Effect of Cold Storage on the Concentrations of some Nutrients, Anti-nutrients and Toxic Substances in the Leaves of Vernonia amygdalina (Bitter leaf)

Aims: In order to maintain the freshness and quality of leafy vegetables after harvesting during glut, vegetables are usually stored in cold condition either in the freezer or refrigerator for certain period as this storage condition is believed to prevent some of the biochemical reactions responsible for food spoilage. This research was carried out to examine the effect of cold storage duration in the freezer at -4ºC on the concentrations of some toxic substances (cyanide, nitrate soluble and total oxalates) and nutrients (β-carotene, vitamin C, Fe, Cu, Mg, Na and K) in the leaves of Vernonia amygdalina.

Methodology: Leaves of Vernonia amygdalina were washed with distilled water and stored in deep freezer at -4ºC for four-weeks. The concentrations of nutrients, antinutrients and toxic substances were determined at weekly intervals.

Results: The results showed that the concentrations of cyanide, soluble and total oxalates, vitamin C and β-carotene in the leaves of Vernonia amygdalina decreased significantly (p < 0.05) in the first three weeks of freezing. Significant (p < 0.05) decrease in the β-carotene concentration was observed in the fourth week of cold storage. The nitrate, Cu and Mg contents in the leaves of Vernonia amygdalina decreased significantly (p < 0.05) during two weeks of freezing and insignificantly (P>0.05) in the third and fourth weeks of cold storage. While freezing has no significant effect on Na content in the leaves of Vernonia amygdalina during the storage period, the concentrations of Fe and K in the vegetable decreased significantly (p < 0.05) in the third week of freezing.

Conclusion: A maximum of two weeks of cold storage condition in freezer at -4oC significantly reduced the concentrations of antinutrients and toxic substances in the leaves of Vernonia amygdalina to tolerable levels without compromising the nutritional benefit in the vegetable.