Interaction of deamidated soluble wheat protein with sodium alginate

Abstract

The viscous behaviour of mixtures of deamidated gluten or soluble wheat protein (SWP) (7.5–13.5%, w/v) and sodium alginate (0.5–1.5%, w/v) in distilled water pH 6.5 were investigated. Mixtures of SWP and sodium alginate mixed under varying conditions indicated greater than expected viscosity values at higher biopolymer concentrations. Measurements made when the biopolymers were mixed at room temperature followed by heating at 60°C showed maximum viscosity at a ratio of 50 parts SWP to 50 parts sodium alginate. When the biopolymers were heated separately and then mixed, the maximum viscosity occurred at a ratio of 80 parts SWP to 20 parts sodium alginate. SWP spontaneously aggregated on hydration. Heating at 60°C caused fragmentation or disaggregation of the SWP leading to a reduction in viscosity and an increase in hydrophobicity ( Friedli, & Howell, (1996) Food Hydrocolloids, 10, 255–261). Sodium alginate inhibited the breakdown of SWP aggregates at 60°C, when both polymers were mixed prior to heating, which was confirmed by phase contrast microscopy. Although the mixture did not appear to separate visually, microphase separation was evident by microscopy. The phase separation may be due to repulsion between the negatively charged sodium alginate and SWP which resulted in bicontinuous and more concentrated networks of the two polymers. The addition of SWP (1–8%) to a 1% (w/w) sodium alginate solution increased the gelation time from 30 to 90 min and resulted in soft opaque creamy gels with lower G′ values.