Emulsifying ability of soy protein isolates obtained at pilot plant under simultaneous heat and reducing treatments

The emulsifying abilities of 12 soy protein isolate samples were studied in relation to their solubilities (Sol) in different solvents and their sulfh ydryl contents (SHL). Samples were obtained at pilot plant under different heat and reducing treatments, according to a central composite design 2(2) + star with a triplicate central point, resulting in 11 samples. An untreat ed sample (standard) was also included. The independent variables were heat treatment temperature (T) and sulfite concentration (C-Na2SO3) while the r esponses were Sol in water (Sol(w)), Sol in phosphate buffer (Sol(buf)), So l in 2-mercaptoethanol (Sol(2-Mer)), Sol in SDS (Sol(SDS)) and SHL. The res ults indicated a good fit to a second order polynomial equation for Sol(w), Sol(buf), Sol(2-Mer) and SHL, while in the case of Sol(SDS) the only signi ficant term was the linear one for T. The dependence of emulsion ability (A (500) as a measure of interfacial area) with time (t) anal protein dispersi on concentration (C) was evaluated using response surface methodology (RSM) . The A(500) showed a very good fit to a second order polynomial equation w ith R-2 higher than 89%. The structural differences among samples caused by different treatments were well explained by the A(500). Simultaneous heat and reducing treatment under mild conditions (T = 60-65 degrees C and C-Na2 SO3 = 0.2-0.4%) were able to open the protein structure, increasing SHL. Sa mples highly soluble in every solvent (without aggregation effects) showed the highest emulsion ability.