Study On Gelation Properties Of Whey Protein/Low Acyl Gellan Gum Mixtures

Proteins and polysaccharides are the two kinds of biopolymers widely existed in food system. The interaction of proteins and polysaccharides is of direct importance for the macroscopic properties of food products such as:flow, stability, microstructure, texture and mouth feel. In order to understand the interaction of protein and polysaccharide thoroughly and obtain the better properties, it is important for us to explore the gelation behavior of whey protein/low acyl gellan gum mixtures which were influenced by polymers concentration, cation types and cation concentration, acid inducer, acidification rate as well as pH. In this thesis, the gelation properties and rheological behavior were mainly studied.When there was no salts addition in the whey protein/low-acyl gellan gum mixed gels, the results showed that fracture strain, fracture stress, fracture work, initial Young’s modulus, opacity index and water holding capacity increased with the increased of gellan gum concentration. The fracture stress and fracture work increased with the whey protein content at first and decreased as whey protein content continued to increased. Meanwhile, the water holding capacity of mixed gels decreased with the increase of whey protein concentration.The values of water holding capacity correlated well with fracture strain(R=0.8665-0.9772).Influences of concentrations, cation type and cation concentrations on the mechanical properties, optical performance and water holding capacity of whey protein/low acyl gellan gum mixed gels were investigated. The results revealed that the whey protein concentration had little influence on the gelation properties of mixed gels. Fracture strain, fracture stress, the initial Young’s modulus, water holding capacity and opacity index of mixed gels increased as the low acyl gellan gum concentration increased. The influence of ion on gelation properties of mixed gels was investigated. The fracture strain and water holding capacity of mixed gels decreased with increasing ion concentration regardless of ion type(Ca2+、 Mg2+、Na+、K+). On the contrary, with the ion concentration increases, the initial Young’s modulus and opacity index appear in the trend of first increased and then remained stable. At each polymer concentration, the fracture stress of mixed gels increased with increasing ions concentration until ion concentration reached a critical level, after which further increases in ion resulted in a reduction of fracture stress. At the critical ion concentration, mixed gellan gum gels containing divalent cations(Ca2+,Mg2+) were stronger than those containing monovalent cations(K+, Na+). There is no synergistic effect between sodium, potassium and calcium. While, there is synergistic effect between sodium, potassium and magnesium.The influence of gellan gum concentration, whey protein concentration and final pH (4.2-6.4) on the mechanical properties, water-holding capacity, turbidity and microstructure of mixed gels formed by acidification with glucono-8-lactone (GDL) and hydrochloric acid respectively was evaluated. The gelation profiles of mixture of whey protein(7.5%,10%,12.5%w/v) and low acyl gellan gum(0.1%,0.2%,0.3%w/v) after the addition of varying rates GDL showed a gradual decrease in the pH. The acidification of GDL can be simulated by the first order kinetic equation. Failure stress increased at higher gellan gum concentration. The optimum pH to the maximum gel strength for the mixed gels induced by GDL was about4.7, while the optimum pH for the mixed gels induced by HCl was5.2. All the gels were turbid and the WHC improved at higher gellan gum concentrations and pH values. The microstructure and turbidity showed good correlation with the mechanical properties.Thermo-rheological properties of whey protein/low acyl gellan gum mixed gels were investigated by using dynamic rheology measurements. The results showed that the system undergo a sol-gel transition during the gelation process. The sol-gel transition of mixtures increased with the increase of whey protein and gellan gum concentration. Moreover, the sol-gel transition of the acid-induced gels increased as pH value decrease.