Interfacial characteristics, colloidal properties and storage stability of dairy protein-stabilized emulsion as a function of heating and homogenization.

Quanyang Li,Zhengtao Zhao

doi:10.1039/d0ra00677g

Abstract

This research investigated the influence of processing history on physicochemical properties of dairy protein-stabilized emulsions. Emulsions were heated (UHT) either before or after a single homogenization (UHTSH, SHUHT) or homogenized both before and after heating (double homogenization, DHUHT). The results demonstrated that UHT treatment increased the protein load at the oil/water interface while homogenization prior to UHT (SHUHT) inhibited displacement of protein by surfactant molecules, and this emulsion exhibited higher interfacial protein coverage and wider size distribution compared to the emulsion produced by UHTSH. The use of the double homogenization with UHT resulted in emulsion droplets with the smallest average size and lowest concentration of unabsorbed protein. However, no difference in the protein load in a specific area was noticed between emulsions produced by DHUHT and SHUHT. When changes of surface tension at the air/water interface were measured using a drop tensiometer, SHUHT emulsion showed the fastest decrease of surface tension due to the occurrence of a lower level of surfactant displacement where more surfactant was available for fast adsorption. Emulsions prepared with DHUHT or UHTSH decreased the surface tension in a slower speed than SHUHT. During storage, partial coalescence of emulsion droplets was observed for emulsions produced with single homogenization, regardless of whether this was carried out before or after heating. Double homogenization formed more stable emulsions than single homogenization. This work clearly showed that it is possible to tailor physico-chemical functionalities of dairy protein-based emulsions by controlling the interactions between proteins or with surfactants during processing.

Highlights

The physico-chemical properties of dairy protein-based emulsions are critical to the stability, functionality and nal structure of dairy products
Proteins with compact structures have poorer surface activity and emulsifying capacity than the ones with a more disordered structure. Milk proteins, such as caseins are o en used as emulsi ers as they have speci c hydrophobic and hydrophilic regions which facilitate protein adsorption at the interface, and allow for areas to protrude in the aqueous phase causing increased electrostatic and steric stabilization.[7,8]
UHT treatment shi ed the peak to smaller size direction due to exposure of buried hydrophobic residues a er heat treatment, for whey proteins which were globular and susceptible to heating the amount of whey proteins (0.1%) was much lower than caseins (0.9%).[7,20]

Summary

Introduction

The physico-chemical properties of dairy protein-based emulsions are critical to the stability, functionality and nal structure of dairy products. During the preparation of emulsions, protein molecules adsorb onto the surface of oil droplets, providing the steric and electrostatic repulsion forces necessary to prevent their aggregation.[5] The structure of protein molecules and their assembly, as well as the overall composition of the interface, determine the thickness of the lm and the stability of droplets.[6] Proteins with compact structures have poorer surface activity and emulsifying capacity than the ones with a more disordered structure Milk proteins, such as caseins are o en used as emulsi ers as they have speci c hydrophobic and hydrophilic regions which facilitate protein adsorption at the interface, and allow for areas to protrude in the aqueous phase causing increased electrostatic and steric stabilization.[7,8]

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Conclusion