Development and evaluation of nutritious fast-cooking bean flours
Nakitto, Aisha Musaazi
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Background: Common beans (Phaseolus vulgaris L) are grown throughout Uganda. Their consumption is however limited by the long cooking time thus high energy requirement and by the presence of anti-nutrients. There was thus a need for processing methods that reduce cooking time and anti-nutrients. Development of quick cooking bean flour with increased nutrient bio-availability to overcome both limitations should lead to increased bean consumption thus increased nutritional benefits of consumers. Objectives: The aim of the study was to develop a fast cooking bean product with enhanced nutritional value. The study specifically sought to develop protocols for production of fast cooking bean flours, to assess the effect of processing on the nutritional and physico-chemical characteristics of the flours, to assess consumer acceptability of gruels made from the developed flours and to assess the potential contribution of bean flours to the nutrient intake of consumers. Methods: Experiments were carried out to develop protocols for production of quick cooking bean flours from the K131 bean variety. The processing methods investigated for protocol development included soaking, sprouting, dehulling, steaming and roasting. Effects of combined processing methods on moisture content, nutritional composition, protein digestibility, mineral extractability and anti-nutrient content were determined. Consumer acceptability and viscosity of gruels prepared from the developed beans flours were evaluated. Results: The study revealed that 12 and 48 hours were the optimum times for soaking and sprouting respectively. The optimum time for roasting at 170 oC was 45 minutes for whole beans and 15 minutes for dehulled beans. Optimum steaming time on the other hand was 25 minutes for whole beans and 15 minutes for dehulled beans. Dehulling eliminated phytates and tannins and markedly enhanced protein digestibility. In whole beans, steaming resulted in the highest reduction of tannins and phytates. In vitro protein digestibility had a significant negative correlation with both tannin and phytate contents. In vitro protein digestibility was highest for dehulled-sprouted-steamed bean flour (64.08 %) and lowest for whole-sprouted-roasted bean flour (41.56 %). Dehulled-sprouted-roasted bean flour had the highest iron and zinc extractability (70.02 % and 70.13 % respectively). Iron extractability was lowest in the control sample (5.76 %) while zinc extractability was lowest in whole-sprouted-roasted bean flour (41.56 %) and the control (42.61 %). Mineral extractability had a negative correlation with tannin and phytate content as well. Total available carbohydrates were highest in moist heat treated bean flours and lowest in roasted samples. Dehulled-sprouted-roasted bean flour had the highest viscosity while whole-sprouted-roasted had the lowest. Conclusions and recommendations: The protocol developed in this study resulted in significant reduction in cooking time and improved the nutritional composition of beans. In order to improve the nutritional status of consumers, the developed protocol needs to be disseminated to all stakeholders. There is also need to investigate the individual effect of the preferred processing methods on nutritional characteristics of the K131 beans since it is not known.