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Antifreeze proteins (AFPs) are a relatively recently discovered group of proteins found in cold tolerant, cold-blooded organisms across many taxa. The proteins have apparently evolved independently multiple times as they have a wide range of primary, secondary, and tertiary structures. However, they all share the ability to recognize, bind to, and inhibit the growth of ice crystal surfaces. In the present chapter we discuss the properties of water related to freezing, the structure and physics of ice, nucleation, and recrystallization as a background for understanding the actions of antifreeze proteins, both within cold-tolerant organisms, and in the context of applications. As an inspiration and background the chapter also deals with the problems of ice formation in cold-tolerant organisms. This leads to an overview of the types of AFPs found in various organisms, with emphasis on those found in fish, insects, and plants. Antifreeze activity is defined and the antifreeze mechanism is explained, as is the binding of the AFPs to ice crystals. Antifreeze activity can be enhanced in various ways: by interaction with organic and inorganic molecules as well as by mutations of the native AFP. These enhancements may be of great importance for applying AFPs in the food industry. A section gives an overview of our present knowledge of the use of AFPs in food preservation. The physical-chemical properties of AFPs are important when dealing with applications, and as these can be quite different from other proteins a section is devoted to a discussion of these. With many new methods, both technical and bio-molecular, the future of applying AFPs in the food industry seems bright. It is our hope that by reading the present chapter the reader will feel inspired to consider AFPs as an interesting addition to old and well-proved techniques within the technologies of food processing.

Publisher Summary Gas hydrates are crystalline compounds formed when water and suitably sized gas molecules are combined at high pressure and low temperature. They consist of polyhedral cavities formed from networks of hydrogen-bonded water molecules in which small gas molecules can enter. Depending on the type of gas molecules present gas hydrates form different structures, known as structure I (sI), structure II (sII) and in special cases structure H (sH). The gases that form hydrates are normally small molecules, many of which are encountered in natural gas. Traditionally the formation of hydrates has been prevented by addition of thermodynamic hydrate inhibitors such as methanol and glycol. However the amounts needed to avoid hydrate formation may reach 50 wt% in the water rich phase. Since water production from fields can be quite severe, especially in cases where water injection has been used to enhance the oil recovery, large amounts of hydrate inhibitor are required.