Effect of Total Solids Level on Heat Inactivation of Pectinesterase in Orange Juice

Abstract
Pectinesterase (PE) heat inactivation at various Brix did not obey first order reaction kinetics. Inactivation of PE at 10 ‐ 35° Brix did follow straight line semilogarithm plots of enzyme activity versus time. However, at 40° Brix and above the semi‐log graph between PE activity versus time was unclear. At high Brix levels a protective effect seemed to occur because the rate of enzyme inactivation declined. Increasing enzyme concentration in the 40° Brix sample showed that the curve was S‐shaped or sigmoidal. Increasing pH from 4 to 7 decreased the “Thermal Death Time” from 18 set to 4 sec.