عنوان مقاله [English]
Background and objectives:Gum tragacanth (GT) is one of the natural secreted hydrocolloids which have many applications in food and pharmaceutical industries. Unfortunately, there is limited scientific information about the electrostatic interactions of gum tragacanth with proteins, especially the proteins that have been unfolded by physical approaches. In this regard, the main objective of this study is investigation the effect of thermal processing on the whey protein isolate (WPI) properties and their complexation with gum tragacanth.
Materials and methods:The influence ofheating time (0, 5, 10, 15, 20, 25, 30 and 35 min at 80C) on the turbidity of WPI, alone and in the mixture with GT (r = 0.1, pH 4.0 and Cp 0.1 w/w) was surveyed. Then the flow behaviour and viscosity of gum tragacanth-WPI mixture solution in the shear rate of 0-100 S-1 (pH 4.0) was compared with the individual solutions of gum and protein. Since the maximum turbidity was observed in the range of 15-35°C, the impact of heating time at three levels (15, 25 and 35 min) and biopolymer mixing ratio at six levels (2:1, 1:1, 1:2, 1:5, 1:10 and 1:20) on the protein and carbohydrate compositions of precipitation and supernatant were investigated by lowry and phenol-sulphuric acid experiments, repectively.
Results:Turbidity of protein solutions were significantly changed with rising the heating time such that the maximum turbidity achieved after 25 min thermal processing. While these solutions were unstable due to protein-protein interaction and formation of protein aggregates, GT addition leads to meaningful changes in the stability of protein solutions which was as a result of protein-polysaccharied interactions. Similar to protein solutions, the maximum turbidity of the complexes was achieved after 25min thermal processing. The rheological measurements showed that the mixture solution has pseudoplastic behavior with a large hysteresis loop as well as the higher viscosity rather than the blank solutions, all of which indicate the formation of electrostatic interactions between protein and polysaccharide and formation of complexes.By calculation of protein and polysaccharide in the supernatant and precipitation, the least ratio of Pr:PS was observed for the 25-min-treated WPI. Furthermore, the ratio of Pr:PS in the precipitation was increased significantly as Pr:PSratio was increased in the mixture.
Conclusion:Addition ofgum tragacanth to the whey protein isolate will leads to a significant stability in the solution. Due to unfolding of WPI, using thermal processing on the whey protein isloate solution results in the meaningful increasing in the turbidity of protein solution and the efficiency of GT-WPI complex formation.