Study On Preparation And Quality Features Of Purple Sweet Potato Granules By Explosion Puffing Drying At Variable Temperature And Pressure

Purple sweet potato is a new special type of sweet potato, riched in nutrients. But fresh purple sweet potato prone to mildew rot, is not easy to storage for a long time, can’t annual supply, influence the development and utilization. In order to solve the problem of fresh purple sweet potato difficult to long-term storage, in this paper, it made the purple sweet potato processed into purple sweet potato granules by explosion puffing drying technology, all its components in fresh sweet potatoes have a few loss, makes it easy to package and storage. And it will extend the storage period, solve the problem of purple sweet potato used by seasonal restrictions, can expand the application scope of purple sweet potato at the same time. At the same time, the physical-chemical properties and processing-application characteristics of purple sweet potato granules by explosion puffing drying technology are studied, and on this basis, it discusses the optimum formula and processing technology when added the purple sweet potato cooked granules to cookies, it will provide theoretical basis for the application of purple potato granules. The researches has very important significance to promote the development of purple potato industry.The main research and results are as follows:(1) The study of sweet potato raw granules by explosion puffing drying technology.In this chapter, the best color-protecting combination and drying technical conditions were studied. Considering the purple sweet potato granules color in processing, the color index b as an index, combining with the sensory analysis, to explore the influence of L-cysteine, scorbic acid, citric acid and salt concentration on the purple sweet potato raw granules. And and optimized the best color-protecting combination by orthogonal test were L-cysteine0.06%, ascorbic acid 0.60% and salt 0.60%; We investigated the effects of different puffing temperature, stagnant time, vacuum drying temperature on the product color index b, content of anthocyanins and iodine blue value. By using Box-Behnken design of the response surface methodology(RSM) to determine the technical conditions as follows:puffing temperature was 80℃, stagnant time was 5min and vacuum drying temperature was 69℃. The prepared purple sweet potato raw granules under the conditions have better color and aromas, its color index value of b was -7.827, anthocyanin content was 1.583 mg/g, and iodine blue value was 5.594.(2) The study of sweet potato cooked granules by explosion purring drying technology.In this chapter, the best steamed conditions of raw material, emulsifier content and drying technical conditions were studied. Considering the purple sweet potato rushing force during cooking and stirring, the iodine blue value as an index, we got the optimal conditions are under 100℃ steam for 15 min, and then added emulsifier 0.6% by the single factor experiment. We investigated the effects of different puffing temperature, stagnant time, vacuum drying temperature on the product color index b, content of anthocyanins and iodine blue value. The Box-Behnken design of the response surface methodology(RSM) was used to determine the technical conditions: puffing temperature 90℃, stagnant time 7min and vacuum drying temperature 70℃. Under these conditions, the color of prepared purple sweet potato cooked granules was purple, its color index value of b was -6.573, anthocyanin content was 1.509 mg/g, and iodine blue value was 19.056.(3) The study of quality on sweet potato granules.In this chapter, the physical-chemical properties and processing-application characteristics of purple sweet potato raw and cooked granules which are prepared by explosion puffing drying and drum wind drying were studied. Measuring the purple sweet potato granules’ indexes, such as basic chemical composition, iodine blue value, anthocyanin content, color, fragrant component, it showed that under different drying methods, the purple sweet potato raw granules starch content is significantly greater than the cooked, and the reducing sugar content is much smaller; The iodine blue value of purple sweet potato cooked granules is around 20, significantly greater than the raw, so the purple sweet potato raw granules cells integrity is greater by different drying methods; The content anthocyanin of purple sweet potato cooked granules is greater than 1.500 mg/g, the color index b is negative, so the purple sweet potato cooked granules color keep better by different drying methods; The types and main components of aromatic substances on purple sweet potato raw and cooked granules were different, purple sweet potato raw granules have 14 kinds, mainly is aldehyde, and purple sweet potato cooked granules can be up to 23 kinds, mainly is hydrocarbons; Comparing with the drum wind drying, explosion puffing drying has more advantages on the retention of color and aromatic substances.Measuring the purple sweet potato granules’ indexes, such as water- absorbent, oil-absorbent, freeze-thaw stability, pasting properties and rheological properties, it showed that under the explosion puffing drying, the purple sweet potato raw granules’ absorbent of water and oil were 4.644 g/g and 1.105 g/g, the freeze-thaw drainage rate is only 3.02%, is better than cooked granules; The gelatinization characteristics show that under the different drying methods, purple sweet potato raw granules’final viscosity>2000.00cP, far more than cooked, setback viscosity> 600.00cP, but the purple sweet potato cooked granules’breakdown viscosity is around 40.00 cP, so the hot paste stability is good; The rheological properties show that all purple sweet potato granules display the characteristics of pseudoplastic fluid, the loss tangent tan delta is less than 1, but cooked granules show weak gel properties; The two kinds of drying methods on purple sweet potato granules’influence on the processing and application characteristics difference is smaller.(4) The study of purple sweet potato cookies.According to the comparative study of purple sweet potato granules that the cooked granules show good characteristic value to added to baked products. So in this chapter, the cooked granules, flour, oil, sugar, etc were used as raw material to make cookies. With the sensory score and hardness value as index, we investigated the effect of the ratio of purple sweet potato cooked granules and weak strength flour, butter and shortening, the addition of sugar powder and water. The results showed that the optimum recipe of purple sweet potato cookies appeared beautiful color and luster, tasted crunchy, which included the ratio of purple sweet potato granules and weak strength flour 20:80, butter and shortening 15:45, sugar powder 15%, salt 0.5%, milk powder 8%, and water 6%.