Thermorheological Characteristics of Soybean Protein Isolate

Abstract

ABSTRACT: Small amplitude oscillation shear measurement was used to study gel rigidity of commercial soy protein isolate (SPI) dispersions during isothermal and non‐isothermal heating. Temperature sweep data (20°C to 90°C atheating rate of 1°C/min) of SPI dispersions demonstrated that elastic modulus (G) predominates over viscous component (G′) for all concentrations studied. The gelation kinetics of SPI was evaluated by a non‐isothermal technique as a function of elastic modulus (G). During experiments, it was observed that a critical concentration of 10% was required to form a true SPI gel. Thermorheological data of 10% and 15% SPI dispersions were adequately fitted by 2nd‐order reaction kinetics. The reaction order of gelation was initially calculated by multiple regression technique correlating dG'/dt, G’and temperature, which finally was verified by linear regression of kinetic equation at selected order. Isothermal data of 15% SPI was also followed by 2nd‐order reaction kinetics. The activation energy during the isothermal technique was significantly higher than non‐isothermal gelation of SPI at same concentration level. Gel strength of the non‐isothermally heated SPI sample (15% to 20%) was compared with isothermally heated (90°C for 30 min) one. Higher protein concentration (20%) and isothermal heating exhibited significantly higher gel rigidity while the difference between the 2 processes was insignificant at 15% concentration at a similar condition.