Effect of spontaneous fermentation of cowpea leaves (Vigna unguiculata) on proximate composition, mineral content, chlorophyll content and beta-carotene content

The practice of fermentation has been used throughout the world for centuries as a means of preservation and or improvement of food safety and quality. Fermented foods gain unique sensory qualities and an increased shelf-life. The effects of fermentation of cowpea leaves (Vigna unguiculata) on the proximate composition, mineral content, chlorophyll and beta-carotene content of the leaves were investigated. The fermentation method was adopted from sauerkraut technology, as practiced in cabbage preservation. Supplementation of the substrate by addition of glucose at 1, 2 and 3% levels was also applied. The fermentation process was monitored by evaluation of the titratable acidity, pH and microbial population development. The treatment was compared to those of the blanched solar dried and fresh solar dried cowpea leaves at P 0.05. Fermentation with the addition of the highest concentration of glucose (3%) gave the highest concentration of lactic acid of 0.6% and the lowest pH of 4.7. Fermented samples had the least crude protein and moisture content of 13.2 and 6.2%, respectively while crude fibre, ash and soluble carbohydrates of fermented samples increased. The fermented samples showed a significant (p 0.05) reduction of iron, calcium, magnesium and zinc. At the end of 90 days storage study period the solar dried leaves retained the highest amount of chlorophyll and beta-carotene of 1590.7μg/g and 1.5μg/g, respectively. It was concluded that fermentation of cowpea leaves coupled with solar drying could be of potential for small scale producers as a method of enhancement of the keeping and nutritive quality. However, like other pulses, cowpeas contain several antinutritional factors, which may limit their consumption and affect the digestibility and bioavailability of nutrients.