| Cottonseed protein is not only an important source of feed protein, but is also a high quality edible vegetable protein suitable for human consumption. However, the utilization and development of its use are insufficient. The goal of our study was to analyze the heat-induced aggregation behavior of cottonseed protein, explores the relationship between cottonseed protein gel properties and its aggregate structure, to further control protein, improve the quality of cottonseed protein products and provide a theoretical base for its development and use. Main results are as follows:The extraction method of CPI, 7S and 12 S protein was determined. Then, the exartction parameters were were optimized by the menas of response surafce methodology, including extacrtion temperature, NaCl concentration and time. Under the optimal conditions,Protein exrtaction yield and protein content of the product were 58.2% and 91.28%, respectively. A very small amount of free gopssypol, about 0.023% was found in the protein. 7S and 12 S protein were obtained when the defatted cottonseed flour extract was fractioned using gel filtration chromatography. By this procedure, 7S and 12 S protein content of the product were 90.26 ± 1.26%and 94.50 ± 0.73%(N×6.25), respectively. To further check purity, the cottonseed 7S and 12 S globulin had higher purity and can be used for follow-up studies.Amino acid analysis indicated that CPI contained all essential amino acids. CPI was an acidic protein because the content of acidic amino acid were higher than the alkaline amino acid. Hydrophobicity Porbe(ANS) and differntial scanning calorimetry(DSC) were used to determine the surface hydrophobicity(S0) and thermal denaturation temperature(Td) of CPI, 7S and 12 S. S0 were 126.41, 91.60 and 142.73, while Td were 94.34℃, 96.27℃ and 103.7℃, respectively. The free sulphydryl(SF), total sulphydyrl(ST) and disulfide bond(-S-S-) estimated by DTNB were 11.84, 98.27 and 43.21μmol/g protein; 6.37, 82.04 and 37.84μmol/g protein; 8.49, 98.31 and 44.91μmol/g protein, respectively. The isoelectric point(ζ value was 0) was about pH 4.8, pH 4.2 and pH 4.2, respectively.Within pH3.0-7.0, it was the lowest gel point when the cottonseed protein isolated concentration was 12%. Protein concentration, p H and ionic strength had a greater impact on the cottonseed protein isolated gel properties. When the cottonseed protein concentration was 16%, the gel displayed the maximum hardness; when it was 14%, elasticity and adhesion reached the maximum values; and cottonseed protein isolated could be easily formed under acidic than alkli conditions. When it comes to the the effect of pH, the gel hardness and elasticity arrived at the peak at pH3.8, while adhesion was the maximum at pH5.2. In the meanwhile, pH was the main factor that affected cottonseed protein gel microstructure. The structure had a larger difference when the gel under different pH. Under acidic conditions(pH3.8, 5.2), it emerged uniformly distributed and dense gel network structure. And the gel network structure was relatively coarse under neutral conditions, morever, the distribution uniformity decreased. The salt concentrition had little infulence on the type of gel network structure, it had, however, a significant influence on the gel hardness and elasticity. When the salt concentration was 0.2 mol/L, the gel of cottonseed protein isolated formed had the higher hardness and elasticity values.Heat treat induced cottonseed 7S and 12 S globulin aggregated under neutral condition(pH 7.0), and the protein comformation changes during the thermal aggregation were characterized by small angle X-ray scattering techniques. The results showed that the 7S protein heated aggragation formed under neutral conditions and still exhibited similar spherical shape, and 12 S globulin aggregates formed a larger scale after heat treatment, the shape and size were nonuniform,though. Solubility analysis of the aggregate found that, although CPI, 7S and 12 S globulin showed raised surface hydrophobicity, dropped surface charge, decreased the solubility when treated higher than than their thermal denaturation temperatures, 7S protein still,relatively speaking, maintained a higher solubility, which could be considered as soluble aggregates. As for 12 S globulin, the aggregates generated after the thermal denaturation showed a sharp decline in the solubility considered to form the insoluble aggregates. Rheological results found the proportion of soluble aggregates had a greater impact on shear viscosity of the protein concentrated solution: the higher proportion of the aggregation, the lower of the shear viscosity. By gel rheology and texture analysis, we found that the proportion of soluble aggregates and insoluble aggregates gel had a greater impact on the fomationg, properties and microstructure of the gel. When 7S and 12 S hot aggregate ratio was 2: 1, the gel could be formed when heated, and the gel rate is faster than that of the cottonseed protein isolated. When 7S and 12 S hot aggregate ratio were 1: 1 and 1: 2 respectively,it was not possible to form a gel. When the content of soluble aggregates increased, the hardness and elasticity were better, the microstructures were more delicate, the particle size was small, and they were homogeneously distributed.When it was acidic conditions(pH 2.0), heat treatment induced the aggregation of cottonseed 7S and 12 S globulins, we systematically studied hydrolysis process and structural changes of the 7S and 12 S globulins, as well as the formation and topographical features of the fiber aggregates. It found that under the same conditions, 7S could generate fibrous aggregates, and the aggregation was limited; while 12 S formed amorphous aggregates, and the aggregation was unlimited. The rheological analysis revealed, fibrous aggregates had a greater impact on the shear viscosity of the solution: the higher of the content, the higher of the shear viscosity. At the same time, the fibrous aggregates had a significant influence on the gel properties and microstructures of cottonseed protein. When the proportion of fibrillar aggregates was higher, the formation of the gel accelerated, the gel was more uniform and delicate, and the gap was more smaller. |
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