Research On The Solid-type Time–temperature Indicators

With the development of market economy, most perishable products especially the food storaged and sold by cold chain, which is easily affected by temperature.When the temperature is below the storage temperature, the actual shelf life of food lengthened which results in the waste of food. Conversely, when the temperature is higher than the storage temperature, the food would deteriorate even within the shelf life.Therefore, the time-temperature indicator(TTI) which monitor the environment temperature to predict the shelf life of food has come into being.At present, most TTIs in foreign research are based on microorganism, enzyme, diffusion and chemistry, and some of these have already commercialized which were applied in the monitoring of perishable food quality such as fish, meat, dairy products and vegetables. In terms of C hina, there is no commercial TTI and the research work is also less than those inforeigh institutions. This study mainly focused on developing the solid-type enzymatic time temperature indicator, which was based on the hydrolysis of enzyme and starch and the phenomenon that starch would change its color into blue when met iodine.Combining the microencapsulation technology to immobilize enzyme, the kinetic parameters and applications of TTI was researched.This study mainly includes:(1) A suitable method for preparing glucoamylase microencapsules was developed. Through single factor and orthogonal experiments, best recipe of microcapsules was obtained. The recipe was: concentration of sodium alginate was 3%, concentration of chitosan was 0.75%, concentration of calcium chloride was 0.4mol/L and concentration of acetic acid was 0.5% to immobilized 0.1g glucoamylase.(2) The solid-type enzymatic TTI was developed in this study. Microcapsules, substrate and emulsifier solution were mixed evenly and then the mixture was coated on the paper. The agar plate was used to activated the reaction layer and the color difference could indicate the reaction degree. This weight of microcapsules, weight of starch, concentration of iodine and thickness of the plate were chosen as the factors to conduct the single factor and orthogonal experiments. Finally, 7 ideal formulas were obtained whose reaction time was 5~6 days and reaction temperature is 4℃.(3) The dynamics of TTIs were determined, the activation energy of TTIs were 106.68kJ/mol, 98.47kJ/mol, 87.66kJ/mol, 89.73kJ/mol, 106.74kJ/mol, 97.51kJ/mol and 87.99kJ/mol respectively.(4) The metamorphic mechanism and dynamics performance of cold meat were studied, and the deterioration activation energy caused by fat oxidation was obtained. Through isothermal and non- isothermal test, one TTI(microcapsules 0.1%, starch 25%, concentration of iodine solution 0.1mol /L, thickness of cover plate 2mm) was verified to be qualified which could meet both activation energy and shelf life of cold meat.The innovation points of this study are: The solid-type time-temperature indicators were developed using microencapsulation of glucoamylase. The activation process was simplified by mixing the enzyme and substrate adequately.