Volatile encapsulation controlled release

FIGU RE 38.3 Retention and controlled release of aroma compounds added at the food surface or entrapped in edible coatings/films. (a) Deposition of volatile-active compound on food surface and (b) food coated with an edible film encapsulating the volatile-active compounds. 

Nanoliposomes compared to liposomes provide more surface area and have the potential to increase solubility, enhance bioavailability, and improve controlled release. The principal constituents of nanoliposomes are phospholipids for example, soya, rapeseed, and marine lecithin used by Zhang et al. (2012b). Jimenez et al. (2014) incorporated antimicrobial volatile compounds (orange EO and limonene) into soy and rapeseed nanoliposomes. These were then added to starch sodium caseinate film, forming dispersions. The antimicrobial activity of these films was not observed probably due to the encapsulation, which made difficult their release from the matrix (Jimenez et al., 2014). 

To lower the volatility, one needs to encapsulate the volatile into a polymer matrix, utilize a complex formation, and use a covalent bonding to a matrix—to mention a few techniques. We therefore need to formulate the volatiles and take many of the techniques from areas where controlled-release formulations have been in use for many years. Especially the area of controlled drug delivery has a large number of such formulations. Today, there exist a large number of sustained drug delivery formulations in both journal publications and patents (Deasy, 1984). 

Hsieh, W. C., Chang, C. P. Gao, Y. L. (2006). Controlled release properties of chitosan encapsulated volatile citronella oil microcapsules by thermal treatments. Colloids and Surfaces B Biointerfaces, 53, 209-214. 

Yimlaz, G. (2003) Thermoplastic starch matrices for encapsulation and controlled release of volatile compounds. PhD Thesis. Utrecht University, the Netherlands. 

It is also possible to generate microcapsules through interfacial polymerization using only one monomer to form the shell. In this class of encapsulations, polymerization must be performed with a surface-active catalyst, a temperature increase, or some other surface chemistry. Herbert Scher of Zeneca Ag Products (formerly Stauffer Chemical Company) developed an excellent example of the latter class of shell formation (Scher 1981 Scher et al. 1998). He used monomers featuring isocyanate groups, like poly(methylene)-poly(phenylisocyanate) (PMPPI), where the isocyanate reacts with water to reveal a free primary amine. Dissolved in the oil-dispersed phase of an oil-in-water emulsion, this monomer contacts water only at the phase boundary. The primary amine can then react with isocyanates to form a polyurea shell. Scher used this technique to encapsulate pesticides, which in their free state would be too volatile or toxic, and to control the rate of pesticide release. 

Nanocapsules can be formulated from a variety of synthetic or natural monomers or polymers by using different techniques in order to fulfil the requirements of various applications. Both, hydrophobic and hydrophilic liquids are of high interest for encapsulation. So, e.g., either sensitive or volatile substances, as drugs or fragrances have to be encapsulated and protected for applications with a sustained demand of the respective compound. DNA, proteins, peptides or other active substances can be encapsulated in order to target them to specific cells. A further benefit of the polymeric shell is the possibility to control the release from the composite particles and hence the concentration in the environment. 

In order to widen the applications of volatiles (essential oils), it is necessary to lower the volatility of the compounds to obtain a longer shelf life of products made with these compounds. By lowering the volatility, one can also imagine a possibility to better test the biological effects of these compounds. The encapsulation processes are means by which a liquid essential oil is enclosed in a carrier matrix to provide a dry, free-flowing powder. However, for the prolonged effect of volatile compounds many other techniques are used, where methods are copied from other fields of research when one wants to control the release of active ingredients. 

The high volatility and limited stabihty represent drawbacks of the storage and applications of essential oils and comphcate the in vitro tests as well [59]. To overcome this, new developments are targeted on delivery systems as (micro) encapsulation as a way to control the release of volatile compounds with various purposes including pharmaceuticals as well as consumer products [103]. 

A capsulated suspension (CS) is basically a suspension concentrate wdiere the active ingredient has been microencapsulated. The technical may have been coated by interfiwial polymerization or other techniques. The encapsulation is used to reduce a.i. toxicity or volatility, or in an attempt to control the active release rate. 

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