Production of stable anthocyanin-based food colorants from Hibiscus sabdariffa L. by copigmentation with different protein isolates

This study investigated the copigmentation of Hibiscus sabdariffa L. anthocyanins with different protein isolates - pea (PP), rice (RP), gluten (GP), and whey (WP) - to enhance color and thermal stability. WPH and RPH samples showed superior stability, with lower polymeric color percentages (35.86% and 38.84%, respectively). WPH had the highest z value (112.78 K; the temperature increase required to reduce the decimal degradation time by a factor of 10), while RPH exhibited the highest activation energy (47.98 kJ/mol; the minimum energy required to initiate the degradation reaction), indicating improved thermal resistance. Despite the enhanced thermal and color stability, UV-Vis and spectroscopic analyses did not exhibit a pronounced hyperchromic effect or bathochromic shift, indicating that anthocyanin stabilization occurred despite a reduced magnitude of spectral changes. FTIR spectra showed prominent bands at 3000–3500 cm⁻¹ (–OH stretch) and 1600–1650 cm⁻¹ (C = O stretch), suggesting strong interactions between anthocyanins and proteins. A notable decrease in fluorescence intensity was also observed after copigmentation. These results indicate that rice and whey protein isolates can effectively stabilize anthocyanins through molecular interactions. The copigmentation approach offers a promising and natural strategy to improve anthocyanin stability for potential use in functional food systems.