Cationic polyacrylamides increase the rate of liquefaction and hydrolysis of cornstarch

Cationic polyacrylamides (c-PAMs) bind to starch granules and decrease the temperature for the onset of gelatinization by 8^°C. c-PAM increases the binding of α-amylase to cornstarch; the rate of cornstarch hydrolysis also increases. By analogy to previous work on the c-PAM promoted hydrolysis of cellulose, it is proposed that the polymer reduces the charge on the surface of starch through a charge-patch mechanism. Because both enzyme and substrate are negatively charged, the bound c-PAM reduces the charge repulsion experienced by the approaching enzyme, which leads to stronger enzyme-substrate binding and faster hydrolysis. Overall, the c-PAM reduces enzyme dose by up to 62% under the conditions used. There is a mirror image relationship between the viscosity of the medium and the hydrolysis rate, which allows optimization of these parameters with enzyme and c-PAM dosage. Low c-PAM levels increase viscosity by agglomerating the substrate, but the viscosity drops at higher c-PAM concentration. © 2012 American Institute of Chemical Engineers AIChE J, 59: 79–83, 2013