Options for enhancing utilization of Jack beans (Canavalia ensiformis) in Tanzania

Abstract

Population increase is forcing mankind to look for alternative food sources from underutilized plants. Jack bean has been earmarked as one of these food sources. The only barrier for its utilization is the presence of inherent toxic compounds that should be removed, to make it edible to humans. A number of researchers have tried various ways in an effort to reach that goal. This study has also tried to perform a number of treatments on jack beans, which included soaking, treatment with trona (magadi soda) and germination. The samples of jack beans were brought from Mlingano Agricultural Research Institute and transported to the Sokoine University of Agriculture, Tanzania. Proximate analysis, mineral and phenolic compounds content were carried out on the treated samples. Acceptability tests were performed on products prepared from composite flour, made from 48 h. germinated jack beans. The products included porridges, breads and buns. Soaking results in lowering mineral concentrations. However, treatment with trona increased mineral profile. The levels of calcium, iron and zinc for the jack bean seeds analysed, gave 8.99, 3.83 and 1.76 mg/100 g, respectively. Proximate analysis revealed that moisture, protein, fibre, fat, ash and carbohydrate content were 4.6, 29.7, 5.2, 3.3, 3.4 and 53.9%, respectively. Phenolic compounds concentrations continued to decrease gradually with various treatments. Soaking had minimal effect in reducing phenolic compounds but, germination of jack beans for 48 h. had the highest (82%) reduction effect. There were significant differences (P ≤ 0.05) in organoleptic properties with regards to breads and porridges but no significant differences (P ≥ 0.05) in all organoleptic properties with respect to the buns. Panelists liked the buns much more compared to the breads and porridges. There were no complaints from all the panelists after consuming the jack bean based products. This outcome shows the potential of jackbean being used as a human food in the near future especially using germinated flour. The reports from researchers that jack beans are consumed by some ethnic groups and personal narrations of people who have consumed the beans, if followed up and comprehend the way they do their preparation, will be a great stride towards utilization of jack beans. Key words: Jack beans, anti-nutritional factors, phenols, germination, soaking, trona.