Advances in food emulsions and foams: reflections on research in the neo-Pickering era

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Highlights

  • Noteworthy research activity in encapsulation, delivery systems, and digestion.

  • Increasing emphasis on plant-based biopolymers as emulsifiers and stabilizers.

  • Significant progress in Pickering stabilization of aqueous and oil-based foams.

  • Novel developments in Pickering stabilization of water-in-water emulsions.

Current trends in the field of food emulsions and foams are outlined. Pickering stabilization of multiphase systems by biopolymer-based particles is a prominent area of ongoing research. This report focuses attention on two classes of dispersed systems where noteworthy recent advances have been reported: (i) bubbles and foams, and (ii) water-in-water emulsions.

Introduction

The colloid science approach to food system formulation is based on the premise that basic physical attributes such as appearance, texture and stability are determined by the intrinsic properties of the system’s molecular and colloidal entities organized in different kinds of structural arrangements. Amongst the most commonly encountered dispersed entities are liquid droplets and gas bubbles. Hence, the study of emulsions and foams remains a prominent area of food-related research activity. Quantitative evidence of the intensity of this activity can be seen in the results of a simple search of journal articles indexed in Web of Science (Core Collection) covering the past five years: more than 3000 publications are generated with the search topic ‘food emulsions’ and around 1000 with ‘food foams’. One obvious consequence of the large number of relevant publications is that any concise overview of recent advances has to be extremely selective in terms of scope and emphasis.

The dictionary definition of ‘advance’ is ‘to move something forward’ or ‘to develop or improve something’. Hence the author of this review has the challenge of deciding what this means in the context of food colloids. One assumes that a big leap forward should not be too difficult to identify. The discovery of a new phenomenon would come into this category. So would the development of a novel method of colloidal characterization or an enhanced theoretical understanding of an already established phenomenon. However, outstandingly obvious advances like these are quite rare in a mature field like food colloids. Much more commonly encountered are the wide-ranging reports of multi-phase systems prepared with specific food-grade materials. Typically these systems are investigated systematically using a range of modern experimental techniques, thereby providing data on emulsion or foam stability that can be explained satisfactorily using established theoretical concepts. Of particular interest to many investigators is the study of unusual natural ingredients with previously unexplored emulsifying/foaming properties. In justification of this research, these less familiar stabilizing agents are promoted as having substantial advantages over traditional ingredients in terms of cost, availability, sustainability, or perceived health benefits. Also frequently encountered are publications reporting investigations of the functional properties of individual or mixed ingredients that have been subjected to traditional or novel methods of processing — physical, chemical or biochemical. There is little doubt that the accumulated insight from these diverse interconnected studies makes a very worthwhile contribution to the steady systematic development of our subject area. Nevertheless, many of these reports have to be regarded as essentially incremental in nature: for the purposes of this review, they are not considered to be advances in the strictest sense of the word.

Section snippets

Some current trends

A subjective impression of the major current trends in food emulsions and foams is presented in Table 1. The different topics are categorized in terms of the perceived levels of research activity. A key driver of ongoing activity relates to the formulation and development of colloidal structures for the encapsulation and delivery of nutrients and bioactives [1]. One major practical challenge is to encapsulate water-insoluble lipophilic compounds with the objective of enhancing nutrient

Bubbles and foams

The principles and practice of making and stabilizing aqueous foams have been set out by Narsimhan and Xiang [34]. The most recent advances relate to the stabilization of bubbles by biopolymer-based particles [17]. Some of these particles appear to accumulate directly at the air–water interface to form particle-laden monolayers around bubble surfaces. Others inhibit bubble coalescence and foam drainage by structuring themselves into particle-rich regions between adjacent bubble surfaces and

Water-in-water emulsions

Water-in-water (W/W) emulsions occur in aqueous solutions of incompatible polymers exhibiting phase separation. A mixture of protein + polysaccharide is especially susceptible to thermodynamic incompatibility due to the large molecular size of the polysaccharide component and its stronger affinity for water than the protein. Compared to air–water or oil–water interfaces, the water–water interface is more ill-defined: in particular, its spatial scale typically exceeds the correlation length of the

Conflict of interest statement

Nothing declared.

References and recommended reading

Papers of particular interest, published within the period of review, have been highlighted as:

  • • of special interest

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