Emulsion electrospinning: Fundamentals,food applications and prospects

BackgroundIn the past decades, many natural bioactive compounds with antioxidant, immunoregulatory, antimicrobial, and anticancer activities have been successfully identified in plant and animal materials. However, due to their poor solubility, unfavorable flavor, low bioavailability and instability during food processing and storage, the development of bioactive compounds used in the food industry presents many technological challenges.Scope and approachEmulsion electrospinning is a novel and simple technique to fabricate core-shell nanofibers, and either water-in-oil (W/O) or oil-in-water (O/W) emulsions can be electrospun to directly encapsulate hydrophilic or hydrophobic compounds into core-shell fibers, respectively. This review introduces fundamentals and advantages of emulsion electrospinning as well as its food applications. The effects of different types of emulsifiers on the formation of emulsion systems and emulsion-based electrospun fibers are highlighted. Further, the existing limitations and scope for future research are discussed.Key findings and conclusionsRecent studies have found that the emulsion-based electrospun nanofibers can enhance the encapsulation efficiency, stability, and bioavailability of bioactive compounds, as well as achieve targeted delivery and controlled release, thus providing new strategies to improve their barrier performance compared to conventional electrospinning and therefore facilitating the development of emulsion-based electrospun mats in the food industry.     

Review on the Stability Mechanism and Application of Water‐in‐Oil Emulsions Encapsulating Various Additives

Water‐in‐oil (W/O) emulsions can be used to encapsulate and control the release of bioactive compounds for nutrition fortification in fat‐based food products. However, long‐term stabilization of W/O emulsions remains a challenging task in food science and thereby limits their potential application in the food industry. To develop high‐quality emulsion‐based food products, it is essential to better understand the factors that affect the emulsions’ stability. In real food system, the stability situation of W/O emulsions is more complicated by the fact that various additives are contained in the products, such as NaCl, sugar, and other large molecular additives. The potential stability issues of W/O emulsions caused by these encapsulated additives are a current concern, and special attention should be given to the relevant theoretical knowledge. This article presents several commonly used methods for the preparation of W/O emulsions, and the roles of different additives (water‐ and oil‐soluble types) in stabilizing W/O emulsions are mainly discussed and illustrated to gain new insights into the stability mechanism of emulsion systems. In addition, the review provides a comprehensive and state‐of‐art overview of the potential applications of W/O emulsions in food systems, for example, as fat replacers, controlled‐release platforms of nutrients, and delivery carrier systems of water‐soluble bioactive compounds. The information may be useful for optimizing the formulation of W/O emulsions for utilization in commercial functional food products.     

Emulsion-based delivery systems for lipophilic bioactive components

ABSTRACT:  There is a pressing need for edible delivery systems to encapsulate, protect, and release bioactive lipids within the food, medical, and pharmaceutical industries. The fact that these delivery systems must be edible puts constraints on the type of ingredients and processing operations that can be used to create them. Emulsion technology is particularly suited for the design and fabrication of delivery systems for encapsulating bioactive lipids. This review provides a brief overview of the major bioactive lipids that need to be delivered within the food industry (for example, ω-3 fatty acids, carotenoids, and phytosterols), highlighting the main challenges to their current incorporation into foods. We then provide an overview of a number of emulsion-based technologies that could be used as edible delivery systems by the food and other industries, including conventional emulsions, multiple emulsions, multilayer emulsions, solid lipid particles, and filled hydrogel particles. Each of these delivery systems could be produced from food-grade (GRAS) ingredients (for example, lipids, proteins, polysaccharides, surfactants, and minerals) using simple processing operations (for example, mixing, homogenizing, and thermal processing). For each type of delivery system, we describe its structure, preparation, advantages, limitations, and potential applications. This knowledge can be used to facilitate the selection of the most appropriate emulsion-based delivery system for specific applications.     

蛋白质氧化影响乳液稳定性研究进展

乳液在食品工业中应用十分广泛,通常可以作为营养与风味物质的良好载体。作为乳液天然稳定剂的蛋白质在食品加工和贮藏过程中会不可避免地发生氧化,进而影响乳液稳定性。近年来,食品蛋白质氧化对乳液稳定性造成的影响已经受到了越来越多的关注。本文首先分析了蛋白质乳液的形成机制以及影响乳液稳定性的主要因素,随后重点探讨了蛋白质柔性对蛋白质乳液稳定性的影响,进而从蛋白质柔性的角度,阐述蛋白质氧化影响乳液稳定性的机理,可为蛋白质乳液的开发及其在食品体系中的应用提供一定的理论参考。     

Characteristics of Sodium Caseinate- and Soy Protein Isolate-Stabilized Emulsion-Gels Formed by Microbial Transglutaminase

ABSTRACT:  Protein-stabilized emulsion gels were prepared via microbial transglutaminase (mTGase) catalysis, and their physicochemical characteristics were examined. Emulsion oil droplet size and interfacial protein load were measured. The sodium caseinate and soy protein isolate emulsion gels exhibited different microstructures and physical properties. The emulsion gels improved the storage stability of aroma compounds. Rheological measurements of the emulsion gels revealed interesting strength, gelation kinetics, and thermal sensitivity properties. The mTGase-induced emulsion gels comprised a fine network which led to less release of aroma compounds upon storage than did emulsions. These results suggest that emulsion gels may be used to improve the texture of food emulsions and to control release of food aromas.     

Interactions between flavor compounds and food ingredients and their influence on flavor perception

Interactions between flavor compounds and food ingredients are reviewed and their influence on flavor perception is discussed. Proteins are known to bind flavor compounds. For β-lactoglobulin, the most-studied example, hydrophobic interactions with volatiles are described. The effect of the medium on the conformation of the protein and its ability to bind flavor compounds is discussed. In general, the retention of volatiles by protein is much lower than that by fat. In emulsions, however, the presence of protein at the oil/water interface induces a significant effect on flavor release and flavor perception of hydrophobic flavor compounds. For starch, an extensively studied hydrocolloid, amylose has been shown to form complexes with aroma compounds. The physical state of carbohydrates is one parameter influencing flavor retention. However, the major effect of hydrocolloids seems to be a limitation for the diffusion of aroma compounds due to changes in viscosity. Addition of fat induces significant retention of hydrophobic flavor compounds resulting in noticeable effects on flavor perception. Changing the fat content modifies the overall perception of a mixture of flavor compounds from different chemical classes. The melting point of the fats influences the solubility of aromas and thus the flavor release. Emulsification and droplet size also affect flavor release and perception. More research is required on the effects of real food samples containing mixtures of different flavor compounds.     

Interfacial design of protein-stabilized emulsions for optimal delivery of nutrients

Proteins are often used as ingredients in food emulsions, as their amphiphilic structures provide electrostatic and steric stabilization. Significant attention has recently been directed at understanding how the composition and structure of oil-water interfaces change during digestion and how these can be manipulated to enhance the delivery of nutrients contained within the oil droplets. These efforts have necessitated the development of more sophisticated in vitro digestion models of greater physiological relevance and increased efforts in research to identify the role of the various digestive parameters on interfacial dynamics. The changes occurring at the oil-water interface will affect the adsorption of gastro-intestinal lipases and, ultimately, affect lipid digestion. The composition of a protein-stabilized oil droplet changes continuously during digestion, because of proteolysis and the formation of peptides with different affinities for the interface. In addition, natural bio-surfactants such as phospholipids and bile salts, other surface- active molecules present in foods, and the products of lipolysis (i.e. mono and diglycerides, lysophospholipids), all compete for access to the interface, and contribute to the dynamic changes occurring on the surface of the oil droplets. A better understanding of how to tailor the composition of oil droplet surfaces in food emulsions will aid in optimizing lipid digestion and, as a result, delivery of lipophilic nutrients. This review focuses on the physico-chemical changes occurring in protein-stabilized oil-in-water emulsions during gastric and small intestine digestion, and on how interfacial engineering could lead to differences in fatty acid release and the potential bioavailability of lipophilic molecules.     

Emulsion design for the delivery of β-carotene in complex food systems

β-Carotene has been widely investigated both in the industry and academia, due to its unique bioactive attributes as an antioxidant and pro-vitamin A. Many attempts were made to design delivery systems for β-carotene to improve its dispersant state and chemical stability, and finally to enhance the functionality. Different types of oil-in-water emulsions were proved to be effective delivery systems for lipophilic bioactive ingredients, and intensive studies were performed on β-carotene emulsions in the last decade. Emulsions are thermodynamically unstable, and emulsions with intact structures are preferable in delivering β-carotene during processing and storage. β-Carotene in emulsions with smaller particle size has poor stability, and protein-type emulsifiers and additional antioxidants are effective in protecting β-carotene from degradation. Recent development in the design of protein-polyphenol conjugates has provided a novel approach to improve the stability of β-carotene emulsions. When β-carotene is consumed, its bioaccessibility is highly influenced by the digestion of lipids, and β-carotene in smaller oil droplets containing long-chain fatty acids has a higher bioaccessibility. In order to better deliver β-carotene in complex food products, some novel emulsions with tailor-made structures have been developed, e.g., multilayer emulsions, solid lipid particles, Pickering emulsions. This review summarizes the updated understanding of emulsion-based delivery systems for β-carotene, and how emulsions can be better designed to fulfill the benefits of β-carotene in functional foods.     

乳液凝胶的基质及质构特性对风味物质释放效果的影响研究进展

乳液凝胶是将乳化的油滴包埋在凝胶基质中的软固体材料,是一种具有凝胶网状结构和较强力学性质的凝胶。近年来,利用乳液凝胶包埋风味物质并对其释控的研究越来越多。乳液凝胶对风味物质的释放效果与凝胶基质、油相、界面组成以及凝胶硬度、粘度等因素密切相关。随着人们对饮食健康要求的提高,乳液凝胶在食品领域尤其是低脂食品行业拥有潜在的应用价值。本文在国内外相关研究的基础上,全面综述了乳液凝胶的基质及质构特性对风味物质释放效果的影响,并对其作为一种食品风味补偿策略在低脂食品行业的应用前景作出展望。     

Pickering emulsions in foods - opportunities and limitations

In order to critically discuss the potential of Pickering-type emulsions in food applications this review provides the theoretical background of the stabilizing mechanisms, the resulting requirements for particles to stabilize these systems and the limitations resulting from these fundamental considerations. Food grade particle systems investigated in the past are presented. It becomes obvious that with a proper choice of a particle type, oil-in-water as well as water-in-oil emulsions can be achieved. For highly viscous products, products with a high internal phase volume and foams Pickering particles offer alternatives to commonly used surfactants. Pickering emulsions might be able to offer new approaches for fat reduction as well as encapsulation and sustained release of active ingredients. Nevertheless, a major part of successful systems have been achieved with silica or modified silica particles, which is not in line with the consumer demand for clean label, natural systems or not even food grade. However, the intriguing possibilities motivate and justify future research on the identification of new suitable ingredients, improvement of existing formulations and identification of new fields of application.     

Structure and stability of heat-treated concentrated dairy-protein-stabilised oil-in-water emulsions: A stability map characterisation approach

Emulsion instabilities such as depletion flocculation, coalescence, aggregation and heat-induced protein aggregation may be detrimental to the production of sterilised food emulsions. The type and the amount of protein present in the continuous phase and at the oil–water interface are crucial in the design of emulsions with appropriate stability. In this study, four oil-in-water model emulsion systems (pH 6.8–7.0) were formulated, characterised and categorised according to the potential interactions between protein-coated or surfactant-coated emulsion droplets and non-adsorbed proteins present in the continuous phase. The heat stability, the creaming behaviour and the flow behaviour of the model emulsions were influenced by both the emulsifier type and the type of protein in the continuous phase. The results suggest that this stability map approach of predicting droplet–droplet, droplet–protein and protein–protein interactions will be useful for the future design of heat-stable emulsion-based beverages with good creaming stability at high protein concentrations.     

Static headspace analysis of volatile compounds released from ��-lactoglobulin-stabilized emulsions determined by the phase ratio variation method

The release of volatile organic compounds (VOCs) from oil-in-water emulsions stabilized by ??-lactoglobulin (??LG) was studied under equilibrium conditions. The effects of lipid type and mass fraction were investigated using soy oil (SO) and anhydrous milk fat (AMF). The release was compared using systems of a buffered aqueous solution, pure oil and emulsions. Gas-matrix partition coefficients (K) for five volatile compounds: 1-propanol, ethyl butyrate, heptanal, octanol and 2-decanone, were determined by static headspace gas chromatography (GC). The compounds were chosen based on their polarity, vapour pressure and functional groups. Two indirect methods to measure K were used: phase ratio variation (PRV) and phase ratio calibration (PRC). These two methods were found to be simple and accurate alternative to measure K without using external calibration. The VOC release depended mainly on the physiochemical properties and affinity of the compounds to the matrix. Higher retention in oil and emulsion systems than in aqueous solution was observed for all VOCs except the more hydrophilic 1-propanol. Ethyl butyrate showed the highest K value for emulsions whereas 2-decanone had the lowest. There was a significant decrease in K values for emulsions with higher lipid content. When comparing lipid type, emulsions made with the more saturated AMF, compared to SO, resulted in lower K values for the more hydrophobic compounds. The role of ??LG on VOC release was compared with Tween 20, both as emulsifiers. A significant decrease in the headspace concentration was seen above the aqueous solution for heptanal, octanol and 2 decanone. This may be attributed to the hydrophobic cavity site of the protein and covalent bonds with the aldehyde. In emulsion systems, the presence of the emulsifier conformation at the interface had an effect on the affinity with intermediate hydrophobic VOCs. This study provides an important understanding of how VOC release can be controlled using ??LG stabilized emulsions in food systems.     

Physical stability of emulsion encapsulated in alginate microgel particles by the impinging aerosol technique

Emulsion filled alginate microgel particles can be applied as carrier systems for lipophilic actives in pharmaceutical and food formulations. In this study, the effects of oil concentration, emulsifier type and oil droplet size on the physical stability of emulsions encapsulated in calcium alginate microgel particles (20–80 μm) produced by a continuous impinging aerosol technique were studied. Oil emulsions emulsified by using either sodium caseinate (SCN) or Tween 80 were encapsulated at different oil concentrations (32.55, 66.66 and 76.68% w/w of total solids content). The emulsions were analysed before and after encapsulation for changes in emulsion size distribution during storage, and compared to unencapsulated emulsions. The size distribution of encapsulated fine emulsion (mean size ~ 0.20 μm) shifted to a larger size distribution range during encapsulation possibly due to the contraction effect of the microgel particles. Coarse emulsion droplets (mean size ~ 18 μm) underwent a size reduction during encapsulation due to the shearing effect of the atomizing nozzle. However, no further size changes in the encapsulated emulsion were detected over four weeks. The type of emulsifier used and emulsion concentration did not significantly affect the emulsion stability. The results suggest that the rigid gel matrix is an effective method for stabilising lipid emulsions and can be used as a carrier for functional ingredients.     

新技术在调香过程中的应用

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Aspects of milk-protein-stabilised emulsions

Milk proteins are widely used as ingredients in prepared foods, in which they perform a wide range of key functions, including emulsification, thickening, gelling and foaming. An important functionality of milk proteins in food colloids is their ability to facilitate the formation and stabilisation of oil droplets in emulsions. The ability of milk proteins to adsorb at the oil–water interface and to stabilise emulsions has been exploited by the food industry in the manufacture of nutritional products, specialised medical foods, dietary formulations, cream liqueurs and dairy desserts. This article provides an overview of the properties and functionalities of food emulsions formed with milk proteins, focusing on the structure and composition of adsorbed protein layers, competition between proteins and the physical and chemical stability of emulsion droplets. Of particular importance is the understanding of the behaviour of milk-protein-based emulsions under the conditions relevant to digestion in the human gastrointestinal tract. Recent relevant research in this area is reviewed and discussed.     

食品功能因子传递系统——双层乳液研究进展

双层乳液是多层乳液的一种,一般通过层-层静电自组装技术形成两层界面层,其两个界面层可由蛋白质、多糖等生物聚合物或磷脂、吐温等小分子表面活性剂以静电吸附或共价结合的方式形成于乳液液滴的表面。作为一种传递体系,与传统的单层乳液相比,双层乳液在结构稳定性和抵抗环境压力（如酸碱度、温度和离子强度等）方面更具优势,能对所包埋的生物活性物质提供更好的保护,且具有一定的控释能力。双层乳液因其独特的优势在食品工业生产以及功能食品的开发等领域具有广阔的发展前景。本文结合近年来双层乳液的研究,从双层乳液的制备、界面层的材料、理化稳定性、作为一种传递体系的特点及其在食品领域的应用等方面进行综述。     

Effects of composition and processing variables on the oxidative stability of protein-based and oil-in-water food emulsions

Because many common foods are emulsions (mayonnaise, coffee creamers, salad dressing, etc.), a better understanding of lipid oxidation mechanisms in these systems is crucial for the formulation, production, and storage of the relevant consumer products. A research body has focused on the microstructural and oxidative stability of protein-stabilized oil-in-water emulsions that are structurally similar to innovative products that have been recently developed by the food industry (e.g., non-dairy creams, vegetable fat spreads, etc.) This review presents recent findings about the factors that determine the development of lipid oxidation in emulsions where proteins constitute the stabilizing interface. Emphasis is given to “endogenous” factors, such as those of compositional (e.g., protein/lipid phases, pH, presence of transition metals) or processing (e.g., temperature, droplet size) nature. Improved knowledge of the conditions that favor the oxidative protection of protein in emulsions can lead to their optimized use as food ingredients and thereby improve the organoleptic and nutritional value of the related products.     

Flavor–food ingredient interactions in fortified or reformulated novel food: Binding behaviors,manipulation strategies,sensory impacts,and future trends in delicious and healthy food design

With consumers gaining prominent awareness of health and well-being, a diverse range of fortified or reformulated novel food is developed to achieve personalized or tailored nutrition using protein, carbohydrates, or fat as building blocks. Flavor property is a critical factor in the acceptability and marketability of fortified or reformulated food. Major food ingredients are able to interact with flavor compounds, leading to a significant change in flavor release from the food matrix and, ultimately, altering flavor perception. Although many efforts have been made to elucidate how food matrix components change flavor binding capacities, the influences on flavor perception and their implications for the innovation of fortified or reformulated novel food have not been systematically summarized up to now. Thus, this review provides detailed knowledge about the binding behaviors of flavors to major food ingredients, as well as their influences on flavor retention, release, and perception. Practical approaches for manipulating these interactions and the resulting flavor quality are also reviewed, from the scope of their intrinsic and extrinsic influencing factors with technologies available, which is helpful for future food innovation. Evaluation of food–ingredient interactions using real food matrices while considering multisensory flavor perception is also prospected, to well motivate food industries to investigate new strategies for tasteful and healthy food design in response to consumers’ unwillingness to compromise on flavor for health.     

Multilayer emulsions as delivery systems for controlled release of volatile compounds using pH and salt triggers

Multilayer oil-in-water (M-O/W) emulsions were compared to primary oil-in-water (P-O/W) emulsions as carriers for volatile organic compounds (VOCs) under various environmental conditions (pH and salt). The M-O/W emulsion consisted of soy oil coated with β-lactoglobulin (βLG) and pectin layers. The release of VOCs with different physiochemical properties from aqueous solutions and emulsion systems was measured using static and dynamic headspace methods. The partition coefficients (K) calculated by the phase ratio variation (PRV) method, showed different volatile release profiles between the emulsion types. An increase in VOC release was found for the unstable P-O/W emulsion at pH 5, whereas M-O/W emulsions were stable at the same pH and retained the hydrophobic VOCs. Hydrophobic interactions and hydrogen bonds with the secondary dense layer of pectin may be responsible for the improved retention. Increasing pH and ionic strength acts as a VOC release trigger to detach the pectin from the interface. The release rates from initial dynamic curves support the results under equilibrium conditions. The results of this study demonstrate the capability of using M-O/W emulsions for controlled release of VOCs, as well as an alternative system to create stable emulsions with similar VOC release profiles.     

A review of the rheological properties of dilute and concentrated food emulsions

Rheology is a powerful and versatile analytical tool for providing information about changes in the composition, structure, and interactions of food emulsions. Moreover, an understanding of emulsion rheology is essential for designing efficient food processing operations and emulsion-based foods with the desired physicochemical, sensory, and nutritional attributes, such as appearance, texture, flavor, shelf life, and bioavailability. This article provides a brief overview of the current understanding of food emulsions, with a focus on how their viscosity is related to the properties of the emulsion droplets present.