Immobilization of laccase on sodium alginate/soluble starch microcapsules to develop a time-temperature indicator for freshness monitoring of Agaricus bisporus

To monitor temperature fluctuation in the process of food storage and transportation and to meet the consumers' requirements for product quality and safety, a time-temperature indicator (TTI) gel was developed for monitoring the freshness of Agaricus bisporus by immobilizing laccase on sodium alginate (SA)/soluble starch microcapsules with laccase microspheres as reactant, guaiacol as substrate and polyvinyl alcohol (PVA)/sodium carboxymethylcellulose (CMC) as the base material. The prepared microcapsules have 50-90 nm pores, which can effectively make the enzyme and the reaction substrate enter into them, and the immobilization rate of laccase is over 90 %, and the specific activity of immobilized laccase is about 82 % of that of free laccase. 11 TTIs were selected for kinetic analysis and the activation energy of the TTIs was calculated to be from 27.32 to 61.13 kJ/mol which was similar to that of meat, milk and mushroom. Meanwhile, the kinetic analysis was fitted with the brightness value L^⁎ of Agaricus bisporus and four TTIs closest to the activation energy of Agaricus bisporus were re-prepared, and verified at 4 °C,15 °C, 25 °C and variable temperature. The results showed that TTI#1 could successfully monitor the freshness of Agaricus bisporus.