Colorimetric gel labels for the non-destructive freshness monitoring of fresh-cut papaya

Colorimetric gel labels (referred to as AKAX) were fabricated to monitor the freshness of fresh-cut papaya in real time using agarose (AR) and konjac glucomannan (KGM) composite gels containing alizarin (AL) and Substance X (X). The AKAX colorimetric gel label produced an ordered color variation from purple to pink-purple to orange-yellow, following the CO2 concentration in the package, to reflect the fresh-cut fruit freshness. Experimental characterization of the gel label structure revealed that AR, KGM, AL, and X were compatible, while the gel label texture, water-holding capacity, rheology, and thermal stability were improved with the addition of KGM. AKAX colorimetric gel labels maintained excellent color stability and CO2 sensitivity during storage at 4 °C. The fresh-cut papaya approached spoilage as the color varied from purple to pink-purple, and an orange-yellow color indicated that the fresh-cut papaya had spoiled. Therefore, the developed AKAX colorimetric gel labels serve as effective tools for monitoring the spoilage of fresh-cut papaya.