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Abstract
A new droplets millifluidic/inverse gelation based process was used to produce core-shell alginate milli-capsules. Water-in-oil (W/O) emulsion dispersed phase containing Ca2+ ions was directly injected into a continuous alginate phase to generate a secondary W/O/W emulsion. Due to the cross-linking of alginate molecules by Ca2+ ions release, core-shell milli-capsules were formed with a very high oil loading. The influence of the curing time and of the storage conditions on capsules physico-chemical properties were investigated. It was first found as expected that alginate membrane thickness increased with curing time in the collecting bath. However, a plateau was reached for the higher curing times, in close relation with previous observations (Martins, Poncelet, Marquis, Davy, & Renard, 2017b) that an external oil layer surrounded the surface of W/O emulsion drops that acted as a barrier and hindered the release of aqueous CaCl2 droplets during curing time. Compression experiments on individual capsules revealed that alginate membrane thickness was inversely related to its mechanical properties, i.e. the thicker membrane, the lower surface Young modulus. Surface Young modulus ranged from 61 to 26 N/m at curing times of 3 and 45 min, respectively. This result was explained in terms of enhanced swelling properties of alginate membrane with curing time or storage conditions. Drying capsules led to much more resistant membranes due to the loss of water. Oil loading of 80 wt% was obtained for dry capsules whatever the conditions used.
Highlights
The study of microcapsules based on biodegradable polymers is of great importance in current scientific research worldwide due to the unusual combination of properties and versatility of these materials.Electronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.Microencapsulation avoids the degradation and volatilization of bioactives, protecting and preserving their biological activity and active functional ingredients
This study demonstrated the success of the production of-capsules based on the inverse gelation mechanism using droplets millifluidic
Marquez et al [17] and Su et al [18] found that higher the emulsifier concentration was, lower was the size of water droplets in W/O emulsion, increasing both its viscosity and stability
Summary
The microencapsulation technique has been mainly described as a process in which small particles or droplets are surrounded by a homogeneous or heterogeneous coating, forming beads or capsules with various applications [1]. There are three major fields of application: food production, e.g. enhancement of nutrition by encapsulated vitamins, minerals or even pro-biotic bacteria; cosmetic industry, where encapsulation of colors and flavors became more and more popular within the last years; and drug delivery field. Oils are widely applied in the formulation of foods, pharmaceutical and cosmetic products; they are often volatile, labile and sensitive to environmental factors such as heat, light, water and oxygen [2]. An efficient strategy to decrease their sensitivity towards environmental conditions consists of its encapsulation in inert polymer matrix using gelation/emulsification technique [3,4,5]
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