Exploration of bigel 4D printing with spontaneous colour change for monitoring bio-actives kinetic behaviour based on the dual-units 3D printer

This work studied the effect of storage at different temperatures on the relationship between the colour change and bio-actives (curcumin and beta-carotene) content change in the bigels 3D printing products. At relatively low temperatures (4 degrees C and 15 degrees C), beta-carotene degraded rapidly, but a* changed slowly because of less migration of curcumin, indicating that colour change cannot be used for monitoring bio-active changes. At relatively high temperatures (25 degrees C and 35 degrees C), the beta-carotene degradation fractions reached 0.924 and 0.967. Meanwhile, a* increased to 7.318 and 11.710 while the curcumin migration fraction increased quickly, which indicated that changes in colour and bio-actives content had high consistency at 25 degrees C and 35 degrees C. At these temperatures, the bigels 3D printing product lost structure stability due to the high freedom of moisture in hydrogel and increased mobility of oleogel, leading to rapid colour change and fast molecular movement of curcumin and beta-carotene.