INTRODUCTION Onion (Allium cepa L.) belongs to the family Liliaceae, an important group of crops worldwide (Best, 2000). The crop is a biennial herb of Central Asian origin and used in soups, salads and in canning industries (Tindal, 1983). The crop nutritional composition includes 2.0 g protein, 70 mg calcium and 53 mg phosphorus (Ado, 2001). It also contains the vitamins thiamine, riboflavin and niacin and is used for its medicinal value especially in the case of heart problems (Mettananda and Fordham, 2001).