Applicability of alginate-based composite microspheres loaded with aqueous extract of Stevia rebaudiana Bertoni leaves in food and pharmaceutical products

To preserve its favorable health and nutritional qualities under processing conditions and oral ingestion, Stevia rebaudiana Bertoni leaf aqueous extract was encapsulated in composite microspheres based on calcium alginate. The addition of other biopolymers to alginate (ALG) (xanthan gum (XG), casein (CA)) influenced molecular interactions (mainly hydrogen bonding and electrostatic interactions) between microsphere constituents causing the change in microsphere structure and thus physicochemical properties (encapsulation effectiveness and ca-pacity, surface morphology, swelling, stability) as well as the release of total polyphenols (TPC) in distilled water, NaCl solutions and in simulated gastrointestinal fluids. The extent of crosslinking of calcium alginate was altered by blending with XG, CA, or XG + CA, but this did not affect the control mechanism of TPC release detected as diffusion. Results revealed the unsuitability of calcium alginate microspheres for implementation in food products with high water content, while composite microspheres showed desired reduction in TPC release. The best performance (the slowest release and the amount released) for implementation in functional food products containing NaCl exhibited composite micro -spheres with ALG + XG + CA. The desired prevention of microsphere degradation in simulated gastro fluids was achieved with ALG + XG + CA microspheres, while in simulated intestinal fluids all microspheres were decomposed and completely released TPC.