Research Progress Of Purple Sweet Potato Granules

Purple sweet potato is a highly nutritious vegetable, riched in a variety of biologically active substances and nutrients. It has increasingly become one of the hotspots at home and abroad. However, due to the high moisture content of purple sweet potato, prone to mildew, rot, the disease has suffered serious losses and short-term storage. Purple sweet potato is processed into purple potato chips, purple fries and other foods, but also the development of extraction of anthocyanins, and so on. But this can’t add high value to meet the domestic and external demand. In this thesis, purple sweet potato powder process was optimised, and purple sweet potato flour physicochemical properties were studied. To carry out the deeply study of the purple sweet potato resources, providing technical support for the purple sweet potato powder processing, the results are as follows:1. The difference between the impacts of different drying methods on the purple sweet potato powder quality was studied, including moisture content, iodine blue value, color, total anthocyanins, nutrients and aromatic components.The experimental results showed that:for the basic nutritional characteristics of the purple sweet potato powder, either drying method resulted in the a certain degree loss of basic components of the purple sweet potato powder, In particular, the fat content, ash content, reducing sugars gradually increased; starch content gradually decreased; protein content did not change. The loss by freeze-dried was less than blast drying and vacuum drying. The loss of the basic chemical composition of the whole powder during vacuum drying was between the other two drying methods, blast dry got the most severely damage.On the comparison of the senses, all products had the unique aroma of purple sweet potato; color, vacuum drying and vacuum freeze-drying maintained the better color of the purple sweet potato than the blast drying, and vacuum drying turned out dark purple, while the vacuum freeze-drying was more white, but both of them was close to the color of raw purple sweet potato. Determination of iodine blue value, water holding capacity, holding oil, total anthocyanin content showed that, vacuum drying and vacuum freeze-drying was superior to blast drying, could be as much as possible to keep the purple sweet potato nutrition, structural integrity, thus demonstrated good quality and better processing performance in subsequent processing as food ingredients or excipients. Different drying methods made significantly difference aromatic components of the purple sweet potato powder.Drying method had a great influence on the aromatic components of the purple sweet potato powder, vacuum freeze-drying could retain the most aromatic substances.Overall, the vacuum freeze-drying brought lightlest loss to the purple sweet potato powder quality, but its time-consuming and consuming too much energy.Considered the currently production conditions, it was better to choose the vacuum drying to get better indicators and better the nutritional value. Later need to study more drying methods to compensate for the higher cost.2. Single factor experiments determine the appropriate process:for 10 min cooking time,100℃cooking temperature,0.08 MPa vacuum pressure,70℃vacuum drying temperature,8 h vacuum drying time. The order of to study the factors affecting the quality of the purple sweet potato powder was as follow:drying temperature drying time and cooking time,which were optimized by response surface methodology; the optimized processing parameters are:the cooking time 7～11 min, vacuum drying temperature 56～61℃, drying time 6～7 h.3. Physicochemical properties were studied before and after the purple sweet potato processing, including:drawing of the drying curve in the purple sweet potato powder processing; dry before and after physical and chemical properties change, including moisture content, and blue iodine value, color, total anthocyanins, nutrientsand aromatic composition changes.In drawing of purple sweet potato powder vacuum drying curve, although 90℃and 100℃, purple potato losy water rapidly, but the high temperature brought the material a series of changes, such as color change, nutritioningredients losses, but the low temperature is excessively and time-consuming, resulting in the increase of the economic costs, therefore, considered above all, 70℃as the drying temperature was more appropriate.From the sensory analysis of the purple sweet potato flour after processing, the product had the purple sweet potato unique aroma, color, dark purple, closer to the color of raw materials. Analysis from nutritional characteristics purple sweet potato powder, the basic ingredients in the purple sweet potato flour got a certain degree of loss. Specifically, the dried powder of ash, reducing sugars, fat increased, reflecting the cells damaged in a certain degree, thus releasing some of the nutrients; starch content got lost, which showed that the structural of processed starch was damaged; there was no significant change in protein during the processing.Determined the product iodine blue value, iodine blue value increased comparing with pre-processing. Determination of water holding capacity, oil holding capacity, total anthocyanin content, vacuum drying as much as possible kept the purple sweet potato nutrition, structural integrity, thus demonstrating a better quality and better processing performance as food ingredient or excipients. Processing made the aromatic components of the raw purple sweet potato changed, heating caused a series of chemical reactions in purple sweet potato, such as the Maillard reaction, which expanded the range of types of aromatic components. After a certaint drying emperature, the aromatic components was lost, alcohols by oxidation to reduce, esters increased, but also generated new aromatic ingredients.