Surface activity of protein

On the basis of available data, it would appear that there are several possible reasons that may account for the observed decrease in surface activity of proteins, depending on the strengths of their thermodynamically favourable interactions with different polysaccharides. In the case of a rather weak interaction, which does not lead to the formation of a stable complex between protein and polysaccharide, the decrease in the surface activity of protein is evidently determined by the corresponding... 

Lefebvre J, Relkin P. Denaturation of globular proteins in relation to their functional properties. In Magdassi S, ed. Surface Activity of Proteins—Chemical and Physiochemical Modifications. New York Marcel Dekker Inc., 1996 181-236. 

The surface activity of proteins (as well as many of their other functions) depends on the so-called tertiary structure of protein molecules, which is determined by the spatial arrangement of their polypeptide chains. This tertiary molecular structure depends in turn on the primary protein structure - the aminoacid sequence, which is determined by the genetic code of a cell. The surface of a protein globule is mosaic-like it contains both polar... 

This chapter describes the origins of surface activity of proteins and some basic characteristics of their adsorption at fluid/fluid and solid/liquid interfaces, which have great importance in various colloidal systems. Understanding the surface activity of proteins would establish the need for various chemical and physicochemical alterations of proteins, which can influence their surface activity. Some of these modifications are presented briefly in this chapter, and in more detail in the following chapters. 

The chemical differences arising from the differences in the primary structure are also very important because the balance of polar, nonpolar and charged amino acid side chains determines the surface activity of proteins in a particular system, i.e., the possibility and mode of their location at interfaces of different types. This amphi-pathic nature of the protein molecule allows it to bind with surfaces of different chemical nature. A very important property is the protein hydrophobicity [17]. It influences adsorption and orientation of proteins at interfaces and in many cases correlates with surface activity [2,21]. 

Evidently, in many cases the effect of each factor can hardly be evaluated, and the differences in surface activity of proteins are complex functions of their molecular properties. 

There are not many reports about the influence of size and molecular weight on the surface activity of proteins. It was shown [55] that sodium caseinate and proteins from whey concentrate diffuse to the... 

There are still many unsolved problems that are extremely important for understanding the mechanisms governing the surface activity of proteins. Numerous investigations deal only with the quantity of adsorbed proteins under various conditions, while many cases lack data on physicochemical characteristics of the surface layer and the functional effects of adsorption. Many modem physical methods do not provide for complete and unequivocal information on the qualitative... 

The most significant and promising trends in research on the surface activity of proteins are ... 

The following chapters will deal wdth the various possibilities of changing the surface activity of proteins and may also provide simple tools for systematic studies on the effect of various isolated parameters on surface activity. 

As described in Chapter 1, various factors may affect the surface activity of proteins, hydrophobicity being a dominant parameter. 

Enhancement of the surface activity of proteins can be achieved by hydrophobic modifications. These modifications are based on the exposure of hydrophobic groups to the outer part of the protein molecule, or by attachment of various groups to the protein molecule. These modifications generally lead to polymer-like surface-active molecules, which are more active at oil-water, air-water, solid-air, and solid-water interfaces. Unique applications, based on such modifications, can be achieved in cosmetics, pharmaceutics, food, and many other industries. 

Surface activity of proteins chemical and physicochemical modifications / edited by Shlomo Magdassi. p. cm. 

I hope that the scientific information and the description of the possible approaches to altering functional properties and surface activity of proteins presented in this book will be useful to scientists interested in understanding the behavior of proteins at interfaces, as well as to those who wish to find new applications and products based on proteins. 

Furthermore, practical problems such as contact lens fouling, foaming of protein solutions, and fouling of equipment in the food processing industry, are direct consequences of the relatively high surface activity of proteins. In general, any process involving an interface in which contact with a protein solution occurs is likely to be influenced by protein adsorption to the interface. Thus, several reviews of protein adsorption have been published (1-5). 

The main topics to be presented include the origins of the surface activity of proteins, multiple states of adsorbed proteins, and the competitive adsorption behavior of proteins. These topics were chosen because it appears that a better understanding of each is necessary... 

Relative surface activities of proteins go some way towards explaining the composition dependence of surface viscosity for films... 

General properties of proteins, including amphoteric nature, large size, and internalization of hydrophobic groups, are probably the most important sources of surface activity of proteins. 

The organization of the adsorbed protein layer is influenced by differences in the surface activity of proteins, competition in mixtures, and complex displacement kinetics. 

The surface active properties of proteins are related to their ability to lower the interfacial tension between air/water or oil/water interfaces. Surface activity is a function of the ease with which proteins can diffuse to, adsorb at, unfold, and rearrange at an interface (11,12). Thus, size, native structure and solubility in the aqueous phase are closely correlated with the surface activity of proteins in model systems (13-16). 

Because of the complexity of actual food systems it is difficult to predict the performance of a protein based on its behavior in a simple model system. Thus, pH, salts, or level of surfactant, e.g. monoglyceride, in a food system could adversely affect the apparent surface activity of protein. 

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