Optimization of Freeze-Dried Microcapsules Containing Polyphenol-Rich Fruit Extracts: Bioactive Compound Retention, Physicochemical Properties, and Thermal Stability

Polyphenol-rich plant extracts contain valuable bioactive compounds, but their limited stability and susceptibility to environmental conditions can restrict their application in food systems, making microencapsulation a promising approach for their protection and controlled incorporation. This study investigated the effects of extract source, wall material, and core-to-matrix ratio on the technological properties, encapsulation performance, and retention of bioactive compounds in freeze-dried microcapsules. Four polyphenol-rich sources (red grape skins, black carrot, chokeberry, and blackcurrant), three wall materials (maltodextrin, soy protein isolate, and trehalose), and three core-to-matrix ratios (2:1, 1:1, and 1:2) were evaluated using a D-optimal experimental design. Dry matter, water activity, encapsulation efficiency, yield, loading capacity, and retention of polyphenols, flavonoids, and anthocyanins were determined. FTIR spectroscopy combined with PCA was used for molecular characterization. DSC and SEM were applied to further investigate the powder's properties. The effects of the factors varied among responses. Maltodextrin generally provided the most favorable technological properties in terms of dry matter content, water activity and encapsulation yield, as well as the highest retention of bioactive compounds, while encapsulation efficiency was primarily determined by the core-to-matrix ratio. Loading capacity was affected by all factors and their interactions. Model optimization identified red grape skin extract with maltodextrin at a 1:1 ratio as the most desirable formulation. These findings highlight the importance of multi-response optimization in designing effective polyphenol encapsulation systems.