Advances in Encapsulation Technology

This item is from a talk presented at the FlavourTalk Raw Materials Roundtable Exhibition and Conference in Amsterdam on 23rd February 2017. The full article first appeared in Issue 21 of Flavour Horizons’ quarterly bulletin http://www.flavourhorizons.com/.

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Introduction

Microencapsulation and nanoencapsulation are established techniques for modifying the properties of a range of materials and ingredients across a number of sectors, including drug delivery, crop protection and food. This article will present a selection of edited highlights of recent developments in micro- and nano-encapsulation and their application to food flavours and flavouring ingredients, revisiting some established technologies and introducing some new ones. In its simplest form, encapsulation provides a cost effective means of converting liquids into a powder to improve handling. It can also improve impact in targeted delivery, mask the taste of bitter plant extracts and reduce intrusive odours from volatile flavours. In controlled and delayed release applications it can improve process stability and can be used for the protection of sensitive ingredients against UV light, heat, moisture and oxidation and for the isolation of reactive components. One of the key benefits is the stabilisation of volatile flavour ingredients to improve the shelf life of finished products. In addition to these familiar challenges, market pressures require products to be produced faster, at lower cost and using natural raw materials.

​Materials

​A wide range of carrier, shell and matrix materials are available to form the building blocks of potential microcapsules and particles into which flavour ingredients can be trapped. These may be familiar food components, for example modified starches, such as maltodextrins, or plant based gums and alginates. In more recent years there has been an emerging range of applications in which proteins, such as zein from maize and milk casein, plant saponins and polysaccharide biopolymers, such as chitosan, have been used. Microcapsules and nanostructured materials come in many shapes and sizes. Most commonly they are liquid or solid filled core shell capsules or matrix particles where flavours are dispersed throughout a solid particle. These can then be dried and processed into a powder or may be collected and used as a dispersion or emulsion.

​Microencapsulation techniques

​The process of forming these materials can be categorised into two main types, physical and chemical techniques. The most common physical method used to process food flavours is spray drying but techniques also include spray chilling, extrusion and fluid bed drying/coating . Chemical methods include simple and complex coacervation and in situ polymerisation. Other emerging approaches include the use of microsieves and microfluidics, vibrating nozzles, electrospraying and electrospinning, sonication, inkjet and 3D printing. These latter technologies are often restricted to local, bespoke and medical applications. A number of issues need to be addressed when tackling a new product application involving microencapsulated ingredients. Obviously it is essential to ensure that a principal component can be encapsulated, which is usually the case. It is also important to consider the preferred trigger of release and the means of cost effectively characterising the products and measuring their performance. Using either core shell or matrix materials, two contrasting patterns of release can be achieved.

A hard core shell capsule can retain flavour until it is broken open by shear forces during chewing to provide a burst of flavour release. Matrix particles have the flavour distributed throughout the micro-bead and may dissolve slowly in saliva providing a sustained release profile. Using carrier material that dissolves rapidly in water may enable both systems to deliver a burst of flavour. This then provides options for selecting the most cost effective materials and processes to meet the demands of the application.  However, the impact on the performance of the material during processing and packaging must be carefully considered. Impact factors may include shear, heat, pressure and moisture, singly or in combination. Compiling both product and process specifications becomes key to selecting the right type of microcapsule technology for the application. There are opportunities for using preformed capsules or carrier materials as vehicles for flavour delivery. Biocapsules, such as bacteria, pollen, microalgae and yeast or fungi, have all been investigated as possible carriers for food ingredients.  For example, the sporopollenin exine shells of pollen are resistant to acids, alkalis and temperatures of up to 250 degC and have antioxidant properties[1]. Yeast was patented for use to absorb functional ingredients for use in range of applications as early as 1973 and has been exploited since then to deliver active ingredients[2]. This includes the use of spent brewery yeast Saccharomyces cerevisiae in food flavour delivery, where a degree of heat stability is required to prevent excess in-process loss of volatile flavours. Yeast cells comprise a heterogeneous complex polysaccharide outer cell wall made up of glucans, mannoproteins and a structural chitin framework overlaying a lipid bilayer. This double envelope provides a robust barrier across which amphiphilic small molecules can pass via a mechanism of passive diffusion. The process has been characterised and lipophilic molecules, such as flavours, accumulate in the complex inner matrix of the cell, which often contains a proportion (up to 40% w/w) of free lipid that can act as a sink for these hydrophobes[3].

Yeast is a readily available, sustainable, natural raw material, often available as a side-stream product. It can be presented in the form of readily dispersible dry powders and granules by using spray drying and spray agglomeration techniques. Encapsulated flavours are protected by a robust cell wall. Products are amenable to blending, extrusion and high heat processing. This approach to encapsulation is ideal for small fat-soluble molecules, such as flavours, particularly for savoury flavour applications. Other recently developed technologies include a product manufactured in the UK by TasteTech called Flavour8. It is a glassy state matrix material, stable in high fat, low water activity systems and provides an easy to handle, high density, low dust powdered flavour. This is ideal for processes where it is important to maintain a low level of contamination to plant and surrounding environment, to reduce the risk of vertical or horizontal cross contamination and to reduce the costs of plant clean down. The products have a finely structured matrix with a smooth continuous surface for good flavour retention. The material is highly water soluble and thus releases flavour rapidly in the mouth when in contact with saliva. This product complements existing spray dried products based on modified starch and gum, which can exhibit flavour loss and are relatively permeable to oxygen. Fat based spray chilled or spray congealed matrix encapsulated flavours have some limitations and are therefore often more suitable where high water activity systems are encountered. A key factor in producing a high quality, evenly dispersed powder or liquid dispersion of encapsulates lies with the formation of a stable monodispersed emulsion. There are many approaches including, for example, high shear mixing using ‘Silverson’ or ‘Ultraturax’ probe rotor-stator homogenisers or in-line high pressure two stage homogenisers from APV. However, membrane emulsification has been developed, enabling improvements in monodispersity without the need for high shear and high pressure processing[4]. One company developing equipment suitable for pilot and manufacturing scale production is Micropore Technologies in the UK. It uses customisable stainless steel screens with pores of, for example, 5 microns with hole geometries modified to suit the particular application. This can include hydrophobic or hydrophilic surface treatments, which can militate against fouling. Equipment for continuous processing with a capacity of 10-250 kg/h or for batch processing at 20-500 kg/h has recently been developed. Complex coacervates and complex emulsion systems can be produced with narrow particle size distributions of 20 to 50 microns in diameter.

Complex coacervation can be achieved as a result of electrostatic interactions between oppositely charged macromolecules, for example gelatine and acacia gum  mixed in a continuous aqueous phase with a surfactant. Liquid-liquid phase separation under defined conditions of pH and temperature leads to formation of self-assembly coacervates enrobing a liquid oil phase and the resulting shell is fixed using a cross-linker. This is an established technology that is constantly being modified to suit individual application needs. Lambson, in the UK, for example, has developed such a product called Vida-Caps. It is free of gelatine and GM ingredients and uses a fungal source of chitosan and a counter-ion of gum Arabic or carboxymethyl cellulose; thus it is suitable for vegetarians and could be suitable for both cosmetic and food flavour applications[5]. There are a number of companies that offer microencapsulation products and services, with contrasting strategies. For example, the French company Capsulae offers an agile approach to contract development services dedicated to each technical challenge, with a range of patent pending platform technologies and turnkey solutions from concept to product manufacture. Some companies offer simple tolling operations, others adopt generic approaches and may specialise in one technique or sector.

​Nanostructured materials

Over the past few years there has been a move towards developing smaller particle sizes in encapsulation technologies: nanostructure materials can indeed offer new opportunities. Nanotechnology has been defined in Europe as the manipulation, development and manufacture of materials typically in the size range 1-100 nm. At this size, as opposed to simply sub-micron, particles can exhibit some physical and chemical properties that are not necessarily observed at greater sizes. These can include colour, melting point, crystal structure, reactivity, conductivity and mechanical strength. They have large specific surface areas and may demonstrate quantum effects; they possess unpredictable properties, which may present additional challenges in new product development. They are extremely mobile in their free state, with a low sedimentation rate, and provide opportunities particularly for formulating beverages requiring added fat soluble colours and flavours. Nanomaterials may be naturally derived and many everyday products, such as beer foam, bread and milk, would not be the same without nanostructures self-assembling during production. Some developments in nanoemulsions include using, for example, plant derived saponins, and proteins from maize (zein) or milk (casein) due to their ability to efficiently form micelles, to stabilise flavours. These can be used an alternative to traditional emulsifiers, such as guar gum and locust bean gum, or polysorbate surfactants, such as tween 80. Molecular inclusion using cyclodextrins (a form of modified starch) is an established nanoencapsulation technology. Three forms have wide approval as a novel food ingredient and can be used as carriers of small fat soluble molecules. Alpha-, beta- and gamma-cyclodextrins have a ring structure and take on a bucket configuration with a hydrophilic outer surface, ensuring a degree of water solubility and a hydrophobic core which can host a single lipophilic guest molecule. Although not normally suitable as carriers for flavourings due to raw material costs and limitations in loading capacity, they have been adopted commercially as carriers for flavours, off-flavours and taints, for use as reference materials as a tool for training sensory panels in the food and beverage industry.

The Technical Research Institute of Sweden has been investigating the loading and release potential of active ingredients in mesoporous carriers, such as mesoporous silica and porous calcium carbonate. These materials are being used to enhance the release and bioavailability of poorly soluble solid and liquid active ingredients. Modified release profiles are being engineered through the use of coatings and additives. Controlled release has been demonstrated for simple drugs, where an amorphous rather than crystalline state has been retained following encapsulation. Future studies will investigate the benefits for food ingredients including flavour delivery. The Spanish company Bionanoplus has developed a SANP technology, which is a delivery system based on the formation of Self-Assembled polymeric NanoParticulate systems. This carrier system uses zein, a food grade protein found in maize (corn). A second technology, NANO-GES is a mucoadhesive delivery system based on the encapsulation of an ingredient using poly-anhydride (Gantrez) polymers (esters of poly(methyl vinyl ether-co-maleic anhydride)). These have yet to be proven effective for flavour delivery but they illustrate the range of emerging technologies to be added to the toolbox available to application technologists and flavourists.

Conclusions

​Micro and nano-encapsulation can provide a range of benefits to the food and beverage industry for developing effective flavour delivery strategies. These include: 
•    Modified flavour profiles
•    Improved impact – including flavour burst or sustained release platforms 
•    Protection from evaporation, high temperature, high shear processes, pH changes including hydrolysis
•    New prospects for new product concepts
•    More stable aqueous dispersions for fat soluble ingredients
•    Easy-to-handle - fine powder and liquid spray coatings
•    Retain Natural ingredient labelling advantages

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​[1] Microencapsulation in the Food Industry (2014) Eds: A Gaonkar N Vasisht A Khare and R Sobel. Academic Press 590p.
​[2] Viability of plant spore exine capsules for microencapsulation (2011). S Barrier, A Diego-Taboada, M J Thomasson, L Madden, J C Pointon, J D Wadhawan, S T Beckett, S L Atkin and G Mackenzie. Mater. Chem., 21, 975-981.
[3] Yeast cells as microcapsules. Analytical tools and process variables in the encapsulation of hydrophobes in S. cerevisiae (2012). F Ciamponi, C Duckham and N Tirelli. Applied Microbiology and Biotechnology 95(6):1445-56.
[4]  Continuous membrane emulsification with pulsed (oscillatory) flow (2013) RG Holdich, MM Dragosavac, GT Vladisavljević and E Piacentini (2013) Industrial and Engineering Chemistry Research, 52(1), 507-515.
[5] Capsules. International patent WO 2016185171. Lambson Limited.