Effects of two types of corn starches on physicochemical and structural properties of red bean protein isolate acid-induced cold gels

A mixture of red bean protein isolate (RBPI) with common starch (CS) or waxy starch (WS) from corn was heated, and induced by glucono-δ-lactone (GDL) to form a RBPI-starch complex cold gel. The physicochemical and structural properties of these gels were also investigated. Compared with the RBPI gels, the complex gels with CS had higher gel strength, water retention, viscoelasticity, and deformation resistance, forming a denser and more continuous microstructure with a high degree of crosslinking and small pores. Compared with the RBPI-CS complex gels, the RBPI-WS complex gels exhibited higher water retention and stronger transformation ability of free water to immobilized water; however, they exhibited poor mechanical properties and microstructures. The difference in the physicochemical properties of the gels was mainly related to the change in the hydrophobic interactions between the two gel systems. In addition, protein structure modification affected the gelation properties of the RBPI-CS and RBPI-WS complexes. The RBPI-CS complex gel exhibited strong X-ray peaks and fluorescence quenching ability. The addition of CS promoted the flexibility of the secondary structure and tightness of the tertiary conformation of the protein in the complex gel, forming a stronger and more compact non-covalent gel structure. However, the protein in the RBPI-WS complex gel showed an ordered secondary structure and a loose tertiary conformation, which weakened the gel network.