Techniques for Nanoencapsulation of Food Ingredients

Nanoscience and nanotechnology are new frontiers of this century and becoming highly important due to its wide application in various fields. Food nanotechnology is an emerging technology being potential to generate innovative products and processes in the food industry. Many reviews and research papers have been published on application of nanotechnology in foods. However, only a few reports are focused on nanoencapsulation of food ingredients. Therefore, the main focus here is to discuss the various nanoencapsulation techniques, their advantages, flaws and variations, as well as to appraise the interesting emerging technologies and trends in this field, along with the safety and regulatory issues.

A combination of high-energy approaches (such as high-speed and high-pressure homogenization or high-pressure homogenization and ultrasonication) can aid in the formation of nanoemulsions with very small droplet diameters. A practical approach is to emulsify the sample under conditions of increasing intensity (e.g., starting at 2,000 rpm and increasing to 20,000 rpm in a rotor-stator), especially if the dispersed phase is highly viscous. One major constraint faced by researchers after the production of nanoemulsions is the process of Ostwald ripening, wherein the mean size of the nanoemulsion increases over time due to diffusion of oil molecules from the small to large droplets through the continuous phase. This is particularly seen in nanoemulsions formed by low-energy emulsification methods. A possible means to overcome this instability mechanism is by increasing the surfactant concentration by altering the oil-to-surfactant ratio. This chapter reviews the various techniques for nanoemulsion preparation.

A delivery system is a formulation or a device that introduces bioactive compounds into the body and improves their efficacy and safety by controlling the rate and targeted release of the bioactive compound. Food-based nanocarrier systems are generally based on carbohydrate, protein, or lipids. There are various types of lipid-based nanoparticulate delivery systems such as nanoemulsions, nanoliposomes, solid lipid nanoparticles, lipid nanotubes, lipid nanospheres, and nanostructured lipid carriers. As nanocarriers, they are expected to be promising oral carriers due to their potential to improve the solubility and bioavailability of poorly water-soluble and lipophilic compounds. The selection of an appropriate delivery system is dictated by the characteristic solubility and stability of the bioactive compound, the safety and efficiency of the bioactive-carrier lipid matrix, intended application, route of administration, etc. Hence, lipid-based nanoencapsulation is emerging as one of the most promising encapsulation technologies in the field of nanotechnology. This chapter reviews the present state of the art of widely used lipid-based nanoparticulate delivery systems such as solid lipid nanoparticles (SLN), nanostructured lipid carriers (NLC), and nanoliposomes.

Nanoencapsulation is one of the most promising new technologies, having the feasibility to entrap bioactive compounds. It has versatile advantages in terms of targeted site-specific delivery and efficient absorption through cells. This chapter focuses on the various liquid-based nanoencapsulation techniques such as coacervation, inclusion encapsulation, nanoprecipitation, emulsification-solvent evaporation, and supercritical fluid. The current state of knowledge, limitations of these techniques, and recent trends are discussed.

In recent years, electrospraying and electrospinning have attracted widespread interest and found applications in the food industry and for drug delivery. These electrohydrodynamic processes are having great potential for making micro- and nanosized particles and fibers. However, more research is needed to optimize the operating conditions for the nanoencapsulation of various food and bioactive compounds. In addition, the properties, and efficiency of the nanocapsules have to be analyzed to improve their application in the food industry. The current state of knowledge, limitations of electrospinning and electrospraying techniques, and recent trends are discussed.

Nanoencapsulation techniques are used to produce nanosuspensions of active compounds with a coating or encapsulated with wall materials, in liquid or dried form. The major problems of nanocapsules are irreversible aggregation and chemical instability and leakage of the encapsulated active ingredients. Therefore, it is desirable to convert nanocapsule suspensions into dried form to maintain their stability. The drying of nanoparticles facilitates easier handling and storage and they are readily dispersible in aqueous solutions. Hence, nanoencapsulation methods in combination with drying techniques are essential for converting encapsulated suspensions to a dried, stable form. This chapter reviews the various drying techniques for nanoencapsulation.

Freeze-drying and spray-drying techniques are commonly employed for drying of nanosuspensions and it is clear that the operating conditions of spray drying and freeze-drying are significantly important in the stabilization of nanocapsules. Besides higher stability compared to the original nanoparticle suspension, the dried powders have the ability to control and promote sustained bioactive compound release. However, drying aggravates additional stress on the nanocapsules during processing. This chapter discusses in detail the different drying techniques used for production of nanoparticles and described in table 6.1 (Ezhilarasi et al. 2013).

Food-grade nanoemulsions constitute one of the most promising systems for improving the solubility, bioavailability, stability, and functionality of many bioactive compounds. These improved properties of nanoemulsions can be exploited for many novel and technological innovations that find various industrial applications. Furthermore, there are challenges such as suitable processing operations and facilities to scale-up for industrial production that need to be overcome for wide utilization of nanoemulsions. This chapter reviews the various applications of nanoemulsions.

Nanoemulsions for encapsulation and delivery of functional compounds is one of the emerging applications of nanotechnology in the food, pharmaceutical, and cosmetic industries. Food-based nanoemulsions are finding increased utilization as oral delivery systems. Emulsion-based delivery systems protect the bioactive compounds against environmental conditions such as heat, moisture, air, and light. They also increase the products’ storage stability, maintain efficiency, and mask unwanted odors and bitter tastes (Madene et al., Int J Food Science Technol 41(1):1–21, 2006). Higher bioavailability in turn enhances the bioactivity of the active compound. A nanoemulsion also has the ability to deliver the bioactive compounds in the skin and is suitable for diffusion in the dermal layers. Other applications of food-grade nanoemulsions include antimicrobial activity, which is utilized in the decontamination of equipment and in food packaging (Gruere G, Narrod C, Abbott L (2011). Agricultural, food, and water nanotechnologies for the poor. Available at: http://​www.​ifpri.​org/​sites/​default/​files/​publications/​ifpridp01064.​pdf. Accessed 14 April 2013), and in extending the shelf life of foods. Most of the applications of nanoemulsions depend on their physicochemical properties and stability, which determines their efficiency. The stability and properties can be controlled by altering their composition, preparation methods and preparation conditions according to the required composition, particle size distribution, interfacial properties, and different droplet concentrations of emulsions (McClements, Ann Rev Food Sci Technol 1:241–269, 2010).

Synthesis of nanoparticles using different techniques of encapsulation has attracted a lot of interest these days and the incorporation of nanoparticles into food items has made food more “functional.” But, this field of research is still under trial and is not yet knocking on the door of industry. There are some limitations that are hindering the path of revolution. Before the incorporation of nanoparticles into any food product or drug, it is necessary to characterize the behavior of the miniature product. This chapter reviews the various techniques for characterization of nanoparticles.

Characterization includes both physical and chemical aspects. Physical characteristics include structure, morphology, size, state of aggregation, dispersion, sorption, surface charge, and solubility whereas the chemical properties include temperature, pH, etc. (Tiede et al., Food Addit Contam A 25(7):795–821, 2008). Different techniques are available for analyzing these aspects. Structure and morphology can be analyzed by the techniques of microscopy including scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. Chromatography-related techniques are used for the separation of particles on the basis of the size and charge on their surface. Different chromatographic techniques include size exclusion chromatography, high performance liquid chromatography, hydrodynamic chromatography, and capillary electrophoresis. Centrifugation and filtration techniques help to filter the particle on the basis of their density and size. X-ray diffraction methodology is also exploited for the identification of crystalline solids from their atomic structure (Luykx et al., J Agr Food Chem 56(18):8231–8247, 2008). The techniques mentioned above are sensitive enough to detect the small particles.

Today’s consumers are conscious about what they eat. “Safety” is the buzzword in the current food scenario. Food safety is an area of major concern today and there are many demands on the food production system. Delivering safe food is the responsibility of all the stakeholders in the food processing chain, including researchers and manufacturers. As with any new technology, nanofoods are also expected to face this safety challenge and gain acceptance before they find a place on the consumer’s shelf. To date, there is no clear implication that nanofoods are either safe or dangerous or that they have harmed human health on ingestion. According to the World Health Organization, it is established that consumers are likely to benefit from nanotechnology, however new data and measurement approaches are needed to ensure the safety of products. Incorporating nanotechnology into food systems should be done with clarity on its health and safety impacts. In this context, the safety considerations of nanofoods are briefly discussed in this chapter.