Morphological, thermal, rheological and retrogradation properties of potato starch fractions varying in granule size

The physicochemical properties of small, medium and large starch granules separated from four potato cultivars were investigated to reveal whether functional properties differed among the various size classes of the starches. Large-size fractions showed higher amylose content and light transmittance and lower swelling power than small-size fractions. The granules from the three fractions had diameters of 5-20, 25-40 and 40-85 µm respectively. The large and medium granules were ellipsoidal to irregular or cuboidal while the small granules were spherical or ellipsoidal in shape. The transition temperatures and gelatinisation temperature range of the fractionated starches increased while the enthalpy of gelatinisation decreased with decreasing granule size. Rheological parameters such as peak storage (Gʹ) and loss (G") moduli increased in the order small-, medium- and large-granule starches when subjected to temperature sweep testing. The breakdown in peak Gʹ during the heating cycle and retrogradation during storage were found to be highest for large- and lowest for small-size fractions. The differences in functional properties among the different size fractions suggested that the granule size distribution is an important parameter that can influence the behaviour of potato starch during processing.