Grain legumes play a major role in providing dietary protein to the populations of many developing countries. In addition, legumes fix nitrogen, and can be grown successfully in relatively poor soils. However, many varieties of grain legumes, particularly those of phaseolus beans, become progressively harder to cook when stored under the high temperature, high humidity conditions prevalent in propical countries. Easy-cook beans.(and other legumes) soften during cooking due to heat-induced dissolution of middle lamella polymers facilitating cell separation. However, legume seeds which have developed the hard-to-cook (HTC) defect can take up to ten times as long to soften due to the development, during storage, of stronger intercellular cross links as shown from our studies on plant tissues that are difficult to soften during heat treatment (e.g. beetroot, sugarbeet and cider apples). In these HTC legumes, tissue softening requires general cell wall breakdown which requires more energy, hence the extended cooking times excessive use of wood fuel and associated deforrestation. The mechanism by which the HTC defect is manifest is unclear. A number of hypotheses have been suggested involving activities of various enzymes, including phytase, pectin methyl esterase and peroxidase activity. However, the changes in the cell wall interpolymeric cross links, particularly those metiated by phenolics, during the development of the HTC defect, and therefore the identity of the underlying chemical and/or biochemical mechanisms, are still unknown. The proposed work will use recently developed methods for the isolation and chemical fractionation of cell walls with the minimum of degradation. By characterising the structural features of the fractionated polymers and changes in their extractability during HTC development, the causative mechanisms will be identified. This will facilitate the development of simplified and robust methods to screen for the Htc defect. such methods will be implemented in on-going breeding programmes to select for non-Htc varieties. In addition, the project intends to exploit processing technologies (milling, pressure and extrusion cooking) to improve the palatability and nutritional quality of Htc grain legume products. This will involve the use of cereal (e.g. rye flour or indigenous cereals) and black gram flour to improve the functional properties of the processed material.
Funding SchemeCSC - Cost-sharing contracts