Food or edible material: processes – compositions – and products – Fermentation processes – Of milk or milk product
Reexamination Certificate
2000-12-04
2003-05-06
Smith, Lynette R. F. (Department: 1645)
Food or edible material: processes, compositions, and products
Fermentation processes
Of milk or milk product
C426S034000, C514S012200, C530S360000, C530S366000, C530S414000, C435S272000
Reexamination Certificate
active
06558717
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for isolation of casein and calcium phosphate from a milk source.
BACKGROUND OF THE INVENTION
The recovery of proteins usually requires auxiliary materials to separate and purify the protein. The separation of proteins can be a complex task which may involve several unit operations and consume substantial amounts of auxiliary compounds like acids and bases, that are released as a by-product in the form of salts. In the precipitation of food proteins, this is a considerable environmental burden, due to the large volumes processed.
A number of food proteins, particularly casein and soy protein, are isolated in large volumes by isoelectric precipitation at pH values of 4.5-4.8, using mineral acids such as hydrochloric or sulfuric acid. It is estimated that food protein precipitation processes like this lead to a waste stream of salts of approximately 64 kilotons per year in Europe alone.
In addition to acid precipitation (acid casein) casein can be isolated by enzymatic treatment (rennet casein). Lactic acid fermentation is another well-known option. Organic acids have been used as well, but are nowadays less common. Most of the acid casein is converted to sodium, potassium, magnesium, or ammonium caseinates, depending on the application.
Casein is not a single protein but a group of proteins, comprising four major fractions: &agr;
s1
casein, &agr;
s2
casein, &bgr; casein, and &kgr; casein. They have in common an isoelectric point around pH 4.6. Besides casein, skimmed milk contains a large amount of lactose, the whey proteins among which &agr;-lactalbumin and &bgr;-lactoglobulin, certain peptides, salts like calcium phosphate, and several minor components.
Although we are not bound here to a particular theory regarding the structure of a casein micelle, there is a model as described by Walstra and Jenness. Dairy Chemistry and Physics; Marcel Dekker; New York (1994) that is very illustrative. Casein molecules associate into casein micelles, aggregates of 20-200 nm. A schematic representation of the structure is shown in FIG.
1
. Within these casein micelles 10 even smaller structures can be identified, so-called sub-micelles
12
(10-20 nm), which are held together by colloidal “bridges”
14
of calcium phosphate connecting phosphatized serine groups in the proteins. Protruding chains
16
are bound to the surfaces of the submicelles
12
. Besides calcium phosphate, also other components are involved in these bridges
14
, among which are magnesium and citrate. Conversely, calcium is not only bound to the protein via these bridges but also by association with negatively charged groups, along with other cations. During acid precipitation, the calcium phosphate dissolves, as a consequence of which the bridges are broken and the micelle structure is lost. In addition, associated cations are exchanged for protons. For manufacturers of casein, it is important that the dissolution and ion exchange are complete, so that the final product, the caseinate of concern, does not contain residual calcium and phosphate, which strongly influence functional properties, such as emulsifying and water binding properties, and viscosity.
Instead of mineral acids, a volatile acid as carbon dioxide can be used, with the advantage of being easily removed by pressure release. Isoelectric precipitation of proteins with carbon dioxide is thus an alternative to conventional acid precipitation as to reduce the amount of inorganic acids and bases used in recovery processes of food- and biochemicals; like casein. However, also here relatively high calcium concentrations are found in the casein end product (Jordan et al., N.Z.J. Dairy Sci. Technol. 22, 247-256 (1987); Tomasula et al., J. Dairy Sci. 78, 506-514 (1995); and Tomasula et al., J. Food Eng. 33, 405-419 (1997)). Furthermore, the functional properties thereof differ from conventional acid casein (Strange et al., J. Dairy Sci. 81, 1517-1524 (1998)).
Besides casein, another component from milk, calcium phosphate, is a highly appreciated ingredient in many calcium enriched food products, since it is derived from a natural dairy source. It is therefore desirable to also be able to obtain calcium phosphate from milk in a substantially pure form.
OBJECT OF THE INVENTION
In view of the above, it is the object of the present invention to provide a method for preparing casein from a milk source while using a lower amount of inorganic acids and bases than used in conventional casein recovery processes, in which method the casein after isolation does not comprise a considerable amount of calcium phosphate. It is a further object of the invention to provide a means for (re)crystallizing weak electrolytes in general and calcium phosphate in particular, in a controlled manner without adding auxiliary compounds.
SUMMARY OF THE INVENTION
The above defined objects are achieved according to the invention by a method for isolating casein and calcium phosphate as separate products from a milk source, comprising the steps of:
a) contacting the milk source with carbon dioxide under pressure in order to precipitate the casein;
b) separating the casein from the milk source while maintaining the pressure to obtain a casein fraction and a whey fraction;
c) releasing the pressure from the whey fraction to allow calcium phosphate to precipitate therefrom.
REFERENCES:
patent: 4519945 (1985-05-01), Ottenhof
Fluka Chemical Catolog, pp. 318. 320 and 338, 1997/1998.*
Tomasula, P.M. et al., “Preparation of Casein Using Carbon Dioxide”, Journal of Dairy Science, vol. 78, pp. 506-514, 1995.*
Gevaudan, S. et al., “Effects of Treatment by Gaseous Carbon Dioxide on the Colloidal Phase of Skim Milk”, Journal of Dairy Science, vol. 79, pp. 1713-1721, 1996.*
Hofland et al., “ Isoelectric Precipitation of Casein Using High- Pressure CO2”, Industrial & Engineering Chemistry Research vol. 38, No. 12, pp. 4919-4927, 1999.*
de la Fuente “ Changes in the mineral balance of milk submitted to technologiacl treatment”, Trends in Food Science & Technology, vol. 9, pp. 281-288, 1998.
Hofland Gerard Willem
Köllmann Clemens Johannes Willibrordus
Van Der Wielen Lucas Antonius Maria
Witkamp Geert-Jan
Campina B.V.
Shahnan-Shah Khatol
Smith Lynette R. F.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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