Comparison of starches isolated from three different Trapa species

Trapa (Trapaceae) is one of the most common aquatic plants. In order to make full use of the resource of Trapa, we investigated two Trapa cultivated species (Trapa quadrispinosa Roxb. and Trapa bispinosa Roxb.) and one Trapa wild species (Trapa pseudoinisa Nakai) popularly found in South China. The morphology, size, weight, and contents of water, starch and soluble sugar of fruit and kernel were significantly different among the three species. Starches isolated from their kernels were all oval in shape with smooth surface and central hilum. The starch granule size was larger and amylose content was higher in the wild species than in the two cultivated species. Starches from the three Trapa species all exhibited CA-type crystalline. T. pseudoinisa starch showed the highest swelling power and solubility. Starches from the three Trapa species had similar thermal properties except that T. pseudoinisa starch had higher onset temperature and lower conclusion temperature. T. pseudoinisa starch showed similar breakdown viscosity and higher setback viscosity compared with starches from the other two species. Similar hydrolysis degree by porcine pancreatic α-amylase was observed in starches isolated from the three species. However, T. bispinosa starch showed the highest hydrolysis degree and T. pseudoinisa starch showed the lowest hydrolysis degree by HCl and Aspergillus niger amyloglucosidase.