| Food polymer science theory combining with modern instrument analysis technique was applied to analyze systemically extraction, purification, as well as physico-chemical properties of tea polysaccharide (TPS). Based on chain fragment and molecule level, we investigated deeply effects of molecular characteristics of TPS on the compatibility, thermodynamics, rheology, crystalline property and gel texture of amylose and amylopection. This will provide the important and solid theory foundation for utilizing and exploring effectively the application of polysaccharide food additive to starch-based food. The main conclusions are as follows:1. Water-extraction and alcohol-precipitation method was applied to extract coarse TPS. Then coarse TPS was graded by exchanging chromatography on DEAE-cellulose column (DEAE-52). Three fractions of polysaccharides TPS1、TPS2and TPS3were obtained by means of water,0.1mol L-1NaCl and0.5mol L-1NaCl gradient elution. The yields of the eluant were0.96%,2.41%and7.89%, respectively. Finally, the Sephadex G-150gel chromatography column was used to further grade and purify TPS3. Two kinds of polysaccharides TPS3-1and TPS3-2were obtained, whose yields were11.30%and5.73%, respectively. TPS3-1was served as the main research subject and the TPS purity was86.64%.2. The molecular characteristics of TPS were carried out by high-performance size exclusion chromatography (HPSEC), multi-angle laser light scattering (MALLS). The results showed that Mw, Mn and Mz(z-average molar mass) are2.351×105g mol-1,2.287×105g mol-1and2.762×105g mol-1, respectively. Weight-average mean square radius (Rw), number-average mean square radius (Rn) and z-average mean square radius (Rz) are135.7nm,132.1nm and145.9nm, respectively. The polydispersity indexes of Mw/Mn and Mz/Mn are1.028and1.208, respectively. The distribution of TPS molecular weight was a single peak as shown by size-exclusion chromatography, which indicated that TPS was homogeneous. The slope of the conformation plot for TPS is0.24±0.00, indicating TPS is a homogeneous spherical polymer in solution. The a value of TPS was0.5379obtained by using Mark-Houwink equation, which indicates that the TPS molecule exists as spherical conformation with branches in solution.3. TPS solution was non Newtonian fluid as pseudoplastics. So, the viscidity of TPS solution decreased as shear velocity increased. The viscidity of TPS was decreased slightly under acid condition, while it did sharply under basic condition. The viscidity of TPS solution increased as heating temperature increased. However, when heating temperature was higher than80℃, the viscidity of TPS solution declined. The viscidity of TPS solution was increased as heating time increased. However, when heating time was longer than110mins, the viscidity of TPS solution declined drastically. The viscidity of TPS solution decreased after freezing-thaw treatment. Compared with refrigeration treatment, the viscidity of TPS solution decreased greatly after freeze treatment. However, when heating time was more than110mins, the viscidity of TPS solution declined drastically.4. When different amylose/amylopectin ratios were1:1,1:2,1:3and1:4,△bm＜0△[η]m＞0, which indicates that amylose and amylopectin mixture exists phase separation and immiscibility. When the concentration of TPS was20%under different amylose/amylopectin ratios (1:1,1:2,1:3and1:4) conditions,△bm＜0,△Bm＜0, μ＜0,△[η]m＞0, which indicates that all mixtures exist phase separation and immiscibility. When the concentration of TPS was40%under different amylose/amylopectin ratios (1:1,1:2and1:3) conditions,△bm＞0,△Bm＞0, μ＞0,△[η]m＜0, indicating good compatibility. While the amylose/amylopectin ratio was1:4,△bm＜0,△Bm＜0, μ＜0,△[η]m＞0, indicating immiscibility. When the concentration of TPS was60%under different amylose/amylopectin ratios (1:1,1:2and1:3) conditions,△bm＞0,△Bm＞0, μ＞0,△[η]m＜0, indicating good compatibility. While the amylose/amylopectin ratio was1:4,△bm＜0,△Bm＜0, μ＜0,△[η]m＞0, indicating immiscibility. When the concentration of TPS was80%under different amylose/amylopectin ratios (1:1,1:2and1:3) conditions, Abm>0,△Bm＞0,μ＞0,△[η]m＜0, indicating good compatibility. While the amylose/amylopectin ratio was1:4,△im＜0,△Bm＜0,μ＜0,△[η]m＞0, indicating immiscibility.5. The mixing ratios (1:1,1:2,1:3and1:4) of TPS/amylose and TPS/amylopectin have only one Tg, so do the different ratios (1:1:1～1:1:5,1:2:1～1:2:5,1:3:1～1:3:5and1:4:1～1:4:5) of the amylose/amylopectin/TPS mixtures. Meanwhile, the Tg changes as the mixing ratios change, and its value is within the Tgs of TPS, amylose and amylopectin. The result shows that the certain mixing ratios of TPS, amylose and amylopectin mixtures can be compatible.6. In view of its molecular structure, TPS can increase plasticization and molecular movement of the potato amylose and amylopectin chains, induce the greater electrostatic repulsion and decrease the relation between the macromolecules, thereby decreasing the glass transition temperatures (Tgs) of the mixed amylose/amylopectin system. And also, the above effects can become more effective with increasing concentration of TPS. The Tgs of amylose and amylopectin at different ratios are lower than that of amylose, and higher than that of amylopectin. The addition of TPS also decreased the crystallinities of amylose and amylopectin if they are mixed, and the Tgs and crystallinities of amylose and amylopectin mixtures declined drastically with increasing concentration of TPS. Besides, the higher the TPS concentration, the smaller the change in Tgs of the mixtures over the storage period (5-30d). The result indicated that TPS can reduce obviously recrystallisation of amylose and amylopectin and inhibit the retrogradation of amylose and amylopectin.7. The addition of TPS could increase the firmness, cohesiveness and index of viscosity of amylose, while decrease its consistency. The addition of TPS could increase the consistency, cohesiveness and index of viscosity of amylopectin. When the concentration of TPS was less than0.24%, the firmness of amylopectin was decreased. While the concentration of TPS was more than0.36%, the firmness of amylopectin was increased. When the amylose/amylopectin ratio was1:1and the concentration of TPS was more than0.12%, the firmness of the mixed amylose/amylopectin/TPS gel was increased with increasing concentration of TPS. In addition, the addition of TPS could increase the consistency, cohesiveness and index of viscosity of the mixed amylose/amylopectin/TPS gel. When the amylose/amylopectin ratio was1:2, the addition of TPS could increase the firmness, cohesiveness and index of viscosity of the mixed amylose/amylopectin/TPS gel. Especially, when the concentration of TPS was0.48%, the firmness, cohesiveness and index of viscosity were increased obviously. When the amylose/amylopectin ratio was1:3, the addition of TPS had hardly any remarkable influence on the firmness of the mixed amylose/amylopectin/TPS gel, while the addition of TPS decreased the consistency of the mixed amylose/amylopectin/TPS gel and the cohesiveness and index of viscosity of the mixed amylose/amylopectin/TPS gel. |
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