Abstract
Waxy wheat starch (WWS) and waxy corn starch (WCS) were cross-linked in an aqueous slurry at c. 37% starch solids with 0·013 to 0·050% phosphoryl chloride (starch basis) at pH 11·5 for 60 min in the presence of c. 2·1% sodium sulphate (starch basis). Increasing levels of phosphoryl chloride caused a steady decline in the final paste consistency of cross-linked WWS, but that of WCS proceeded through an optimum. Starch paste consistency was the resistance to stirring measured in a pasting instrument. WWS cross-linked at a low level gave a higher final paste consistency compared with cross-linked WCS. WWS and WCS were hydroxypropylated (HP) to low (c. 2·0%) and medium (c. 4·0%) levels by reaction with propylene oxide at pH 11·5 and 45 °C, and the HP starches were then cross-linked with 0·008 to 0·018% phosphoryl chloride. Again, cross-linked HP-WWS gave pasting curves with higher consistency at 6·25% starch solids compared with HP-WCS. WWS and its modified forms yielded pastes of lower clarity than those from WCS, but the pastes from HP/cross-linked WWS had better freeze-thaw stability. Cross-linking with phosphoryl chloride (0·025%) followed by acetylation with acetic anhydride (8·0%) yielded modified waxy wheat and waxy corn starches with similar paste consistencies, but a force-distance instrument indicated that the modified WCS was significantly stringier than the modified WWS.
Published Version
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