Edible nonaqueous foams: Recent advances in the formation, stabilization, characterization, and applications

Edible nonaqueous foam has emerged as a novel direction for the development of fat-reducing products in recent years. This review critically summarizes the current progress of research on this foam mainly over the past decade. Initially, destabilization mechanisms that hinder its rational design are highlighted. Then, the preparation of nonaqueous foam is discussed, focusing on the types of stabilizers and foam properties. Additionally, the characterization methods of this foam and its applications are discussed. Finally, the gaps in the current research on edible nonaqueous foam and future perspectives are pointed out. Edible nonaqueous foam offers a novel avenue for developing fat replacers while preserving desirable sensory attributes. Moreover, this foam has demonstrated its potential in encapsulating flavor ingredients as well as developing responsive systems, thereby contributing to future advancements in personalized nutrition. This review has the potential to inspire innovative ideas for future research endeavors within the field of foam.

Micromechanical finite element modeling of crystalline lipid-based materials: monoglyceride-based oleogels and their composites

The mechanical properties of crystalline lipid-based materials are dependent on the microscale structure formed during the crystallization process. In this work, we show for the first time that the mechanical properties of such materials can be mathematically calculated by performing 3D mechanistic modeling on the exact microstructure obtained by non-destructive imaging. Initially, we obtained a digital twin of a monoglyceride-based oleogel from phase-contrast X-ray tomography. The microstructure was found to be composed of an interconnected network of crystalline platelets. Then, we applied micromechanical finite element modeling on the microstructure, which revealed that the effective shear modulus scales with the local solid fraction and also depends on the precise crystalline arrangement. Lastly, we designed composite materials in a digital environment by adding particle inclusions to the digital twin. The particle material, concentration and size are varied to demonstrate their effect on the composite's mechanical properties. The designed materials reveal that particle inclusions can either decrease or greatly increase the shear modulus of lipid-based materials. Our new micromechanical approach accelerates the design of lipid-based materials by leveraging virtual environments, leading the path towards materials with tailored mechanical properties.

Impact of Air Bubbles on the Saltiness Perception of NaCl-Loaded Oleogel-Stabilized Water-in-Oil Emulsions

Reducing salt intake without affecting the saltiness perception remains a great challenge for the food industry. Herein, the demulsification of water droplets and air bubbles was controlled to modulate the release of sodium from oleogel-stabilized water-in-oil emulsions (OGEs) stabilized by monoglyceride crystals. The effect of monoglycerides with carbon chain length (glycerol monolaurate-GML, glyceryl monostearate-GMS, and glycerol monopalmitate-GMP) and homogenization methods (hand-shaking or high-speed blender) on sodium release and saltiness was investigated by in vitro and in vivo oral processing tests. Milky-white stable emulsions were formed with both water droplets and air bubbles dispersing in the oil phase, regardless of the selected homogenization methods. Air bubbles were more unstable than water droplets during oral digestion. GML OGEs with more and larger air bubbles and the lowest hardness exhibited the highest sodium release rate and the strongest saltiness, independent of homogenization methods. The balance between air bubbles and water droplets in the GMS and GMP OGEs caused slower sodium release and lower saltiness. Overall, the presence of air bubbles in NaCl-loaded W/O oleogel-based emulsions was shown to have important implications for tailoring their sodium release and saltiness.

Producing superior oleofoams: Unraveling the impact of oil type, surfactant concentration, and production temperature on foam stability and functional characteristics

This study explores the impact of oil type, surfactant concentration, and production temperature on oleofoam properties. Oleofoams were prepared using different concentrations (5, 8, and 10 % w/w) of monoglyceride (MG) in olive, soybean, and sunflower oils at temperatures of 25 °C and 5 °C. The results indicate that higher surfactant concentrations and lower production temperatures enhance the stability, foamability, melting behavior, and hardness of the oleofoams, while minimizing oil drainage. Microscopic analysis reveals that lower production temperatures result in smaller bubble sizes in all oil blends which reduces oil loss and increases the hardness of the oleofoam. Also, oleofoams derived from different oils exhibit solid-like behavior. Among the oils studied, the oleofoam prepared with sunflower oil, at a concentration of 10 % MG and a production temperature of 5 °C, demonstrates superior properties. These findings provide valuable insights into optimizing oleofoam properties by controlling the oil type, surfactant concentration, and production temperature.

Oleofoams: The impact of formulating air-in-oil systems from a lipid oxidation perspective

Air-in-oil foams, or oleofoams, have a great potential for food applications as they can at least partially replace animal or hydrogenated fats, without compromising on textural properties. Yet, there are some challenges to tackle before they can largely be implemented for real-life applications. One of those is the lack of data regarding their oxidative stability. This is an important point to consider, as although using oils rich in polyunsaturated fatty acids (PUFAs) is highly desirable from a nutritional perspective, these fatty acids are particularly prone to oxidation, which leads to major degradations of food quality. This work thus aimed to investigate the oxidative stability of oleofoams prepared with omega-3 PUFA-rich vegetable oils (rapeseed or flaxseed oil) and various types of high melting point lipid-based oleogelators (stearic acid, glyceryl monostearate and stearyl alcohol) when incubated at room temperature. The physical structure and stability of the oleofoams was monitored by various techniques (visual observations, microscopy, DSC, NMR, SAXS and WAXS). Lipid oxidation was assessed by combined measurements of primary (conjugated diene hydroperoxides) and secondary (thiobarbituric acid reactive substances - TBARS) products. We found that the oxidative stability of oleofoams was higher compared to that of the corresponding bulk oil. This protective effect was also found when the oil was simply mixed with the oleogelator without incorporation of air bubbles (i.e., forming an oleogel), and was somewhat modulated depending on the type of oleogelator. These results suggest that oleogelators and the structural changes that they induce limit the cascaded propagation of lipid oxidation in oil-continuous matrices, which is promising in the perspective of future applications.

An overview of edible foams in food and modern cuisine: Destabilization and stabilization mechanisms and applications

Foam, as a structured multi-scale colloidal system, is becoming increasingly popular in food because it gives a series of unique textures, structures, and appearances to foods while maintaining clean labels. Recently, developing green and healthy food-grade foaming agents, improving the stability of edible foams, and exploring the application of foam structures and new foaming agents have been the focus of foam systems. This review comprehensively introduces the destabilization mechanisms of foam and summarizes the main mechanisms controlling the foam stability and progress of different food-grade materials (small-molecular surfactants, biopolymers, and edible Pickering particles). Furthermore, the classic foam systems in food and modern cuisine, their applications, developments, and challenges are also underlined. Natural small-molecular surfactants, novel plant/microalgae proteins, and edible colloidal particles are the research hotspots of high-efficiency food-grade foam stabilizers. They have apparent differences in foam stability mechanisms, and each exerts its advantages. However, the development of foam stabilizers remains to be enriched compared with emulsions. Food foams are diverse and widely used, bringing unique enjoyment and benefit to consumers regarding sense, innovation, and health attributes. In addition to industrial inflatable foods, the foam foods in molecular gastronomy are also worthy of exploration. Moreover, edible foams may have greater potential in structured food design, 3D/4D printing, and controlled flavor release in the future. This review will provide a reference for the efficient development of functional inflatable foods and the advancement of foam technologies in modern cuisine.

Oleo-foams and emulsion-foams as lipid-based foam systems: a review of their formulation, characterization, and applications

Lipid-based foam systems (LBFs) have grown in popularity recently because of their effectiveness and potential uses. As a result, in order to stabilize them, considerable work has been put into developing more biodegradable and environmentally friendly materials. However, the use of natural stabilizing agents has been constrained due to a lack of thorough knowledge of them. This review offers insightful data that will encourage more studies into the development and use of LBFs. Emulsifiers or gelling agents, as well as new preparation and characterization methods, can be used to increase or prolong the functional performance of LBFs. Special emphasis has been given on the connections between their structures and properties and expanding the range of industries in which they can be applied. In conclusion, it is crucial to gain a deeper understanding of the preparation mechanisms and influencing factors in order to improve the quality of foam products and create novel LBFs.

Oleofoams stabilized by monoacylglycerides: Impact of chain length and concentration

Oleofoams are plant oil based whipped systems which have drawn academic and industry attention in recent years. The aim of this study was to determine the effect of fatty acid chain length and monoacylglyceride (MAG) concentration on the performance and structural properties of MAG-based oleofoams. Four different MAGs (monolaurin, monomyrystin, monopalmitin, and monostearin) were studied at three concentration levels (5, 10, and 15 wt%). The fatty acid chain length had a statistically significant impact on the size and shape of crystals formed, while higher MAG concentrations led to higher numbers of crystals in the continuous oil phase. These differences affected the performance and physical properties of the oleofoams: compared to other MAGs, monostearin based oleofoams were harder and exhibited higher values of G' and G″, had higher overrun and showed better stability. Lastly, through microscopy techniques it was successfully proved that monostearin-based oleofoams are stabilized by both bulk and Pickering stabilization.

Interfacial behavior, gelation and foaming properties of diacylglycerols with different acyl chain lengths and isomer ratios

Diacylglycerols (DAG) of varying chain lengths were synthesized and the acyl migrated samples with different 1,3-DAG/1,2-DAG ratios were obtained. The crystallization profile and surface adsorption differed depending on DAG structure. C12 and C14 DAGs formed small platelet- and needle-like crystals at the oil-air interface which can better reduce surface tension and pack in an ordered lamellar structure in oil. The acyl migrated DAGs with higher ratios of 1,2-DAG showed reduced crystal size and lower oil-air interfacial activity. C14 and C12 DAG oleogels exhibited higher elasticity and whipping ability with crystal shells surrounding bubbles, whereas C16 and C18 DAG oleogels had low elasticity and limited whipping ability due to the formation of aggregated needle-like crystals and loose gel network. Thus, acyl chain length dramatically influences the gelation and foaming behaviors of DAGs whereas the isomers exert little influence. This study provides basis for applying DAG of different structures in food products.

Thermal-reversible lacquer wax-based oleofoams in dual stabilization with high ambient stability

In this study, the effect of the content of the lacquer wax and whipping time on the overrun was explored. It was found that an appropriate amount of wax content and whipping time could promote crystal dual stabilization through the Pickering mechanism and the close packing in the bulk phase. Otherwise, it would result in low overrun caused by high viscous and crystal bridging. The addition of polyglycerol polyricinoleate (PGPR) could effectively enhance the overrun by apace absorbing. At the same time, adding PGPR also improved the contact angle, which was beneficial to the adsorption at the A-O interface. The 8 wt% oleogel was partially substituted by high-melting fat palm stearin (POs) and oleofoams were prepared based on blended fat. POs increased the melting point, structural strength, and β'-form crystal of oleofoams, thus improving the storage and temperature stability. The oleofoam has a maximum overrun of 189% and could maintain the shape of the decorating over 15 d at the ambient temperature, showing great potential in low-fat food applications and other delivery systems.

Conversion of Pulse Protein Foam-Templated Oleogels into Oleofoams for Improved Baking Application

The food industry has long been searching for an efficient replacement for saturated-fatty-acid-rich fats for baking applications. Although oleogels have been considered a potential alternative for saturated and trans fats, their success in food application has been poor. The present study explored the use of oleofoams obtained by whipping the pulse protein foam-templated oleogels for cake baking. Oleogels were prepared at room temperature by adding canola oil containing high-melting monoglyceride (MAG) or candelilla wax (CW) to the freeze-dried pea or faba bean protein-stabilized foams. Oleogels were then whipped to create the oleofoams; however, only the oleogels containing MAG could form oleofoams. CW-oleogel could not form any oleofoam. The most stable oleofoams with the highest overrun, stability, and storage modulus were obtained from 3% MAG+pulse protein foam-templated oleogels. The MAG plus protein foam-templated oleogels showed smaller and more packed air bubbles than MAG-only oleofoam, which was ascribed to the protein's ability to stabilize air bubbles and provide a network in the continuous oil phase to restrict air bubble movement. A novel batter preparation method for oleofoam was developed to increase air bubble incorporation. The X-ray microtomography images of the cakes showed a non-homogeneous distribution of larger air bubbles in the oleofoam cake compared to the shortening cake although their total porosity was not much different. The oleofoam cakes made with the new method yielded similar hardness and chewiness compared to the shortening cakes. By improving rheology and increasing air incorporation in the batter, high-quality cakes can be obtained with MAG-containing oleofoams made from pulse protein foam-templated oleogels.

Wax based oleogels and their application in sponge cakes

The use of high amounts of saturated fatty acids mainly obtained from tropical fats and oils gains increasing rejection from consumers. Use of liquid plant based oils, however, does not deliver necessary functionalities. In this contribution, sunflower-(SFW), bees-wax (BW), ricebran wax (RBW) and a BW-wax mixture (BW : SFWh) were investigated as a potential alternative fat phase in low-density bakery products. Since the food product matrix is composed of complex ingredients, key-functionalities (foam-stabilization, viscoelastic properties, and oil-binding) were first investigated for pure oleogels as oleofoams. It could be demonstrated that all waxes investigated were able to form oleofoams. The location of wax crystal aggregates, at the oil-air interface or in the bulk, was shown to be a significant factor regarding oil-binding and viscoelastic properties. However, it was not possible to transfer all findings made for the oleofoams to the ones made for the oleogel based sponge cakes. There, all oleogels showed improvement compared to the canola oil variant regarding oil-leaping and visual appearance (volume). Sensory evaluation attested satisfactory results for all wax-based oleogel applications. This contribution aims to deliver novel findings for wax-based oleogels as oleofoams as well as an alternative fat phase in low-density bakery products. The gathered results aim to enable a target-oriented characterization of oleogel applications and hence facilitate future use to deliver beneficial products to the market.

Pickering foams and parameters influencing their characteristics

Pickering foams are available in many applications and have been continually gaining interest in the last two decades. Pickering foams are multifaceted, and their characteristics are highly dependent on many factors, such as particle size, charge, hydrophobicity and concentration as well as the charge and concentration of surfactants and salts available in the system. A literature review of these individual studies at first might seem confusing and somewhat contradictory, particularly in multi-component systems with particles and surfactants with different charges in the presence of salts. This paper provides a comprehensive overview of particle-stabilized foams, also known as Pickering foams and froths. Underlying mechanisms of foam stabilization by particles with different morphology, surface chemistry, size and type are reviewed and clarified. This paper also outlines the role of salts and different factors such as pH, temperature and gas type on Pickering foams. Further, we highlight recent developments in Pickering foams in different applications such as food, mining, oil and gas, and wastewater treatment industries, where Pickering foams are abundant. We conclude this overview by presenting important research avenues based on the gaps identified here. The focus of this review is limited to Pickering foams of surfactants with added salts and does not include studies on polymers, proteins, or other macromolecules.

Buckling versus Crystal Expulsion Controlled by Deformation Rate of Particle-Coated Air Bubbles in Oil

Oil foams stabilized by crystallizing agents exhibit outstanding stability and show promise for applications in consumer products. The stability and mechanics imparted by the interfacial layer of crystals underpin product shelf life, as well as optimal processing conditions and performance in applications. Shelf life is affected by the stability against bubble dissolution over a long time scale, which leads to slow compression of the interfacial layer. In processing flow conditions, the imposed deformation is characterized by much shorter time scales. In practical situations, the crystal layer is therefore subjected to deformation on extremely different time scales. Despite its importance, our understanding of the behavior of such interfacial layers at different time scales remains limited. To address this gap, here we investigate the dynamics of single, crystal-coated bubbles isolated from an oleofoam, at two extreme time scales: the diffusion-limited time scale characteristic of bubble dissolution, ∼10⁴ s, and a fast time scale characteristic of processing flow conditions, ∼10^-3 s. In our experiments, slow deformation is obtained by bubble dissolution, and fast deformation in controlled conditions with real-time imaging is obtained using ultrasound-induced bubble oscillations. The experiments reveal that the fate of the interfacial layer is dramatically affected by the dynamics of deformation: after complete bubble dissolution, a continuous solid layer remains; after fast, oscillatory deformation of the layer, small crystals are expelled from the layer. This observation shows promise toward developing stimuli-responsive systems, with sensitivity to deformation rate, in addition to the already known thermoresponsiveness and photoresponsiveness of oleofoams.

Recent progress in Pickering emulsions stabilised by bioderived particles

In recent years, the demand for non-surfactant based Pickering emulsions in many industrial applications has grown significantly because of the option to select biodegradable and sustainable materials with low toxicity as emulsion stabilisers. Usually, emulsions are a dispersion system, where synthetic surfactants or macromolecules stabilise two immiscible phases (typically water and oil phases) to prevent coalescence. However, synthetic surfactants are not always a suitable choice in some applications, especially in pharmaceuticals, food and cosmetics, due to toxicity and lack of compatibility and biodegradability. Therefore, this review reports recent literature (2018-2021) on the use of comparatively safer biodegradable polysaccharide particles, proteins, lipids and combinations of these species in various Pickering emulsion formulations. Also, an overview of the various tuneable factors associated with the functionalisation or surface modification of these solid particles, that govern the stability of the Pickering emulsions is provided.