Physicochemical properties of soya bean protein gel prepared by microbial transglutaminase in the presence of okara

Summary The influences of okara on the gelling and secondary protein structure of soya protein isolate (SPI) were investigated. Okara was ultra‐refined by high‐pressure homogenisation. The resulting particle sizes and microscopic morphologies were determined using a laser particle size analyser and a confocal laser scanning microscope, respectively. After okara homogenisation, surface area average particle size (D32) decreased from 49.68 to 23.29 μm and volume average particle size (D43) decreased from 118.94 to 55.08 μm. Dynamic rheological measurements showed that the storage (G′) and loss (G′′) moduli of SPI gelled in the presence of okara were mostly higher than those of SPI gels alone and were increased as the okara amounts increased. Linear law analysis revealed that SPI–okara gels were weak gels and frequency independent. Fourier transform infrared spectroscopy showed that okara and transglutaminase influenced the prevalence of α‐helices, β‐turns, β‐sheet and random coils.