Nano-encapsulation is the process of trapping extremely small particles within a coating or matrix. More specifically it is a technique in which small particles or droplets of a solid, liquid, or gas is entrapped within another substance. In its simplest form a microcapsule is a small sphere with a uniform shell around it; this sphere can range in size from a few nanometers to a few micrometers. Many microcapsules however bear little resemblance to their simplest form. In many cases the microcapsule will have multiple walls and the core may be a crystal, a jagged adsorbent particle, an emulsion, a suspension of solids, or even a suspension of smaller microcapsules.
The food and nutraceutical industries have taken advantage of the variety of microencapsulation techniques. The benefits of using common microencapsulation technologies such as spray drying, fluid coating, spray chilling or cooling, melt injection, melt extrusion, emulsification, coacervation, co-extrusion, inclusion complexation, and liposome entrapment are numerous. Coating or entrapping a particle within a shell adds a layer of protection increasing the stability and shelf life of the ingredients and ultimately allowing for greater ease of use and superior handling of the core material. The extra layer of the coating provides a protective barrier between the entrapped particle and its reactive surroundings slowing down degradative processes. Additionally, a coating can provide a mask for undesirable odors, tastes, or textures greatly improving the appeal of the active agent and opening the door to a broader consumer base. Furthermore, a specialized coating can allow for controlled delivery and release of the encapsulated material. Specific nanotechnologies such as liposomes can also help to increase the bioavailability or solubility of certain food or nutritional agents.
Liposomes are most often used within the food and nutraceutical industries as a vehicle for dissolving water-soluble and lipid-soluble or multiple lipid soluble materials simultaneously. This is extremely beneficial when these compounds are best used in a symbiotic relationship. For instance, curcumin, a highly available nutritional supplement, is a lipid soluble molecule. On its own, the curcumin molecule has been shown to have low solubility and high metabolic rates within the serum. However, when the molecule is incorporated into a liposome and coupled with other lipid soluble enzymes, such as, Piperine and Quercetin that block curcumin metabolites the bioavailability of the molecule increases exponentially. Creating a symbiotic relationship within the liposome structure which enhances the effect of the active agent is a valuable tool within the food and nutraceutical industries.
Liposomes can be formulated in either the matrix or the reservoir structure. Within the matrix form the active agent or food particle tends to be dispersed throughout or on the surface of the membrane. The reservoir structure, on the other hand, consists of a single membrane wrapped around the active ingredient. When using liposomes in food or nutraceutical formulations one of the main difficulties is maintaining the stability of the formulation at room temperature. Chemical degradation will occur in the form of hydrolysis, oxidation, aggregation, or fusion as the chemical compounds sit at higher temperatures over time. The most problematic of these is the process is hydrolysis. While hydrolysis is a naturally occurring phenomenon, the acceleration of liposomal degradation could be increased though certain conditions such as lack of buffer or incorrect pH levels. The optimal pH for the lowest amount of hydrolysis to occur at any temperature has been proven to be 6.5, however, this pH is not always the most ideal for food preparation. Oxidation can also pose a problem, however, not as significant as hydrolysis. Oxidation of lipids only becomes problematic when the formulation is composed of poly unsaturated phospholipids. Oxidation of phospholipids can be significantly decreased when the buffers are degassed and purged with nitrogen or argon. To avoid such issues as hydrolysis and oxidation synthetic, saturated ether lipid could be used, however, due to the high cost of the phospholipid it is nearly impossible to use them in the food or nutraceutical industries.
Liposomes are also applied in a number of other different scenarios within the food and nutraceutical industries. Liposomes can be used as a protective agent against premature degradation, hydrolysis, and inappropriate interactions. For example, encapsulated nisin acts as a long-term preservative with a controlled release property. Liposome encapsulated nisin enhances its antimicrobial activity. Liposome encapsulated nisin was used to control the growth of bacterial during cheese storage and it was shown that the liposomal formulation could be used for the control of food-borne pathogens in cheese. Additionally, liposome technologies have also been associated with accelerating the ripening process of cheese. Certain studies have noted the encapsulation of exogenous enzymes with helping to improve the enzyme retention within the curd and decreasing the loss of whey ultimately reducing the amount of time required for cheese to ripen. Moreover, liposomes have been used in the Maillard reaction or browning reaction. Liposomes can be used to achieve the perfectly brown ‘cooked’ effect by conjugating a reducing sugar containing free carbonyl to its surface.
Liquid compositions of liposome formulations are not widely used. This is due to the instability of phospholipids in high temperature and low pH, formulation of liposomes with a long shelf life at room temperature cannot be developed. All the liquid liposome formulations that are developed in the pharmaceutical industry have to be kept refrigerated. One way to get around this problem is by using an innovative microencapsulation technology. Freeze-drying proliposomes and storing the liposomal formulation in a powdered form stops lipid degradation and destabilization. The process increases the shelf-life of the lipid and allows the product to be stored at room temperature. Additionally, by packaging the freeze-dried material in powder release caps the consumer can easily make the final liposome by simply releasing the contents into water when they are ready to consume it.