2003 IRISH SCIENTIST YEAR BOOK

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Teagasc - Dairy Products Research Centre, Moorepark, Fermoy, Co. Cork
Brendan O'Kennedy
The use of Transglutaminase in food products

Heat stability (on re-constitution to 20% solids) of UHT treated skim milk treated with Tgase (at 40�C for 1 hour) followed by enzyme de-activation (78�C for 30 min.).

Tranglutaminases (Tgase) are aminoacyltransferases that catalyse acyl transfer reactions from glutamine residues in proteins to primary amines. When the e-amino group of a lysine residue acts as a substrate, the two residues are covalently linked through an e-(g-glutamyl)lysine bond. The creation of additional covalent bonds within a protein molecule or between two protein molecules can significantly change the resulting texture/ structure of protein containing food products.

Studies carried out at Moorepark suggested that pre-incubation of different food systems with Tgase had significant effects on the subsequent behaviour of the product. Preliminary investigations of Tgase effects on skim milk suggested that intra-micellar cross-linking was not a major occurrence, no change in casein micelle size distribution parameters being observed by Dynamic Light Scattering.

Incubation of skim milk with Tgase after pre-heating at 120�C x 2 minutes and subsequent evaporation and drying resulted in a marked increase in the heat stability of the milk protein, especially at more alkaline pH (> 6.7), when the powder was reconstituted to 20% solids. This was interpreted as an inter-micellar protein crosslinking resulting in an inhibition of casein dissociation at high temperatures (120�C).

The strength of acid gels produced from casein dispersions was dramatically increased when Tgase was present during the slow acidification step. It was concluded that changes in the casein micellar structure during acidification facilitated the cross-linking function of Tgase. When ice-cream formulations were pre-incubated with Tgase, prior to pasteurisation of the mix and subsequent freezing, the melting profile of the frozen ice-cream was variably affected depending on the time of incubation and the enzyme concentration. It was concluded that controlled partial cross-linking of casein aggregates was necessary to enhance this particular attribute in ice-cream.

The water-binding capacity of sodium caseinate, a commodity milk protein ingredient could be increased 5-10 times by judicial treatment of the skim milk prior to processing. This involved close control on the partial cross-linking process. While this work is still ongoing, it was evident that strict control of the degree and type of Tgase-induced protein cross-linking was required to maximise any beneficial effects in food.

Contact: Dr Brendan O'Kennedy; Tel: 025 42446;
E-mail: [email protected]