Investigation of the mechanical, rheological and microstructural properties of sugar beet pectin/soy protein isolate-based emulsion-filled gels

Emulsion stabilized by 1 wt% Tween 20 was added to the sugar beet pectin (SBP)/soy protein isolate (SPI)-based gel matrix to obtain emulsion-filled gels via laccase-induced cross-linking reaction and heat treatment. The influence of emulsion concentrations (the ratio of the emulsion to the mixed colloidal solution) on the textural characteristics, swelling degrees, rheological properties and microstructural properties of gels was investigated. The highest hardness, adhesiveness and chewiness of the gels were reached with an emulsion concentration of 10 wt%, accompanied by the formation of a stiffer gel with smoother surface. The results indicated that the increase in emulsion concentration helped to improve the swelling properties of the gel. The rheological property of the gel filled with 5 wt% of emulsion was mainly influenced by the SPI solutions. The presence of emulsion slowed down the gelling process. Furthermore, the loss tangent (G ''/G') of the gel with emulsion concentration at 10 wt% exhibited a slight increase during the gelling process, suggesting a stronger interaction between SBP and SPI. The microstructure results showed that the integrated and interconnected pores appeared in the gel with 10 wt% emulsion concentration. The CLSM observations indicated that the interactions among the matrix macromolecules were influenced by the addition of emulsion and droplet clusters could be observed in gel with higher concentration of emulsion. Overall, the addition of suitable concentration of emulsion was beneficial for improving the texture and microstructure of emulsion filled-gel as a controlled-release delivery system.