Clustering of oil droplets in o/w emulsions: Controlling cluster size and interaction strength.

Philipp L Fuhrmann,Markus Stieger,Guido Sala,Elke Scholten

doi:10.1016/j.foodres.2019.04.027

Philipp L Fuhrmann, Markus Stieger + Show 2 more

Open Access

https://doi.org/10.1016/j.foodres.2019.04.027

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Abstract

Clustering of oil droplets changes the rheological properties of oil-in-water (o/w) emulsions and can be used as a tool to structure foods. The aim of this study was to manipulate both oil droplet cluster size and cluster strength in liquid o/w emulsions, and to investigate the effect of these parameters on the rheological properties. Clustered emulsions were prepared using three different methods: (i) clustering by protein-proanthocyanidin interactions, (ii) clustering by hetero-aggregation of oppositely-charged emulsion droplets, and (iii) enzymatic clustering of protein-stabilised droplets using transglutaminase. Clustering by protein-proanthocyanidin interactions allowed to control oil droplet cluster size from 1 to 140 μm. Clusters decreased in size upon both an increase and decrease in pH, but were stable against changes in ionic strength. Hetero-aggregation of oppositely-charged oil droplets (gelatine/whey protein and gelatine/DATEM) allowed to control cluster size from 1 to 40 μm. Clusters showed a strong decrease in size in response to changes in pH and a small decrease in size with increasing ionic strength. Enzymatic clustering did not allow to control cluster size. Cluster strength of proanthocyanidin-stabilised clusters was found to be higher than that of hetero-aggregated clusters. Stabilisation of clusters was likely induced by different protein-proanthocyanidin interactions such as H-bridges, π-π stacking, and hydrophobic interactions, whereas hetero-aggregation is based on electrostatic interactions. Upon clustering, emulsion viscosity increased by up to three orders of magnitude. We conclude that protein-proanthocyanidin interactions and hetero-aggregation are effective methods to tune droplet cluster size and strength in o/w emulsions, and that cluster size and interaction strength control the rheological properties of o/w emulsions with clustered oil droplets.

Highlights

Fat is an essential ingredient of many foods, such as milk, yogurt, and mayonnaise
Grape seed extract (%w/w protein) stabilised o/w emulsions varying in oil content
Bohin et al (2012, 2014) argued that complexation of β-lactoglobulin with proanthocyanidins is based on an extended hydrogen bond network. We suggest that such interactions are responsible for the clustering of WPI-stabilised o/w emulsion droplets by proanthocyanidins present in grape seed extract since WPI contains β-lactoglobulin as the main constituent

Summary

Introduction

Fat composition and oil droplet size largely influence the rheological properties of emulsions and have a large effect on sensory perception of o/w emulsion-based foods. A critical parameter for the rheological properties of o/w emulsions is the spatial distribution of oil droplets (Mao & McClements, 2012b; Mosca, Rocha, Sala, van de Velde, & Stieger, 2012; Sala, van Vliet, Cohen Stuart, van Aken, & van de Velde, 2009). Clustering of oil droplets has been shown to cause significant changes in the rheological properties of liquid emulsions (Mao & McClements, 2011). The entrapment of continuous aqueous phase in the oil droplet cluster causes a strong increase in viscosity in liquid systems, since the effective volume fraction of the oil phase increases to a large extent McClements (2012).

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