Breakup and Coalescence of Oil Droplets in Protein-Stabilized Emulsions During the Atomization and the Drying Step of a Spray Drying Process

Martha L. Taboada,Doll Chutani,Volker Gaukel,Heike P. Karbstein

doi:10.1007/s11947-021-02606-1

Martha L. Taboada, Doll Chutani + Show 2 more

Open Access

https://doi.org/10.1007/s11947-021-02606-1

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Abstract

The goal of this study was to investigate the changes in oil droplet size in whey protein–stabilized emulsions during the atomization and the subsequent drying step of a spray drying process. For this purpose, experiments were performed in an atomization rig and a pilot spray dryer with two commercial pressure swirl atomizers. By comparing the oil droplet size before atomization, after atomization, and after spray drying, the changes in oil droplet size during each process step were quantified. The effect of oil droplet breakup during atomization was isolated by atomizing emulsions with 1 wt.% oil content and a protein to oil concentration ratio of 0.1. At 100 bar, the Sauter mean diameter of oil droplet size was reduced from 3.13 to 0.61 μm. Directly after breakup, coalescence of the oil droplets was observed for emulsions with a high oil content of 30 wt.%, leading to a droplet size after atomization of 1.15 μm. Increasing the protein to oil concentration ratio to 0.2 reduced coalescence during atomization and oil droplets with a mean diameter of 0.92 μm were obtained. Further coalescence was observed during the drying step: for an oil content of 30 wt.% and a protein to oil concentration ratio of 0.1 the mean droplet size increased to 1.77 μm. Powders produced at high oil contents showed a strong tendency to clump. Comparable effects were observed for a spray drying process with a different nozzle at 250 bar. The results confirm that droplet breakup and coalescence during atomization and coalescence during drying have to be taken into consideration when targeting specific oil droplet sizes in the product. This is relevant for product design in spray drying applications, in which the oil droplet size in the powder or after its redispersion determines product quality and stability.

Highlights

Spray drying of protein-stabilized emulsions is a widely used technique for the production of food powders with encapsulated oily components (Barbosa-Cánovas et al 2005)
We demonstrated that atomization with the widely used pressure swirl atomizers can lead to a breakup of the oil droplets (Taboada et al 2020b)
The results indicate that while the oil droplet size after disruption depends directly on the atomization pressure, coalescence after disruption seems to take place independently of the applied pressure

Summary

Introduction

Spray drying of protein-stabilized emulsions is a widely used technique for the production of food powders with encapsulated oily components (Barbosa-Cánovas et al 2005). Most of the studies found in literature on the spray drying of emulsions focus on the optimization of parameters for the encapsulation of specific functional oils (Aghbashlo et al 2013; Koç et al 2015; Osorio Carmona et al 2018; Ramakrishnan et al 2013; Sanchez-Reinoso and Gutiérrez 2017). In most of these studies, the focus is set on the encapsulation efficiency and not on the changes in the droplet size of the dispersed phase. Knowledge on these phenomena would deepen the process know-how and facilitate product design via spray drying of emulsions

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