Monitoring storage shelf life for chilled fresh pork using enzymatic time-temperature indicator

Abstract: The temperature in a cold chain is the key factor for the quality of food that relies on low temperature in its distribution, as it may cause safety problems and economic losses. The Time-Temperature Indicator (TTI) is more and more important in the application of food stored and transported in a cold chain as a simple, inexpensive and user-friendly quality record device that overcomes the shortage of traditional open shelf-life and has experienced a deep development in the past few decades. The developed TTI is based on the diffusion and reaction between solidified alkaline lipase and three acetic acid glycerol ester that reduces the pH of the system and emerges as a yellow band moves forward to indicate the quality change of the food. Furthermore, chilled fresh pork was chosen to evaluate the applicability of the TTI. First, the dynamic characteristics of the quality change of chilled fresh pork based on TVB-N (Total Volatile Basic Nitrogen) value was studied by a storage experiment at 5 different isothermal temperatures. Then the Ea of the pork was attained by an Arrhenius model and a suitable TTI with specific ingredients was developed according to it at the base of the principle of Ea matching. Moreover, several storage experiments of both TTI and chilled fresh pork was conducted at an identical 5 different isothermal temperatures and 4 different non-isothermal conditions to evaluate the indicating characteristics of the TTI. In the research of the dynamic characteristics of the quality change of chilled fresh pork based on TVB-N value, the result shows that in the same level of temperature the longer the time, the higher the TVB-N value of chilled fresh pork; and as the temperature rises, the TVB-N value increases fast. Based on the Arrhenius Equation, the activation energy Ea of the chilled fresh pork was 51.346 kJ/mol, the pre-exponential factor k0 was 6.224×108 d-1. The TTI which matching the chilled fresh pork was selected as the basis of the Ea of the chilled fresh pork and the ingredients of the TTI are that the glycine - NaOH buffer dosage was 3.5 mL, the enzyme concentration was 20.0 g/mL, the alkaline lipase solution dosage was 0.5 mL, the glycerol triacetate dosage was 2.0 mL and the activation energy was 51.604 kJ/mol. In the research of reliability between TTI and chilled fresh pork, the results indicated that the color change of TTI was steady in both isothermal and non-isothermal conditions that were proved by the little difference between the final diffusion values. In non-isothermal conditions, the deterioration rate of the chilled fresh pork increases with the rising storage temperature. In addition, the deteriorating times of the pork in the 4 different non-isothermal conditions (TP1, TP2, TP3, TP4) are 4.8 d, 3.4 d, 3.3 d and 5.3 d respectively.The results also indicate that the TTI which was chosen by the base of the principle of Ea matching corresponded to the change of chilled fresh pork in both isothermal and non-isothermal conditions, which means that the TTI could be well used in the quality indication of chilled fresh pork based on TVB-N value. In addition, this TTI can be used to monitor the shelf life of chilled fresh pork during cold chain storage.