| Antifreeze proteins(AFPs) are a widespread class of proteins that can bind to ice to inhibit the growth of ice crystal. The binding of AFPs to ice causes a non-colligative decreasing of freezing point of ice crystal. And a separation between the melting point and the freezing point of the ice crystal is defined as thermal hysteresis(TH). There are huge commercial value and wide rang of applications on biotechnology, pharmaceutical, medical and food for the special function of AFPs.Recent experimental studies have shown that the accumulation of AFPs on surface of ice crystal is time dependent. The adsorption process is irreversible. The annealing temperature has effect on TH. The TH activities increase with lowering annealing temperature. When the annealing temperature drops with a certain cooling rate, TH activities decrease with increase of cooling rate. These results indicate that TH is affected not only by concentration but also the adsorption time, annealing temperature and the cooling rate.Based on the adsorption-inhibition theory, an irreversible model is proposed according to AFPs adsorption kinetics on the ice surface. The influence of water molecules on the type Ⅲ AFP adsorption on the ice crystal has been considered in this theoretical model. At low supercooling degree, water molecules are in favor of the adsorption of AFPs for they add the binding sites on the ice surface. But the ice crystal will be rapidly and uncontrollably growth at high supercooling degree. According to experimental data, we obtain the competitive relation between the water molecules and AFPs for the condition that the annealing temperature is constant and decreased with a certain cooling rate. The coverage on the ice crystal surface of AFPs change with time is obtained based on the change of vacancy sites distribution. And time-dependent TH activities of AFPIII with different cooling rate have been gained. The calculated results are consistent with the literature data qualitatively. |
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