Technology is helping food companies create efficient emulsifiers—among the most critical aspects in the formation of successful emulsion-based food and beverage products. Without emulsifiers, most of the sauces and condiments consumers enjoy, and many of the beverages, would not be possible. When thinking of emulsifiers, one has to include desserts, dressings, dips, creams, milk-based products, sauces, and even soft drinks.
In principle, food emulsions are one of the simplest forms of oil-in-water emulsions, consisting of small oil droplets dispersed within an aqueous medium. There are, however, a number of challenges associated with developing successful commercial products. Ingredients appropriate for emulsion-based products to be marketed as healthful and natural also tend to fluctuate and cause changes in the properties and stability of finished products.
Emulsions can be formed using either high- or low-energy methods. Historically, food processors have used high-energy approaches, such as colloid mills, high-pressure homogenizers, sonicators, and microfluidizers. These rely on established and large-scale specialized equipment to disrupt and blend oil and water phases to form and disperse them in small droplets. The result is a smooth texture and mouthfeel that holds together from the beginning to the end of usage.
Low-energy approaches, in contrast, leverage the physicochemical properties of surfactants, oil, and water to spontaneously generate emulsion droplets but without investing in specialized equipment. These emulsions typically employ finessed mixing procedures and strategically adjusted compositions. They also can be effected by changing the temperature of the formulation. Low-energy methods are gaining interest, due to their low cost and ease of implementation, plus an associated competitive advantage from less processing.
Emulsifiers are fundamentally surface-active (“surfactants”) substances. They play two pivotal roles in the mixing of immiscible components: First, they facilitate the basic formation of the mix, and then they foster the stability of that mix. Food manufacturers rely on a number of synthetic and natural emulsifiers, but the ‘clean label’ movement is creating a paradigm shift and moving interest from the traditionally less-expensive synthetics to exploring what nature has to offer.
Never before has interest been greater in the identification, characterization, and utilization of naturally occurring proteins, polysaccharides, phospholipids, and saponins. The goal is to determine which have the appropriate structural properties to efficaciously (and in a commercially viable way) help form and stabilize emulsions.
“The food industry is investing in natural emulsifiers that are inexpensive, label friendly, and can provide good emulsion stability in a range of different products,” says Julian McClements, PhD, the Fergus Clydesdale Endowed Chair professor in the Department of Food Science, University of Massachusetts, Amherst. “At present, we only know of a limited number of natural emulsifiers, and each has certain advantages but also several limitations. The quest is for an economically viable source of natural emulsification that can be utilized in multiple types of products.”
The range of variation in emulsification functionality is due to differences in the ability of ingredients to adsorb to surfaces, reduce interfacial tensions, and prevent droplet aggregation. The quest to identify and characterize naturally occurring emulsifiers is somewhat in its infancy, while formulators understand the specific emulsifying needs in various food categories and types of manufacturing processes entailed.
To be an effective emulsifier, the ingredient must have a number of physicochemical characteristics, including the appropriate ratio of polar and nonpolar groups. These polar and nonpolar groups spur surface activity and facilitate rapid adsorption of oil-water interfaces, strong steric or electrostatic repulsive interactions.
The right adsorption kinetics rapidly reduce interfacial tension, in order to prevent droplet aggregation, and most importantly, a low surface load. Therefore, very little is required to form and stabilize the emulsion.
Potent Proteins
Proteins contain a mixture of hydrophilic and hydrophobic amino acids along their polypeptide chains that render them naturally surface active. This enables them to quickly adsorb to oil-water interfaces and coat the oil droplets formed during mixing and homogenization. The negative carboxylic ions (-COO—) or positive amino (–NH3+) of amino acids that make up proteins can stabilize droplets from aggregation by generating an electrostatic repulsion.
These surface-active agents can inhibit aggregation via steric repulsion by forming thick interfacial layers or by having carbohydrate moieties attached and are therefore, generating considerable interest in glycoproteins that naturally have these carbohydrate moieties. Proteins are generally relatively small molecules (about 10–50 kDa) that rapidly adsorb to droplet surfaces and form thin, electrically charged interfacial layers. Such layers are important in forming and stabilizing emulsions.
Bovine milk caseins and whey proteins are currently the most commonly used naturally occurring protein-based emulsifiers in the food industry.
Caseins are amphiphilic proteins with flexible structures (as1, as2, b, and k-caseins) whereas whey proteins are globular proteins with fairly rigid structures (a-lactalbumin, b-lactoglobulin,bovine serum albumin/BSA, and immunoglobulins).
Casein and gelatin are flexible proteins that rapidly undergo conformational changes, with the hydrophilic groups protruding into water and the hydrophobic groups into oil. Whey and egg proteins tend to be rigid globular proteins that partially unfold after adsorption and form cohesive viscoelastic layers. Gelatins, whether derived from cow, pig, or fish, have flexible structures and surface activity. However, they are not as effective in stabilizing emulsions.
Pea proteins—gaining popularity in the plant-derived protein arena—also appeal to formulators because of emulsification properties on par with those of egg proteins.
The high content of hydrophilic amino acids gives pea protein an increased foaming capacity that’s as good as egg albumin in tenderizing food, decreasing the bulk density of a food product, and creating a light, spongy texture especially in gluten-free bakery products. Pea isolates exhibit excellent whipping ability and foam stability.
“This illustrates the advantages of this ingredient with respect to these current trends,” says Tanya Der, food innovation and marketing manager for Pulse Canada.
Pea and certain other plant proteins can function as suitable egg replacers in bakery products, such as cookies, cakes, muffins, or waffles, since they provide structure. But pea protein’s water-binding capacity and small emulsion droplet size distribution helps create creaminess in beverages. It has found favor among many manufacturers of such products as sport beverages, both dairy- and non-dairy-based.
Lupin beans, another type of legume popular in the Mediterranean, recently has gained ground with product developers. This is because lupin proteins have excellent emulsifying and foaming properties. Formulators have demonstrated emulsification functionality with lupin, and also with corn germ proteins in a number of food categories, including beverages, refrigerated and frozen desserts, salad dressings, sauces, and soups.
Continuing in the legume family, combinations of red bean powder and gum Arabic have been used to help keep meat emulsions together for a superior eating experience. Tyson Foods has utilized just this combination in its Ball Park’s Finest Slow Cooked Chili Dog Uncured Beef Frankfurters. The company still is able to label the product as 100% premium, USDA-certified beef, fully cooked and naturally smoked frankfurters, free of artificial preservatives, nitrates, nitrites, by-products, MSG, artificial flavors, colors and fillers.
A crucial challenge with each of these plant proteins, however, is identifying an economically viable source. Also challenging is the development of commercially viable and effective methods for isolating, fractionating, and purifying these proteins. Moreover, characterizing and quantifying their emulsion forming and stabilizing functionality is key to their gaining interest from processors. Until then, some processors turn to combinations of legume flours with hydrocolloids for their synergistic emulsification.
Polysaccharides in Play
Polysaccharides tend to be highly hydrophilic substances but are not particularly surface-active. This means they tend to stabilize emulsions by making the aqueous phase more viscous and inhibiting movement of fat droplets. Polysaccharides can be rendered surface-active by chemically or enzymatically attaching non-polar groups or protein molecules to their hydrophilic backbones. This converts them into what are popularly known as modified starches.
Maillard complexes of proteins and carbohydrates are another example of such emulsifier complexes, and, like modified starches, can be considered natural or synthetic depending on how the transformation is achieved.
Some polysaccharides, such as gum Arabic, pectin, and galactomannans, are naturally surface-active and are, therefore, good emulsifiers because of proteins or non-polar groups intrinsically attached to their hydrophilic carbohydrate chains. The ancient ingredient gum Arabic is probably the most widely used as an emulsifier in food applications (especially in beverage emulsions) because of its ability to increase viscosity at very low concentrations.
Gum Arabic helps retain creamy textures in Hostess Brands Inc.’s Pumpkin Spice Cake and Filling. Gum Arabic, however, requires a relatively high emulsifier-to-oil ratio of 1:1 to stabilize emulsions. Formulators are turning to citrus pectins for their efficacy in forming and stabilizing emulsions as a function of their molecular weight and degree of methoxylation.
Polysaccharides isolated from basil seed, labeled as basil seed gum (BSG), are also good emulsifiers and are thus up-and-coming in food and beverage processing. Their surface activity is a result of naturally occurring protein moieties and non-polar groups on their core carbohydrate. Corn fiber gum, too, has naturally occurring protein moieties that contribute to its emulsifying properties.
Chia seeds are valued for their healthy oil profile and for being a rich source of dietary fibers. They also are valued as polysaccharides with water-holding capacity, oil-holding capacity, viscosity, emulsion activity, and freeze-thaw stability similar to that of guar gum and gelatin. Chia seed gel has potential application in food formulation as an egg replacer and stabilizer in frozen food products.
Evolution Brands Inc. uses chia seeds to emulsify and retain creaminess without separation in its Fresh Cold-Pressed Organic Avocado Greens Juice Blend. The product is a blend of avocado, fruit, and vegetable juices made using a high-pressure process. It is marketed with GMO-free, kosher, organic, and no additives/preservatives claims.
Polysaccharide-based emulsifiers from naturally occurring sources are poised for growth once suppliers identify, isolate, and characterize the properties of polysaccharide-based emulsifiers from natural sources in an economic manner.
Phospholipids
Phospholipids are amphiphilic molecules (loving both water and oil) with hydrophobic fatty acid tail groups and phosphoric acid esterified with glycerol and other substitutes as the hydrophilic head groups. Also known as lecithin, they occur in nature in the cell membranes of animals, plants, and microbial species and are industrially extracted from soybeans, egg yolk, milk, sunflower kernels, canola (rapeseed) for use in foods.
Processors have long used “lecithin”—a term that refers to a mixture of phospholipids—as an effective and inexpensive emulsifier. Lecithin usually is derived from soybeans, because of their abundance and low cost. Soy lecithin, however, most often is extracted from genetically modified soybean sources. Also, as a legume, it needs to be declared as an allergen on food labels.
Typically, lecithin ingredients are mixtures of different phospholipids, with the most common being phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylinositol (PI). While lecithin ingredients are surface-active and effective in facilitating the mixing of oil and water, they also are prone to coalescence because they form interfacial layers. Combining lecithin with proteins can minimize this issue and help form stable emulsion.
The market interest in non-genetically modified sources is making phospholipids from sunflowers more popular with formulators. Sunflower phospholipids tend to be more expensive and are more difficult to extract. But they are not genetically modified and contain no declared allergens.
Another alternative is to blend phospholipids to arrive at the most effective combination of fractions with more well-defined functionality. Exploration is under way on novel phospholipid blends for commercial introduction. Sunflower oil contains the following four major phospholipids: phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, and phosphatidic acid (PA), each of which have distinctly different properties that in turn influence their functional performance as emulsifiers.
Phosphatidylcholine, for instance, can form and stabilize emulsions by enveloping lipid droplets with mono- and bilayers. phosphatidylethanol-amine, however, cannot envelop lipid droplets. This is because of PE’s tendency to assemble into reversed hexagonal structures that are sensitive to pH. Combining the two in a high PC-to-PE ratio helps create highly stable emulsions.
Emulsion stability changes during storage, and both temperature and physical shock can change particle size, visual appearance, creaming index, and microstructure. Higher sunflower lecithin levels typically slow creaming and coalescence, which can be further reduced by increasing the viscosity of the continuous phase using starches, gums, or proteins.
Emulsifiers play a crucial role in milk-alternative products, such as soy and almond milk. They simultaneously address several distinct technical issues: stability, homogeneity, viscosity, and the necessary mouthfeel for consumer acceptance. While integrated emulsifier and stabilizer systems containing mono- and diglycerides and carrageenan have been used in these products, the focus on clean label and consumer backlash has led more companies to use sunflower lecithin.
Sunflower lecithin helps create the creamy texture for this healthful alternative to milk that is made with responsibly sourced ingredients. It also is GMO- and cholesterol-free, with no artificial colors and flavors, saturated fat, or HFCS. It is free of dairy, gluten, soy, lactose, eggs and casein, as well.
It helps that lecithin, besides acting as an emulsifier, is also a healthful nutraceutical. Phosophatidylserine, highly enriched in the brain, also governs membrane fluidity and, therefore, regulates cell activities. Phosphatidylcholine is required for normal liver function and can help reduce the risk of cardiovascular disease by lowering blood cholesterol levels and improving LDL/HDL ratios. Nutrition experts recommend adults consume 1,200mg of lecithin daily to achieve the nerve, brain, and muscle benefits.
Saponins
Saponins are a new breed of emulsifiers gaining popularity because, in addition to being efficacious surfactants, they also come with an eco-friendly and ancient heritage of being “good for you.” Quillaja saponins (from the Quillajaceae genus of plants), extracted and processed with just water from the bark of Q. saponaria Molina, a plant native to Chile, have been used for more than a century as a beverage foaming stabilizer.
In addition to being a superior alternative to gum Arabic, a plant that has been plagued by climatic and political conditions affecting price and availability, quillaja saponins can stabilize a higher load—as much as four times higher than traditional systems for considerably lower usage levels. Processors like that concentrated emulsions made with quillaja saponin can reduce inventory, shipping, and labor costs, and they are ready to use.
Formulators further find that quillaja’s fine droplet emulsion, with d50 less than 0.5 microns, is stable and ideal for delivering challenging bioactives, such as omega-3s, vitamins, and minerals in weighted and non-weighted beverages. It’s especially helpful for those products marketed as “natural” or healthful that cannot use weighting agents; i.e., ingredients used to increase fluid density.
Weighting agents constitute approximately half of the cost in emulsions; tend to make beverages opaque; and are regulated in terms of how much can be used.
Quillaja saponins contain hydrophilic sugar groups attached to non-polar aglycone groups that work particularly well in clear beverages without making them cloudy. Quillaja saponins are GRAS for use as emulsifiers or encapsulation agents in flavor concentrates, beverage products, chewing gum, gravies and sauces, snack foods, soups and soup mixes, and dietary supplements; they are likely to find increased use in the prepared food sector.
Saponins from quillaja are approved for use as a natural flavoring substance and adjuvant in food and beverages by FDA under 21 CFR 172.510 and 172.515, and FEMA GRAS number 2973.
Healthful Approach
Overweight and obesity incidence has encouraged food manufacturers to create lower fat/calorie versions of consumer favorites. In the process, they have been replacing some or all of the fat droplets in these products with starches, gums, proteins, and their derivatives as a common strategy.
Each of these ingredients mimics the desirable physicochemical and sensory attributes normally provided by fat droplets, while modulating the rheology of low-fat emulsion foods by a distinctly different mechanism. Some emulsions from them effectively emulate the texture or taste of fat, while others mimic its appearance. Still others have helped solve important processing issues in the beverage sector—a sector that probably has advanced emulsion science and technology further than any other category in the industry.
Locust bean gum, for example, forms hydrogen bonds between polysaccharide helices. The resulting hydrogel particles alter both the physicochemical properties and sensory attributes of multicomponent food emulsions, like salad dressings.
All-natural and clean label claims top recent and emerging developments, despite the higher cost implications and occasional sub-par functionality. Naturally occurring ingredients simply are not as consistent, robust, or as long-lasting as their synthetic counterparts. The appreciable increase in the global sales of bottled waters in recent years partly is attributed to the technologies that enable the addition of ingredients to enhance, flavor, and fortify waters.
Conventional emulsions have not performed well in beverages with oil-soluble flavors and nutraceuticals because of the opacity caused by light scattering from the oil droplets. Another reason can be attributed to negative public opinion of processed emulsifiers, such as brominated vegetable oil (BVO), sucrose-acetateisobutyrate (SAIB), and polysorbate.
On the Small Side
Beverage suppliers have resorted to alternative weighting agents, such as dammar gums (resins), in conjunction with emulsifiers, such as gum Arabic. Micro-emulsions containing very fine fat droplets that do not scatter light as strongly also may be used for this purpose.
Microemulsions are self-assembling isotropic, thermodynamically stable, low-viscosity solutions with several advantages over conventional dispersions, such as emulsions and double emulsions. They are relatively easy to prepare and scale up for commercial applications. They also have a long shelflife and offer the possibility of improved solubilization and protection of encapsulated bioactives.
Biocompatible microemulsions can act as reservoirs and delivery vehicles of bioactive substances that have positive health benefits when consumed in specific concentrations and are limited by poor bioavailability or poor solubility. Until recently, microemulsions have been limited in food applications because most viable surfactants are prohibited or permitted in very low concentrations by the FDA or the European Food and Safety Authority (EFSA).
This is changing with the recognition of substances like caprylic/capric triglycerides. These are a type of vegetable oil in which three medium-chain saturated fats—consisting of six to twelve carbon atoms—are bound to the hydrophilic glycerol backbone and isopropyl myristate (IPM), an oil composed of isopropyl alcohol and myristic acid (a naturally-occurring fatty acid).
These medium-chain triglycerides are invaluable for forming and stabilizing biocompatible micro-emulsion formulations. These formulations deliver bioactives proffering anti-allergic, anti-mutagenic, anti-inflammatory, and anti-carcinogenic activities found in a variety of plant-derived foods—but which are limited by sensory qualities and bio-availability.
Emulsifiers in Action
Chocolate makers use emulsifiers to reduce the friction between the liquid cocoa butter and the solid ingredients—sugar, cacao solids, and milk powder. The resulting chocolate tends to flow more easily. The process also helps preserve the smooth melting texture, glossy appearance, and snap hardness–all characteristics of premium chocolate.
Emulsifiers also help prolong the shelflife of chocolate and prevent reduced chocolate blooming. (Blooming is the harmless, but unattractive, formation of white streaks and blotches on the surface of chocolate due to the migration and subsequent crystallization of fat).
Emulsifiers provide cost-effective and stable viscosity control of chocolate and compound coating, without the off-tastes and off-notes sometimes occurring with lecithin. Non-GMO, sunflower-based emulsifiers at a dosage of around 0.3-0.5% can help replace as much as 5-6% of the cocoa butter, and the associated savings and profit margins, without off-flavors.
The growing focus on calories, fat, and sugar is driving demand for emulsifiers more than ever in the food industry. This is most especially true in baking. One of the challenges with reduced-fat baked goods is the taste, flavor, and appearance created by fat and sugar. A multifaceted emulsifier can help create cakes and pastry products that are just as moist and tasty as the original—but without the pain or guilt.
It’s possible to engineer various functions into a formulation by combining mono- and di-glycerides from, for example, sunflower with citric acid esters to produce satisfying results that keep consumers returning for more.
Gluten-free baked goods are difficult as-is, but sugar-free and/or low- or no-fat, gluten-free baked products often are a nightmare challenge for product developers and consumers. This is because gluten provides stability to cake batter and crumb, while sugar helps create the characteristic mouthfeel and sweetness.
In combination with fat, this “holy trinity” also helps create the taste, appearance, and overall comforting organoleptic profile of a bakery product.
Both natural and applied technology has been impressive, when it comes to tailoring ingredients for successful emulsion-based and -dependent products. The opportunity is there for developing robust production that also ensures standardized and reproducible quality. With a fundamental understanding of the molecular basis of emulsifier performance, processors can work with suppliers to select the most appropriate natural emulsifier for each application.
Originally appeared in the February, 2016 issue of Prepared Foods as Immiscibly Yours.
