Protein adsorption in the food industry
Protein adsorption refers to the adhesion of proteins to solid surfaces. This phenomenon is an important issue in the food processing industry, particularly in milk processing and wine and beer making. Excessive adsorption, or protein fouling, can lead to health and sanitation issues, as the adsorbed protein is very difficult to clean and can harbor bacteria, as is the case in biofilms. Product quality can be adversely affected if the adsorbed material interferes with processing steps, like pasteurization. However, in some cases protein adsorption is used to improve food quality, as is the case in fining of wines. Protein adsorption Protein adsorption and protein fouling can cause major problems in the food industry (particularly the dairy industry) when proteins from food adsorb to processing surfaces, such as stainless steel or plastic (e.g. polypropylene). Protein fouling is the gathering of protein aggregates on a surface. This is most common in heating processes that create a temperature gradient between the equipment and the bulk substance being heated. In protein-fouled heating equipment, adsorbed proteins can create an insulating layer between the heater and the bulk material, reducing heating efficiency. This leads to inefficient sterilization and pasteurization. Also, proteins stuck to the heater may cause a burned taste or color in the bulk material. Additionally, in processes that employ filtration, protein aggregates that gather on the surface of the filter can block the flow of the bulk material and greatly reduce filter efficiency. Examples of adsorption Beer stone Beerstone is a buildup that forms when oxalate, proteins, and calcium or magnesium salts from the grains and water in the beer brewing process precipitate and form scale on kegs, barrels and tap lines. The minerals adsorb to the surface of the container first, driven by charge attractions. Proteins are often coordinated to these minerals in the solution and can bind with them to the surface. In other cases proteins also adsorb to the minerals on the surface, making deposits difficult to remove, as well as providing a surface that can easily harbor microorganisms. If built-up beer stone inside tap lines flakes off, it can negatively affect the quality of the finished product by making beer hazy and contributing "off" flavors. It is also harmful from a nutritional standpoint: oxalates can decrease absorption of calcium in the body, in addition to increasing risk of kidney stone formation. Wine making Grape and wine proteins tend to aggregate and form hazes and sediment in finished wines, especially white wines. Haze-causing proteins can persist in wine due to low settling velocities or charge repulsion on individual particles. Fining agents, such as bentonite clays, are used to clarify wine by removing these proteins. Also, proteinaceous agents such as albumin, casein, or gelatin are used in wine clarification to remove tannins or other phenols. Biofilms A biofilm is a community of microorganisms adsorbed to a surface. Microorganisms in biofilms are enclosed in a polymeric matrix consisting of exopolysaccharides, extracellular DNA and proteins. Seconds after a surface (usually metal) is placed in