Effects Of Air-impingement Jet Drying On Characteristics And Antioxidants Of Purple Sweet Potato

In the food industry, air-impingement jet technology is widely used in food reach and development. This kind of technology has a broad application prospect because of characteristics of high drying velocity, drying quality and lower power consumption. In order to enhance the drying quality and drying efficiency of the Purple Sweet Potato (PSP) in this paper, under the effects of different drying conditions of air-impingement jet on purple potato drying was studied, and fitting drying mathematical models was sereened out. And the effects of the ordinary and hypoxia air-impingement at different drying conditions on color, total anthocyanins, polyphenol oxidase (PPO) activity and total phenol and total phenolic antioxidant capacity was also studied. And further adopt hot air cross-flow drying, forced air drying, air-impingement jet drying and hypoxia air-impingement jet drying methods processing PSP to prove the high drying efficiency and high quality of air-impingement jet drying PSP. Mainly to obtain the following results:(1) The drying velocity and effective moisture diffusion coefficient (Deff) of air-impingement jet drying is higher than hot air cross-flow drying and forced air drying. But three are no Constant veloctity drying period between hot air cross-flow drying, forced air drying and air-impingement jet drying, mainly for the falling velocity drying.(2) The air-impingement jet drying properties of PSP were effected by pretreatment, sample thickness, air temperature and air velocity. The internal temperature of PSP increased with the time of microwave pretreatment increased, but the microwave pretreatment can decrease air-impingement drying rateof PSP. The drying velocity decrease with the increase of material slice thickness, but increase with the air temperature and air velocity increases. Three are no significant effect of sample thickness and air velocity on warming velocity of PSP, but the air temperature on the impact of warming velocity of PSP is more obvious. (3) The Deff increases with the slice thickness of PSP, air temperature and air velocity increases. The Deff of air-impingement jet drying is higher than the Deffs of hot air cross-flow drying and forced air drying.(4) The most fitting mathematical model of air-impingement jet drying PSP is Modified Henderson and Pabis because of it has the maximum R2, minimum χ2and RMSE among all8kinds of models.(5) Air-impingement jet drying leads to the total anthocyanin content, total phenol content, DPPH-scavenging activity and PPO activity of PSP decreased significantly.(6) The△E, TPC, TAC and DPPH-scavenging activity incearses with the time of microwave treatment before drying, slice thickness, nozzle height, air temperature and air velocity decreased.The PPO activity of dried PSP decreases with the time of microwave treatment before drying and air temperature increases, but there are no significantly affect of air velocity, slice thickness and nozzle height on PPO activity.(7) The critical period of to avoid color and TPC, TAC and DPPH· scavenging activity decreases of PSP is the first1h since the drying openning.(8) Compared to the air-impingement jet drying, hot air cross-flow drying and forced air drying, the dried PSP of hypoxia air-impingement jet drying has the better color, higher TAC, TPC and DPPH· scavenging activity. In the process of hypoxia air-impingement jet drying PSP, the TAC, TPC, DPPH· scavenging activity and the quality of color decreases with the air temperature, air velocity, slice thickness and nozzle height decreases.