Effect of Processing Methods on the Nutritional Contents of Bitter Leaf (Vernonia amygdalina).

Abstract

This study was conducted to determine the effect of four different processing methods on the nutritional contents of bitter leaf (Vernonia amygdalia). Fresh bitter leaves were subjected to different conventional food processing techniques, namely soaking in water (over night), blanching, abrasion with salt and without salt (Nacl) as well as fresh leave samples replicated three times. The fresh and treated samples were analyzed for antioxidant properties (reducing power and free radical scavenging ability), proximate compositions, mineral contents and antinutrient contents (tannin and phytate). The results obtained revealed that the reducing power of bitter leaf (0.53) was significant decreased with all the processing methods in the study. The free radical scavenging ability of fresh bitter leaf sample (70%) was significantly higher than in other treated samples (53-57%).The protein (6.0 – 7.3% ) and moisture contents (81.5 – 84.0% ) of variously treated bitter leaf were significantly (p≤0.05) lower than that of fresh leaves (8.4%) and (84.4%) respectively. Similarly, there was a decrease in the fat content by blanching and abrasion without salt 1.0% and 0.9% respectively , while soaking and abrasion with salt was increased by 2.2% and 2.3% respectively. The crude fiber content was lower with soaking while it was significantly (p≤0.05) higher with abrasion with salt. Blanching and soaking caused a significant (p≤0.05) decreased in the ash content while abrasions elevated its contents. Also, the various processing methods caused a significant reduction in mineral content of vegetable. The tannin content of v. amygdalina leaf (0.6%) was significantly (p≤0.05) reduced by the various treatments (0.4-0.5%). Similar trend was observed for phytate content with the exception of the soaked sample which showed no decrease. It could therefore be concluded that soaking overnight and blanching caused a significant reduction in the nutritional values of bitter leaf than other processing methods studied.