Two membrane-bound peroxidases, mPOD-I and mPOD-II, have been isolated and purified from Metroxylon sagu, using a combination of temperature-induced phase partitioning, DEAE-Toyopearl 650M, CM-Toyopearl 650 M and gel filtration. The mPOD-I and mPOD-II had molecular mass of 51.2 and 43.8 kDa, respectively, as determined by SDS-PAGE. Both enzymes showed high efficiency of interaction with the substrates. The isoenzymes were highly inhibited by ascorbic acid, metabisulfite, l-cysteine and p-coumaric acid. The inhibition mode of action and inhibition rate constant (Ki) values for these inhibitors were determined. Their activities were highly enhanced by Al3+, Ca2+ and Fe3+ but they were moderately inhibited by Zn2+.

Thermal inactivation kinetics for the purified membrane‐bound polyphenol oxidases (mPPOs) and peroxidases (mPODs) isolated from Metroxylon sagu were analyzed. Each isoenzyme was treated at different time–temperature combinations in the range of 0–70 min and 20–70C. Thermal inactivation rates constant (k) at 70C for mPOD‐I (72.9 × 10‐3/min) and mPOD‐II (97.9 × 10‐3/min) were lower than that of mPPO‐I (379.7 × 10‐3/min) and mPPO‐II (138.1 × 10‐3/min). The activation energy for inactivation of mPPO‐I (32.94 kcal/mol) and mPPO‐II (40.34 kcal/mol) was lower compared with mPOD‐I (45.77 kcal/mol) and mPOD‐II (40.62 kcal/mol). The enthalpy values for mPOD‐I (45.08 kcal/mol) and mPOD‐II (39.94 kcal/mol) were higher than those of mPPOs (mPPO‐I, 32.26 kcal/mol; mPPO‐II, 39.66 kcal/mol). This result implies that both mPOD‐I and mPOD‐II are more thermostable. PRACTICAL APPLICATIONS Sago starch has a great potential for application in various food systems. However, its further development and exploitation was hindered by browning‐associated problems due to polyphenol oxidases and peroxidases. In this work, we have investigated the effect of heat treatment on the stability and inactivation kinetics of membrane‐bound polyphenol oxidases and membrane‐bound peroxidases. The results from this work will enable the food industry to develop optimum process parameters with respect to heating time and temperature during processing and production of sago starch to produce high‐quality starch.