Protein constitutes an indispensable part of the diets of many people. It is not only used for its nutritional value but also imparts desirable texture and stabilisation to foods. For instance, in fat-containing products, the fat must remain stabilized over the entire shelf life of the product, so that no phase separation occurs.
To this end, emulsifying agents are utilised, that provide a stabilization of the emulsion once formed, based on their inherent property of a lipophilic or hydrophobic part being soluble in the non-aqueous phase and a polar or hydrophilic part being soluble in water such that said molecules facilitate emulsifying one phase in the other phase. Additionally, the emulsifying agents also protect the once formed droplets from aggregation and coalescence. As emulsifying agents naturally occurring substances are used, such as hydrocolloids, phospholipids (lecithin) or glycolipids and on the other hand synthetic agents like stearyl-2-lactylate or mono-, diacylglycerides, etc. may also be used.
One of the major drawbacks of the agents resides in that they sometimes substantially add to the costs of the final product, and do not add to the nutritional value of the product. Sometimes, such kinds of materials also do not show adequate stabilising properties because of an interfacial competition with proteins.
Increasingly, therefore, protein is also being used as an emulsifier and as a partial substitute for fat.
U.S. Pat. No. 6,767,575 B1 discloses a preparation of an aggregate whey protein product, whereby whey protein is denatured by acidification and heating. The protein aggregates thus obtained are used in food application.
GB 1079604 describes improvements in the manufacture of cheese, whereby whey proteins undergo heat treatment at an optimum pH value, in order to obtain insoluble whey proteins which are then added to raw milk.
WO 93/07761 is concerned with the provision of a dry microparticulated protein product which can be used as a fat substitute.
U.S. Pat. No. 5,750,183 discloses a process for producing proteinaceous microparticles which are useful as fat substitute containing no fat.
A proteinaceous fat substitute is also disclosed in WO 91/17665 whereby the proteins are in the form of a water-dispersible microparticulated denatured whey protein.
Apart from the food applications, proteins are also present in many pharmaceutical and cosmetic compositions.
One of the problems encountered with the production of products containing globular proteins in general, and whey protein in particular, however is their limited processability in industrial food production. Indeed, protein molecules when heated, or when subjected to acidic or alkaline environment or in the presence of salts tend to lose their native structure and reassemble in various random structures such as gels, for example.
The preparation of gelled aqueous compositions of whey proteins is the subject of EP 1281322.
Elofsson et al. in International Dairy Journal, 1997, p. 601-608 describe cold gelling of whey protein concentrates.
Similarly, Kilara et al. in Journal of Agriculture and Food 20 Chemistry, 1998, p. 1830-1835 describes the effect of pH on the aggregation of whey proteins and their gelation.
This gel effect presents limitation in terms of not only processability (e.g. clogging of machines used in the manufacture of protein-containing products) but also in terms of the texture thus obtained, which may not be desirable for the wide range of protein applications.
Controlled denaturation of proteins is thus desirable in order to widen the use of proteins.
In the Proceedings of the Second International Whey Conference, Chicago, October 1997, reported in International Dairy Federation, 1998, 189-196, Britten M. discusses heat treatments to improve functional properties of whey proteins. A process for producing whey protein micro-particle dispersion at 95° C. is described.
Erdman in Journal of American College of Nutrition, 1990, p. 398-409 describes that the quality of microparticulated protein is not affected despite using high shear and heat.
EP 0603981 also describes a heat stable oil-in-water emulsion containing proteins.
Sato et al. in U.S. Pat. No. 5,882,705 obtained micellar whey protein by heat treating a hydrolysed whey protein solution. The micellar whey protein are characterised by an irregular shape.
Thus, an object of the invention is to improve the usability of proteins in industrial production processes.