EFFECT OF AMYLOSE CONTENT ON THE RHEOLOGICAL PROPERTY OF RICE STARCH

The effects of starch variety and amylose on the rheological property of rice starch during heating were investigated with mechanical spectr ometry. The results indicated that the storage modulus (G)' of Kaoshiu ng Sen 7 (KSS7, indica) starch with sufficient concentration increased dramatically at gelatinization temperature (T-G'). T-G' was close to T phi = 1, the temperature for the starch granule to become close-pack ed. Nevertheless, T-G' was slightly lower than T phi = 1 in the low st arch concentration system, and slightly higher in the high concentrati on system. The addition of amylose inhibited the swelling of the starc h granule, and consequently, T-G' raised slightly. With the addition o f amylose, the G' of the starch gel decreased during heating, but may have reinforced the close-packed swollen granule matrix during the per iod of aging process at 5 degrees C. The waxy rice starch (Taichung wa xy 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 b e in proportion to its amylose content and in inverse proportion to th e degree of granular swelling. Hence, the higher G' for KSS7 rice star ch than that for TCW70 can be explained by its high inherent amylose c ontent, which could enhance the rigidity of the starch granular struct ure. Also, the high G' value for the system with the high starch conce ntration could be attributed to the low swelling and the strong intera ction among the granules. From these results, it was concluded that th e 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.