Research And Application On Properties Of Purple Sweet Potato Starch/Carrageenan Mixed Systems

Purple sweet potato, an annual ipomoea plant, is widely distributed in most regions of China. The purple sweet potato starch contains a large amount of amylase which is easy to aging, resulting in the starch product with poor stability. It limits the development of the deep-processed purple sweet potato products. Therefore, in this paper, carrageenan and purple sweet potato starch are compounded for a systematical study. The pasting property, rheological property and gel property in this mixture were determined to investigate the mutual synergy between carrageenan and purple sweet potato starch, to study the stability of the mixture, and to develop a new purple sweet potato fruitcake products based on the properties of the blended system.(1) Study on the pasting characteristics of purple sweet potato starch/ carrageenan mixed systemsThe pasting characteristics of the mixed system were studied with diffirent ratios of the purple sweet potato starch to carrageenan. The results showed that the pasting temperature, the peak viscosity, the final viscosity, the breakdown viscosity and the regenerative value of the starch paste with the addition of carrageenan were higher than that without carrageenan. The expansion degree and solubility of the mixed systems increased with the increasing of temperature. The swelling degree of purple sweet potato enhanced while the amount of the carrageenan in the mixed system increased, leading to the reduction of solubility, the lower retrogradation property of mixture, and the improved freeze-thaw stability. The structure of the formed mixture was much more homogeneous and smooth under the same conditions. Thus, the existence of the carrageenan can protect the starch granule of purple sweet potato from retrogradation and can improve the stability of the product.(2) Study on the rheological properties of purple sweet potato starch/ carrageenan mixed systemsThe static and dynamic rheological properties, shear restoring force of the mixture were tested by rheometer. The static rheological properties of purple sweet potato starch/carrageenan mixed systems were typically non-Newtonian fluid with pseudoplastic characteristics. The purple sweet potato starch with carrageenan exhibited a more thickening effect, decreased the mobility, and improved the pseudoplastic and shear stability. The dynamic rheological properties showed purple sweet potato starch/carrageenan mixed systems possessed higher storage modulus (G ),higher loss modulus (G ") and more superior viscoelastic properties. In the shear restoring force testing, it was found that shear restoring force was significantly increased with the increasing of the carrageenan amount in the mixed system. The results suggested that adding carrageenan could improve the stability of the purple sweet potato starch, and also demonstrated the potential application of carrageenan in purple sweet potato products.(3) Study on the gel properties of purple sweet potato starch/carrageenan mixed systemsThe effects of salt concentration, pH value and other factors on the texture of the mixted system were studied with TA-XT2i texture analyzer. It was suggested that the hardness, chewiness, springiness and cohesiveness of the mixed gel increaseed with the increasing of carrageenan amount. The hardness and springness reached the maximum when the ratio of purple sweet potato starch to carrageenan was 8:2. Moderate salt concentration could enhance the hardness and chewiness of the mixed gel, and the K+ affected much more than other salts. While excess salt added could decrease the hardness and chewiness of the gel. Thus the salt concentration should be controlled at a proper level. The mixed gel has good hardness and chewiness when pH >6; while it was not easy for material forming with decreased hardness and chewiness under acidic condition. This implied that mixted gel was stable with alkali but sensitive to acid. The hardness, chewiness, springness and cohesiveness of the mixed gel decreased with the increasing of citrate concentration, while adhesiveness increased. In addition, hardness and springness of mixed gel decreased with the addition of saccharose. And the adhesiveness of the mixed gel reached the minimum when saccharose concentration was 0.6g/100mL. This study further established a foundation for the development of purple sweet potato deep-processing products.(4) Develop new purple sweet potato fruitcake products based on the properties of purple sweet potato starch/carrageenan mixed systemsThis study focused on the recipe of making purple sweet potato fruitcake. Based on the single factor experiment, carrageenan content, the ratio of sucrose to fructose syrup and the citric acid amount were optimized. The hardness, springness and sensory evaluation were investigated using orthogonal experiment to obtain the recipe for purple sweet potato fruitcake. Sequence of factors that affect the product quality was carrageenan>proportion of saccharose and fructose syrup> citric acid. Based on the results, the best recipe for making purple sweet potato fruitcake was determined with 8% of carrageenan, the ratio of sucrose to fructose syrup= 1:2.5 (total amount of sweetening agent was 80%),0.3% of citric acid and 0.1%o of KCl. The purple sweet potato fruitcake obtained by following this recipe showed purplish red color, luster, tasty and sweet flavor, and great stability.