Effects Of Drying Methods On Drying Characteristics And Quality Of Purple Potato

Purple potato is rich in nutrients.Its anthocyanins have various health care functions,and the lysine,an amino acid lacking in rice and wheat flour,can effectively make up for the nutritional deficiencies of traditional staple food.However,the high content of water and carbohydrates of purple potato make it perishable and germinate during storage,which is inconvenient for storage,transportation,processing and utilization.Traditional drying method requires long drying times and great energy that have a negative impact on the quality of purple potato and its anthocyanin.Therefore,it is of great significance to explore a high efficiency and high product quality drying method to dry purple potato.In this study,the effects of hot air drying（HAD）,far-infrared radiation assisted heat pump drying（FIHPD）and air-impingement jet drying（AIJD）on the drying characteristics and quality of purple potato were investigated.Optimal drying method and drying process were obtained by comparison and optimization.And the effect of optimum drying conditions on anthocyanins was studied.The main reseach contents and results were as followings,which provide a theoretical basis for the production and processing of purple potato powder.（1）Purple potato was dried by HAD,FIHPD and AIJD at 65°C.Its drying characteristics were analyzed and results showed AIJD had the highest drying rate,followed by FIHPD and HAD.The effective diffusion coefficients were 3.65×10^-10 m²/s,4.56×10^-10 m²/s and 5.47×10^-10 m²/s for HAD,FIHPD,and AIJD,respectively,which was consistent with the order of drying rate.In addition,Midilli model gave the best fit for drying dynamics of purple potato dried by different methods,and the highest goodness of fit was found in AIJD（r=0.9996）.Thus,AIJD had obvious advantages in drying efficiency.（2）Physicochemical characteristics reflected the effects of drying method on the quality of purple potato.It was found that HAD,FIHPD and AIJD-purple potato flours exhibited lower L^*and a^*values than the control sample,and AIJD-sample showed the lowest total color difference（?E）value.The protein content of purple potato flour decreased after thermal drying,but the digestibility of starch increased（up to 92%）.In addition,AIJD-and control samples showed no significant difference in total anthocyanin content,DPPH radical scavenging ability and reducing ability.Therefore,the effect of AIJD on the physicochemical properties of purple potato was less than FIHPD or HAD.（3）Drying process of purple potato dried by AIJD was optimized by orthogonal experiment,and its effect on anthocyanins was studied.Results showed that the optimum drying parameters were drying temperature at65°C,air velocity at 2.30 m/s and slice thickness of 3 mm.Petunidin-3-p-coumaroylrutinoside-5-glucoside and peonidin-3-p-coumaroylrutinoside-5-glucoside,the two main anthocyanins in AIJD-purple potato flour,were acylated anthocyanins.Their structures were more stable so that their contents were positively correlated with antioxidant activities（r≥0.672,p<0.05）.The degradation of anthocyanins was a non-spontaneous endothermic reaction that followed the first-order kinetics.And the anthocyanin degradation rates accelerated with the increase of drying temperature.However,anthocyanin content was not only affected by drying temperature but also by drying time.Compared with the sample dried at50°C and 80°C,the purple potatoes dried at 65°C had the highest anthocyanin content,which reflected the optimum drying conditions of AIJD had the smallest effect on anthocyanin of purple potato.