Abstract

Pickering o/w emulsions prepared with 40 wt % rapeseed oil were stabilized with the use of low charged enzymatically treated cellulose nanofibrils (CNFs) and highly charged 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized CNFs. The emulsion-forming abilities and storage stability of the two qualities were tested in the presence of NaCl and acetic acid, at concentrations relevant to food applications. Food emulsions may be an important future application area for CNFs due to their availability and excellent viscosifying abilities. The emulsion characterization was carried out by visual inspection, light microscopy, viscosity measurements, dynamic light scattering and mild centrifugation, which showed that stable emulsions could be obtained for both CNF qualities in the absence of salt and acid. In addition, the enzymatically stabilized CNFs were able to stabilize emulsions in the presence of acid and NaCl, with little change in the appearance or droplet size distribution over one month of storage at room temperature. The work showed that enzymatically treated CNFs could be suitable for use in food systems where NaCl and acid are present, while the more highly charged TEMPO-CNFs might be more suited for other applications, where they can contribute to a high emulsion viscosity even at low concentrations.

Highlights

  • Emulsions, systems where droplets of one immiscible liquid are dispersed in another liquid, are important in many different applications, ranging from oil recovery, via cosmetics and pharmaceuticals, to food applications

  • Another way of stabilizing emulsions is with solid particles, giving rise to what is known as Pickering emulsions [4,5]

  • Gestranius et al [13] reported that centrifugation of emulsions stabilized with mechanically fibrillated cellulose nanofibrils (CNFs) or TEMPO-oxidized CNFs, led to denser packing of the oil droplets in the already existing creaming layer, and there was some free oil at the top of the emulsions, indicating coalescence of some of the oil droplets

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Summary

Introduction

Systems where droplets of one immiscible liquid are dispersed in another liquid, are important in many different applications, ranging from oil recovery, via cosmetics and pharmaceuticals, to food applications. Gestranius et al [13] reported that centrifugation of emulsions stabilized with mechanically fibrillated CNFs or TEMPO-oxidized CNFs, led to denser packing of the oil droplets in the already existing creaming layer, and there was some free oil at the top of the emulsions, indicating coalescence of some of the oil droplets. Comparing emulsions stabilized by CNFs and CNCs, the CNC stabilization allows for the formation of smaller droplets, as the shorter CNCs can accommodate a larger curvature of the oil droplets [12,16,23] These emulsions may be more vulnerable to coalescence, high shear and temperature, as they do not have the same ability as CNFs to form strong networks in the continuous phase [13]. Stable emulsions in the absence of salt and acid were obtained for both CNF qualities, and the enzymatically stabilized CNFs were able to stabilize emulsions in the presence of acid and NaCl

Materials
Characterization of Rapeseed Oil
Characterization of CNF Film
Characterization of CNF Samples
Visual Stability
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