There were a lot of large lumps of starch (size > 6.3 μm) distributed through the dried rice noodle without NaCl (see the arrow in Fig. 2A). In contrast, smaller lumps (about 3 μm) were observed in rice noodle with NaCl (Fig. 2B). This observation indicated that starch molecules were less packed and looser inside the dried rice noodle with the presence of NaCl. The less packed starch in the dried rice noodle with NaCl may have been due to the Na+ ions interrupting the formation of hydrogen bonds between the glucose molecules of amylose or amylopectin during ageing, resulting in the prevention of starch retrogradation. Beck, Jekle, and Becker (2011) monitored the retrogradation rate (starch re-crystallization rate) of maize starch with NaCl solution using DSC and found that the retrogradation rate of samples with NaCl was slower than the control (without NaCl). They explained that the H+ ions of the starch hydroxyl group migrate from starch molecules into water leading to the Na+ ions being pushed and entrapped by the starch molecules. Since the radius of Na+ ions is greater than for H+ ions, the formation of hydrogen bonds and starch retrogradation are limited. Fu, Chen, Luo, Liu, and Liu (2015) also stated that the intramolecular repulsive force of starch is changed due to the presence of Na+ and starch retrogradation is disturbed. Using DSC, Baker and Rayas-Duarte (1998) also reported that the addition of NaCl caused decreased retrogradation in amaranth starch.
There were a lot of large lumps of starch (size > 6.3 μm) distributed through the dried rice noodle without NaCl (see the arrow in Fig. 2A). In contrast, smaller lumps (about 3 μm) were observed in rice noodle with NaCl (Fig. 2B). This observation indicated that starch molecules were less packed and looser inside the dried rice noodle with the presence of NaCl. The less packed starch in the dried rice noodle with NaCl may have been due to the Na+ ions interrupting the formation of hydrogen bonds between the glucose molecules of amylose or amylopectin during ageing, resulting in the prevention of starch retrogradation. Beck, Jekle, and Becker (2011) monitored the retrogradation rate (starch re-crystallization rate) of maize starch with NaCl solution using DSC and found that the retrogradation rate of samples with NaCl was slower than the control (without NaCl). They explained that the H+ ions of the starch hydroxyl group migrate from starch molecules into water leading to the Na+ ions being pushed and entrapped by the starch molecules. Since the radius of Na+ ions is greater than for H+ ions, the formation of hydrogen bonds and starch retrogradation are limited. Fu, Chen, Luo, Liu, and Liu (2015) also stated that the intramolecular repulsive force of starch is changed due to the presence of Na+ and starch retrogradation is disturbed. Using DSC, Baker and Rayas-Duarte (1998) also reported that the addition of NaCl caused decreased retrogradation in amaranth starch.
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