Study On The Preparation Of Purple Sweet Potato Powder And Its Processing Characteristics

The production of sweet potato of China is the largest in the world, and its planting area and yield rank fourth in China only after rice, wheat and corn. Various sweet potato are planted in China, in which purple sweet potato has many excellent functions besides what the normal sweet potato has, such as antioxidant activity, antimutagenic activity, radical scavengers, protection for liver and lowering blood pressure because of the rich anthocyanins content. So the purple sweet potato has great exploitation potentialities.In order to solve the problem of the intolerance of strorage and transpotation of the purple sweet potato, this study investigated the preparation technology for purple sweet potato powder with enzymatic hydrolysis and spray drying, and found out the optimum processing conditions. The purple sweet potato powder, made by the optimal technology, were evaluated its physical and chemical quality as well as processing characteristics. The final study result would provide the theore ical basis for industrial production and application of purple sweet potato powder in food industry. The principal contents were as follows:1. According to the analysis of basic compounds of purple sweet potato, it is obvious that purple sweet potato contained a high level of anthocyanin pigments, which will be degraded because of polyphenol oxidase during processing. Steam blanching for 2 min before processing could inactivate the native polyphenolxidase that can cause enzymatic browing and quality decrease of purple sweet potato.2. In this paper, High-Temperature Resistant a-Amylase were used to hydrolyze purple sweet potato slurry, and the optimum process parameters of purple sweet potato starch enzymatic hydrolysis were determined with Box-Behnken response surface methodology based on the single factor experiments. Then the optimal technology of enzymatic was:enzyme dosage 25 U/g starch, pH 6.0, enzymatic hydrolysis temperature 85℃, enzymatic hydrolysis time 70 min. Under these conditions, the viscosity of purple sweet potato juice was reduced by 84% to fit to spray drying.3. With the content of anthocyanin as an evaluating index, spray-drying technology used to make purple sweet potato powder was studied. On the base of single factor experimental analysis, the condition of spray drying was determined as:the inlet air temperature was 130℃, the outlet temperature was 65℃, the flow rate was 60mL/min. Then the products sprayed drying, with the losing anthocyanin content below 10%, had a good solubility.4. The processing characteristics of purple sweet potato powder in food were studied to promote its application. The results showed that:compared with air-drying powder, purple sweet potato powder made with enzymatic hydrolysis and spray drying technology, has a higher solubility and water absorb index. However, emulsifying activity index, gelling intensity and freeze-thaw stability of it is relatively low.5. The product with the water residue below 5%, which was rich in anthocyanin, had original colour and flavor, and could be an aid in efficient storing and transporting. So the purple sweet potato powder was an effective form of elaborately and profoundly processed projects.