Engineering Emulsion Gels as Functional Colloids Emphasizing Food Applications: A Review

Abstract

Gels are functional materials with well-defined structures (three-dimensional networks) assembled from the dispersed colloids, and capable of containing a large amount of water, oil, or air (by replacing the liquid within the gel pores), known as a hydrogel, oleogel, and aerogel, respectively. An emulsion gel is a gelled matrix filled with emulsion dispersion in which at least one phase, either continuous phase or dispersed phase forms spatial networks leading to the formation of a semisolid texture. Recently, the interest in the application of gels as functional colloids has attracted great attention in the food industry due to their tunable morphology and microstructure, promising physicochemical, mechanical, and functional properties, and superior stability, as well as controlled release, features for the encapsulated bioactive compounds. This article covers recent research progress on functional colloids (emulsion gels), including their fabrication, classification (protein-, polysaccharide-, and mixed emulsion gels), and properties specifically those related to the gel-body interactions (texture perception, digestion, and absorption), and industrial applications. The emerging applications, including encapsulation and controlled release, texture design and modification, fat replacement, and probiotics delivery are summarized. A summary of future perspectives to promote emulsion gels' use as functional colloids and delivery systems for scouting potential new applications in the food industry is also proposed. Emulsion gels are promising colloids being used to tailor breakdown behavior and sensory perception of food, as well as for the processing, transportation, and targeted release of food additives, functional ingredients, and bioactive substances with flexibility in designing structural and functional parameters.

Keywords: biopolymer-based colloids; delivery systems; emulsion gels; food applications; functional material; gel-body interactions.

Figure 1

Schematic representation of different types of emulsion gels; oil/hydrogel (A), oleogel/water (B), water/oleogel (C), hydrogel/oil (D), water/oil/hydrogel (E), water/oleogel/water (F), hydrogel/oil/water (G), oil/water/oleogel (H), oil/hydrogel/oil (I), and oleogel/water/oil (J).

Figure 2

Publications per year during the last 10 years (2011-2021) were analyzed by “Sci-finder” using “emulsion gel” as the keyword for searching.

Figure 3

An overview of emulsion gels, indicating their classification, gel-body interactions (texture perception, digestion, and absorption), and emerging industrial food applications.

Figure 4

Optical microscopic image and visual appearances of emulsion gels; (A) Emulsion dispersion droplets, (B) Blank emulsion gel, and (C) Epigallocatechin-3-gallate and quercetin co-loaded emulsion gel. The formed gel showed an encapsulation efficiency of 65.5 and 97.2%, whereas enhanced the bioaccessibility by 48.4 and 49% for (-)-epigallocatechin-3-gallate and quercetin, respectively. In addition, emulsion gel showed lower release rates of 73.3 and 31.7% and improved stability by 63.6 and 82.3% for epigallocatechin-3-gallate and quercetin after 8-h incubation in specific environmental conditions (simulated intestinal fluid) and remained stable to phase separation during 30-days storage at 4°C (D) (103).

Figure 5

Emerging industrial food applications of emulsion gels (emulgels).