Effects of microwave-acid treatment on physicochemical properties of corn starch differing in amylose content
Date Issued
2009
Date
2009
Author(s)
Chen, Chin-Chin
Abstract
Starch is in granular form in nature and easily to disperse in cold water. After cooked, starch produces high viscosity and tends to retrograde. Acid modification is conducted to overcome the high viscosity and retrograding tendency of native starch for industrial applications and is also one of means to study microstructure of starch granules. Microwave heating is a more efficient process than traditional heating since it ensures homogenous operation on the whole volume of substance, greater penetrating depth, and selective absorption by water in food systems. Microwave assisted acid modification of starch granules was the main theme of this study to reduce the reaction time and acid waste. Waxy, normal and Hylon V (high-amylose) corn starches were impregnated with different concentrations (0 N(control), 0.05 N, 0.1 N, 0.5 N, 1.0 N, 2.0 N) of HCl solution to adjust water content of starch to the range of 34 ~ 43 % before being heated in a domestic microwave oven for 30 seconds. After heating, all sample temperatures were around 56 ℃ which was below the gelatinization temperature of native starch samples. The susceptibility significantly varied among of selected starch samples on microwave assisted acid modification. The solubility of starch granule increased as concentration of HCl increased but varied among different starch samples. Microwave alone without acid was sufficient to cause 21.9 % by weight loss of waxy starch but only had slightly effects on normal and Hylon V starch samples with solubility of 0.9 and 0.68 %, respectively. Increased acid concentration significantly caused higher solubility and reduced the yield, viscosity and apparent molecular weighted of starch. The microwave-heating caused partially swelling and birefringence loss from region around the helium toward periphery of starch granules with significantly corresponding of HCl concentration increasing. Substantial amount of broken and disintegrated debris appeared as 1.0 N and 2.0 N of HCl solutions were used to treat the starch granules. According the size-exclusion chromatographic analysis, the products from high concentration groups (1.0 N and 2.0 N of HCl solution) had been converted to small molecular amylodextrin, and significantly lost their viscosity and gel forming capability on dynamic rheological and Rapid Visco-Amylographic analysis. The microwave energy could alter starch molecular structure and selectively heated on lose packed and amorphous region of starch granules and caused heterogeneous acid hydrolysis revealed by x-ray diffraction and differential scanning calorimetric analysis.
Subjects
starch
acid hydrolysis
microwave
Type
thesis
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