Structural thermostability of commercial canola protein–hydrocolloid mixtures

Abstract

Proteins in a mixed system with polysaccharides may behave differently than when used alone. The thermal transition properties (denaturation temperature, T d; enthalpy of denaturation, Δ H) of canola protein isolate (CPI)–hydrocolloid ( κ-carrageenan, guar gum) mixtures were assessed using differential scanning calorimetry. Factorial and response surface models were used to examine the effects of pH, salt, protein, guar gum and κ-carrageenan concentrations on the conformational stability of CPI ( T d=86 °C, Δ H=16.2 J/g). CPI– κ-carrageenan mixtures treated with sodium acetate (NaC 2H 3O 2, 68 g/l) had the highest T d values (103.2 °C), whereas mixtures treated with sodium thiocyanate (NaSCN, 40.5 g/l) had the lowest T d (92.3 °C) values. Salts decreased Δ H values of CPI– κ-carrageenan mixtures in the order: acetate<sulphate=chloride<thiocyanate. CPI–guar gum mixtures treated with NaC 2H 3O 2 (68 g/l) and NaSCN (40.5 g/l) had the highest (18.1 J/g) and lowest (12.3 J/g) Δ H values, respectively. CPI– κ-carrageenan and CPI–guar gum mixtures treated with urea or dithiothreitol had low T d and Δ H values; this supports the involvement of noncovalent interactions and disulphide bonds in the structural stability of the mixed biopolymers.