Encapsulation of procyanidins in double emulsions stabilized by protein–polysaccharide complexes
- Autores: Rikkert Berendsen
- Directores de la Tesis: María Montserrat Ferrado Cogollos (dir. tes.), Carme Güell Saperas (codir. tes.)
- Lectura: En la Universitat Rovira i Virgili ( España ) en 2014
- Idioma: español
- Tribunal Calificador de la Tesis: Marilyn Rayner (presid.), María Paz Romero Fabregat (secret.), Juan Carlos Arboleya Payo (voc.)
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
The regular intake of foods rich in bioactive compounds, such as polyphenols, has been linked to a risk reduction in cardiovascular diseases and certain types of cancer. Although their particular role on reducing risks factors requires a better understanding, in vitro and clinical studies show consistently their positive effects on human health. As a result, the use of commercial extracts rich in polyphenols from different sources (i.e. grapes, tea, apple, etc.) to formulate foods and beverages has become a trend in the sector. Nevertheless, the effectiveness of those extracts depends on preserving the stability, bioactivity and bioavailability of the active ingredients.
A strategy to improve the stability and bioavailability of sensitive bioactive compounds is encapsulation. In this work, we investigated two encapsulation systems to entrap a procyanidin-rich extract: double (water-in-oil-in-water, W1/O/W2) emulsions and solid microcapsules (spray dried double emulsions). Premix membrane emulsification was the methodology applied to produce emulsions because it uses low shear stresses (what reduces the release of W1 droplets during emulsification), requires low energy input and shows a good control of droplet size distribution.
We have focused on how the type and structure of the layer at the oil-water interface, made of whey proteins and polysaccharides, affects the physical and chemical stability of emulsions, and their capacity to retain procyanidins during processing and further storage. To understand the role of the interfacial layer, the properties of the several amphiphilic emulsifiers in aqueous solution and absorbed to plane surfaces, which mimic the O¿W interfaces in real emulsions, have been determined.
Premix ME enables to produce single and double emulsions with a droplet size close to the membrane pore size (10 µm). To stabilize emulsions, several hydrophilic emulsifiers were used to adsorb on the O/W interface: whey protein isolate (WPI), and WPI¿Carboxymethyl cellulose (WPI¿CMC), WPI¿Gum Arabic (WPI¿GA) and WPI¿Chitosan (WPI¿Chi) complexes. Adsorption measurements by means of Surface Plasmon Resonance (SPRi) showed that WPI¿polysaccharides interfaces form thicker but less dense layers than only WPI. Furthermore, WPI¿CMC and WPI¿GA produced an interface with a negative surface charge, while WPI and WPI¿Chi lead to an interfacial layer positively charged.
Initially we assess that premix ME enabled to produce O/W emulsions stabilized by different interfacial structures made of WPI and CMC. WPI or WPI¿CMC stabilized O/W emulsions were stable but showed large differences in lipid oxidation. While emulsions stabilized by WPI presented a relatively low rate of lipid oxidation, this was two orders of magnitude higher in emulsions stabilized with WPI¿CMC complex. This large discrepancy was mainly explained by the differences in surface charge. The negatively charged lipid droplets of the emulsions stabilized with WPI-CMC would attract positively charged transition metals to their surfaces, promoting lipid oxidation.
In the case of procyanidin-loaded W1/O/W2 emulsions stabilized by WPI¿CMC, WPI¿GA, or WPI¿Chi complexes, the procyanidin encapsulation was at least 70% at the end of premix ME, regardless of the hydrophilic emulsifier used. Encapsulation of procyanidin decreased with each premix ME cycle, mainly linked to the escape of the inner W1 phase as a result of the breakup of W1/O droplets. Emulsion stability depended on the type of interfacial layer and the environmental conditions of the W2 phase (mainly pH). Different windows of pH, in which emulsions kept droplet size distribution stable, were identified for each WPI¿polysaccharide complex. The release rate of procyanidins could be correlated to the interfacial thickness of the complex layer: thicker layers lowered the release rate. WPI¿Chi complex lead to the lowest procyanidin release rate, due to its thick layer.
To obtain solid microcapsules from W1/O/W2 emulsions, a wall material (maltodextrin) was added to the freshly produced double emulsions and, subsequently, the mixture was spray dried. All the W1/O/W2 emulsions investigated, that is, stabilized with WPI, WPI¿CMC, WPI¿GA or WPI¿Chi, were able to produce procyanidin-loaded microcapsules after spray drying. Furthermore, they could all recover their W1/O/W2 emulsion structure upon rehydration. Microcapsules after spray drying and W1/O/W2 emulsions after rehydration showed profound differences in particle size distribution depending on the interfacial composition. Particularly, WPI¿CMC complex was able to truly stabilize the W1/O droplets during the different stages of microcapsule production although it moderately retained the migration of procyanidins through the O¿W2 interface. According to these results, small changes in hydrophilic emulsifiers have large influence on the solid and rehydrated microcapsules.
For each type of encapsulation system (single emulsion, double emulsion and spray dried double emulsion) a tailor-made hydrophilic emulsifier is required to comply with the type of protection needed, the addenda used and the delivery conditions.
