Spray-Drying Microencapsulation of Grape Pomace Extracts with Alginate-Based Coatings and Bioaccessibility of Phenolic Compounds

Spray-drying is a common technique for the microencapsulation of bioactive compounds, which is crucial for improving their stability and bioavailability. In this study, the encapsulation efficiency (<i>EE</i>), physicochemical properties and in vitro bioaccessibility of phenolic compounds from spray-dried encapsulated phenol-rich extracts of grape pomace, a winery waste, were evaluated. Sodium alginate alone (SA) or in a mixture with gum Arabic (SA-GA) or gelatin (SA-GEL) was used as a coating. SA-GEL achieved the highest <i>EE</i> (95.90-98.01%) and outperformed the intestinal release of phenolics by achieving a bioaccessibility index (<i>BI</i>) for total phenolic compounds of 37.8-96.2%. The release mechanism of phenolics from the microcapsules adhered to Fickian diffusion. Encapsulation significantly improved the <i>BI</i> of individual phenolics, with the highest <i>BI</i> values for gallocatechin gallate (2028.7%), epicatechin gallate (476.4%) and <i>o</i>-coumaric acid (464.2%) obtained from the SA-GEL microcapsules. Structural analysis confirmed amorphous matrices in all systems, which improved solubility and stability. These results suggest that encapsulation by spray-drying effectively protects phenolics during digestion and ensures efficient release in the intestine, which improves bioaccessibility. This study contributes to the understanding of biopolymer-based encapsulation systems, but also to the valorisation of grape pomace as a high-value functional ingredient in sustainable food processing.