Starch composition, glycemic indices, phenolic constituents, and antioxidative and antidiabetic properties of some common tropical fruits

Background: Studies have supported the protective effect of high fruit consumption in the management of chronic diseases such as diabetes. Methods: Thirteen fresh tropical fruits were sourced for and the fruits juices were extracted, freeze dried, and then reconstituted for analysis. The sugar, starch, amylose, and amylopectin contents as well as glycemic indices, antioxidant properties, and the ability of the fruits to inhibit starch-hydrolyzing enzymes were determined. Also, the phenolic constituents of the fruits were characterized using high-performance liquid chromatography coupled with diode array detector. Results: The starch, sugar, amylase, and amylopectin contents were 3.01–3.89 g/100 g, 35.34–60.91 g/100 g, 0.84–1.46 g/100 g, and 1.68–2.86 g/100 g, respectively, while the glycemic indices were 28.01–68.34, with African star apple (28.01) having the lowest and watermelon (68.34) the highest. Furthermore, the fruits exhibited high antioxidant properties as exemplified by their DPPH, ABTS+, ·≡OH, and NO radical scavenging abilities. Likewise, the fruits also demonstrated α-amylase and α-glucosidase inhibitory property with Soursop (IC50 = 18.52 μg/mL), guava (IC50 = 19.77 μg/mL), and African star apple (IC50 = 20.86 μg/mL) showing the highest inhibitory potential among the 13 fruits. Similarly, the same trend was followed for α-glucosidase inhibitory activity. Conclusion: The fruits' low glycemic indices, strong antioxidant properties, and inhibition of α-amylase and α-glucosidase activities could be possible mechanisms for their use in the management and prevention of type-2 diabetes