Production of flour from roasted beans and determination of its nutritional, sensory and storage properties
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Beans are a cheap source of protein worldwide and are finding more uses because of associated health benefits. Roasting of dry beans presents the possibility of a value-added precooked product with potential use in different food systems. Increasing utilization and acceptability of valued added bean products is critical to ensuring wider benefit from the health effects associated with consumption of beans. In this study, the effect of roasting temperature and time on proximate composition, sensory and functional properties of bean flour was determined. The optimal conditions for production of roasted bean flour were determined using response surface methodology and its properties investigated. Sensory profiling using quantitative descriptive analysis was done to describe sauces from beans that had been optimally roasted, boiled, extruded, traditionally roasted and not processed, and using partial least squares regression the factors influencing consumer preference of the sauces were identified. Increase in roasting temperature and time significantly altered the proximate composition, sensory and functional properties of bean flour. Higher roasting temperature resulted in bean flours with significantly (p ≤ 0.05) lower moisture content and higher fat, dietary fiber and ash; reduced foaming capacity, foaming stability, water absorption index, water solubility index and pasting viscosities and increased water absorption capacity. Appearance, color, taste and overall acceptability in bean sauces were significantly improved as a result of increased roasting temperature and time. Roasting temperature of 185.9°C and roasting time of 7.5 minutes were the optimal roasting conditions for production of bean flour with maximum in vitro protein digestibility of 57.74% and overall acceptability of 6.47 which corresponds to “like slightly” on a 9-point hedonic scale. In vitro protein digestibility of optimally roasted beans was significantly lower than that of unprocessed, traditionally roasted and extruded beans but significantly higher than that of boiled beans. Flour from optimally roasted beans had significantly higher fat than flour from extruded, boiled and unprocessed beans. Moisture content, free fatty acids and thiobarbituric acid values of optimally roasted bean flour significantly increased during storage for 12 weeks but did not exceed maximum acceptable values while scores for sensory attributes of sauce made from the flour did not decline during the same period. Differences in sauces from beans were more in appearance, taste and mouthfeel than in aroma, flavor and aftertaste. Processing increased consumer preference of bean sauces and appearance was a major determinant of preference compared to other sensory attributes. Based on results from this study it can be concluded that xiii flour from roasted beans is suitable for use in food formulations for nutrient and energy enhancement particularly those for use as complementary foods and in bakery products where prevention of staling is of importance. Roasted bean flour is a suitable replacement for boiled beans as a more convenient, nutritious and shelf stable product with reduced cooking time. Value addition can be done more successfully for beans through processing by paying particular attention to the appearance of developed bean products. Promotion of bean roasting protocol should therefore be encouraged amongst community nutrition practitioners, bean processors as well as agencies interested in investing in agro processing as a means of livelihood improvement.