Technical Study Of Vacuum Fried Purple Sweet Potato

With purple sweet potato as raw material, through protecting color, blanching, freezing technology and frying, we expect to developes a new kind of vacuum fried food which contains high anthocyanin content, low oil content, and is unique in flavor and taste crunchy. The purpose of this article is to provide a new way for deep processing of purple sweet potato, and have a positive effect on purple sweet potato to drive stable development of planting system and adjustment of agriculture structure. The main contents and the results are as follows:Purple sweet potato processing characteristics were researched. The main nutrient component, gelatinization properties and thermodynamic properties of five kinds of purple sweet potato raw material were studied. Sensory quality of vacuum fried purple sweet potato chips were discussed using paired sort comparison method and consumer hobby sensitivity test. The result showed that:the product quality was negatively correlated to the reducing sugar content, pectin content, gelatinization temperature and pasting heat enthalpy; But it was positively correlated with the relative density, anthocyanin and peak viscosity. Therefore,the varieties suitable for vacuum Fried purple sweet potato chips was that reducing sugar content was centered, pectin content, heat enthalpy and the gelatinization temperature was low; anthocyanin content, relative density and the peak viscosity was high. Comprehensive consideration, the purple sweet potato met the requirements of the vacuum frying varieties.Optimum processing parameters of the vacuum fried purple sweet potato chips pretreatment process were discussed. During color protection technology, anthocyanin content, sensory scores and color value were used to test the L-ascorbic acid, citric acid and the sodium sulfite single color fixative impacting on the product quality. And orthogonal test determine the optimal complex color protection agent. The optimum conditions determined were as follows:0.05%L-ascorbic acid,0.50%citric acid,0.10%sodium sulphite. Other pretreatment process of the vacuum Fried purple was studied. Effects of slice thickness, blanching conditions and freezing conditions on the quality of vacuum fried purple sweet potato chips were studied by single factor, and the processing operations were optimized by orthogonal and uniform test designed methods in this study. During pretreatment process, purple sweet potato was sliced with3.0mm, scalded at95℃for3.5min and frozen at-20℃for18h. Compared without color fixative, it anthocyanins retention content increased significantly from42.67%to73.99%.Vacuum fried might preserve nutrition value of the purple sweet potato for the greatest degree. And the anthocyanin content of the product were80.68%,the oil content was decreased from20.83%to17.40%respectively, crushing force was declined from736.8N to468.9N, thus the product presented some pleasant properties:a clear texture, crispy taste and non-greasy feeling.The factors that affected the oil content of the vacuum fried purple sweet potato chip were studied.Three factors which greater affected the oil content of purple sweet potato chips during vacuum fried process were selected by Plackett-Burman test methods based on single factor experiments. From the results of response surface analysis for vacuum fried process, it was found that the optimum conditions for the purple potato chips based on oil content of purple potato chips were operations of vacuum fried at87.7℃for11.8min and followed by centrifuging at the speed of369.18r/min for7min. And three factors had a very significant effect on vacuum fried purple sweet potato chips, the primary and secondary order were Fried time> Fried temperature> centrifugal speed. The interaction of the factors of vacuum fried purple potato chips oil content significantly affected. Under the modified processing conditions, the actual value of oil content in purple potato chips was13.92%declining20%and exhibiting1.37%relative error when compared to the theoretically predicted value.Different packaging methods and storage environment affecting on the quality of vacuum fried purple sweet potato slices were compared during shelf period. The results showed that nitrogen filled packaging had effectively eliminated moisture content. The oxidation degree was small. Durning storage process, determination acid value of purple sweet potato chips less than3mg/g, and oil oxidation time was9.2h. Durning storage process, oil oxidation time of vacuum Fried purple sweet potato chips downtrend was in line with a dynamic index variation, and calculated the shelf life at10℃,25℃,37℃were9.12,6.26,4.87months. As the temperature increased, the content of anthocyanins decreased and the chromatic aberration also changed. We concluded that nitrogen packaging should be used to preserve purple sweet potato slices, but we needed to avoid long-term and high-temperature during storage.The thermodynamic properties and crystallization properties of the purple sweet potato chips were studied. Along with the extension of storage time, the recrystallization degree of amylopectin and amylose starch increased, recrystallization region became more orderly and stablely and the rebound degree increased. In the process of storage, the quality of the product declined, at the same time, the hardness of purple potato chips increased.