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Introduction
Yam (Dioscorea spp) is one of the most important food crops in West Africa, especially Nigeria, forming the basic carbohydrate for most homes ([11] Igyor et al. , 2004). Some important edible species of yam (Dioscorea ) in Nigeria are D. rotundata (white yam), D. cayenensis (yellow yam), D. alata (water yam), D. esculenta (Chinese yam), D. bulbifera (aerial yam) and D. dumetorum (trifoliate yam) ([12] Ike and Inoni, 2006). Trifoliate yam is among the underutilized yam species and is known by various names including three leaved yam, bitter yam and cluster yam. The tuber is large and coarse; one plant usually produced a cluster of tubers which are bitter due to the presence of alkaloids dioscorine ([23] Onwueme, 1978). Trifoliate yam is high yielding compared to other species and the starch grains are smaller, more soluble and more digestible than those of other yam species ([25] Treche and Guion, 1980). The proteins are, however, more balanced than those of white yam ([18] Mbome and Treche, 1994). It is also rich in vitamins and minerals. Processing of trifoliate yam tubers into flour have been reported to be a means of adding longer term value to the tubers with a high nutritional potential ([20] Medoua et al. , 2005; [1] Abiodun et al. , 2009).
Although, yam is grown in large quantity and forms part of the staples in Africa, its industrial utilization is yet to be maximized. Sefa-Dedeh and Afoakwa (2002) and other researchers have reported loss of minerals, polyphenols, starch and some functional properties of yam during storage. Processing of yam into industrial products such as flour would not only prevent postharvest loss but also promote its use industrially and increase the income of the yam producers thereby encourage more production.
[4] Bell and Favier (1981) reported that flour has the advantage of being a product that keeps well and is easy to market at great distances. Pre-gelatinized flours are used as puddings and can be incorporated into baby food formulation especially where normal cooking methods are not employed ([3] Adeyemi and Oke, 1991). Pre-gelatinization improves the nutritional and aesthetic value of the product ([10] Idowu et al. , 1993). Research has been carried out on processing of pre-gelatinized yam...