Characterisation of resistant starch in selected banana cultivars

Abstract

In the green stage of the banana, starch accumulates most of which is resistant to degradation by amylases. The resistant starch is utilised in industry for development of nutraceuticals and as a functional food for countering the advance of corresponding NCDs and promoting a healthy gut. Depending on the genotype and cultivar, the starch composition and corresponding properties vary significantly across the banana family. The aim of this study was to determine the molecular, physicochemical and functional properties of the resistant starch (RSII) in economically important banana cultivars of Uganda. Banana RS was isolated from 15 different cultivars using a combination of alkaline and enzyme treatment. The resultant powder (RSII) was then assayed for RS content and polymer composition. Granule structure, size and distribution was determined using light and scanning electron microscopy (SEM). The molecular organisation and crystallinity of the RS was deduced using Fourier Transform Infrared Spectroscopy (FTIR) and the corresponding functional properties of the starches were also explored. The RS content significantly varied across the banana cultivars from 29.3±7.9 to 79.27±3.2 g/100g dry weight basis in Ndiizi and Kayinja respectively. The granules isolated RS were smooth, elliptical with ridges and a few irregulars having a diameter of approximately 17 to 36µm in Kibuzi and Kivuvu respectively as analysed by SEM. The results revealed significant differences in microstructure and physicochemical characteristics among the resistant starch samples with amylose contents of the RS ranging from 9.2% in Fhia17 to 22.4% in Kayinja. Generally, all the banana RS exhibited similar chemical structure of the A and B Types but had varying intensity ratios of the crystalline peaks 0.95 to 1.09 in Narita23 and Kayinja respectively. Multivariate analysis revealed strong correlations among the RS properties, prompting a conclusion that the effects of most RS characteristics are strongly interrelated. The RS content, amylose, and granule size contributed more to the grouping of the cultivars than other properties. Group 1 consisted of Kivuvu, Kayinja and Nfuuka that would be suitable for development of high RS, low moisture content products such as nutritional supplements and extruded foods. In addition to FTIR combined with chemometric data analysis presenting a powerful tool for reliable discrimination between banana RS, results of this study are useful in determining the prospective applications of banana resistant starch as a functional ingredient in the food and non-food industries.