Whey and Plant (Pea, Rice, and Gluten) Protein Amyloid Fibrils as Copigmentation Agents for Anthocyanin‐Rich Hibiscus sabdariffa Extract: A Comparative Study

ABSTRACT Amyloid fibrils derived from whey, pea, rice, and gluten proteins were evaluated as copigmentation agents to enhance the stability of anthocyanin‐rich Hibiscus sabdariffa extracts. Fibrils were prepared via heat‐induced self‐assembly for 24, 36, or 48 h, and their effects on color enhancement and thermal stability were assessed using UV–Vis spectroscopy, FTIR, fluorescence, and kinetic modeling. The most effective samples combined high bathochromic and hyperchromic shifts with improved thermal stability. Among these, 36‐h whey nanofibrils copigmented with hibiscus extract (36WH) exhibited the greatest bathochromic shift (6 nm) and the highest hyperchromic effect (33.84%), while 24‐h whey nanofibrils copigmented with hibiscus extract (24WH) showed similarly high color enhancement (33.00%) along with high activation energy ( E a : 103.54 kJ mol −1 ) and low degradation rates. The 24‐h pea nanofibrils copigmented with hibiscus extract (24PH) achieved the highest E a (141.08 kJ mol −1 ), indicating exceptional thermal resistance. In addition, 36‐h rice nanofibrils copigmented with hibiscus extract (36RH) displayed strong performance with an E a of 89.69 kJ mol −1 and a bathochromic shift of 4 nm, whereas 24‐h gluten nanofibrils copigmented with hibiscus extract (24GH) had the highest z value (75.72 K), reflecting strong resistance to temperature changes. FTIR spectra confirmed hydrogen bonding and aromatic interactions, while fluorescence quenching from 100 to 1000 au to 3–5 au indicated strong pigment–protein binding. Overall, 24WH, 36WH, 24PH, 36RH, and 24GH emerged as the most promising fibril–pigment systems, offering significant color enhancement and/or thermal stability.