Encapsulation of betalains from beetroot pomace in protein-gum blends: characterization, antioxidant and color stability analysis

• Beetroot pomace valorized as a sustainable source of betalains for natural food colorants. • Beetroot leaf protein and flaxseed gum successfully used as novel plant-based wall materials. • Ultrasound-assisted encapsulation achieved high efficiency and strong stability. • Encapsulation improved betalain thermal stability, color retention, and antioxidant activity. • Demonstrated a sustainable approach for developing stable natural colorants. Betalains exhibit strong potential as natural food colorants; however, their practical application is limited by instability under exposure to heat, oxygen, and light. To address these challenges while incorporating sustainable and circular approaches, betalains were extracted from beetroot (Beta vulgaris L. var. conditiva) pomace and encapsulated using optimized plant-based wall materials, namely beetroot leaf protein and flaxseed gum. Freeze-drying was employed for the encapsulation of betalains. The encapsulation efficiency reached 98.14% at a core-to-wall ratio of 1:1.5:0.5 (betalains: beetroot leaf protein: flaxseed gum). Fourier-transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction confirmed the effective incorporation of betalains into the wall matrix. The zeta potential (−32.27 mV) indicated good physical stability of the encapsulated sample, while the water activity (0.36) remained within a favorable range. Encapsulation improved both physicochemical properties and thermal stability compared to free betalains. Antioxidant activity and color stability were evaluated over nine weeks of storage at 4°C or 22°C under both light and dark conditions. Encapsulated betalains exhibited higher pigment retention, improved color stability, and significantly greater antioxidant activity (DPPH and FRAP assays) than free betalains, particularly under storage at 4°C in both light and dark conditions. This study demonstrated, for the first time, the use of beetroot leaf protein and flaxseed gum as wall materials for betalain encapsulation. The developed encapsulated betalains effectively stabilized the pigments and showed promising potential for future application as sustainable natural colorants in the food industry.