Coacervation, complex gelatins

Complex Coacervation. This process occurs ia aqueous media and is used primarily to encapsulate water-iminiscible Hquids or water-iasoluble soHds (7). In the complex coacervation of gelatin with gum arabic (Eig. 2), a water-iasoluble core material is dispersed to a desired drop size ia a warm gelatin solution. After gum arabic and water are added to this emulsion, pH of the aqueous phase is typically adjusted to pH 4.0—4.5. This causes a Hquid complex coacervate of gelatin, gum arabic, and water to form. When the coacervate adsorbs on the surface of the core material, a Hquid complex coacervate film surrounds the dispersed core material thereby forming embryo microcapsules. The system is cooled, often below 10°C, ia order to gel the Hquid coacervate sheU. Glutaraldehyde is added and allowed to chemically cross-link the capsule sheU. After treatment with glutaraldehyde, the capsules are either coated onto a substrate or dried to a free-flow powder. 

Eig. 2. Elow diagram of a typical encapsulation process based on the complex coacervation of gelatin with gum arabic. 

Xing, F., Cheng, G., Yang, B., Ma, F. (2004). Microencapsulation of capsaicin by the complex coacervation of gelatin, acacia and tannins. Journal of Applied Polymer Science, 91,2669-2675. 

The encapsulation of various essential oils has intrigued the food, cosmetic, and pharmaceutical industries for some time. Several encapsulation systems based on the complex coacervation of gelatin have been used to encapsulate a range of essential oils. However, variable results have been obtained, especially with citrus oils. 

Complex Coacervation Procedures. Gelatin/alginate (G/A), gelatin/ polyphosphate (G/P), and gelatin/gum arabic (G/GA) complex coacervate and supernatant phases were used in this study. G/A complex coacervate and supernatant phases were formed at pH 4.2 with a 3.7 1 (w/w) mixture of gelatin (227 bloom) and sodium alginate (total solids 1.8 wt. percent). G/P complex coacervate and supernatant phases were formed at pH 4.4 with a 9 1 (w/w) mixture of gelatin (283 bloom) and polyphosphate (total solids ... 

Citrus oils contain a number of components and are complex liquids. The same is true for the aqueous phases formed by complex coacervation of gelatin. Accordingly, the IFT behavior of citrus oils against water and the aqueous phases produced by compex coacervation reflects the interfacial behavior of complex systems. Changes in IFT can be caused by a number of possible chemical and/or physical changes. For example, several chemical reactions could occur. 

Carboxymethylcellulose sodium forms complex coacervates with gelatin and pectin. It also forms a complex with collagen and is capable of precipitating certain positively charged proteins. 

Brungenberg de Jong and coworkers carried out the first extensive studies of complex coacervation (1). They characterized the gelatin-gum arabic coacervation system, a system that later was developed into a process capable of producing microcapsules loaded with a variety of lyophobic materials (2). More recently, an encapsulation process based on the coacervation of gelatin with a polyphosphate has been reported (3). The present paper describes results of a study designed to characterize the gelatin-polyphosphate coacervation interaction and define how various experimental paramenters affect it. 

The development of early encapsulation technology and preparation of microcapsules dates back to 1950s when Green and coworkers produced microencapsulated dyes by complex coacervation of gelatin and gum Arabic, for the manufacture of carbonless copying paper. The technologies developed for carbonless copy paper have led to the development of various microcapsule products in later years. 

FIGURE 12.4 Flow diagram of a typical microencapsulation process based on complex coacervation of gelatin and gum arabic. 

FIGURE 47.5 General process scheme of complex coacervation using gelatin/gum arabic. 

They are obviously of different solubility. Now it is probable that then the smallest solubility will be present when as large a number as possible of salt bonds per unit weight of gelatin-arabinate is present. For everything points to this salt bond being the immediate cause of the complex coacervation indeed gelatin and gum arabic in the uncharged state are both soluble. 

Fig. 14. Continuous valency rule in the in-fluence of added salts on the electrophoretic Velocity of complex coacervate drops (gelatin and gum arabic).

See for example Fig. 16, which relates to a positively charged complex coacervate of gelatin and a soya bean phosphatide. ... 

Fig. 30. Comparison of the complex coacervation of gelatin -f- nucleate with gelatin + arabinate (pn 3.7)...

Complex gels can also be obtained in another — really much more natural —way namely by cooling complex coacervates containing gelatin. If for example the separation into layers has taken place at 40° to a clear equilibrium liquid and clear coacervate layer and one subsequently cools the tube to room temperature both layers become turbid. The coacervate layer becomes solid thereby and on microscopic examination the turbidity is seen to be caused by a large number of small vacuoles in the gel. The equilibrium liquid becomes turbid because some fresh coacervate separates out of it in small drops. These drops also gelate and stick to each other forming loosely built flakes. 

Fig. 16. Gelatinised complex coacervate drops (gelatin-gum arabic) with coarse vacuolation (after very slow cooling of the drops kept in suspension in their equilibrium liquid) 177 X lin. For the origin of small granular flakes (see p. 382). ...

Much has been published on ethanol and sodium sulfate for inducing simple coacervation in gelatin solutions, and on the gelatin-gum arabic complex coacer-vate system. Polyphosphates have been relatively little studied in the literature, but are examples of polyelectrolytes which can participate in both simple and complex coacervate formation. 

Table 1 Hsts representative examples of capsule shell materials used to produce commercial microcapsules along with preferred appHcations. The gelatin—gum arabic complex coacervate treated with glutaraldehyde is specified as nonedible for the intended appHcation, ie, carbonless copy paper, but it has been approved for limited consumption as a shell material for the encapsulation of selected food flavors. Shell material costs vary greatly. The cheapest acceptable shell materials capable of providing desired performance are favored, however, defining the optimal shell material for a given appHcation is not an easy task.

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