Quality Analysis of Purple Sweet Potato Flour under Different Drying Processes

The research is aim to screen out a technology which is suitable for producing a kind of raw purple sweet potato flour (RPSPF) with high anthocyanin content and low gelatinization degree (GD) in industry. Therefore, the changes of anthocyanins, GD, sensory score and comprehensive score of purple sweet potato flour (PSPF) prepared by hot-air drying (HD), microwave drying (MD), and combined hot-air and microwave drying (HD-MD) were measured and analyzed. The results showed that the optimal HD condition was 40 ℃ for 8 h. At the moment, the anthocyanin content was 1.648 mg/g, the GD was 23.39%, and the comprehensive score was 97.01 points. It had the best quality but took a lot of time. The optimal MD condition was 420 W for 10 min, the anthocyanin content of PSPF was 2.645 mg/g, the GD rose to 93.33%, and the comprehensive score was 82.00 points. But the GD of PSPF prepared by MD was widely too high to produce RPSPF. The optimal HD-MD was 50 ℃ drying to the 40% moisture content, and then converted to 280 W microwave drying the moisture content to less than 8%. Then the anthocyanin content was 1.161 mg/g, the GD was 59.11%, and the comprehensive score of PSPF was 84.04 points. HD-MD has a simple operation and control. In addition, it can ensure the quality of RPSPF on the premise of extremely shortening the drying time. In conclusion, HD-MD is suitable for rapid industrial production.