Modification of starches in tapioca and rice flours by acetylation
1995
Eakaphan Keowmameechai
Native starches considerably show retrogradation at low temperature. Consequently, some food products produce undesirable characteristics. Tapioca, rice and waxy rice starches, therefore, were modified by acetylation at 20, 30, 40 and 50 deg C and pH 7.5-8.0, 8.0-8.5, 8.5-9.0 and 9.0-9.5 to improve their properties. It was found that the optimum temperature was 30 deg C and pH range was 8.0-8.5 for the modification. The amount of acetic anhydride used for acetylation showed the linear relations to the acetyl contents of the modified starches. When the starches were modified at desired acetyl contents, 0.6, 1.5 and 2.4 percent, the errors were less than 5 percent. When properties of native flours and the modified starches having acetyl group 0.6, 1.5 and 2.4 percent were determined and compared, it was found that most of them were in granule form. Their brightness were increased, but yellow color was decreased. Their gelatinization and pasting temperature were decreased, whereas peak viscosity was higher by the increasing of acetyl content. Their solubility and swelling power were increased. After freeze-thawing, the clarity were slightly changes and filtrate contents were reduced. The native tapioca, rice and waxy rice flours and their modified starches were used to make Lod-Chong-Singapore, Thai-styled custard and oyster sauce respectively. All their products were accepted at the highest scores for 2.4 percent acetyl group of modified starches after 1 freeze-thaw cycle for Lod-Chong-Singapore and Thai-styled custard and 9 freeze-thaw cycles for oyster sauce.
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