Some engineering properties of yam setts from two species of yams O.B. Aluko a, * , O.A. Koya b a Department of Agricultural Engineering, Obafemi Awolowo University, Ile-Ife, Nigeria b Department of Mechanical Engineering, Obafemi Awolowo University, Ile-Ife, Nigeria Received 26 October 2004; accepted 21 May 2005 Available online 24 August 2005 Abstract Yam production is still mainly carried out manually by peasant farmers using yam setts as planting material. Adequate knowl- edge of their engineering properties is an essential prerequisite for the scientific design and development of equipment for planting and handling yam setts mechanically. Some engineering properties of yam setts from two species of yams, namely white yam (D. rotundata) and yellow yam (D. cayenensis), were investigated at different moisture contents. The properties investigated include sett density, static coefficient of friction on plywood, galvanized steel and formica surfaces, force–deformation behaviour during quasi- static radial compression, stiffness moduli and sett toughness. The coefficient of friction of yam setts of both species on formica was considerably lower than the corresponding coefficients on wood and galvanized steel, respectively. The results further showed that a considerable reduction in the coefficient of friction was achieved (0.41–0.29 and 0.45–0.25 on formica, for D. rotundata and D. cay- enensis, respectively) by air-drying freshly prepared setts at ambient room temperature for at least 4 days. Sett density over the dry- ing period ranged between 1020 and 1180 kg m À3 for D. rotundata and between 1030 and 1140 kg m À3 for D. cayenensis. The stiffness moduli were 3.53 and 5.36 kN m À1 for freshly prepared yam setts of D. rotundata and D. cayenensis, respectively. However, sett stiff- ness generally decreased as sett moisture content decreased. The toughness of freshly prepared yam setts initially increased, attaining a maximum value within the first 4 days of air-drying, and subsequently decreased with further sett drying. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Yam setts; Structural material surfaces; Friction coefficient; Stiffness; Mechanisation 1. Introduction Tropical root crops such as cassava, yam, sweet pota- to and cocoyam are important staple foods throughout Africa. These root crops are more efficient producers of calories than any other food crop in the tropics (Otoo, Okoli, & Ilona, 2001). Indeed yams (Dioscorea), grown principally for the carbohydrate they provide, account for about 20 per cent of the daily caloric intake of Nigerians (Iwueke, Mbata, & Okereke, 1983). In addition to being a major staple food, yam is also known to have a longstanding socio-cultural significance in the lives of some communities (Degras, 1993; Hahn, Osiru, Akoroda, & Otoo, 1987). The fact that the traditional methods of cultivating yams are arduous, labour intensive and time consuming is well attested to in the literature (Hahn et al., 1987; Nwuba & Kaul, 1987; Odigboh & Akubuo, 1991). In an attempt to alleviate the drudgery that characterises the traditional methods of yam cultivation, some efforts to mechanise some aspects of yam production have been reported. In particular, Odigboh and Akubuo (1989, 1991) have reported the development of mechan- ical planters for planting seed yams and minisetts, respectively. However, as pointed out by Aluko and Makanjuola (2002), compared to seed yams and mini- setts, yam setts (normally obtained by cutting large whole tubers into head, middle and tail pieces) are 0260-8774/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2005.05.051 * Corresponding author. Tel.: +234 36230290; fax: +234 36232041. E-mail address: elbeeluxe@yahoo.com (O.B. Aluko). www.elsevier.com/locate/jfoodeng Journal of Food Engineering 76 (2006) 396–401