Study On Preparation Of Purple Sweet Potato Suspended Beverage With Tremella Fruits And Its Storage Stability

The purple sweet potato is rich in nutrients such as anthocyanins, selenium, minerals and vitamins. Anthocyanins are natural potent free radical scavengers and have effects on anti-oxidation, prevention of cardiovascular diseases and antimicrobial efficacy. Therefore, the development and utilization of natural plants containing anthocynins become one of the current hot topics. Purple sweet potato was taken as the main raw material and dual enzymatic method was used to hydrolyze the starch in this essay in order to get the clear purple sweet potato juice. Compound stabilizers were chosen and mixed in proper ratio to guarantee the suspension of tremella fruits. The apple juice and sodium citrate was selected as the flavoring agents to make the purple sweet potato suspended beverage with tremella fruits. At the same time, the quality indicators and component contents of the product were analyzed, and its anti-oxidation effect was studied. At last, the pigment stability, suspension stability and microbial changes during the storage period were investigated. The main research results are as follow:(1) Blanching and cooking trails shows that the activity of polyphenol oxidase can be effectively inhibited and a good gelatinization result can be obtained by blanching purple sweet potato for5min and cooking for40min. The optimal liquefaction condition obtained by orthogonal experiment was at70U/100mL enzyme concentration,1:4material to water ratio and70℃for65min. In this condition, the DE value was28.5%. The DE value of saccharification will reach the maximum when the extent of liquefaction was22%. The optimal condition of saccharification get by response surface design method was at7700U/100mL enzyme concentration at62℃for150min. in this condition, the measured DE value was70.54%, indicating that the regression model has a good predictive result.(2) A better suspension stability and sensory effect can be obtained when the dosage of tremella fruits was0.3g/100mL. The optimal condition of compound stabilizers obtained by orthogonal experiment was:0.15%xanthan gum dosage,0.10%CMC-Na dosage and0.15%sodium alginate dosage. Purple sweet potato juice, apple juice and sodium citrate were blended with tremella fruits and compound stabilizers after mixing and clarification. The best formula of the beverage was purple sweet potato juice60%, tremella fruits0.3g/100mL, apple juice20%, sodium citrate0.3%and compound stabilizers0.2%. The best sterilization process of the beverage was at85℃for15min. (3) In the beverage, Soluble solids content is over8%, total acid content is about0.5%, anthocyanin content is6.18mg/100mL and light transmission rate is about62.3%. The microbiological indicators meet the requirements of the GB/T4789.21and the beverage is of nice color and good taste. Twelve kinds of free amino acids including five essential amino acids (EAA) are detected by the automatic amino acid analyzer. The amount of total amino acids (TAA) and EAA is33.68mg/100mL and9.15mg/100mL respectively. Sugar composition and content are analyzed by high-performance liquid chromatography system. The beverage contains glucose38.94mg/mL, fructose7.59mg/mL and sucrose0.84mg/mL. According to the test, hydroxyl radical scavenging rate of laboratory-made purple sweet-potato compound beverage is44.79%; DPPH radical scavenging rate is94.49%and superoxide anion scavenging rate is83.02%. Comparing to the relevant beverage sold in the market, laboratory-made purple sweet-potato compound beverage shows significant antioxidant activities.(4) The experiment of storage stability shows that the main reason for the change of beverage color was temperature and time. The temperature and the time increased, browning of the beverage became more serious. The viscosity of the beverage is almost unchanged during storage period. However, as the storage temperature increased, the suspension stability of the beverage was deteriorating. Therefore, the temperature was the leading reason to the deterioration of the beverage suspension stability during the storage period. With the extension of storage time, the total number of colonies in drinks increased, but the change was slightly. In the storage time of six months, the total number of bacteria in the drink met GB/T4789.21standard. The quality of the product was good and the total number of bacteria was within the range of standard required by GB/T4789.21at4℃for180days. The color change of the product was little, while the suspension stability was deteriorating and the total number of bacteria was out of the standard at25℃for180days.