Effects of cooking on chemical and phytochemical compositions of raw and cooked melon (Citrullus colocynthis L) and walnut (Tetracarpidium conophorum L) seeds

Abstract

Effects of cooking on proximate, phytochemicals and selected vitamins composition of melon and walnut were investigated in this study. Melon Seeds (MS) and Walnut Seed (WS) weighing 500 g each were obtained from open market and each was halved into two. One half o was boiled for one hour and oven dried at 60 C for 48 hours till constant weight was attained to obtain treated melon seed and treated walnut seed, respectively. The other halves were left un-cooked and were labelled uncooked melon seed and uncooked walnut seed, respectively. In MS, cooking reduced the crude protein, crude fibre and ash compositions but increased the moisture and ether extracts contents significantly (p<0.05). In WS, cooking reduced the crude protein and crude fibre but increased the ether extracts and moisture significantly (p<0.05) without any effect on ash contents (p>0.05). Aside from flavonoids which increased (p<0.05), other phytochemicals in MS were significantly reduced by cooking (p<0.05). Also, there were reduced tannins, steroids, terpenoids and alkaloids. The phytates and flavonoids increased significantly (p<0.05) while saponins composition remained significantly unaffected (p>0.05) by cooking. Ascorbic acid and tocopherol in MS as well as â-carotene and ergosterol contents were not affected significantly (p>0.05) by cooking. However, the â-carotene of 0.16 and ergosterol of 0.57 in raw MS reduced significantly (p<0.05) to 0.13 and 0.25 mg/kg, respectively by cooking. Also, tocopherol and ascorbic acid with respective values of 69.40 and 4.41 mg/kg in WS were lowered significantly (p<0.05) by cooking to 58.65 and 3.95 mg/kg, respectively. Processing reduced antinutrients in melon and walnut seeds and improve their nutrient sources.