In this study, an intelligent pH indicator composite film was prepared using purple sophora flower pigment (PS) as a pH indicator and a mixture of pectin (P) and sodium alginate (SA) as a film-forming substate by the casting method. The effect of PS content on the surface morphology, water sensitivity, opacity, mechanical properties, coloration reversibility and thermal decomposition characteristics of the composite film was analyzed. The effect of the composite film on the preservation of cherries and its performance in monitoring the freshness of lamb meat were evaluated. The results showed that the composite film became denser with the increase in PS content. The addition of PS significantly improved the ultraviolet (UV) barrier capacity of the composite film while decreasing the water solubility and water contact angle. With the addition of 20% PS, the swelling property of the composite film decreased from (604.86 ± 83.61)% to (272.85 ± 27.84)%. The thickness of the composite film with 20% PS was (87.33 ± 8.62) μm, and its water vapor permeability was as low as (0.57 ± 0.09) × 10^–11 g·cm/(cm²·s·Pa). Compared with uncoated samples, the mass loss of cherries coated with the composite film reduced by 35.42% after 8 days of storage at 25 ℃. Lamb meat with pH above 6.70 made the composite film turn from purplish red to yellow-green, showing spoilage. Moreover, changes in the total color difference of the composite film showed a strong linear relationship with the pH of lamb meat. The results from this study provide evidence supporting the application of pigments extracted from purple sophora flowers in intelligent pH indicator composite film.

In this study, binary and ternary complexes were prepared by heat treatment or combined heat and ultrasonic treatment using casein micelles (MC) as matrix and proanthocyanidin (PC), catechin (Cat) and chlorophyllin sodium copper salt (Chl) or their binary combinations as ligands. The interactions between PC, Cat, Chl or their binary combinations and MC were analyzed, and the binding capacity of MC to the various active molecules was evaluated. In addition, the structure, microscopic morphology and thermal stability of the complexes were characterized, and the antioxidant properties and in vitro digestibility of the ternary complexes were investigated as well. The results showed that PC, Cat and Chl formed binary complexes with MC through hydrophobic interactions, among which MC showed the highest affinity for Chl. Under heat treatment conditions, MC bound one molecule through hydrophobic interaction and another one by van der Waals forces and hydrogen bonds. At 298 K, the binding of the first molecule improved the binding constant and the number of binding sites of the second one. The binding of PC, Cat, Chl or their binary complexes had no significant effect on the spatial structure or microscopic morphology of MC. The thermal stability of MC was enhanced after the binding of bioactive molecules under heat treatment conditions. In terms of antioxidant properties, heat treatment promoted the 2,2′-azino bis-(3-ethylbenzthiazoline-6-sulfonicacid) (ABTS) radical cation scavenging activity of the ternary complexes, while combined heat and ultrasonic treatment promoted their 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity. In addition, the loading of active molecules improved the digestibility of MC in simulated intestinal fluid. This study could provide a reference for the application of MC in the loading of bioactive molecules.

In this work, oil-in-water (O/W) emulsion gels with 70% oil phase were prepared using micellar casein (MC) and sodium alginate (SA) as substrates with the addition of gluconate-δ-lactone (GDL) as acidifying agent. The effects of GDL addition on the microstructure, stability and rheological properties of emulsion gels were studied, and the release characteristics of emulsion gels loaded with proanthocyanidins (PC) were analyzed. The results showed that with increasing GDL concentration, the average size of oil droplets in emulsion gels decreased, and it gradually decreased during the storage period. GDL acidification improved the apparent viscosity and storage modulus of emulsion gels, and this effect increased with GDL concentration. The microstructure of emulsion gels did not change significantly after heat treatment at 65 or 80 ℃ for 30 min. Meanwhile, the emulsion gels were stable to acidic and basic conditions as well as storage. In addition, the release rate of PC-loaded emulsion gels was higher than that of free PC during simulated intestinal digestion, and the cumulative release rate at 10 h increased with GDL concentration. The results of this study could provide a reference for the preparation of emulsion gels based on MC and the improvement of PC stability.