• The WPI-R complex was prepared by pH-driven method (pH-DM) combined with ultrasonic treatment. • The interaction between whey protein and rutin is covalent, and appropriate ultrasonic treatment could promote degree of polyphenol binding and grafting between whey protein isolate and rutin. • The ultrasonic treatment increased the WPI-R complex's solubility while decreasing its surface hydrophobicity and free sulfhydryl. • The secondary structure of the complex was improved with ultrasonic treatment, which results in three-dimensional honeycomb structures with small and uniform pore sizes.

To explore the influence of pH values on the properties of a compound system containing tea polyphenols (TPs) and low acyl gellan gum (LGG), the color, texture characteristics, rheological properties, water holding capacity (WHC), and microstructure of the compound system were measured. The results showed that the pH value noticeably affects the color and WHC of compound gels. Gels from pH 3 to 5 were yellow, gels from pH 6 to 7 were light brown, and gels from pH 8 to 9 were dark brown. The hardness decreased and the springiness increased with an increase in pH. The steady shear results showed that the viscosity of the compound gel solutions with different pH values decreased with increasing shear rates, indicating that all of the compound gel solutions were pseudoplastic fluids. The dynamic frequency results showed that the G′ and G″ of the compound gel solutions gradually decreased with increasing pH and that G′ was higher than G″. No phase transition occurred in the gel state under heating or cooling conditions at pH 3, indicating that the pH 3 compound gel solution was elastic. The WHC of the pH 3 compound gel was only 79.97% but the WHC of compound gels pH 6 and pH 7 was almost 100%. The network structure of the gels was dense and stable under acidic conditions. The electrostatic repulsion between the carboxyl groups was shielded by H⁺ with increasing acidity. The three-dimensional network structure was easily formed by an increase in the interactions of the hydrogen bonds.

A smart packaging film was developed employing the pH-indicating activity of elderberry anthocyanins to solve the problem of refrigerated food freshness monitoring. The effect of elderberry anthocyanins on the properties of gellan gum, gelatin composite films and preservation of fresh shrimp as an indicator of freshness was investigated. The results showed that the elderberry anthocyanin-gellan gum/gelatin film had improved on film thickness (7.8×10⁻² mm), TS (tensile strength) (14.57×10³ MPa), WVP (water vapor permeability) (36.96×10⁻⁸ g/m·s·Pa), and a reduced EAB (elongation at break) (17.92%), and water solubility (water-soluble time of 60.5 s). SEM (scanning electron microscopy) and FTIR (infrared spectrum analysis) showed excellent compatibility between its components. Moreover, the elderberry anthocyanin film exhibited good mechanical properties and pH indication effects. Therefore, the film can be considered suitable for maintaining the quality of fresh shrimp. The results could provide a reference for research and development into new active intelligent packaging films.

To enhance the antioxidant activity and bioaccessibility of quercetin (QU), in this study, the gellan gum (GG) and QU complex was prepared by the free radical grafting method. The covalent bond between GG and QU was confirmed by UV–visible, Fourier transform infrared (FT-IR) spectroscopy and Nuclear magnetic resonance (NMR). FT-IR showed that the GG-QU complex forms a new peak at 1079 cm⁻¹. Thermal analysis indicated that the GG-QU complex had higher heat resistance. Compared to QU, antioxidant assays showed that the DPPH radical scavenging and reducing power of the GG-QU complex were increased by 59.17 % and 36.93 %, respectively. And the GG-QU complex significantly improved gastric retention and intestinal release of QU. This result suggested the bioaccessibility of GG-QU complex was enhanced. This resulted in higher in intracellular antioxidant activity and better effect on reducing Malondialdehyde (MDA) content. The research provides theoretical support for the construction of high-performance food distribution system.