Kinetic Studies on the Heat Inactivation of Peroxidase in Sweet Corn^a

Abstract

SUMMARY A kinetic procedure employing D values was used instead of the usual end‐point method to study heat inactivation of peroxidase in whole‐kernel sweet corn. Results at 150–200°F indicated that a heat‐labile fraction and a heat‐stable fraction were being inactivated. The resistant fraction represented 5% of total enzyme activity, and was concentrated in the pericarp. Increasing the blanch time at 200°F from 2 to 5 min decreased residual enzyme activity from 3.3% to 1.7%. Inactivation of the heat‐resistant fraction at 210–290°F also followed a first‐order reaction. The phantom inactivation‐time curve showed that an HTST process based on microbial destruction could leave residual enzyme activity.

Separation and thermal characterization of ionically and tightly cell-wall-bound pectin methylesterase from cucumbers ( Cucumis sativus )

“…Each inactivation curve consisted of an initial portion with a high inactivation rate (heat-labile fraction, HLF) and a final portion with a lower inactivation rate (heat-stable fraction, HSF). These kinds of inactivation curves are typical for the inactivation of crude enzymes and indicate the presence of isoenzymes with varying heat stabilities [13][14][15]. The decimal reduction times (D value: the time required for 90% inactivation of enzyme activity at a given temperature) and the inactivation rates (k) for the inactivation of bound PME from cucumbers are given in Table 2.…”

Heat Inactivation of the Ethylene‐Forming Enzyme System in Cucumbers

“…The existence of two types of EFE systems with different sensitivities to heat treatments has been previously reported for papayas (Chan, 1986). The existence of biphasic first order curves in other enzyme systems have generally suggested either the presence of isozymes, as for papaya invertase (Chan and Kwok, 1976), papaya catalase (Chan et al, 1978), papaya acid phosphatase (Carreno and Chan, 1982), and corn peroxidase (Yamamoto et al, 1962), or the presence of multiple forms of enzymes, as in the case of papaya exo-and endo-polygalacturonases (Ghan and Tam, 1982). In the case of the EFE system, the interpretation of the presence of biphasic thermal inactivation curves must be restricted at this time to only the existence of at least two forms of EFEs with different heat resistances.…”

“…The stability of the enzymes is presented as D values (Table I), i.e. decimal reduction times, which are defined as the time required for 90% destruction of enzyme activity at constant temperature (Yamamoto et al, 1962). The D values for the HREFE were considerably larger (>12 X) than those for the HSEFE, which indicate that much longer heating times were required for the heat inactivation of HREFE.…”

Partial Purification and Thermal Characterization of Peroxidase from Okra (Hibiscus esculentum)

“…The inactivation curves were biphasic, which indicated the presence of heat-labile and heat-stable portions (Yamamoto et al, 1962;Ling and Lund, 1978;Naveh et al, 1982;Miller et al, 1990). Table 3 shows the values of the heating times required to inactivate 90% of POX activity at a constant temperature (D-values) and the inactivation rate constants (k-values).…”