Effect of amylose content on the rheological property of rice starch

The effects of starch variety and amylose on the theological property of rice starch during heating were investigated with mechanical spectrometry. The results indicated that the storage modulus (G)' of Kaoshiung Sen 7 (KSS7, indica) starch with sufficient concentration increased dramatically at gelatinization temperature (TG'). TG' was close to Tφ = 1, the temperature for the starch granule to become close-packed. Nevertheless, TG' was slightly lower than Tφ = 1 in the low starch concentration system, and slightly higher in the high concentration system. The addition of amylose inhibited the swelling of the starch granule, and consequently, TG' raised slightly. With the addition of amylose, the G' of the starch gel decreased during heating, but may have reinforced the close-packed swollen granule matrix during the period of aging process at 5°C. The waxy rice starch (Taichung waxy 70, TCW70) with trace amylose content, showed much higher swelling power than that of indica rice starch (KSS7). Paste was formed even at high concentration. The rigidity of starch granular structure might be in proportion to its amylose content and in inverse proportion to the degree of granular swelling. Hence, the higher G' for KSS7 rice starch than that for TCW70 can be explained by its high inherent amylose content, which could enhance the rigidity of the starch granular structure. Also, the high G' value for the system with the high starch concentration could be attributed to the low swelling and the strong interaction among the granules. From these results, it was concluded that the major influencing factors on the rheological property of the starch during heating were the granular structure and component, followed by the amount of leached-out amylose in the process.