Encapsulation: Winning the Shell Game
Encapsulation technology encompasses a variety of methods such as spray drying, spray chilling, fluid-bed encapsulation, hot-melt extrusion and coacervation. Several of these methods will be described in some detail to illustrate how encapsulates are formed, the types of materials used and how the core may be released. Regardless of its properties, the product developer must acquire the encapsulated ingredient that best serves the formulation goal. To this end, ingredient suppliers can best guide food formulators by understanding the type of delivery desired, formulation and process parameters, storage conditions and end-user preparation methods.
Setting a GoalControlled release is a “time spectrum,” notes Ronald J. Versic, PhD, president of a company that supplies encapsulation services and ingredients for various markets. The amount of core material released and the rate of delivery can be designed to match a customer's specification. For instance, cherry flavor in a drink mix will release instantaneously upon dissolution with water. This is called a “burst effect.” On the other hand, applications such as salt on the surface of meat destined for microwave heating require a slower, more phased release. Thus, a product developer must work with the supplier of an encapsulated ingredient when seeking a customized product so that controlled release can be timed to specification.
Encapsulation techniques are designed to protect a key ingredient from environmental conditions that could either minimize or damage its effectiveness. The encapsulate may protect the ingredient from heat, low pH, oxidation, light impact, flavor loss and/or the interaction with other ingredients, notes Rodger Jonas, national business development manager of an ingredient supplier.
Extending the shelflife of bread and other yeast-leavened products is a common goal of many bakers. Sorbic acid, an antimicrobial, is one effective method of accomplishing this task; however, sorbic acid will not only kill mold, it also kills yeast, which prevents the bread from leavening. By encapsulating sorbic acid, the baker not only protects the bread from mold growth (thereby increasing shelflife), but also does so without adversely affecting dough development or proof time, notes Kristine Lukasik, PhD, application manager for another ingredient supplier.
It's All in the TechniqueEncapsulation techniques are “tried and true methods,” says Versic, “and today, there is more impetus than ever for controlled flavor release.” Spray drying dates back to the late 1880s, where it was applied to milk solids so they could be more easily transported in a “dry state.” A dried drink mix is an example of a spray-dried application, where the release mechanism is effectively dissolution in water.
The process for spray drying oils was awarded a patent in the 1920s. Spray-dried material typically contains an oil-based core surrounded by a water-soluble, carbohydrate-based material such as maltodextrin, modified starch, corn syrup solids or a hydrocolloid gum such as gum Arabic, alginates or cellulose derivatives. An oil-in-water emulsion is formed prior to spray drying by combining the immiscible substances, adding an emulsifier and homogenizing the mixture. The mixture is subsequently atomized in a column of heated air in the spray-dry chamber where the core takes on a spherical shape and is surrounded by the soluble coating material, which hardens as the water evaporates. The inner core droplets typically measure 1m to 2m and the outer matrix 15m to 50m, notes Versic. The resulting unit per volume composition contains 20% to 30% oil.
Spray chilling is very similar to spray-drying, except the soluble material forms the core and the insoluble substance (i.e., waxes, fatty acids or edible oils) forms the outer matrix. The coating solidifies in a cooling chamber as opposed to the heated chamber used during spray drying. This process is used in applications where protecting the core from moisture is desirable. Release of the inner core is accomplished when the outer matrix melts upon exposure to heat.
Fluidized bed coating is used to encapsulate solid particles. In this process, particles are placed in a chamber and suspended by an upward-flowing temperature and humidity-controlled air current. The coating material is atomized in the air current and evaporates onto the solid particle. Multiple layers and different types of coating may be applied using this technique.
Coacervation, a batch process in contrast to the continuous processes described above, is a more materially efficient method for coating liquids, notes Versic. The shell morphology can range from 80:20 wall to core material to a ratio of the opposite extreme, or 20:80 wall to core material. Versic describes the gelatin coacervation process as follows:
Gelatin is dissolved in warm water (at 35°C, 95°F). Oil, which must be completely immiscible in water, is added. The mixture is mixed until tiny droplets form (at 25m to 50m). When the gelatin mixture containing the oil droplets cools, it forms three phases—little droplets of oil; an aggregate of colloidal droplets, or the coacervate comprised of gelatin; and water largely devoid of gelatin. The coacervate shrinks and exudes water as the mixture continues to chill, forming a capsule around the gelatin particles. Cross-linking it with an aldehyde may strengthen the structure of this gelatin capsule. This cross-linking process will keep the gelatin capsule together until the food is processed. Exposure to heat and moisture ultimately will dissolve the capsule and release its inner core.
A heat-stable, protein-encapsulated flavor also has been developed via coacervation. This encapsulate survives a range of thermal processes including baking, frying and microwave heating. The capsules protect the flavor during heating and are released during chewing.
Nanoencapsulation produces an ingredient less than 30nm (typically 9nm to 11nm), notes Jonas. Nanoencapsulated oils are water-soluble and remain clear when added to water or a beverage. On the other hand, microencapsulated ingredients produce a cloudy product when added to water, but are suitable for use in dairy and bakery products that do not require clarity.
The PayoffMany ingredients, particularly those offering functional or nutritional benefits, impart off-flavors to foods without enough inherent masking capability. For instance, “vitamin supplement producers have been frustrated in not being able to deliver the therapeutic effects of omega-3 fatty acids from fish oil in compressed tablets,” explains Lukasik. “However, similar therapeutic benefits can be delivered with the nutrient choline. Choline's reactivity with other tablet components and the need for long shelflife recommended it as an ideal candidate for encapsulation. A form of encapsulated choline was specifically designed for compressed tableting, providing tablet stability and nutrient efficacy through a patented controlled release technology, which led to the introduction of a differentiated product on the market, and the patent provided exclusivity for one particular multivitamin producer.”
Lukasik describes another successful application of flavor-masking: “Chewing gum has been featured recently as a delivery matrix for vitamins. However, when caffeine is included in the formula, its bitterness is constantly pulsed into the consumer's mouth with every chew. Taste-masking through encapsulation changes the entire flavor profile of the gum to a satisfying experience combined with energy enhancement.”
The term “overages” applies to the additional levels of ingredients such as vitamins and minerals added to finished goods in order to obtain the stated amount on the package at the end of shelflife, notes Jonas. “Encapsulation helps eliminate this issue.” Examples of products available for nanoencapsulation include co-enzyme Q10, isoflavones, vitamins and minerals, lutein, omega-cran oil, citrus oils, phytosterols, mint and menthol and oil-based flavors. Examples of products available for microencapsulation include vitamins and minerals, caffeine, vitamin C for use in soft cheeses and dairy beverages, aspartame, folic acid and carnine, adds Jonas.
Encapsulation techniques not only protect ingredients from harsh environmental conditions, but provide perhaps the most versatile means of innovation for many processors, particularly in terms of time-release. Even though encapsulation methods were developed many years ago, researchers continue to find novel ways of adapting them to new ingredient applications.
References:Wolfson, W. 2004. Innovation news: fish-oil cookies; Technology Review. 7 (7):27.
Yuliani, S., et al. 2004. Application of microencapsulated flavor to extrusion product; Food Review International. 20 (2):163-185.
Website Resources:www.rtdodge.com — Ronald T. Dodge Company; innovators and information service provider of microencapsulation
www.balchem.com — Searchable Balchem Corporation website with information on encapsulated ingredients
www.plthomas.com — P.L. Thomas & Co. Inc.