ICE proteins

In the case of aerated protein icings, however, stabilizers are essential. Where hot water is used, gelling-type stabilizers work best (agar, gelatin, Irish moss extract). In cold foams, prepared with cold water, cellulose-type gums are used to contain water in the foams colloidal precipitates, such as are formed through the reaction of carrageenin and protein, are very helpful. 

The ability to inhibit the growth of ice has potential medical, industrial and commercial applications. Unfortunately, many of these applications have not been fully realized. One reason for this is that the isolation and purification of AFGP is a laborious and costly process often resulting in mixtures, making characterization difficult (5). Additional reasons include the fact that the AFGP mechanism of action is not understood at the molecular level and the nature of the protein-ice interface remains in question (6). 

Dehydration of Proteins. Ice crystal formation, especially when brought about by slow freezing, results in a redistribution of water. When a cell is thawed water has difficulty returning to its original sites (e.g., associated with proteins) and some of this water leaves the tissue (drip). Denaturation or association of protein molecules that may occur during freezing and frozen storage hinders the process of protein rehydration (1,2,4). 

In addition to the milk proteins, ice cream also contains other surface active molecules, namely emulsifiers, such as mono- and diglycerides or lecithin (from egg yolk). Despite their name, emulsifiers, as we will see in Chapter 4, are actually used in ice cream to de-emulsify some of the fat. 

Milk is an emulsion ofbutterfat droplets in an aqueous mixture of sugars, mineral salts and proteins. Ice cream is another emulsion with a similar composition. The emulsifying agents in both emulsions are proteins with smaller amounts of phospholipids, mainly lecithin. In egg yolk, the emulsifying agents are phospholipids and cholesterol. 

This study helps to further the hypothesis that the key features of a univeral structure-function relationship, with respect to protein-ice recognition and binding, rely upon the contoured fit of the protein backbone to the corrugation of ice surface and utilitzation of threonine/serine and lysine residues for creating a hydrogen bond network between the surface and the protein. 

The protein-ice modeling was conducted using the averaged simulation protein structure on the (100) ice plane. The protein was manually docked with the C-face of the Type III antifreeze protein on the (100) ice surface. This particular face of ice was chosen because of the three conseiwed residues (N14, T18, and Q44) which have been identified through mutation studies as being crucial for... 

The process of docking followed by energy minimization was repeated many times. This was done to locate the lowest protein-ice complex. Once the lowest protein-ice complex was located, the antifreeze protein was then translated in the x and y directions by 0.5 A along the ice surface. After each translation a short energy minimization was performed. 

A. Twomey, R. Less, K. Kurata, H. Takamatsu, A. Aksan, In situ spectroscopic quantification of protein-ice interactions. J. Phys. Chem. B 117(26), 7889-7897 (2013)... 

Figure Bl.17.6. A protein complex (myosin SI decorated filamentous actin) embedded in a vitrified ice layer. Shown is a defociis series at (a) 580 mn, (b) 1130 mn, (c) 1700 mn and (d) 2600 mn underfocus. The pictures result from averagmg about 100 individual images from one electron micrograph the decorated filament length shown is 76.8 nm.

Ice formation is both beneficial and detrimental. Benefits, which include the strengthening of food stmctures and the removal of free moisture, are often outweighed by deleterious effects that ice crystal formation may have on plant cell walls in fmits and vegetable products preserved by freezing. Ice crystal formation can result in partial dehydration of the tissue surrounding the ice crystal and the freeze concentration of potential reactants. Ice crystals mechanically dismpt cell stmctures and increase the concentration of cell electrolytes which can result in the chemical denaturation of proteins. Other quaHty losses can also occur (12). 

Soybean-based ice cream products, technologically feasible, are generally not in use because of flavor problems. An acceptable ice cream has been made by replacing 50% of the nonfat milk soHds with a dried soy protein isolate made up of cheese whey (21). Chocolate flavor has been widely used to mask the flavor of soybean proteins in ice cream (see Flavors and spices). 

Ice-cream is a product which has been developed since mechanical refrigeration became available. Ice-cream mixes comprise fats (not always dairy), milk protein, sugar and additives such as emulsifiers, stabilizers, colourings, together with extra items such as fruit, nuts, pieces of chocolate, etc., according to the particular type and flavour. The presence of this mixture of constituents means that the freezing... 

The milk and cream in ice cream contain butterfat, proteins, and milk sugars. Butterfat adds rich flavor, smooth texture, body, and good melting properties. The triglycerides in butterfat melt over a wide range of temperatures, so there is always some bit of solid and some liquid butterfat. Some of the butterfat almost turns into butter while the ice cream is being churned, adding to the unique texture of ice cream. 

Some ice creams contain sodium citrate to decrease the tendency of fat globules to coalesce, and to decrease protein aggregation. This results in a wetter ice cream. The citrates and phosphates are both used for this effect. Calcium and magnesium salts have the opposite effect, making a dryer ice cream. 

In addition to their nutrient value, casein proteins have many other uses. They are good emulsifiers, helping fats to stay suspended in water-based products such as milkshakes, coffee creamers, and ice creams. They are used as binders in processed meats (lunch meats, sausages, etc.). 

Polysorbate 80 is an emulsifying agent that is often used in ice cream to prevent milk proteins from completely coating the fat droplets. This allows them to join together in chains and nets, to hold air in the mixture, and to provide a firmer texture that holds its shape as the ice cream melts. 

Carrageenan is widely used in dairy products because it forms complexes with calcium and milk proteins. It thickens and helps suspend cocoa particles in chocolate milk. It stabilizes ice cream to protect it from thawing and refreezing, and enables it to hold more air. 

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