The molecular structure of starch from different Musa genotypes: Higher branching density of amylose chains seems to promote enzyme-resistant structures

Starch from bananas/plantains, belonging to the genus Musa spp, is gaining prominence given its great potential as a healthy food ingredient made from an inexpensive raw material. Recent works highlight the outstanding potential of Musa starch to develop enzyme-resistant structures upon retrogradation. However, despite the wide variety of Musa cultivars (due to both natural mutation and breeding selection), there is no comparative investigation of the starch molecular structure from the most commonly cultivated Musa genotypes. In this work, the starch from six Musa cultivars harvested during the same growing season from the same parcel, was purified and analyzed for amylose ratio, amylose chain length distribution, and amylopectin unit and internal chain length distribution. Results showed significant differences between the fine structure of all Musa amylopectin molecules, which were structurally categorized as type 4 (consisting of a high number of B3-chains, few BS- and B-fp-chains, and low S:L and BS:BL ratios). Moreover, the different Musa starches exhibited dramatic differences in amylose ratio (17.7-27.6%), amylose branching degree (as evidenced by differences in the population of short chains of approximately 260 glucose units, GU) and a shorter average length (approximately 1000 GU) of the population of long amylose unit chains. Remarkably, these differences in amylose structure resulted in the cultivar Manzano (Musa AAB, silk subgroup) to possess a dramatically lower extension of in vitro starch digestion (C-90 = 4.70%) than the rest of the cultivars (C-90 = 17-18%) after full gelatinization and retrogradation for 7 days.