Preparation and application of time temperature indicator in cold chain logistics

Here Maillard reaction time-temperature indicator (TTI) was prepared to observe the quality and remaining shelf life of mulberry during cold chain storage and transportation. The catalysts were used the xylose and glycine as the substrates and K₂HPO₄. The color change pattern of TTI was explored to adjust the concentration ratio of xylose, glycine, and K₂HPO₄. The results showed that the glycine concentration was 2.00 mol/L, when the xylose concentration was 1.00 mol/L. The attention of K₂HPO₄ was 1.00 mol/L, and the absorbance of TTI was higher. There were more stages of discoloration and more uniform discoloration. In addition, the intrinsic mechanism of the color change of TTI was also explored by FTIR and UV-visible absorption spectroscopy. The overall change trend of the spectra was slight with the long storage time of TTI. Still, there was no noticeable change in the FTIR spectra except for the weak difference in peak positions and intensities. The generation of new peaks was absence in the spectrograms. There was the benign effect of the mixture of xylose, glycine, whereas the K₂HPO₄ solution was produced a soothing effect. Meanwhile, C-O, C-H, C=O, C=C, C=N, amide I, amide II, amide III, C-N, N-H, and C-H were involved in the formation of melanoidin. The UV-vis absorption spectra showed that the absorbance change of TTI increased with the increase of storage time. The higher the temperature was, the shorter the time was required for the appearance of the characteristic peaks of color. The hardness, total soluble solids, titratable acid, and vitamin C in mulberries showed the different decreasing trends with the extension of storage time during refrigerated storage. By contrast, the weight loss rate and anthocyanins showed the increasing trends. Mulberry storage at ice temperature (-1℃) was favorable to maintain the quality of mulberry, which was used as the long-term refrigerated storage. The activation energies of 36.08, 40.42, 43.35, 38.28, 43.72, and 40.41 kJ/mol were calculated from the weight loss, anthocyanin, hardness, total soluble solids, titratable acid and vitamin C contents of mulberry at 25, 15, 10, 4 and -1 °C, respectively. The activation energy of the TTI was fitted to be 40.13 kJ/mol by the Arrhenius equation. There was no more than 25 kJ/mol difference in the calculated activation energy between each quality indicator and the TTI. As such, the quality change of mulberry at different ambient temperatures was more accurately matched with the time-temperature indicator. A chain-breaking simulation experiment was designed to verify the TTI monitoring under temperature fluctuation. Some changes were observed in the TTI color for the mulberry quality under different chain-breaking situations. The results showed that the abuse of temperature was accelerated the color change of TTI, even for the deterioration of mulberry quality. When the TTI color reached the endpoint, the mulberries began to decay. Furthermore, the change in TTI color was consistent with the shift in the mulberry quality. In addition, the kinetic analysis was performed by equivalent temperature. The difference between the comparable temperature values of TTI and each index of mulberry was calculated to be less than 1℃, thus verifying the monitoring ability of TTI. The TTI can be expected to monitor quality of mulberry for the long shelf life.