Synergistic Regulation of Characteristics of Bigel System by pH of Hydrogel and Biphase Ratio

The physicochemical properties of bigel system are important factors affecting its application in food processing. In this study, the pH of whey protein isolate (WPI) hydrogel and oleogel/hydrogel (O/H) ratio were regulated to prepare bigel systems with different morphological structures, and their physicochemical properties and related mechanisms were analyzed. The results showed that the pH of WPI hydrogel and the O/H ratio could synergistically affect the gel state, spreadability and extrusion-flowability of the bigel system. With the increase of oleogel content, the gel state of the bigel system could be improved, and the spreadability and extrusion-flowability of the bigel system could be reduced. The pH of hydrogel could change the apparent properties of the system by affecting the characteristics of the hydrogel and the oil/water interactions. The bigel system had poor oil and water binding capacity near the isoelectric point of the WPI, however, the increase of O/H ratio was favorable to improve its water binding capacity. The microstructure of the bigel system showed that the pH of the hydrogel and the O/H ratio could affect the crystal morphology in the oil phase. At pH6.0, the bigel system showed a water in oil structure, while at other pH, the system showed a complex bicontinuous gel structure. At high O/H ratio, oil droplets tended to accumulate and affected the network structure of the system. The texture and rheological properties analysis of the bigel system indicated that the increase of the O/H ratio was conducive to the improvement of the texture, and the increase of the gel modulus and apparent viscosity. The bigel system had better textural and rheological properties at pH7.0, whereas at pH3.0, it showed better structural recovery. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis confirmed that hydrogen bonding was predominant between the two phases, and the crystal structures of bigel were mainly of α, β′ crystalline types. The above research is helpful to realize the regulation of physicochemical properties of the bigel system by using hydrogel pH and O/H ratio, so as to make it suitable for products with different sensory properties.