Abstract
The influence of granule-bound starch synthase (GBSS) on viscoelastic properties of gelatinized starch pastes was studied using a normal, a waxy null, and two GBSS-containing waxy mutant maize starches (waxy protein was synthesized with no GBSS activity). The four starches were isolated using the toluene method (isolation procedure I) (IP I) and were then further purified using an extended period of washing (isolation procedure II) (IP II). Dynamic rheological measurements of IP I gelatinized starches showed that storage moduli ( G′) were higher in the two GBSS-containing waxy starches than in the waxy null mutant starch not containing GBSS. The total non-GBSS granule-associated proteins of the three waxy starches were similar. Further removal of granule-associated proteins by purification decreased the G′, with decreases higher in the two GBSS-containing waxy mutants than in the waxy null mutant starch. This was interpreted to be due to the removal of GBSS during purification of the former. High shear broke gelatinized IP I waxy and normal maize starches starch granule or remnant structure, which caused a decrease in G′. Cox–Merz plots showed that the elastic properties of the starch pastes were reduced by removal of starch granule-associated proteins.
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