Preparation Of Sweet Potato Granules And Its Characteristics Of Extrusion Cooking

Sweet potato granules which have a longer shelf-life and kept the most nutrition and flavor of fresh sweet potato are a good raw material in sweet potato food industry.First, this paper studied on color-protecting techniques during the process of sweet potato granules. By applying Regression Orthogonal Design we determined the optimal compound color fixative which contained 0.58% citric acid and 0.5% sodium sulfite. The optimum hours of color protection was confirmed with single factor experiment, the result showed that the optimum time of color-protecting is 45min.By the process of color-protecting the activity of Polyphenol Oxidase in Huangshi sweet potato is0.085, with the inhibition rate of 86.82%, while the activity of Polyphenol Oxidase in Hongan sweet potato is 0.093, with the inhibition rate of 87.23%.Second, three new processing technologies which are making-slice, making-mire by stirring, making-mire by pounding of sweet potato granules was given, influences of the different processing technologies and different sweet potato variety on the characteristics and sensory of sweet potato granules were discussed. The results showed that the characteristics which contained free starch rate, fat binding capacity, water retention, grain degree, starch pasting properties and sensory evaluation of sweet potato granules by different new processing technologies existed great differences. The quality of sweet potato granules produced by making–mire by stirring was the best to compare with other sweet potato granules produced by other processing technologies. There were also some differences between the two different sweet potato granules. General speaking, the quality of Hongan sweet potato granules produced by making-mire stirring was the best.In addition, we studied the optimal extrusion cooking process parameters of sweet potato granules by regression orthogonal design. The optimum combination scheme about Huangshi sweet potato granules had been obtained: material additive water 33%, screw speed was 60r/ min, barrel temperature (sectionⅢ) was 120℃. The optimum combination scheme about Hongan sweet potato granules: material additive water 33%, screw speed was 60r/min, barrel temperature (sectionⅢ) was 125℃. After extrusion cooking, The content of starch in Huangshi sweet potato granules decreased 6.85,the content of soluble sugar increased 8.65,the content of starch in Hongan sweet potato granules decreased 8.31,the content of soluble sugar increased 10.67; The content of protein in Huangshi sweet potato Hongan sweet potato granules decreased 0.4 and 0.54 respectively; The content of combinative lipid in Huangshi sweet potato granules and Hongan sweet potato granules both decreased 0.39; The content of fiber in Huangshi sweet potato granules and Hongan sweet potato granules decreased 0.56 and 0.61 respectively. After extrusion cooking, the properties of sweet potato granules changed. After extrusion cooking, water retention of Huangshi sweet potato granules and Hongan sweet potato granules increased 2.0 and 1.9 respectively; Fat binding capacity of them were within 0.98ml/g and 1.18ml/g; Onset temperature of Huangshi sweet potato granules and Hongan sweet potato granules decreased 29.87℃and 47.77℃respectively, enthalpy of transition of them decreased 443.5J/g and 306.58J/g respectively. It became easier to gelatinize.The results of this study might guide the deep processing of sweet potato foods.