Structuring alginate beads with different biopolymers for the development of functional ingredients loaded with olive leaves phenolic extract

Olive leaves are a main source of polyphenols, compounds exhibiting very interesting functional and healthy properties. Nevertheless, the bitter taste of phenolics, together with their physico-chemical instability, are still limiting their use as free compounds into food products. Microencapsulation could represent a promising technique to increase polyphenols stability and bioavailability, as well as to mask unpleasant flavours. In this work microspheres loaded with olive leaves phenolic extracts were produced through emulsification-internal gelation by using alginate alone (Alg) (reference) or mixed with pectin (Alg-Pec), whey proteins (Alg-WPI) or sodium caseinate (Alg-Cas). Encapsulation efficiency was evaluated along with particle size and microstructure, swelling, release kinetics, antioxidant capacity and molecular interaction by using FT-IR spectroscopy. Enriched particles with a mean diameter in the 45-70 mu m range were produced. In respect to the Alg beads, whose encapsulation efficiency was 21%, the use of structurant polymers significantly increased the encapsulation efficiency which ranged from 52% up to 78% for the Alg-Pec systems. Significant changes in the FT-IR spectra due to the presence of the extract in Alg-Pec, Alg-WPI and Alg-Cas microparticles were observed, suggesting that molecular interactions were formed between the extract and the encapsulating matrix via hydrogen bonding. Higher swelling and release rates were found for all the tested systems at pH 6.0 compared to pH 4.5; at pH 4.5 Alg-Pec immediately released most of the trapped phenolics, contrarily to Alg-WPI which showed lower and delayed release. Release data were modelled with the Peppas-Sahlin equation which evidenced a main contribution of diffusional processes in the release mechanism.