Baby Boomers and even a few Gen-Xers reading this article may remember the General Foods product called Tang, the orange-flavored, powdered beverage that was introduced nationally in March 1965. Prior to this, the product was included in astronaut menus in NASA’s Apollo Space Program. It was made from sugar, citric acid, gum Arabic, orange flavors, vitamin C and other ingredients and featured a sophisticated flavor system that offered the aroma, as well as the flavor, of a freshly cut orange, when the powder was rehydrated. The orange flavor was encapsulated in a sucrose glass by extrusion. The ability to retain flavor and aroma and release them when combined with water was a new science, as was the encapsulation technique used at the time (IFT, 2000).1
Because the astronauts had Tang for breakfast in outer space, kids all over the country had to have it, too. At the time, many adults also were certainly intrigued with the novelty of a powdered, instant orange breakfast beverage that provided vitamin C and needed no refrigeration. How times have changed! Everything old is new again…but with new technological twists!
Protecting IngredientsMicroencapsulation is a technology that is proving to be invaluable to ingredient suppliers who want to differentiate and build value into their products by offering improved stability and functional performance for a growing array of applications. “The need to utilize stable nutrients and ingredients with health benefits, and new and exotic flavors, is driving the need to microencapsulate and new ways to do it,” says Pretima Titoria, Ph.D., section manager of Ingredients at Leatherhead Food International in the U.K. (Some primary reasons for ingredient encapsulation are shown in the chart “Why Encapsulate?”)
Today, there is pressure on the global food industry for all ingredients and even processes to go back to being as “natural” as possible. But, natural ingredients that have a specific functional role in food and beverage systems, or that provide unique health benefits, tend to be more reactive. This means they often require encapsulation as a protective barrier to prevent them from interacting with other components in their immediate environment and vice versa. The addition of sensitive ingredients--including flavors, nutrients, phytonutrients, enzymes, long-chain lipids, natural colors, antimicrobials, antioxidants, natural preservatives and even probiotic organisms--to food systems where they are traditionally incompatible, is now the norm. This drives the demand for specialized delivery systems in all kinds of food products, such as frozen and prepared foods, beverages, chewing gum and other confectionery items, dry baking mixes and finished baked goods. (See chart “Technology Assists New Products.”)
Encapsulation also is important to product developers as a means to offer protection to sensitive ingredients from hostile product, package or consumer environments, or, alternatively, protecting a food formulation from a “hostile ingredient,” such as reactive, iron-based fortificants that have high bioavailability. In addition, microencapsulation can be used as a tool to control the retention, release profile, function and targeted delivery of a host of different ingredients. Many nutrients and phytochemicals are “bad actors” in various food systems, because they can impart their own undesirable flavors, foster lipid breakdown or even interact with other nutrients in a way that fosters either molecular deterioration, precipitation or loss in bioavailability. Encapsulation can create a barrier between a reactive compound and its immediate environment and is a means to overcome these challenges in nutrient fortification. Creative systems that release aromas only when the product is heated in the consumer’s microwave, or deliver different flavors in a consecutive order when a chewing gum is chewed, also benefit from microencapsulation. Controlled release technologies used in many industrial, cosmetic and pharmaceutical applications are finding creative approaches for use in foods.
Microencapsulation technology is no longer a laboratory curiosity, but it has become a key competitive technology for food ingredient suppliers who are seeking to broaden the portfolio of applications for their ingredient offerings and to differentiate their products. Today’s new proprietary techniques of more complex encapsulation methods make what was once sophisticated food science in the days of Tang and the astronauts now seem like child’s play. The encapsulation of sensitive ingredients has become one of the most important and innovative technology areas in the food industry, helping to meet consumer demands for uniquely healthy and natural products, while making incompatible ingredients actually coexist and function properly in food and beverage systems (where their use was never before thought possible). Compatibility aside, some of these ingredients cannot always withstand the rigors of processing, storage or further preparation in the home without some kind of protection from heat, shear, oxygen, light or other environmental insult. Encapsulation helps address these issues, as well.
Titoria believes that four key areas in which product developers should consider utilizing microencapsulated ingredients are:
Luckily, the technology for adding and maintaining nutrients, flavors and other ingredients in a growing variety of products has grown at a good pace. As will be discussed, nanotechnology has been one avenue used to address the need to add nutrients to clear beverages (such that added ingredients are invisible to the naked eye) and suspension in the finished product, without imparting off-flavors. Fortified and flavored waters are a good example where nanoencapsulation can play a role.
Encapsulation and Microencapsulation: Definitions and PrinciplesA general definition of encapsulation might be the entrapment of a compound or system of compounds inside a dispersed material in order to immobilize, protect, control the release, provide needed structure or maximize its ability to perform a certain function (Poncelet, 2006).2 In order to provide unique functionalities, an encapsulation system may be quite complex. For example, one article describes a system where nanospheres that encapsulated ingredients such as flavorings, sweeteners and/or heating and cooling agents, were themselves encapsulated in larger microspheres. Upon exposure to water or a certain pH level, the microspheres would release their nanospheres, which would in turn release their content, when triggered by a specific environment. (Shefer, A. and Shefer, S., 2003. Food Technology. 11:40-42)
Microencapsulation typically describes processes for coating materials to create much smaller particles than traditional agglomeration or beadlet-type technologies in systems where the performance parameters, such as release rates and times, are more clearly defined. Particulates can range from nano-sized to over 200µm.
The definition of microencapsulation varies slightly, depending on the world of applications in which it is being applied. For the biochemist, life itself would not be possible if it were not for membrane-bound structures and receptors enclosed within cellular systems. For the chemist, molecular encapsulation means the confinement of one type of molecule (often called the guest) within a much larger molecule (called the host), of which cyclodextrins are probably the most popular example among food applications. In the more complex, often polymeric world of food chemistry, encapsulation can also refer to the coating of tiny (e.g., microscopic or sometimes nano-sized) particles of solids, liquid droplets or even gases with another material, in order to protect them from their immediate or potential surroundings; often, they will be released at a later time, under different environmental conditions.
Most “microcapsules” have diameters as small as a few micrometers, though nanotechnology continues to bring down the size to a much smaller scale. On a slightly larger scale than cyclodextrins, more complex molecular structures could form nanospheres, nanocapsules or lipid-like structures, such as liposomes. Larger sizes could be hydrogel beads, microcapsules or microspheres. Some consider the term “macroencapsulation” for particle sizes larger than about 1mm. Encapsulation also includes agglomeration of fine particles or the coating of solid particles. Emulsions can be considered liquid/liquid encapsulation, if they are stable enough to meet the definitions above (Poncelet, 2006).2
Spray-drying is the process that accounts for most of the commercially encapsulated materials used in food products and is one of the most cost-effective approaches. Historically, it has been used extensively in the flavor industry to protect heat-labile flavors. The process is well-known, and the encapsulated ingredients can be easily incorporated into dry products and powders. Typically, the protected actives, such as flavors or colors, are released upon contact of the product with water, which dissolves the spray-dried coating or capsule.
In the spray-drying process, a fluid is encased within a carrier material by atomizing a mixture of the two into a chamber with hot air currents. Spray-drying something like an oil-based vitamin with a modified starch is an example of a liquid material that can be converted to a dry powder for addition to other dry ingredients. Carrier materials vary widely, but typical examples include modified starches, maltodextrins or gums. The final product application should be kept in mind when choosing a carrier: for example, a powdered beverage mix would require a carrier highly soluble in cold water, whereas a bar or other solid food form would not need this requirement. Multiple ingredients can often be encapsulated; for example, antioxidants can be added to enhance the finished powder’s shelflife.
An alternative process is melt extrusion. In this process, a melting system, such as an extruder, is employed to form the carrier melt in a continuous process. The flavor, sweetener or other ingredients to be encapsulated are either mixed with or injected into the molten carbohydrate carrier. The amount of encapsulated ingredients typically entrapped by this means is relatively low, typically below 20%. Like spray-dried ingredient systems, these systems can be incorporated into dry products or powders, and the encapsulated active ingredients will be released upon contact of the product with water.
Spray-chilling is another common process in which cool particles of the encapsulate (such as a flavor) are mixed with hot-coating materials (such as a melted fat) to create either a solution or dispersion. This mixture is then atomized into a chamber, where it is contacted with a cool air stream that causes the atomized droplets to solidify, forming a crude encapsulated product. It is then cooled with air to create a powder. Though spray-chilling is a good choice for products that require higher substrate coating levels, up to 80%, there are disadvantages to this process. Drawbacks include interactions between the fat and the active, or the volatilization of lipid-soluble materials over time. Spray-chilling is often used for vitamins, acidulants and reactive minerals that need to be protected from reacting with their ingredient environment, such as various iron fortificants. Volatile actives can be lost during both spray-drying and spray-chilling processes.
Neither spray-drying, melt extrusion or spray-chilling allow the formation of coated materials that have the ability to release multiple active ingredients in a controlled, consecutive manner; this is desirable for a sustained flavor release. More sophisticated encapsulating technologies are needed to achieve these objectives.
Fluid-bed systems for encapsulation are sometimes utilized when the release characteristics of the finished ingredient system are well-defined. The process suspends particles in a controlled air stream, where they are coated with the material of choice. These systems take many forms and may be utilized for drying, granulating and agglomerating, as well as coating. These systems often are used for hot-melt coatings, such as stearines, fatty acids and waxes, which solidify in cool air and release their core material upon heating or shear. They are used to encapsulate ascorbic acid and sodium bicarbonate leavening used in baked goods (Foster, 2005).3
Molecular EncapsulationEncapsulation at the molecular level, sometimes called the inclusion complexation technique, is best illustrated for food applications with cyclodextrins. Briefly, cyclodextrins that many might call “natural” are produced from starch by the action of cyclodextrin glycosyltransferase, an enzyme produced by several microorganisms. Structurally, cyclodextrins consist of 6, 7 or 8 D-glucopyranose units connected by alpha-(1,4) glycosidic linkages (just like starch). (See the cyclodextrin illustration.) The chemically and physically stable, bucket-shaped polysaccharides (with a hydrophobic interior) form stable complexes sometimes instantaneously, with a variety of different molecules. How well the guest molecule fits into and is released from the host “bucket” is a function of the interplay of a number of different molecular interactions, ranging from Van Der Wals forces to hydrogen bonding to interactions with the solvent medium. Cyclodextrins can effectively entrap aromatic oils, such as those from onions and garlic, or various extracts from herbs and spices, making them more water-soluble and control their release (for example, under the moisture and temperature conditions typically found in the mouth). They also have been shown to entrap various flavonols, such as quercetin and myricetin, a potent anti-inflammatory compound and antioxidant, respectively. Both are found naturally in many fruits and vegetables (Lucas-Abellána, 2007a,b).4,5
Some cyclodextrins already are used as carriers for protecting vulnerable natural colors, flavors and vitamins, or serve as a means to solubilize lipids, stabilize oil in water emulsions, or flavor or aroma modifiers in a variety of processed foods. Accelerated and long-term storage stability test results showed that the stability of cyclodextrin-entrapped food ingredients surpassed that of the traditionally formulated ones. Cyclodextrins can offer improved sensory, nutritional and performance properties as a result (Szente and Szejtli, 2004).6 Recent laboratory successes have shown that cyclodextrins can be a means to successfully encapsulate and protect ingredients from oxidation.
Liposomes are composed of a lipid bilayer separating an aqueous internal compartment from the larger aqueous environment. This type of lipid entrapment got its start in the pharmaceutical and cosmetics industries, but is finding more popularity in food applications. Liposomes containing antioxidants can help prevent oxidation of unsaturated fat in margarine or spread emulsions. They often are used to encapsulate heat-sensitive ingredients, such as enzymes and volatile flavors, under mild conditions.
Other Research Developments“Other encapsulation technologies under development include rotating disc methods and vibrating nozzle co-extrusion,” says Titoria, “and they provide flexibility in particle size.” (A comparison of particle sizes formed by various technologies and processes is shown in the chart “A Matter of Size.”) “In the rotating disc process, the core material, which is emulsified in a liquid shell material, is fed onto the center of the rotating disc. The centrifugal force causes the ‘coarse’ droplets to migrate to the outer edge of the disk, and these are spun off as ‘fine’ droplets. Vibrating nozzle co-extrusion involves two fluid nozzles, where the center nozzle carries the liquid that is to be encapsulated, and the external nozzle carries the encapsulation material. The nozzle system is subjected to controlled vibration and flow rate, which together determine the particle size. Then there is complex coacervation technology, in which polysaccharides (such as pectin or gum Arabic) and proteins (such as gelatin) complex to form shells around oil droplets when the pH is lowered; this technology is reported to give better coverage.”
Product applications for encapsulated ingredients can be seen in the following recent developments:
Nanoencapsulation: A Whole New (and Very Tiny) Emerging WorldNanotechnology is another potential tool for developing novel methods of nutrient and flavor protection, not only through encapsulation, but also as a means to provide delivery systems that carry, protect and deliver their “cargo” to the desired site of action.
A nanometer is one one-millionth of a meter. The technology involves the manufacture, processing and application of materials that have one or more dimensions that are about 100nm or less. In the case of nutrients, phytochemicals or medications, the site of action might be inside the intestinal tract or in the bloodstream. In the case of flavors, the site of action is likely the mouth and olfactory organelles.
The applications of nanotechnology in the food sector are only just emerging, but they are predicted to grow rapidly in the coming years. Several products based on nano-micelle-based carrier systems or nano-sized, self-assembled liquid structures (NSSL) are currently available on the global market for use in supplement, food, beverage, cosmetic and pharmaceutical products. Product micelles with a diameter of around 30nm can be created that either entrap hydrophobic substances in a hydrophilic shell or encapsulate water-soluble materials in a lipophilic shell.
This allows for the dissolution of lipid-based materials in water, or of water-soluble vitamins in oil, with visibly clear solutions resulting in either case. Currently, there are only a handful of food and nutrition products containing nano-ingredients or additives available commercially.
The technologies include those for liquid solutions, described by some as “solubilisates,” that are clear solutions containing antioxidants, nutrients, preservatives, colorants or custom active compounds; systems that solubilize co-enzyme Q10, lutein, lycopene, phytosterols, vitamins D and E for water- or oil-based foods and beverages; and “nanocochleates delivery systems,” based on phosphatidylserine, for nutrients and antioxidants.
What This Means for Product Developers“Developers should start looking now for encapsulated or microencapsulated products that provide them with added benefits for their particular applications,” says Titoria. “For instance, encapsulated probiotics might be added to chocolate confections--or a host of other products--now that consumer interest in probiotics is growing. Manufacturers of prepared foods could consider adding ingredients with health benefits, such as omega-3 oils, or provide the consumer with new flavor experiences through encapsulated or timed release flavor systems. The conversion of liquid ingredients to powders or combining ingredients into pre-mixes, even if less sensitive to their food and air environment relative to LC-PUFAs or vitamins, may prove to be cost-effective in some cases, because of improved shelflife and easier use in production.”
The old technology of encapsulation has been rejuvenated with today’s scientific tools to help food formulators to bring both science and creativity to their development efforts. pf
Kathie L. Wrick, PhD, RD, is a partner of The Food Group.
1 IFT, 2000. A Century of Food Science (www.ift.org)
2 Poncelet, D. 2006. Microencapsulation: Fundamentals, Methods and Applications, Chapter 21 in JP Blitz and V. Gun’ko, Surface Chemistry in Biomedical and Environmental Science, NATO Science Series II. Mathematics, Physics and Chemistry, volume 228, Springer Netherlands.
3 Foster, RJ. 2005. Preventing a “Nutrient” Breakdown, Food Product Design. January 2005, www.foodproductdesign.com/articles/462/462_0105HN.html.
4 Lucas-Abellána, C, et al. 2007a. Encapsulation of Quercetin and Myricetin in Cyclodextrins at Acidic pH, J Agric Food Chem. 1:255-259.
5 Lucas-Abellána, C, et al. 2007b, Cyclodextrins as Resveratrol Carrier System, Food Chemistry. 1:39-44.
6 Szente, L, and Szejtli, J, 2004. Cyclodextrins as Food Ingredients. Trends Food Sci Technol. 3-4: 137-142.
7 Homayouni, A, et al. Effect of Microencapsulation and Resistant Starch on the Probiotic Survival and Sensory Properties of Synbiotic Ice Cream. Food Chemistry, In Press, Corrected Proof, Available online 16 March 2008.
8 Gunasekaran S, et al. 2007. Use of Whey Proteins for Encapsulation and Controlled Delivery Applications. J. Food Engin. 83(1): 31-40.
9 Mourtzinos, I, et al., 2008. Encapsulation of Nutraceutical Monoterpenes in B-cyclodextrin and Modified Starch. Food Sci. 1: S89-S94.
www.PreparedFoods.com -- Keyword searchable archives on food science and technology, encapsulation and ingredient use
www.aquanova.de -- Nanotechnology system for clear beverages
www.nutralease.com -- Nanotechnology systems, some of which help improve bioavailability
www.bdsinternational.com -- Website of BioDelivery Sciences that describes technology for drug delivery through nanotechnology. Chaudhry Q, et al. 2008. Applications and implications of nanotechnologies for the food sector, Food Additives and Contaminants. Food Addit Contam. 3:241-58.