Small and Large Deformation Rheology of Acid Gels from Transglutaminase Treated Milks

Abstract

The purpose of this study was to evaluate the effects of microbial transglutaminase on the rheological and mechanical properties of gels from a commercial UHT milk made by acidification with D-gluconic-acid-δ-lactone. Although further heating of UHT milk, primarily carried out to inactivate the enzyme, showed a significant impact on gel firmness, we observed no enzyme-related effects at small deformation. The impact of the additional thermal treatment was also evident in large deformation measurements. In these experiments, gels from enzyme-treated milk revealed much higher elasticity and rupture force. Prolonged incubation time or increased enzyme concentration resulted in lower gel firmness (small deformation), indicating a reduced number of total bonds as a result of the restriction of proper rearrangements during acidification. Large deformation measurements revealed a heat-induced amplification of this effect, i.e., lower rupture forces at almost constant elasticity levels. In gels from milk, which was not subjected to thermal enzyme inactivation, we observed a further increase in both parameters. This is presumably caused by a combination of residual enzyme activity and of additional substrate, liberated during acidification.

Structure and stability of nanogel particles prepared by internal cross-linking of casein micelles

“…3A). Similar results were reported by Schorsch, Carrie, and Norton (2000), while others (Anema, Lauber, Lee, Henle, & Klostermeyer, 2005;Jaros, Patzold, Schwarzenbolz, & Rohm, 2006b;Lauber, Henle, & Klostermeyer, 2000;Lorenzen, Mautner, & Schlimme, 1999) have observed that pre-treatment of milk with TGase yields firmer acid milk gels. The mechanism for the TGaseinduced increase in acid-flocculation pH has not been elucidated thus far.…”

Excessive cross-linking of caseins by microbial transglutaminase and its impact on physical properties of acidified milk gels

“…Measurements were started within 1 min after addition of GDL. During gelation a strain of 0.003, low enough to ensure undisturbed gelation (Jaros et al, 2006b), was applied at a frequency of 1 rad s À1 . Storage modulus, G 0 (Pa) and loss tangent, tan d (À), were monitored as a function of time.…”

“…In several studies on whole or skim milk, the action of mTGase has been controlled by inactivation through heating (e.g., Anema, Lauber, Lee, Henle, & Klostermeyer, 2005;Jaros, Pä tzold, Schwarzenbolz, & Rohm, 2006b;Lauber et al, 2000;Sharma, Lorenzen, & Qvist, 2001). As the heat-induced denaturation of whey proteins also contributes to the rheological properties of acid milk gels, a careful design of the experiments is necessary to allow a causal assignment of the observed effects (Jaros et al, 2006a).…”

Structural mechanisms leading to improved water retention in acid milk gels by use of transglutaminase

“…Modification of the protein matrix, which is mainly formed of weak physical interactions, directly by introducing strong covalent bonds within or between protein particles is one method to improve structural properties of skim milk gels. Use of transglutaminase (TG), a transferase which creates (g-glutamyl)-lysine isopeptide linkages (Folk & Finlayson, 1977;Griffin, Casadio, & Bergamini, 2002), for that purpose has been extensively studied and reviewed Jaros, Partschefeld, Henle, & Rohm, 2006;Ozrenk, 2006). We have previously shown the effects of TG on texture and microstructure of acid-induced skim milk gels with the emphasis on the effect of pre-heat treatment (Ercili Cura et al, 2010).…”