Structure of acid casein gels : a study of gels formed after acidification in the cold

P.F.M. Roefs

    Research output: Thesisinternal PhD, WU

    Abstract

    <p>The structure of acid casein gels was studied by rheology, permeametry, electron microscopy and pulse NMR. Gels were mainly formed by heating at rest of casein solutions acidified in the cold (0- 2 °C). The structure of such gels involves both the spatial distribution of the structural elements and the interaction forces between them. An acid casein gel has an irregular particulate structure. Gelation results from the aggregation of casein particles, which themselves have a complex internal structure due to the association of numerous different casein molecules. Dense areas of coagulated particles are separated by large pores. Gelation at pH=4.6 appears to be subject to an activation Helmholtz energy, which is largely due to the stabilizing effect of the glycomacropeptide part of K-casein. At ageing temperatures above 283 K, the dynamic moduli G' and G'' linearly increase with the logarithm of time. Their absolute values primarily depend on the heterogeneity of the network. The moduli decrease with increasing time scale of measurement. From the effect of variation of experimental conditions (pH, ageing and measuring temperatures, ionic strength and ionic composition) it may be concluded that electrostatic interactions and hydrophobic bonding are involved in keeping the network together. Moreover, Van der Waals attraction, steric interactions and possibly hydrogen bonds may play a part. Differences in the internal structure of the casein particles appear to be paramount in determining differences in the number and character of the interparticle bonds; this was in agreement with results on the spin-spin relaxation time of water protons. Addition of rennet enables gel formation in a much broader range of temperature and pH; the character of the gels changes considerably around pH=5.2.
    Original languageEnglish
    QualificationDoctor of Philosophy
    Awarding Institution
    Supervisors/Advisors
    • Prins, A., Promotor
    • van Vliet, T., Promotor, External person
    Award date11 Apr 1986
    Place of PublicationWageningen
    Publisher
    Publication statusPublished - 1986

    Keywords

    • animal products
    • gels
    • milk proteins
    • tenderness
    • texture

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