Flour composition and starch functional and physicochemical properties of runner bean (Phaseolus coccineus) starches

There is an increasing demand for alternative sources of starch beyond conventional corn, especially for various food and industrial applications. Runner beans, an underutilised pulse grain, offer a promising alternative due to their relatively high protein and carbohydrate content, including starch. Understanding their functional and physicochemical properties is important for their adoption and utilisation. This study investigates the proximate composition of flour and the physiochemical properties of starch isolates from two varieties of runner bean (scarlet emperor and white swan) grown in the UK, comparing them with corn starch. Scarlet emperor runner beans exhibited 1.2 times higher protein content than the white swan, while their carbohydrate content was similar (average of 61%). Starch isolated from scarlet emperor and white swan beans showed similar water absorption capacity in comparison (approximately 100%), with both significantly outperforming the control corn starch (72.8%). The pasting properties and gel hardness of runner bean starches differed significantly from corn starch. For instance, the final viscosities were higher for scarlet (3942.17 cP) and white swan (3464.00 cP) starches compared to the control corn starch (3325.17 cP). Furthermore, the gels formed after pasting and subsequent cooling were 2.5 times firmer than those with corn starch on the initial day. However, after 5 days of storage, the firmness increased by a factor of 4. This is likely due to variations in amylose content. The higher viscosity of runner bean starches suggests their potential as effective thickening agents in food products and ingredient development. Further studies on morphology, crystallinity patterns, and thermal properties are needed to fully understand the potential use of these starches in various food applications.