Effect of pH on phosphorylation of sago starch

Sage starch, in a semidry state was phosphorylated with 2% sodium trimetaph osphate (STMP), 5% sodium tripolyphosphate (STPP) singly, and in combinatio n at pH levels between 6 and 11. As the reaction pH was increased from 6 to 11, the degree of phosphorylation was observed to decrease from 0.186 to 0 .083% P with STPP, except at pH 9 where the degree of phosphorylation was i ncreased to 0.224% P. In the case of STMP, the degree of phosphorylation in creased from 0.066 to 0.119% P as reaction pH was increased from 6 to 10. I n the reactions using a mixture of STPP and STMP, the P content decreased f rom 0.320 to 0.115% when a similar range of pH was employed. At the reactio n pH of 9, a starch phosphate obtained using STPP exhibited low hot paste v iscosity but high cold paste viscosity and shear stability when cooked at 9 5 degrees C. Treatment of sage starch with a mixture of STPP and STMP yield ed the best starch phosphate at the reaction pH of 9.5 which showed lower h ot paste viscosity and much higher cold paste viscosity than that of sage s tarch phosphates prepared at pH 9 using STPP. Paste clarity measurements of the phosphorylated starches indicated that cross-linking accelerated rapid ly above pH 8 with STMP, above pH 9 with STPP, and above pH 6 with a mixtur e of the two. (C) 2000 Elsevier Science Ltd. All rights reserved.