Physicochemical and structural characterization of resistant starch isolated from Vigna unguiculata

In this study, characterization was conducted on resistant starch, isolated from different cultivars of V. unguiculata (Bechuana White, Fahari, PAN 311, TVU 11424 and DT 129-4). The fraction of resistant starch obtained was found in the range of 9.42–13.74%, with DT 129-4 yielding the highest fraction. Amylose content of the starches varied between 18.72 and 19.67%. Swelling power, solubility index and syneresis was directly proportional to the different temperatures. A correlation between amylose content and swelling power was observed as swelling power was indirectly proportional to amylose content. Water and oil absorption capacity was 31.93–88.06% and 10.29–27.71% respectively. Foaming, emulsion capacity, and stability were done, however, due to the lack of protein in the resistant starch samples, results obtained were relatively low, ranging between 0.00 and 22.41%. The degree of whiteness during colour analysis ranged between 80.81 and 84.61%. The FTIR-spectra displayed no distinctive difference amongst the vibration bands on the hydroxyl, methine and carbonyl frequency stretches and confirmed the polysaccharide nature of the resistant starch. The XRD spectra displayed a Ca-type crystalline structure for all 5 cultivars. Overall, this study shows that resistant starch has the potential to be used in many food applications and as a microencapsulation membrane. •Vigna unguiculata cultivars contain approximately 9–14% resistant starch.•Swelling power of resistant starch is indirectly proportional to amylose content.•Resistant starch displayed a Ca-type crystalline structure.•Resistant starch has the potential to be used in various food applications.