Physico-chemical, rheological and structural properties of fractionated potato starches

In an attempt to reveal whether behaviour differs between various granule size classes of potato starches, small (SGF), medium (MGF) and large (LGF) granule fractions were separated from the native starches of three potato cultivars, and some of their physico-chemical and functional properties studied. There was a significant variation in the granule size distribution of the native starches and their separated fractions, when studied using particle size analysis and scanning electron microscopy. The granule size ranges for LGF, MGF and SGF were 40–65, 20–40, and 1–20 μm, respectively. The granule sizes in the fractions separated from the native starch of the cultivar Kufri Ashoka were larger than in the corresponding fractions separated from the other two cultivars (Kufri Kunden and Kufri Dewa). For all three cultivars, LGF had higher amylose content and a lower swelling power than the corresponding MGF and SGF. The light transmittance and solubility of the native starches and their three fractions increased, while enzymatic digestibility decreased with the increase in granule size. Among the three fractions, pasting properties such as peak and final viscosities were observed to be lower for SGF, while peak viscosity temperatures were lower for LGF. The breakdown and setback in viscosity were observed to be highest for LGF and lowest for SGF, for all three cultivars. The lowest values of dynamic mechanical properties such as G′, G″, G∗, η∗ and η′ were recorded for gels of native Kufri Dewa starch and its fractions during frequency sweep testing on a dynamic rheometer. The textural attributes of the gels obtained from the native starches and their fractions showed a relationship with their respective pasting behaviours. A significant and progressive change was observed in the texture of gels during 7 days storage at 4 °C.