Effects of pH and incubation temperature on properties of konjac glucomannan and zein composites with or without freeze-thaw treatment

Abstract

This work investigated the effect of pH and incubation temperature on the morphology and properties of konjac glucomannan (KGM)-zein composites with or without freeze-thaw treatment. When the incubation temperature was 90 °C, the composites prepared in the pH range of 10.5–11.5 were concentrated polymer solutions, while the composites prepared in the pH range of 12.0–13.0 were gels. The pH of 12.5 was found to form the composites with the most dense microstructure, the highest storage modulus and crystallinity, and the greatest ability to resist plastic deformation during compression. The composites tended to form gels with the increase of incubation temperature from 40 °C to 90 °C at pH = 12.5. The temperature of 90 °C was found to form the composites with the most dense microstructure, the greatest ability to resist plastic deformation during compression, and the highest crystallinity and frequency stability. The composite prepared at an incubation temperature of 70 °C and a pH = 12.5 had similar microstructure, rheological properties, and texture properties to that prepared at an incubation temperature of 80 °C and a pH = 12.0. The freeze-thaw treatment caused a slight increase in storage modulus (G′) and crystallinity when the composites were concentrated polymer solutions. When the composites were gels, the freeze-thaw treatment caused a rough and inhomogeneous microstructure, increased the G′ and the ability to resist plastic deformation during compression, decreased the springiness, and altered the internal water mobility. pH and incubation temperature play important roles in the morphology and properties of KGM-zein composites. • The composites were concentrated polymer solutions prepared at 80 °C and pH ≤ 11.5. • The composites were gels prepared at 40 °C–80 °C and pH = 12.5. • 70 °C and pH = 12.5 endowed the composite with similar properties to 80 °C and pH = 12.0. • Freeze-thaw treatment had different effects on gel and concentrated polymer solution.