ICE BINDING PROTEINS FOR PRESERVATION OF FROZEN FOOD TEXTURE - A STUDY OF ICE SHAPING

Ice-binding proteins (IBP) are expressed in a variety of organisms living in cold environments to help them survive sub-zero temperatures and freeze injuries. Their abilities to affect ice growth and to inhibit ice recrystallization at micromolar concentrations may be exploited in a variety of fields ranging from material sciences to medicine, agriculture and the food industry. In particular, inhibition of ice recrystallization improves the texture and elongates the shelf life of frozen food. Although some IBPs are already authorized by the FDA as food additives, they have only been added to few ice creams and ice pops. The potential of IBPs in the frozen food industry is far from being realized as more and more IBPs are being discovered and characterized, differing dramatically in structure and specific activities. We conducted a systematic study of the ability of various IBPs to shape ice crystals in distinguishable forms, characteristic of the particular protein type. We found that while IBPs with moderate thermal hysteresis activity induce hexagonal bipyramid shapes during growth, hyperactive IBPs, which are over one hundred fold more active than the moderate IBPs, induce faceted crystal shapes during melting. We suggest that these melting shapes result from affinity of the hyperactive IBPs for the basal plane of ice. Our results demonstrate a simple and useful tool for characterization of the influence of IBPs on ice crystals, a far less time consuming method as compared to measuring thermal hysteresis or ice recrystallization inhibition. In addition, we have shown a clear difference in the ice shaping mechanisms of moderate and hyperactive IBPs. Understanding the differences between the activities of the various IBPs is important not only for unraveling the mechanism of their function but also for the proper selection of a particular IBP for a particular task.