Physicochemical Properties of a Time- Temperature Indicator Based on Immobilization of Aspergillus oryzae -Amylase in Polyacrylamide Gel as Affected by Degree of Cross-linking Agent and Salt Content

Currently available time-temperature indicators (TTIs) with favorable thermal inactivation kinetics are physically incompatible with microwave or radio frequency systems. Here, TTIs for microwave and radio frequency food pasteurization processes were developed that have dielectric properties that match target foods. The TTI can be easily recovered from a food and assayed using a rapid, simple colorimetric assay. Enzyme recovery was reduced by 8% but diffusion was retarded by 20% when bisacrylamide content was increased from 3.3% to 5.3%. The specific enzyme activity was highest in 20% polyacrylamide gels containing 2% NaCl. The residual enzyme activity in the TTI following 2 mo of storage at 8 °C exceeded 70%.