Microstructure‐driven modulation of polyphenol stability and antidiabetic activity in alginate microspheres loaded with pomegranate and tomato by‐products

Abstract BACKGROUND Plant‐derived by‐products are a valuable source of polyphenols with well‐documented antioxidant and antidiabetic properties. However, their limited stability restricts their application in functional food systems. This study investigated alginate‐based encapsulation by ionotropic gelation as a strategy to improve polyphenol retention and bioactivity, using pomegranate peel and tomato pomace as contrasting plant matrices. Attention was given to the effects of processing parameters, including nozzle diameter, on encapsulation efficiency and functional properties. RESULTS Plant matrix and processing conditions both significantly affected polyphenol retention, antioxidant capacity (oxygen radical absorbance capacity (ORAC)), and antidiabetic activity (dipeptidyl peptidase‐4 (DPP‐4) and α ‐amylase inhibition), confirming strong matrix‐dependent behavior. Microspheres prepared from pomegranate peel showed greater retention of key phenolic compounds, including gallic acid (29.7 mg kg −1 FW), ellagic acid (5.0 mg kg −1 FW), flavonols (18.0 mg kg −1 FW), and polymeric procyanidins (1337.6 mg kg −1 FW), and enhanced biological activity. In contrast, tomato pomace showed lower stability, with the highest flavonol retention (45.6 mg kg −1 FW) observed under less restrictive encapsulation conditions. Increasing nozzle diameter (750–1000 μm) improved microsphere morphology, surface integrity, and extract distribution, while reducing structural instability. Correlation analysis indicated that flavan‐3‐ols, phenolic acids, and punicalagin were the principal contributors to antioxidant and antidiabetic effects. CONCLUSION Alginate‐based encapsulation efficiency was influenced strongly by plant matrix and process parameters, particularly nozzle diameter. Optimization of these factors enables improved retention of bioactive compounds and enhanced biological activity. The developed system shows potential for the design of stable, functional microspheres applicable in functional foods, nutraceuticals, and controlled‐release delivery systems. © 2026 Society of Chemical Industry.