Micro-encapsulation can be used for different reasons — to protect reactive materials, to facilitate handling, to achieve controlled release or to inhibit separation. Stefan Theuringer details some of the micro-encapsulation technologies available for protecting and delivering your most valuable ingredients
Growing demand for healthy foods has driven the functional-foods market in recent years, giving manufacturers the opportunity to differentiate their products by adding a range of functional ingredients to them. Growth markets such as heart health, satiety/weight management and gut health offer tremendous opportunities for food and beverage manufacturers. An ever-increasing number of functional ingredients are available to food producers — from vitamins and minerals to omega-3s, prebiotics, probiotics, polyphenols and more — and manufacturers are spoiled for choice as to which functional ingredients will work best for their product.
Yet when it comes down to using these ingredients in a food or beverage, the range of available options is often greatly narrowed down based on stability and taste of the ingredient in the final food or beverage product. Certainly, some ingredients are relatively easy to work with regardless of the type of food to which they are added, but in many cases the type of food or beverage application determines whether an ingredient can be used 'as is' or whether technology is needed to stabilise the ingredient in the food.
Omega-3s are one of these all-star ingredients that offer a number of health benefits for a broad target group. Most scientific research on omega-3s has focused on cardiovascular health; however, growing evidence supports omega-3s benefits for cognitive development and performance, eye health, joint health, ADHD and depression, and more. Clearly, there is still a lot of room for growth for omega-3s as a functional-food ingredient.
One of the main growth inhibitors of omega-3 food products, especially in Europe, has been regulatory status — a hurdle that in the past few years has not made it easy for food manufacturers to launch innovative functional-food products. Another obstacle has been the available omega-3 oil quality and stabilisation technologies. With EFSA's evaluation of health claims ongoing, the regulatory issues should soon be removed. Technology-wise, there have been tremendous improvements in recent years, both with respect to oil quality and the technologies available to stabilise these oils. Due to the high degree of unsaturation of omega-3s (five or six double bonds, depending on the type of omega-3 fatty acid), they are highly prone to oxidation. In food processing, some of the catalysts of oxidation, such as oxygen, light, metal ions, pH and heat, can hardly be avoided, making it extremely difficult to work with omega-3s.
Micro-encapsulation technologies have long been used in the pharmaceutical industry to stabilise sensitive active ingredients. With increasing focus on creating healthy food and beverage products, some of these technologies have been adapted for use in foods or beverages. Micro-encapsulation can be used for different reasons — to protect reactive materials from degradation, to facilitate handling, to achieve controlled release or to inhibit separation. There are a lot of different microencapsulation processes, some of which are outlined ahead.
Matrix solidification by spray drying
Spray drying is a commonly used process to stabilise a range of sensitive active ingredients, including vitamins, minerals, fats and flavours. The active ingredient is dissolved or emulsified in a continuous phase (usually in water), and atomised at the top of a spray tower through which hot air is passing. The water evaporates from the droplets as they fall through the hot air, thus forming dry particles. The active ingredient is entrapped by a matrix (mostly starch- or protein-based) and the release is controlled by dissolution of that matrix. It is thus less of a targeted than a timed release.
Spray drying is a widespread and cost-efficient process for encapsulation of functional-food ingredients. However, due to a high amount of free surface oil (up to 10 per cent), its use for omega-3 oils is limited to applications that are not too taste-sensitive. Use in liquid applications can result in shelf-life limitations due to dissolution of the entrapment matrix over time. Moreover, particle size varies greatly, between 2?m and 100?m, making it difficult to achieve a homogenous distribution of the active ingredient in the final food or beverage.
Spray coating by fluid bed
Fluidised bed encapsulation is a process that is often done as a second, additional step after spray drying to further improve stability against oxidation. It is achieved by suspending solid particles in an upward-moving stream of air. A liquid coating material is sprayed from the top in very small droplets onto the bed of fluidised particles. The fluidised particles are coated by evaporation of the water or solvent. By cooling, the coating material around the particles is hardened. The particle size of these capsules is usually rather large — between 80?m and 2mm. The release properties for the particles are determined by the nature of the coating. Water-soluble coating produces release by contact with water, hot melted encapsulated ingredients are released upon reaching the melting point, and enteric coating produces release upon change of pH. Fluidised bed coating offers increased stability for oxygen-sensitive materials, but it is also more expensive than spray drying.
Coacervation is formed by dissolution of a gelling protein in water, followed by emulsification of a core material — usually an oil — into the protein solution. It is formed by a positively charged macromolecule — proteins such as gelatine or casein — and a negatively charged hydrocolloid, usually gum arabic or pectin. There are two different types of coacervation: simple and complex, depending on the number of polymers used in the process. Coacervation only has limited use in foods due to its high cost and limited availability of food-grade coating materials.
GAT Food Essentials has developed a proprietary micro-encapsulation process that results in a water/oil/water emulsion protected by shell of cross-linked polymers. The microcapsules consist of an inner-water phase surrounded by an oil phase and dispersed in an outer-water phase. The two inner phases are protected by a capsule wall composed of polymers. These polymers are very sensitive to pH — they are stable in any environment with a pH of 3.5 or higher (up to about 7.5); once the pH drops below 3.5, the capsule walls break and release the active ingredient contained inside.
Once encapsulated, the ingredients are stable against oxidation and degradation, as they are protected from the effects of harsh processing conditions such as pasteurization/UHT treatments, homogenisation and baking/drying processes. Only when the pH drops (inside the stomach after consumption) do the capsule walls break and completely release the active ingredient contained inside.
Both the inner-water phase and the oil phase can contain active ingredients, meaning that the same technology works for both water- and oil-soluble ingredients. The two phases are necessary for the stability of the microcapsules; however, their respective size can be adjusted depending on the active ingredient(s) incorporated.
For instance, a microcapsule containing a water-soluble ingredient such as vitamin C will have a maximised water phase in order to deliver as much of the vitamin as possible. By contrast, a microcapsule containing omega-3s has a minimised, 'empty' inner-water phase surrounded by a maximised-oil phase. This approach results in a technology platform that can be used for a variety of sensitive active ingredients, thus giving the customer the opportunity to work with the same technology for a number of ingredients. This increases flexibility and, at the same time, reduces the cost of new-product development, because the characteristics of the encapsulated ingredient remain the same regardless if it is fish oil, plant extracts or minerals.
The ingredients, so encapsulated, can be added to a variety of applications without negatively affecting taste, texture or shelf life. Key applications include dairy (fresh, ESL and aseptic milks, yoghurt, smoothies, cheese, ice cream), baked goods (bread, cookies, granola, cereals, cereal bars), beverages (juices, nectars, concentrates), meats (ham, cold cuts, sausages, p?t?s), and convenience foods (sauces, dressings, ready meals). With micro-encapsulation, your omega-3s can work better for your downstream consumers.
Stefan Thueringer is chief marketing officer and general manager at GAT Food Essentials GmbH (GAT). He has been with GAT since its founding in 2004, in charge of developing the company from a small start-up with a technology concept to a recognised and internationally operating micro-encapsulation specialist in the functional-foods and beverages industry. www.gat-foodessentials.com