusifolia leaves improve nutritional value of this vegetable but does not considerably reduce secondary metabolites which could be considered as antinutrients and might be responsible of the toxicity in albino rats and chickens.