Paste properties of modified starches from partial waxy wheats

Properties of modified starches from partial waxy wheats have not been examined. Protease digestion of cracked kernels of three hard winter wheats varying in amylose content led to 82-85% recovery of starch, whereas kneading of the flour-water doughs gave 75-83% recovery. All starches had a protein content of < 0.3% and ash content of < 0.01%. Granule size distributions showed that starch from Ike kernels contained 86% A-type granules with a peak size of approximately 18 micrometers, and Karl-92 starch contained 77% A-type granules with a peak size of approximately 16 micrometers. The A-type granules (82%) from Rio Blanco starch were intermediate in size. The amylose content of Karl-92 starch, determined by concanavalin-A precipitation of amylpectin, was 28%, which was 17% higher than that of Ike starch (23%). The amylose content of Rio Blanco starch was 26%. The lipid content of Karl-92 starch, determined as fatty acid methyl esters, also was 18% higher than that of Ike starch (601 vs. 488 mg/100 g of starch, respectively). Wheat starches were modified with hydroxypropyl (HP) groups to low (1.5-2.5%) and medium (approximately 4.0%) levels, and the HP starches were cross-linked with phosphoryl chloride at levels of 0.003-0.075%. Pasting curves (amylograms) showed that Ike starch substituted with a low level of HP and optimally cross-linked with 0.025% phosphoryl chloride (starch basis) had a greater paste consistency than low HP cross-linked Karl-92, and Rio Blanco starches. At 4% HP and optimum cross-linking (0.003% phosphoryl chloride), the paste consistencies of the modified starches were nearly the same. The clarity of unmodified Ike starch paste was higher than that of Karl-92 or Rio Blanco starch pastes, and the clarity of all three pastes decreased as cross-linking was increased. Unmodified Ike starch formed a stronger gel than unmodified Karl-92 and Rio Blanco starches, but gel properties largely converged as the starches were modified.