Denaturation surface pressure

We also noticed that the molecular area decreases gradually when the surface pressure is held at a certain value. Two possible explanations for this are (1) there may be some leakage of protein molecules from the surface into the subphase, since the protein is water soluble (2) protein denaturation may be taking place at the air-water interface. 

Although very interesting biotranformations have been reported in supercritical carbon dioxide, this solvent has been found to affect enzyme activity adversely. CO can react reversibly with free amino groups (lysine residues, specifically) on the surface of the protein to form carbamates, leading to low activity enzyme. [21]. Furthermore, carbon dioxide dissolves in water at molar concentrations at moderate pressures (<100 bar) and rapidly forms H COj. This can create some problems in biocatalytic reactions because many enzymes are denatured (unfolded and/or deactivated) at low pH. Enzymes can also be denatured by pressurization/depressuriza-tion cycles. For all of them, it is necessary to develop new enzyme stabilization strategies. 

The adsorption of proteins at interfaces is a key step in the stabilization of numerous food and non-food foams and emulsions. Our goal is to improve our understanding of the relationships between the sequence of proteins and their surface properties. A theoretical approach has been developed to model the structure and properties of protein adsorption layers using the analogy between proteins and multiblock copolymers. This model seems to be particularly well suited to /5-casein. However, the exponent relating surface pressure to surface concentration is indicative of a polymer structure intermediate between that of a two-dimensional excluded volume chain and a partially collapsed chain. For the protein structure, this would correspond to attractive interactions between some amino acids (hydrogen bonds, for instance). To test this possibility, guanidine hydrochloride was added to the buffer. A transition in the structure and properties of the layer is noticed for a 1.5 molar concentration of the denaturant. Beyond the transition, the properties of the layer are those of a two-dimensional excluded volume chain, a situation expected when there are no attractive interac-... 

These estimates oversimplify both the enthalpic effects of interaction and the entropic effects of size differences. First, interactions between adsorbed molecules as described by Frumkin type models do not allow for the formation of dimers or larger aggregates in the surface layer which can occur in practice. Equations of state for monolayers showing such two-dimensional aggregation have been proposed for various models [32-42]. Second, proteins differ from surfactants in more than just the size. For proteins, surface denaturation can take place, leading to their unfolding at the surface, at least at low surface pressures. The partial molar surface area for proteins, in contrast to surfactants, is large and variable. The interrelation between the... 

It is seen that for low values of n the adsorption achieves its maximum at = max = 40 nmVmolecule. With the increase of n the value of (Oj(rmax) decreases monotonously, while finally at n 2.0 mN/m the maximum adsorption corresponds to the state which possesses minimum partial molar area of tOmin = 2 nmVmolecule. Therefore, the protein adsorption layer is characterised by almost a complete denaturation at low surface pressure while at large surface pressures the adsorption layer is comprised of molecules in a state with minimum surface area demand. 

From Eq. (65) one can calculate the portion of adsorbed molecules which exist in the state (o j. The dependencies of the distribution function T omega969j and the area per protein molecule in flie maximum of the distribution function are shown in Fig. 4. It is seen that the adsorption layer of proteins is characterized by an almost complete denaturation at low surface pressure while at large surface pressures the adsorption layer is composed of molecules in a state with a minimum molecular surface area demand. 

It was demonstrated that the emulsification capability (average droplet size diameter) of heat-treated gum arabic was reduced dramatically by the denatur-ation effect of the active protein (Fig. 52). A similar effect was recorded at a low pH. The effect of the protein content on the emulsifying activity was found to correlate well with measurements of the surface pressure and surface elasticity. 

In confectionery manufacture aerated products such as frappe, mazetta, or ice cream are based on the use ot foams. Foams are affected by vapor pressure, surface tension, crystallization, denature-tion, and gelation. The production of foams in aerated icings and in whipped cream products is analyzed. 

Denaturation is a change in which the natural protein becomes insoluble in solutions in which it was previously soluble. It is brought about by physical means such as heat, pressure, and surface force, or by chemical means, although very few chemical agents are used in this connection in the food field. Gel-type solutions are usually beaten before they become too thick or firmly set. As air is incorporated, the volume increases and the firmness of the gel stabilizer sets the foam. 

Mechanical forces, such as shearing, shaking, and pressure, may also denature proteins [44,45], Shaking proteins may lead to inactivation owing to an increase in the area of the gas/liquid interface. At the interface, the protein unfolds and maximizes exposure of hydrophobic residues to the air. Surface denaturation may also occur at the protein/container interface and has been observed following adsorption of proteins to filter materials [46]. 

However, liquids that are commonly used, e.g., alka-nols, may dissolve and denature the actives such as macromolecules. The recent discovery of fluorocarbon (EC) liquids including perfluorodecalin and perfluoro-octyl bromide as alternatives may be useful because they are hydrophobic and do not dissolve proteins. In addition, EC has a low surface tension relatively weak bonds are expected to form between the fine particles of the loose agglomerates, which can be then redispersed readily as an aerosol. The high vapor pressure of EC renders low solvent residue in the final product. Fluorocarbon does not contain chlorine atoms, and is therefore ozone friendly. 

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