Effects of processing on proximate, mineral composition and storage of Dioscorea rotundata (White yam) tubers.

Abstract

This study investigated the nutritional qualities of raw yams and the effects of roasting on the proximate composition and retention, and its contribution to storability. Ten yams tubers with average weight of 2Kg that were firm, undamaged by any cracks, soft spots, or bruises were purchased from Ipata market in Ilorin, Nigeria in the month of November, 2015 during the dry season. Five yam tubers (10Kg) were peeled with well sterilized knife and designated Peeled Raw Yam (PRY). They were cut into very thin slices, air dried and homogenized into fine powder. The remaining 5 tubers (10Kg) were not peeled but were roasted with coal fire on iron wire mesh, air dried and homogenized into fine powder. Proximate and mineral compositions were determined before the powdered samples (RYT) were put into a screw top bottle and stored for two months. The results revealed that the moisture content (MC) of the raw roasted yam (RYT) (0.93%) was significantly P<0.05) lower than that of the peeled raw yam (PRY) (58.80%). The dry matter (ash) content of the two samples were significantly different; 1.28% (RYT) and 10.93%) (PRY). Carbohydrate content obtained in this study from RYT (73.20%) was higher than PRY (69.56%). The crude protein, crude fat and fiber contents of RYT and PRY were not significantly different. The level of K, Fe and Al content of RYT and PRY were not significantly different (P<0.005). The two samples had higher composition of Zn, Fe and Cu level compared to other mineral contents. A total of six fungi from four genera were isolated at the end of day 60.The study therefore, concluded that yams should be roasted before grindinginto flour for longer storage, better retention of the food content and reduction in the population of fungi.