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Improving milk protein functionality by treatment with transglutaminase.

The functional properties of milk proteins determine many physicochemical physicochemical /phys·i·co·chem·i·cal/ (fiz?i-ko-kem´ik-il) pertaining to both physics and chemistry.

phys·i·co·chem·i·cal
adj.
1. Relating to both physical and chemical properties.
 properties of dairy products, such as the texture of cheese, the viscosity of yogurt or the stability of milk to heat treatment. In addition, milk protein ingredients are used in a wide variety of other foods, e.g., clinical and infant foods, bakery products and beverages, where they provide desirable functionalities such as nutrition, emulsification, water-binding and stabilization.

The main fraction of milk proteins, the caseins, occurs in milk as sterically-stabilized association colloids, called casein casein (kā`sēn), well-defined group of proteins found in milk, constituting about 80% of the proteins in cow's milk, but only 40% in human milk.  micelles. They have a diameter of about 200 nm. It is the purposely induced destabilization of casein micelles that leads to the formation of a yogurt gel or a cheese curd curd

the proteinaceous part of milk precipitated by rennin. Usually contains some fat when whole milk is used.
 or the first step in the isolation of the casein fraction for production of caseins or caseinates.

Recent research has shown that treating caseins with the enzyme transglutaminase, which catalyses the formation of covalent co·va·lent
adj.
Of or relating to a chemical bond characterized by one or more pairs of shared electrons.
 cross-links between proteins, can considerably improve the functional properties of milk proteins. Transglutaminase cross-links both caseins on the micelle micelle (mīsel´),
n a space formed by the brush structure of fibrils in colloidal gels. The spaces are occupied by water in hydrocolloid impressions.
 surface as well as those in the core of the micelles. As a result of these cross-linking reactions, the stability of casein micelles against acid-induced coagulation coagulation (kōăg'ylā`shən), the collecting into a mass of minute particles of a solid dispersed throughout a liquid (a sol), usually followed by the precipitation or  is reduced, leading to firmer yogurt gels.

Transglutaminase treatment of milk prior to yogurt manufacture can be used to improve the texture and reduce syneresis syneresis /syn·er·e·sis/ (si-ner´e-sis) a drawing together of the particles of the dispersed phase of a gel, with separation of some of the disperse medium and shrinkage of the gel.

syn·er·e·sis
n.
 of particularly reduced-fat yogurt products. In addition, treatment with transglutaminase can also help in saving ingredient costs by reducing the amount of protein required to create a desirable texture, firmness and stability of yogurt. Current work at NIZO food research is aimed at the creating novel milk protein ingredients for such tailored uses.

Furthermore, transglutaminase-treated casein micelles are less susceptible to enzyme-induced coagulation than their untreated counterparts, and extensive cross-linking even makes them unrennetable. This aspect is naturally undesirable for cheese-making; however, it can be beneficial in ultra-high temperature-treated milk products, in which the proteolytic pro·te·o·lyt·ic
adj.
Relating to, characterized by, or promoting proteolysis.


proteolytic (pro″teolit´ik),
adj
 degradation of caseins contributes to age-gelation during storage. For other types of cheese, e.g., cream cheese, treatment with transglutaminase can be used to increase product yield and increase viscosity and reduce syneresis of the product. Opportunities for using transglutaminase to design ingredients for reduced-fat and/or reduced-protein processed cheese products also exist.

Caseins in transglutaminase-treated micelles are less susceptible to dissociation. Hence, for products in which casein dissociation has been implicated as a major culprit in inducing instability, such as in concentrated or evaporated milk proteins, treatment with transglutaminase can improve product stability. Also, cross-linking milk proteins on the milk fat globule globule /glob·ule/ (glob´ul)
1. a small spherical mass or body.

2. a small spherical drop of fluid or semifluid substance.

3. a little globe or pellet, as of medicine.
 membrane can increase the stability of these globules against coalescence coalescence /co·a·les·cence/ (ko?ah-les´ens) the fusion or blending of parts.

co·a·les·cence
n.
See concrescence.



coalescence

a fusion or blending of parts.
 when cream-based products are in storage.

Besides using transglutaminase in traditional dairy products, efforts to prepare novel dairy ingredients, such as caseins or caseinates, with tailor-made stability and functionality through the enzymatic cross-linking of milk proteins, are currently underway at NIZO food research. These novel ingredients can potentially open new areas for the application of milk proteins.

Further information. Thom Huppertz, NIZO Food Research BV, P.O. Box 20, 6710 BA Ede, The Netherlands; phone: +31(0)318 659 600; fax: +31(0)318 650 400; email: Thom.Huppertz@nizo.nl.
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Publication:Emerging Food R&D Report
Date:Jan 1, 2009
Words:518
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