Stability of casein micelles cross-linked with genipin: a physicochemical study as a function of pH

TL;DR

This study investigates how genipin cross-linking enhances the stability of casein micelles across different pH levels, especially against heat and ethanol, revealing increased stability due to chemical modification.

Contribution

It provides a comparative physicochemical analysis of native and genipin-cross-linked casein micelles as a function of pH, highlighting the stabilizing effect of genipin cross-linking.

Findings

Genipin cross-linking shifts the precipitation pH range of casein micelles.

Cross-linked micelles show increased stability against heat and ethanol.

Maximum stability observed at pH 2 for cross-linked micelles.

Abstract

Chemical or enzymatic cross-linking of casein micelles (CMs) increases their stability against dissociating agents. In this paper, a comparative study of stability between native CMs and CMs cross-linked with genipin (CMs-GP) as a function of pH is described. Stability to temperature and ethanol were investigated in the pH range 2.0-7.0. The size and the charge ($\zeta$-potential) of the particles were determined by dynamic light scattering. Native CMs precipitated below pH 5.5, CMs-GP precipitated from pH 3.5 to 4.5, whereas no precipitation was observed at pH 2.0-3.0 or pH 4.5-7.0. The isoelectric point of CMs-GP was determined to be pH 3.7. Highest stability against heat and ethanol was observed for CMs-GP at pH 2, where visible coagulation was determined only after 800 s at 140 $^\circ$C or 87.5% (v/v) of ethanol. These results confirmed the hypothesis that cross-linking by GP increased the stability of CMs.