Effect of acid type and concentration on the physicochemical properties of acid-methanol treated starch

• Main Authors: Ciao-Ling Pan, 潘巧玲
• Other Authors: Yung-Ho Chang
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/eh6a3x

碩士 === 靜宜大學 === 食品營養研究所 === 94 === Effects of acid type and concentration on the physicochemical properties of acid-methanol treated rice starches were studied. Rice starches (TKW1, TNG67 and TCS17) were modified with different concentrations (25, 50, 75 and 100 mN) and types (HCl, HNO3 and H2SO4) of acids in methanol at 45°C for 1 h. The physicochemical properties including granule size, pasting properties, solubility, thermal properties, molecular characteristics and chain length distribution were examined. The recovery yields of acid-methanol treated starches were all above 95%. Starch granules did not show significant change after modification and the average granule size of acid-methanol treated starches (TKW: 4.26~5.06 μm; TNG67: 4.84~5.62 μm; TCS17: 5.15~5.51μm) were smaller than their counterpart native starches (TKW: 5.76 μm; TNG67: 5.75μm; TCS17: 5.71μm). In spite of acid type, pasting viscosity and molecular weight of acid-methanol treated starches, and the average chain length of amyloses of TNG67 and TCS17 modified starches decreased with the increase of acid concentration, but the solubility of acid-methanol treated starches increased with the increase of acid concentration. The most obvious changes were found on HCl-methanol treated starches. The obvious changes of viscosity or solubility were found on TKW1 rice starch. The gelatinization temperature and enthalpies of acid- methanol treated starches were similar to their counterpart native starches except for the HCl-methanol treated starches of TNG67 and TCS17. The Peak temperature (Tp) of HCl-methanol treated starches of TNG67 (64.5~65.2°C) and TCS17 (64.3~64.4°C) were lower than their counterpart native starches (TNG67: 66.5°C; TCS17: 65.0°C). HCl-methanol solution had lower pH value than those of HNO3 or H2SO4 –methanol solutions. This finding implies that HCl in methanol could dissociate more hydrogen ion, and results in the higher degradation occurred in HCl -methanol solution than in HNO3 or H2SO4-methanol solutions. TNG67 rice starches treated in methanol with different concentrations or types of acid showed stepwise increasing patterns in viscosity. The viscosity profile of native starch showed a smoothly increasing pattern from the initial pasting temperature to the peak temperature, while those of acid-methanol treated starches depicted two-step increasing profiles. The first step increased from the initial pasting temperature to the critical temperature, and the second step from the critical temperature to the peak temperature. Therefore, two slopes could be obtained from the increasing viscosity profiles of methanol-treated starches. The slopes of the first steps (S1) were similar for the starches treated with different acids in methanol, however the slopes of the second step (S2) increased in the order of HCl, H2SO4 and HNO3. The peak viscosity of the methanol-treated starch also decreased in the same order. It was found that the chain length of amylose of treated starch positively correlated with S2 (r=0.907, p<0.001) and peak viscosity (r=0.918, p<0.001) in spite of the type or concentration of acid used. This finding implies that the degradation of amylose reduces the restriction effect of amylose on swelling of starch granules.