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Conference Poster Year : 2022

Yielding properties of milk gels

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Abstract

Enzymatic and acid-induced milk gels form when the colloidal stability of casein micelles is suppressed by enzymatic proteolysis and lactic acid production by microorganisms, respectively. These gels are then cut during aging to promote syneresis and expulsion of the soluble phase of milk during cheese manufacture, or stirred for yoghurt production. While the rheological properties of milk gels at low strain or stress have been extensively studied, studies reporting on their non-linear properties are rather scarce. However, the ability of these gels to be cut and handled is expected to depend on their non-linear behaviour1. The latter is usually characterized by applying constant stress during creep or step-shear rate tests, respectively. The gel “yielding” is the shear-induced transition from solid to liquid state. During creep experiments, Gibaud et al.2 have proposed that the functional form of the fluidization time as function of the shear stress was a distinctive feature of the yielding scenario. In recent years, non-linear properties of gel and soft materials have also been studied using large angle oscillatory shear (LAOS)3. Upon increasing stress-amplitude, the gel can harden or soften before complete failure which has been referred as strain-hardening or strain-softening, respectively. In this study, we report on the non-linear rheology of an enzymatic milk gel formed at pH 6.6 and compare it to acid-induced dairy gels. As reported for acid-induced caseinate gel4, enzymatic milk gel displayed irreversible failure, being the succession of Andrade’s creep and fracture growth. The slight deviance form the Monkman-Grant relation suggests that enzymatic milk gel yielding involves higher degree of plasticity compare to the acid-induced caseinate gel. Unlike acid-induced milk gels, that display only hardening during stress sweep test, enzymatic milk gel displayed strain-softening and strain-hardening before failure. We investigated the dependence of this non-linear behaviour with the gel aging time and the volume fraction of casein micelles and discussed the possible mechanisms to account for it.
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Dates and versions

hal-03841539 , version 1 (07-11-2022)

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  • HAL Id : hal-03841539 , version 1

Cite

Julien Bauland, Mathieu Leocmach, Marie-Hélène Famelart, Thomas Croguennec. Yielding properties of milk gels. 56ème Congrès du GFR, Oct 2022, Rennes, France. , 2022. ⟨hal-03841539⟩
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