Morphological, thermal and rheological characterization of starch isolated from New Zealand Kamo Kamo (Cucurbita pepo) fruit – A novel source

New Zealand Kamo Kamo, a unique fruit, was freeze dried, ground into flour and analyzed for its proximate composition. With high levels of glucose (17.7% d.w.), fructose (22.6% d.w.) and starch (23.2% d.w.), Kamo Kamo is also a rich source of potassium, zinc and dietary fibre. The morphological, thermal and rheological characteristics of the starch isolated from Kamo Kamo fruit were measured and compared with those of a normal potato starch. The Kamo Kamo starch granules had less smooth granule surfaces and appeared as a mixture of spherical, polyhedral and dome shaped granules with sizes ranging from 3 to 23 μm (medium and small) in contrast to the large size ovoid or cuboid potato starch granules, when studied by particle size analysis and scanning electron microscopy. With a low amylose content of 17.2%, the Kamo Kamo starch swelled in water to a considerable extent, and exhibited a lower solubility than potato starch in both water and DMSO. The light transmittance of the Kamo Kamo starch paste was significantly lower than that of potato starch paste, irrespective of storage period at 4 °C. The Kamo Kamo starch had significantly higher transition temperatures (To; Tp; and Tc), enthalpy of gelatinization (ΔHgel) and range of gelatinization (R), than potato starch, which suggests differences in the strength and stability of the crystalline structures between the two starches. A range of oscillatory rheological measurements using temperature (heating, cooling) and frequency sweep testing were performed, which showed that Kamo Kamo starch dispersions had lower storage (G′), loss (G″) and complex modulus (G∗) than potato starch. Differences between Kamo Kamo and potato starches in terms of thermal and rheological properties were attributed to differences in granule structure and in the stability of the crystalline structures inside the granule.