Normal maize, waxy maize and amylomaize V starches were treated at a moisture content of 70% by ultrasonic treatment. The results showed that the surface of normal and waxy maize starches was porous after treatment and a fissure could be clearly observed in the surface of amylomaize V starch. Ultrasonic treatment did not change the X-ray pattern of the three maize starches. The swelling power (amylomaize V (B-type) . normal maize . waxy maize (A-type)) and solubility (amylomaize V . normal maize . waxy maize), the syneresis of amylomaize V starch and the gelatinization transition temperatures of the three starches increased on this treatment. Ultrasonic treatment decreased the syneresis of normal and waxy maize starches, the enthalpy of gelatinization (amylomaize V . waxy maize < normal maize) and the gelatinization temperature range (amylomaize V . normal maize < waxy maize) of all starches. A drop in viscosity of all three starches was observed and the viscosity patterns of three starches remained unchanged after ultrasonic treatment. The data showed that ultrasonic treatment degraded preferentially the amorphous regions and more easily attacked linear amylose than highly branched amylopectin.

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Normal maize, waxy maize and amylomaize V starches were treated at a moisture content of 30% by microwave radiation. The results showed that the surface was porous and a cavity could be clearly observed at the center of the three starches. Microwave treatment increased the X‐ray intensities of the major d‐spacings of all starches and changed the X‐ray pattern of amylomaize V from B to A+B. The swelling power (amylomaize V < normal maize < waxy maize) and solubility (amylomaize V < normal maize < waxy maize), syneresis (waxy maize > normal maize > amylomaize V) and the enthalpy of gelatinization (amylomaize V (B‐type)> normal maize waxy maize (A‐type)) decreased on this treatment. Microwave treatment increased the gelatinization transition temperatures (amylomaize V > waxy maize > normal maize) and the gelatinization temperature range (amylomaize V > normal maize ¡Ö waxy maize) of all starches. A rise in pasting temperature and a drop in viscosity of the three starches were observed after microwave irradiation. The viscosity patterns of waxy and normal starches remained unchanged, while that of amylomaize V starches changed from C to D on microwave treatment. The data showed that rearrangements restricted to sections of the starch molecules resulted in the formation of new crystallites of different stabilities and led to a more ordered crystalline array.

Cooking and sensory properties of rice are largely determined by the amylose content and structure. For relationships between functional and structural properties, a more accurate method to determine the structure of amylose is required. Here we calibrate size exclusion chromatography (SEC) columns, using Mark-Houwink parameters for linear starch and pullulan standards, to obtain the true molecular weight distribution of linear starch. When the molecular weight distribution is reported relative to pullulan, rather than the actual molecular weight which is readily obtained from universal calibration, it is seen that the molecular weights of longer amylose chains are greatly underestimated. We validate the SEC method to enable the measurement of the hydrodynamic volume distribution of the starch by examining reproducibility and recovery. Analysis of the starch in the sample pre- and post-SEC shows that 20% of the carbohydrate is not recovered. Comparison of the weight-average degree of polymerization, X(w), of (undebranched) starch of pre- and post-SEC is made using iodine binding as well as Berry plots of data from multi-angle laser light scattering (MALLS). These both show that current SEC techniques for starch analysis lead to significant loss of high molecular weight material. Indeed, for the systems studied here, the values for X(w) after SEC are about three times lower than those before SEC. Iodine-starch complexes of pre- and post-SEC samples reveals that the SEC techniques give reliable data for the amylose fraction but not for amylopectin. We address reports in the literature suggesting that the conventional isoamylase method for debranching starch would lead to incomplete debranching and thus incorrect molecular weight distributions. However, it is shown using (1)H NMR that isoamylase can completely debranch the amylose (to within the detection limit of 0.5%), and by SEC that successive incubation with isoamylase, alpha-amylase, and beta-amylase can degrade the amylose-rich fraction completely to maltose. We develop a method to obtain a hot water soluble fraction (HWSF), rich in undamaged amylose molecules, directly from rice flour, avoiding the structural degradation of previous techniques. With appropriate sample handling, the formation of associations between starch chains is minimized. With the combination of calibrated and validated SEC methods, and an improved extraction of amylose from rice, the X(w) for both HWSF and debranched HWSF are found to be much larger than has previously been reported.