Effect of processing including domestic cooking on nutritional quality of legumes

Food legumes are divided broadly into two types, those in which energy is stored as lipid material-the leguminous oilseeds such as soya bean and groundnut and those in which energy is stored as starch-the pulses such as peas, beans and lentils.The cluster bean (Cyamopsis tetragonoloba (L.) 'raub.) is used for the extraction of guar gum and is unusual among the food legumes in that most of the energy is stored as a galactomannan.However, the mature seeds are not normally eaten as food by humans.Most studies of the effects of processing on grain legumes have been carried out with soya beans; however, in this discussion consideration is primarily given to pulses.Table I shows names of commonly-eaten pulses with the region in which they are eaten.Confusion has arisen in the past over the nomenclature of pulses for several reasons.First, many species previously classified as Phaseolus have now been reclassified as belonging to the genus Vicia.Secondly, common names for two species may be the same, such as the use of the term field bean for varieties of both P. vulgaris and V. faba (see Table I).Finally, a single species may contain within it many morphological types and therefore it is difficult to distinguish the species from the seeds alone.This is particularly true now that unfamiliar varieties are being released from breeding stations.Thus, for example, coloured varieties of cowpea may be identical to seeds of P. vulgaris.Legumes contain a wide range of toxic components (Aykroyd el af.1981).(The term toxic being defined in the liberal sense according to Liener (1980) as 'an adverse physiological response produced in man or animals by a particular food or substance derived therefrom').The effects of most of these components are small or negligible in a mixed diet especially when legumes are properly cooked.However, a few (shown in Table 2) deserve mention as their presence in foods does have some public health significance.During the processing of legumes it is important that toxic components be reduced to levels that pose no threat to health.However, improvements in breeding legumes may result in higher levels of toxins, requiring more severe processing conditions for detoxification.Until recently only those legumes of primary importance in the industrialized countries, such as beans (P.vulgaris), peas, groundnuts and soya beans had received much attention from plant breeders.In the early 1970s a number of international agricultural research centres were established for the breeding of tropical and subtropical legumes.At these centres most of the breeding effort is aimed at higher, more stable yield.One aspect which contributes to low yield is the particular susceptibility of legume plants to insect attack in the field.Therefore,