| China is a major sweet potato planting country,with large planting area and annual output,accounting for 65.4% and 85.9% of the world,respectively.With the continuous improvement of food demand,more importance has given to sweet potato because of its rich nutrients.Fresh sweet potato has a high water content,and is easily rotted due to environmental factors during storage and transportation.Dehydration of sweet potato can not only extend the storage period,but also facilitate transportation.At the same time,people's emphasis on sweet potato drying products quality requires scientific and rational use of drying technology,and dried food can retain its nutrients to the greatest extent.At present,the processing industry of sweet potato in China is still dominated by traditional processing,and the processing mode is also dominated by traditional hot air drying,which has low drying efficiency and long drying time,resulting in poor product quality after drying.Compared with hot air drying,infrared drying has the advantages of high heating efficiency,uniform heating and energy saving.In this paper,the characteristics of infrared drying of sweet potato slices were studied by the self-made infrared drying device.The effects of different drying temperature,slice thickness and steaming time conditions on the infrared drying process of sweet potato slices were studied.Based on the orthogonal experiment,the optimal drying process of sweet potato slices of infrared drying was obtained by taking the total color difference,energy consumption per unit mass of moisture removal and drying time as evaluation indexes,and the mathematical models of sweet potato slice was established.On this basis,changing of infrared heating mode was made.The effect of stage-varying temperature on the infrared drying sweet potato chips was studied.The main conclusions of this study are as follows:Firstly,the infrared drying of sweet potato slice was mainly the falling rate drying stage,and there was no obvious constant drying stage.Under different dryingtemperatures(60,65,70,75?),slice thickness(3,5,7,9mm)and steaming time(4,6,8,10min),the effective moisture diffusion coefficient increases with the increase of drying temperature and the decrease of slice thickness.With the increase of steaming time,the effective water diffusion coefficient showed a trend of increasing first and then decreasing.Secondly,the result of orthogonal test shows slice thickness is the most important factor affecting comprehensive evaluation,followed by drying temperature and steaming time.Considering total color difference,energy consumption per unit mass of moisture removal and drying time,the optimal infrared drying process of sweet potato slice is drying temperature of 70°C,slice thickness of 3mm,steaming time of 6min.The corresponding total color difference,unit energy consumption,and drying time under this drying condition were 17.773,113.659kJ/g and 75.748 min,respectively.The Midilli and Kucuk model is the suitable mathematical model to describe the infrared drying characteristics of sweet potato slice.Thirdly,the infrared drying temperature in the first stage of temperature-varying drying has a significant effect on the drying rate,but the drying temperature in the second stage has no significant effect on the drying rate.The cooling mode drying has better energy consumption and the heating mode has better total color difference.Taking the total color difference and unit energy consumption indicators into consideration,the optimal heating process for stage-varying temperature infrared drying of sweet potato slice is 70°C(75min)-65°C(end).The energy consumption per unit mass of moisture removal under this drying condition is 75.905kJ/g,which is 33.2% lower than the constant temperature drying.Compared with constant temperature infrared drying,the drying rate of sweet potato slice can be accelerated and the drying energy consumption can be effectively reduced by decreasing the drying temperature at the second stage. |
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