This paper discusses the definition, methods, advantages and disadvantages of microencapsulation, and identifies the improvements achieved in animal nutrition with the advent of microencapsulation. Microencapsulation is used to improve product bioavailability, delivering nutrients and additives to the digestive tract at varying rates or sites of delivery with an aim to improve animal performance. Several techniques used for microencapsulating feed ingredients will be discussed in detail. These will include spray- drying, spray chilling or spray cooling, extrusion, and coacervation. Microencapsulation can be advantageous in delivering certain nutrients to animals. This review addresses this advantage in ruminants, non ruminants and aquatic animal species. When properly used, microencapsulation is a tool that can be effectively utilized in animal diets by providing or delivering nutrients and/ or drugs to a specific site at a desired rate.
Microencapsulation technology development and usage has been in place for over 60 years (Desai and Park, 2005). Microencapsulation is defined as the protection of a material (the core) in another material (the capsule or coating). The capsule or coating protects the core from a particular environment, allowing the core to be strategically released to perform its specific biological function in a target area of the digestive tract and at a target rate (Gibbs et al., 1999). Microencapsulation processes result in various size and shape of the product. This process is used in the industry to achieve a set of goals that require either a slow release of the core material or its release to a particular site of the intestinal tract and is often delivered as a dietary component of the feed. Microencapsulation may be used for many purposes in animal nutrition. It may be used for differentiation of products, to mask taste of unpalatable products, to guarantee the product content after long storage periods, to deliver ingredients to a particular site of the gastrointestinal (GI) tract, to improve product bioavailability or to improve animal performance (Putnam et al., 2003). Additionally, microencapsulation may protect the core material from heat, moisture or other environmental conditions that would cause the core to degrade. This technology may also be used to provide two reactant substances in the same diet, without them being in direct contact (Bakan, 1973; Gibbs, et al, 1999).
Early encapsulation technology developed capsules that were impermeable to the aqueous environment of the digestive tract and the core ingredient was generally released by mechanical action (Seiss and Divies, 1975). Sugar, protein, lipids or synthetic polymers were the main components of the capsule (Gibbs et al., 1999). This early technology paved the way for the use of current microencapsulation technology. This innovative technology may increase the life span of the food ingredient, reduce the amount of ingredient needed in the diet and/or control its release rate for absorption across the gut wall.
The objective of this paper is to review the different methods of microencapsulation, discuss the advantages and disadvantages of microencapsulation and identify the improvements achieved in ruminant, nonruminant, and aquaculture nutrition with the advent of microencapsulation.
Methods of Microencapsulation
Several techniques can be used for microencapsulating feed ingredients. The determination of the best method is directly related to the physical and chemical characteristics of the ingredient to be encapsulated and the capsule material to be used. A wide variation of capsule material and technology exist. Careful consideration of these is critical in achieving the objectives for a specific core material. For example one can choose a capsule material to release the core in a specific pH change or enzymatic reaction (Desai and Park, 2005). The following is a brief description of some techniques for microencapsulation:
Spray drying is the most widely used technique of combining the capsule with the core (Desai and Park, 2005). In this process the material to be encapsulated is mixed with the core material, both in suspension, and then placed into a spray dryer. The mixture is then sprayed across a nozzle while the water is evaporated by hot air (Gibbs et al, 1999). Figure 1 shows particles after spray-dried microencapsulation. The shape of the powder becomes more crumpled when the molecular weight of polyethylene oxide, a widely used core material in spray drying, increases (Sugiyama et al., 2006).
• Spray chilling or spray cooling:
In this case the mixed material (Core and coating) is sprayed with cold air instead of hot air and it does not include any evaporation. The coating material is normally vegetable oil or derivatives (Risch, 1995). It is used for heat sensitive material, high fat contents like vitamins and enzymes. Figure 2 describes the process of producing microencapsulates utilizing spray cooling technology (Kawanami et al., 2006).
This type of microencapsulation is a different technique from extrusion process used normally in the rations by the feed industry. In microencapsulation it is done using lower temperature forcing a core material in a molten carbohydrate and then extruded into a dehydrating liquid. The wall material in this technique includes a variety of products to include cellulose derivatives, gums, fats, waxes, polyethylene glycol, etc. Figure 3 below demonstrates the steps of microencapsulation utilizing the extrusion technology (Desai and Park, 2005).
In this technique the core material is covered by the precipitation of a fine-particle as a coating material (Slink, 1975).The most common material used as a coating is gelatin/gum acacia (Desai and Park, 2005). However, other materials can be used such as soy protein or carboxymethylcellulose (Gouin, 2004). This method can be used with high efficiency to hydrophobic material as vegetable oil or vitamin A (Gibbs, et al, 1999). Figure 4 shows the different phases of microencapsulation when utilizing the coacervation technology (Sliwka, 1975).
Modifications of different older processes as well as new microencapsulation processes are now available which prevent the loss of volatile compounds as well as to coat individual particles to ensure optimum activity of the ingredient as well as delivery. These newer proprietary processes result in more efficient and robust microencapsulation according to the manufacturers.
Ruminants have a unique digestive system that must be considered when formulating diets. Encapsulation can be a very useful tool when presenting material to the small intestine that could be altered or degraded by the microbial fermentation occurring in the ruminant compartments. Products can be designed to escape microbial fermentation/ degradation in the rumen-reticular compartments of the stomach and later released for absorption in the abomasum or small intestine. This technology can be advantageous for the delivery of nutrients or drugs to the small intestine and also to protect the ruminal microflora from the negative effects that various drugs may have as they flow through the stomach compartments of the digestive tract (Wu and Papas, 1997).
The first work conducted in ruminants was the protection of feed proteins and amino acids to provide low levels of the limiting amino acids to the host animal (Nimrick et al., 1970). Other studies have protected lipids, starch and glucose (Wu and Papas, 1997). Heat and chemical treatment, low solubility analogues and lipid based formulations have been used for protecting feed additives from ruminal microorganism degradation (Wu and Papas, 1997).
Bauman et al. (2003) suggested that because of difference in pH between the ruminal compartment (about 5.5 to 6.5) and the abomasum (about 2 to 4) it is possible to have rumen fat protection with a pH dependent capsule. The main goal of microencapsulation is to have rumen protection without losing post-ruminal bioavailability (Wu and Papas, 1997). Yoshimaru et al. (2000b) working with rumen protected microcapsules found that microencapsulated L-lysine was highly stable under neutral conditions (pH 6.5) and had between 70 and 85% release in the abomasal media (pH 3.0). This response varied according to the type of coating agent.
Gulati et al. (2000) working with ruminal and abomasal protected conjugated linoleic acid (CLA) isomers showed that the amount of CLA isomers absorbed in the small intestine was 3.5 to 4% higher than that for unprotected CLA isomers. Bonomi et al. (1991, 2005) supplementing dairy cows with microencapsulated fatty acids with different vitamins as A, D3, E, beta-carotene, choline, biotin, pyridoxine, riboflavin found no difference in reproductive efficiency and health status using the lower doses of protected product compared to the unprotected supplement at a higher dose.
Garrett et al. (2007) using an “in vitro” experiment found that two different forms of rumen protected ascorbic acid (vitamin C) was protected at rates of 50% or more when exposed to rumen bacteria for a 24 h period. These studies show that microencapsulation is a valuable tool in delivering products to ruminants. Stabilized forms of microencapsulated ascorbic acid are commercially available which when used as a supplement in animal feeds are temperature and low pH resistant, protected from ruminal degradation and become biologically available to all ruminants and nonruminants. By microencapsulating vitamin C, the nutrient is physically protected from air, light and metals, which prevent oxidation and maintain potency.
Organic acids are used to reduce the pH in the small intestine of nonruminant diets to provide a greater resistance to pathogenic bacterial infections. Piva et al. (2007) working with piglets microencapsulated organic acid with a dose ten fold lower than the normal dose of unprotected organic acid and obtained a similar response from the lower dose microencapsulated product.
Lin et al., (2002) prepared an oral vaccine with either spray drying or solvent evaporation and showed both microencapsulation techniques were effective in protecting the core material against gastric acid. The microencapsulation technique can also make fats easier to use by the swine feed industry. Solid fat must be liquefied before use in feed and liquid fat requires special equipment when added to diets (Walter, 1990). Microencapsulated fat can be mixed directly into the diet as fine particles (Kim et al., 1996; Re, 1998) making it more user friendly in diet preparation. In addition to the handling advantage, Xing et al. (2004), used encapsulation spray-dried fat in a pelleted diet for nursery pigs and increased ADG and gain: feed.
According to Lee (2003) the microencapsulation makes the food particles stable in water, which is important in aquatic feedstuffs. However, feeding pelleted diets may become difficult to digestion and therefore kill fish larvae because of gut filling. Marine fish, during larvae stage need to be fed live diets until metamorphosis, and only after this period they can be fed an inert feed (Blair et al., 2003).
Yufera et al. (1999) working with microencapsulated diets prepared by interfacial polymerization of protein found satisfactory larval growth in marine fish. These authors concluded that microencapsulated diets can become an alternative to replace live food in the early larval stages.
Chen et al., (1992) working with arginine as dietary supplement in juvenile Penaeus monodon found a higher weight gain and feed conversion rate of shrimp fed microencapsulated L-arginine when compared to crystalline L-arginine. They suggested that microencapsulation is an important technique to help in satisfying the amino acids requirements of shrimp. Additionally, slow release ascorbic acid is available commercially for use in pelleted aquaculture diets. Shrimp have a requirement for ascorbic acid.
Microencapsulation is a tool that can be effectively utilized in animal diets. Among its benefits are to:
- Protect the shelf life and stability of labile ingredients
- Protect ingredients from air, light and metals to maintain potency
- Taste masking of undesirable flavors and odors while delivering desirable attributes
- Prevent nuisance and dust control
- Prevent ingredient interactions
- Delivering the ingredient to a specific site and delivering it at a desired release rate