Correlation of structure and properties of cassava starch compared between varieties and harvesting date
1998
Kanjana Kurotjanavong
Fine structures of amylose-amylopectin and pasting properties of starch extracted from two popular varieties of cassava. Kasetsart 50 (KU50) and Rayong 90 (R90) at different harvesting dates were determined. The crops were cultivated during October 1994 to January 1996 at Rayong province roots were harvested at the age of 6 to 16 months. Structural analysis was done, including determination of the relationship of amylose size (Degree of polymerization DPn) and content, average chain length (CL) and average number of chains (NC) of amylopectin on paste properties. It was apparent that the period of harvesting has a marked influence on both amylose size and content as well as on the fine structures of amylopectin. Starch extracted from the roots of age beyond 12 months, contained less amylose but had bigger size while the number of chains the amylopectin cluster decreased with longer chain length. Pasting properties of starch were analysed by Rapid Viscosity Analyser (RVA). The appropriate root age for harvesting was ten months when compromising for root productivity and starch quality (peak viscosity at 280 RVU) was considered. The amount of rainfall one month prior to harvesting affected fine structure and paste properties of starch. When rainfall was high, cultivation at 12 months, amylose and amylopectin were hydrolyzed and consequently the size of amylose and chain length of amylopectin were reduced, resulting in higher number of chains. Meanwhile, the modified fine structure affected pasting properties by lowering peak viscosity and increasing pasting temperature, thus leading to lower starch quality. The high direct correlation of pasting temperature to amylose content and NC in amylopectin (R=0.92) was found in R90. The DPn of amylose in both R90 and KU50 showed significantly correlation (R=-0.96) with pasting temperature.
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