Resistant Starch, Physicochemical and Structural Properties of Bananas from Different Cultivars with an Effect of Ripening and Processing

Abstract

The objective was to determine the functionalities of ‘Kluai Hom’, ‘Kluai Khai’, ‘Kluai Lebmuenang’ and ‘Kluai Namwa’ from the green and the green-to-yellow stages. Starch, fl our and fl ake samples were prepared and determined for resistant starch (RS), physicochemical and structural properties. Starch extraction showed the highest yield of 13.5% for Kluai Namwa and all starches from both stages had a very high RS. The starch of Kluai Namwa contained the highest RS of 77.3±1.1 to 81.1±0.4 g per 100g, while the drum-dried bananas had almost no RS. The rapid viscosity analyzer profi les showed a signifi cantly higher peak, fi nal and setback viscosities of the starches than the fl ours and the fl akes from both stages. Kluai Lebmuenang starches showed the highest peak (315.1 ± 0.7 to 318.5 ± 1.5 RVU) and fi nal (308.4 ± 2.3 to 375.5 ± 1.9 RVU) viscosities. The differential scanning calorimeter results showed that the starches from green bananas had similar thermal enthalpies from 17.1 ± 0.3 to 17.9 ± 0.2 J.g-1, while Kluai Khai in the green-to-yellow stage had the lowest enthalpy of 16.0 ± 0.1 J.g-1. Kluai Hom showed signifi cantly higher gelatinization temperatures than the others, as infl uenced by molecules of amylose and the more confi ned structure of the amylopectin crystallinity. The lowest gelatinization temperature of Kluai Lebmuenang was accounted for by its lowest relative crystallinity revealed by the X-ray diffractograms and all bananas exhibited typical B-crystallites. The electron micrographs of the starches showed irregularly shapes with elongated and oval forms and the surface looked quite smooth, but a slight blister was found only with the Kluai Hom starch.