METHOD FOR CROSS-LINKING PROTEINS
TECHNICAL FIELD
The present invention relates to a method
for cross-linking proteins for providing modified proteins having improved functionality.
BACKGROUND OF THE INVENTION
Increasing
interest is directed towards modifying proteins to enhance functionality and
thereby add value to the proteins. Protein functionality can be changed by
chemical, physical and enzymatic methods. The advantage of using enzymatic
modification instead of chemical modification is the higher specificity of
enzymatic reactions, thus minimizing the risk of formation of possible toxic
products.
� � � � � � � � � Enzymatic cross-linking has been investigated in some
detail using the enzyme transglutaminase (EC 2.3.2.13). Transglutaminase
catalyzes acyl transfer reactions using peptide-bound glutamine residues as
donors and various primary amines, for example, peptide-bound lysine, as acyl
acceptors (Folk and Finlayson, 1977). The enzyme is thus able to form intra- or
intermolecular έ-(y-glutamyl)-lysine cross-links. Many food proteins are good
substrates for transglutaminase-catalyzed cross-linking, and among the milk
proteins the caseins are especially excellent substrates for transglutaminase
(Ikura et al., 1980; Sakamoto et al., 1994; Traoré and Meunier, 1991, 1992). It
is possible to polymerise the other main part of the milk proteins, the whey
proteins quite extensively using transglutaminase (Færgemand et al., 1997), but
only when the whey proteins are partly unfolded. It is therefore of interest to
investigate other possibilities for cross-linking native whey proteins.
� � � � � � � � � Matheis and Whitaker (1987) have
reviewed various enzymatic reactions that may possibly induce cross-linking in
food proteins and proposed that besides the transglutaminase-catalyzed
reaction, especially oxidative cross-linking, using various oxidoreductases,
should be considered.
Consequently
peroxidase mediated cross-linking may be an alternative to the use of
transglutaminases in protein products, such as dairy products. However, the
addition of hydrogen peroxide may not be acceptable in food applications and
high concentrations of hydrogen peroxide is problematic in e.g. fermented
products due to its inhibiting effect on bacterial growth.
In view of the
above disadvantages there is a need for an improved method for cross-linking
proteins.
An object of
the present invention is to provide a method for preparing a source of protein
to be used in food industry, the method being an improvement over presently known
methods.
A further
object of the present invention is to provide a source of protein to be used in
food industry.
SUMMARY OF THE INVENTION
According to
the invention it has been found that by the use of a combination of a
peroxidase and a carbohydrate oxidase proteins may be cross-linked in a more
efficient and advantageous way.
Thus, the present invention relates to a method for
cross-linking proteins comprising adding to a protein a...