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Effect of Controlled -Casein Hydrolysis on Rheological Properties of Acid Milk Gels

E. Gastaldi^*, N. Trial^*, C. Guillaume^*, E. Bourret, N. Gontard^* and J. L. Cuq^*

^* Laboratoire de Génie des Procédés et Sciences des Aliments, Université Montpellier II, 34095 Montpellier Cedex 05, France
Laboratorie de Physique Moléculaire et Structurale, Faculté de Pharmacie de Montpellier, 34093 Montpellier Cedex 5, France.

Corresponding author:
E. Gastaldi; e-mail:
gastaldi{at}arpb.univ-montp2.fr.

An experimental method based on the controlled chymosin-induced -casein hydrolysis of milk was proposed to modify micellar reactivity. Milk samples with a degree of -casein hydrolysis of 19, 35, and 51% were obtained. The physicochemical properties of partially converted casein micelles were determined. The net negative charge of casein micelles was reduced with increasing degree of -casein hydrolysis and a small but significant decrease in hydrodynamic diameter and micellar hydration were noted. Dynamic low amplitude oscillatory rheology was used to monitor the rheological properties of acid milk gels (GDL) made with partially chymosin-hydrolyzed milks in comparison with those of strictly acid and rennet gels. An increase in the gelation pH value was observed with increasing the degree of -casein hydrolysis. The moduli values (G' and G'') reached 2 h after the point of gel were, for all degrees of hydrolysis tested, significantly higher than those of strictly rennet and acid gels. Comparison of changes in G'/t with time indicated differences in gel formation that could be related to the increased values of G' obtained for acid gel made with chymosin-treated milk. At a given time after gelation (2 h), increasing the degree of -casein hydrolysis in milk led also to an increase in the loss tangent and the serum holding capacity of acid milk gels suggesting a correlation between these two parameters.

Key Words: -casein hydrolysis • acid milk gel • rheological property • serum-holding capacity

Abbreviation key: CCP = colloidal calcium phosphate, CMP = caseinomacropeptide, DMSO = dimethylsulfoxide, EI = enzyme/inhibitor, ES = enzyme/substrate, GDL = glucono--lactone, tg = gelation time

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