Molecular weight, chain profile of rice amylopectin and starch pasting properties

• M¯n and Mw¯ of high amylose amylopectin (AP) were ∼42% and ∼81% of those of waxy AP.
• High amylose AP with high CL¯, ECL¯, and % mol of DP ≥ 37 had [η] ∼ 20% higher than waxy AP.
• Large APs increased starch peak viscosity but lessened trough and final viscosity.
• Increasing ECL¯ and a fraction of DP > 37 increased starch final viscosity.
• Clarity of AP solution increased when molecular size of AP increased.

Differences in fine structure, average molecular size of amylopectin (AP) as well as clarity of the AP solution from indica waxy rice and high amylose (HAM) rice were examined. Despite similar amylose content (AM), rice starches displayed different pasting properties. Waxy APs had higher values of both number–average and weight–average molecular weight (Mn¯ and Mw¯) but lower values of intrinsic viscosity [η  ], compared to HAM APs. HAM APs had higher values of average chain length (CL¯), average external chain length (ECL¯), and a proportion of DP ≥ 37. Statistical correlations of mol proportions of debranched AP, branching parameters, and molecular weight of AP were calculated. The study showed that starch pasting properties and clarity of AP solutions were influenced by molecular weight and branching characteristics of AP.