| Sunflower protein has many benefits, such as high nutritional value, gentle absorption and comfortable colour. It is a potential resource of plant protein. Protein has been widely used in industrial production as a major functional ingredient to improve the yield, waterholding capacity of meat products to meet the low fat-high protein demand of consumers. However, high temperature treatment of the proteins during the actual processing, often limits processing and utilization. It is very meaningful to discuss the effect of thermal treatment on rheological properties of the gel prepared from sunflower protein. In addition, the effect of natural polymer additives on protein gel properties also important as the people pursuit for high quality life.In this work, sunflower protein isolates(SPI) and its main constitutes(11S globulin) suspensions(7%, w/v) were heated at the denature tempreture and higher or lower denature tempreture ± 10 °C for 10 min, to investigate the influences of different heating temperatures on structural, rheological and gelling properties. The effect of starch on rheological and gel properties of SPI was also investigated as the same total solids content, increasing the potao starch addition. The ratios of protein/starch were 15/0, 14/1, 13/2 and 12/3, respectively. The structural characteristics and its physicochemical properties of the modified proteins were characterized by SDS-PAGE, contents of sulfhydryl and disulfide bonds, distribution of particle size and differential scanning calorimetry(DSC). Rheological and gelling properties, the microstructure, water hoding capacity and protein solubility of the modified sunflower protein were also investigated. At the same time, original protein was used as a control. The main results were as followed:(1) The structural and rheological properties of thermal modified sunflower proteinThe structural characteristics showed that thermal treatment induced SPI and 11 S globulin protein aggregate, microstructure irregularities, molecules stretch. The surface hydrophobicity and fluorescence intensity of modified SPI and 11 S globulin protein were descreased. The content of sulfhydryl of modified SPI and 11 S globulin protein decreased, disulfide bonds increased, 102 °C modified SPI had the minimum surface sulfhydryl values(1.80 ± 0.028 ?mol/g) and 112 °C modified SPI had the minimum total sulfhydryl values(1.86 ± 0.049 ?mol/g), 98 °C modified 11 S globulin protein had the minimum surface sulfhydryl values(1.86 ± 0.037 ?mol/g) and minimum total sulfhydryl values(2.78 ± 0.071 ?mol/g). DSC analysis showed that the themal modification did not induced SPI and 11 S globulin protein denature completely, all the modified protein become more thermostability. The aggregation of SPI and 11 S globulin protein was more obvious at the denature tempreture.The results of rheological properties indicated that the apparent viscosity of thermal modified protein were increased, the dispersion stability decreased, and the protein treated at denature tempretures had the maximum modification. The water holding capacity of thermal modified SPI and 11 S globulin protein gel were higer than nature protein, 102 °C modified SPI and 98 °C modified 11 S globulin protein had the maximum values of 50.14 ± 5.6 % and 46.32 ± 2.6 % respectively. As the chemical bond of modified SPI and 11 S globulin protein contributed to gel network decreased, the gelation time extend and elastic moduls decreased. The gel temperature of SPI were increased from 46.29 °C(nature protein) to 56.86 °C(102 °C modified protein); 11 S globulin protein increased from 40.81 °C(nature protein) to 51.59 °C(98 °C modified protein). The maximum strain of modified SPI and 11 S globulin protein were lower than nature potein, the minimum values of modified SPI and 11 S globulin protein were 0.32%(102 °C modified protein) and 0.11%(98 °C modified protein) respectively. Pictures of gel microstructure showed that the aggregation of natural protein was cluster orderly and modified SPI and 11 S globulin protein were irregular. Protein solubility of modified SPI and 11 S globulin protein gel decreased, and the minimum values were 77.82 ± 4.26% and 72.93 ± 3.52% respectively.(2) Effect of potato starch addition on rheological properties of sunflower protein isolatesResults indicated that rheological properties of SPI were significantly improved by potato starch. With content of potato starch increased, gelation time of protein-starch(P-S) dispersion extend; the microstructure of SPI gel became irregular and apparent morphology became delicate yellowish. Water hoding capacity of P-S gel increased obviously from 47.46 ± 3.76%(SPI/ST = 15:0, w/w) to 66.47 ± 1.85%(SPI/ST = 12/3, w/w), elastic moduls increased from 1.68 Pa(SPI/ST = 15/0, w/w) to 44.15 Pa(SPI/ST = 12/3, w/w). Researchs find that starch accelerated protein denature, the denature temperature of protein changed from 110.36 °C(SPI/ST = 15/0, w:w) to 109.66 °C(SPI/ST = 12/3, w/w). Starch innhibited the protein aggregation and the protein solubility of gel became higher with 8.4% increasation. The addition of starch significantly improved food quality and reduced the costs of food production, it has instructive meaning to the processing and utilization of protein. |
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