Effects of processing methods on nutrient retention and contribution of white yam (Dioscorea rotundata) products to nutritional intake of Nigerians

Abstract

Consumption of indigenous foods is being encouraged globally as a means of meeting dietary needs of people. Yam products constitute staple source of energy to many Nigerians but little is documented on their nutrient composition. This study was carried out to determine the effects of processing methods on nutrient retention and possible contribution of some diets prepared from yam to nutrient intake of consumers. Fresh yam tubers were purchased from Sango market in Ibadan, peeled and cut into small pieces, then divided to eight portions. One portion was treated as raw sample while others were processed into roasted, fried, boiled, pounded yam (two samples), amala and porridge. All samples were analysed for proximate, energy and mineral composition using standard methods of AOAC and atomic absorption spectrophotometric methods. Raw yam was very low in crude protein (2.3 g), lipid (0.8 g), and fibre (1.4 g) moderate in ash (3.4 g), iron (4.1 mg) and zinc (5.6 mg), high in carbohydrates (33.3 g), energy (369.6 kcal), sodium (580 mg) and potassium (470 mg) /100 g edible portion. Roasting and frying brought significant improvement on crude protein, lipid and energy content of the products (p<0.05). Boiling yam caused significant reduction in all nutrient content except fibre, while boiling and pounding yam significantly improved its crude lipid, ash and energy content (p<0.05). Frying and using water for boiling yam in pounded yam preparation brought significant retention of nutrients in yam. Processing yam to amala and porridge resulted in significant improvement in nutrient content of the diets. Diets from yam can serve as good source of energy and minerals, and their 100 g portion can contribute between 12.4 to 20.9% gross energy, 11.0 to 46.0% iron and 17.3 to 48.7% zinc to recommended dietary allowances (RDAs) of consumers.