The Effect of Cooking on the Goitrogenic (cyanogenic glycosides and glucosinolates) Content of Pumpkin Leaves (Telfairia occidentalis) and Spinach Leaves (Spinacia olairaceae)
Fresh ugwu (Telfairia occidentalis) and spinach (Spinacia olairaceae) leaves play important roles in human nutrition. Leafy vegetables including Telfairia occidentalis and Spinacia olairaceae are considered as agents of transmission of goitrogens which interfere with iodine uptake thus causing goiter. Cyanogenic glycosides are naturally occurring goitrogens found in staple foods in the tropics. Thiocyanate and isothiocyanate have been demonstrated as the goitrogenic principles of cyanogenic plants Thiocyanate ion acts as a goitrogen when present at high concentration especially when the iodine content of the diet is low. Thiocyanate inhibits the uptake of iodine by the iodide pump of the thyroid gland thus acting as a goitrogen which suppresses thyroid function leading to goiter. This study examined the effect of cooking on the goitrogenic potential of Ugwu and Spinach leaves. A total of (10g) of fresh/ andraw ugwu and spinach leaves were randomly collected and cooked. All samples were examined according to standard methods for detection of goitrogens. The cyanogenic glycosides content of rawand fresh ugwu leaves were 1. 6mg /kg - 1. 82mg/ kg while that of cooked leaves were 0. 004mg/ kg - 0. 0 l3mg/ kg. The glucosinolates content for raw and fresh Ugwu leaves were15.7mg/kg-17.28mg/kg, while that of cooked Ugwu leaves were 11.18mg/kg- 12.51mg/kg . For Spinach the cyanogenic glycosides content for raw and fresh were 0.24mg/kg-1.28mg/kg, while that of cooked spinach were 0.013mg/kg- 0.00Smg/kg. The glucosinolates content for raw and fresh spinach were 4.0mg/kg-2.64mg/kg while those of the cooked leaves were 2.52mg/kg-1.82mg/kg. there was a significant diference (P=0.085) in the level of reduction of glucosinolate content between raw and cooked Ugwu leaves and Spinach. There is also a significant difference (p=3.04) in the concentration of glucosinolates between Ugwu leaves and Spinach. Ugwu leaves had a higher concentration of glucosinolates than spinach in both fresh (raw) and cooked conditions respectively. These findings provide evidence that the risk of acquiring goiter from the consumption of ugwu and spinach leaves is reduced when cooked.
Keywords: Ugwu leaves, Spinach leaves, Cooking, Goitrogens, Cyanogenic glycosides, Glucosinolates
The Faculty of Science, Federal University Dutse. Jigawa State, Nigeria.