Abstract

Vernonia amygdalina leaves are used as soup condiment in Nigeria either in the processed or unprocessed forms. This study assessed the effect of some conventional post-harvest treatments on the proximate, vitamins, minerals and anti-nutrient compositions of the leafy vegetable. Fresh leaves of V. amygdalina were subjected to two different processing methods; abrasion with salt (AWS) and abrasion without salt (AWOS). The proximate, β-carotene, vitamins B₁, B₃, C and E, minerals sodium (Na), potassium (K), calcium (Ca), phosphorus (P), iron (Fe), manganese (Mn), magnesium (Mg), zinc (Zn), cupper (Cu), aluminium (Al), selenium (Se), cobalt (Co), arsenic (As), cadmium (Cd) and lead (Pb) and anti-nutrients (phytate, tannin, oxalate and cyanide) contents of the vegetable were subsequently evaluated by standard methods. The results showed that unprocessed V. amygdalina had 34.56% protein, 6.04% fat, 9.08% fibre, 5.60% ash and 44.73% carbohydrate on dry weight (DW) basis. However, processing techniques employed caused a significant decrease (p<0.05) in the protein, fat and ash contents of V. amygdalina leaf; while there was no significant difference in the fibre and carbohydrate contents. Processing with or without salt significantly decreased (p<0.05) the levels of vitamins B₁, B₃, C, E and β-carotene compared with the unprocessed leaf. Elemental analysis revealed varied activities for all the elements except As and Cd that were non-detectable. The processing also depleted the levels of all the minerals detected in the fresh leaf. Phytate, tannins, oxalate and cyanide were detected in the fresh leaf and were notable to decrease by processing steps. In conclusion, V. amygdalina has very high nutrient and anti-nutrient potentials; however, the various conventional post-harvest processing tend to cause a significant decrease (p<0.05) in these parameters. Abrasion with minimal salt is most advisable.

Key words: Vernonia amygdalina, proximate, vitamins, minerals, anti-nutrients, processing.

Abbreviation

ANOVA, Analysis of variance; LSD, least significant difference;DW, dry weight; HCN, hydrogen cyanide; AWS, abrasion with salt; AWOS, abrasion without salt.