Resonant Raman spectroscopy elucidates pH-reversible chelation of blueberry anthocyanins with metal ions and carrageenan-enhanced photothermal stability

Blueberry anthocyanins (BA) are commonly incorporated into foods and beverages to enhance their functionality, and the stability of BA in metal-ion-rich systems has attracted considerable attention. The structural dynamics and stability of BA-metal ion complexes were investigated using resonant Raman spectroscopy combined with Gaussian multi-peak fitting techniques. BA form pH-reversible chelates with Fe 2+ or Zn 2+ , characterized by distinct Raman peaks at 1524 cm −1 and 1640 cm −1 , respectively. Adding carrageenan (CG) significantly improved the complexes' stability. During thermal treatment at 80 °C, the degradation of CG-stabilized complexes followed second-order kinetics, with rate constants (0.0001–0.0002 min −1 ) only one-fifth to one-tenth of the unstabilized system (0.001 min −1 ). Under UV light, degradation was zero-order, with rates (0.0014–0.0039 h −1 ) also significantly lower than the control (0.0097 h −1 ). In conclusion, this study demonstrates that CG-stabilized anthocyanin-metal complexes exhibit enhanced stability, offering promising applications in functional foods, with Raman spectroscopy serving as an effective tool for real-time monitoring. • pH-reversible chelation of blueberry anthocyanins with Fe 2+ and Zn 2+ . • Characteristic Raman peaks at 1524 cm −1 and 1640 cm −1 identify Fe 2+ /Zn 2+ chelation. • Carrageenan greatly enhances thermal and UV stability of anthocyanin-metal complexes. • Carrageenan slows heat (2nd-order) and UV (zero-order) degradation of chelation. • Resonance Raman combined Gaussian fitting monitors anthocyanin structural dynamics.