Alginate–butterfly pea microbeads as anthocyanin-based colorimetric sensors for biogenic amines and chicken spoilage monitoring

Alginate microbeads incorporating blue butterfly pea (Clitoria ternatea L.) extract were developed as natural, pH-responsive colorimetric indicators for monitoring food spoilage. The blue butterfly pea extract, rich in anthocyanins, exhibited distinct pH-dependent color transitions from red (pH 2) to green (pH 10), supported by UV–Vis bathochromic shifts. Structural analyses revealed the successful incorporation of blue butterfly pea extract into the alginate matrix, as demonstrated by SEM images that showed extract addition produced smoother bead morphologies compared to plain alginate beads. The incorporation of the extract also enhanced bead swelling from 74 % to 86 % within 60 min, reduced water activity from 0.954 to 0.233, and moisture content from 95.0 % to 87.0 %, thereby improving structural stability and microbial safety. The total anthocyanin content of the extract was 343 ± 25 mg Cy-3-glc/kg BBP powder. Anthocyanin release studies showed that release profile strongly depended on the polarity of the surrounding medium, with the highest release observed in 50 % ethanol and the lowest in 95 % ethanol. Furthermore, the beads exhibited a sensitive, concentration- and time-dependent chromatic response to biogenic amines, reaching nearly complete transition within 60 min at 1 mmol/L. The beads were also responsive to ammonia vapor. Finally, when applied to chicken breast storage tests, the beads provided clear and progressive color changes from deep blue to green (day 7) and colorless (day 10). These results highlight alginate-blue butterfly pea extract-containing beads as promising low-cost, natural, and practical sensing components for integration into intelligent packaging systems to ensure food quality and safety.