| Peanut moisture content(m.c.)is an important basis for the drying progress of fresh peanuts and the safe storage of dried peanuts.At present,the research on peanut drying and storage mostly focuses on the changes of quality or the changes of moisture in the whole peanuts.It is lacking in research on the moisture changes of peanut pods,shells and kernels during the drying and storage.The moisture changes of peanut pods,kernels,and shells during drying and storage were assayed in different ventilation and drying media and storage conditions,which is beneficial to grasp the drying characteristics,formulate the scheme of variable temperature and segmental drying of wet peanut;and realize the scientific utilization of energy.Clarifying the influence of different storage conditions on the hygroscopicity,safe moisture content and mildew time in peanut storage is conducive to controlling storage environmental conditions reasonably.In this paper,the moisture change range and change rate of peanut pods,kernels,and shells of fresh peanut with 46.51%m.c.and high-oleic fresh peanut with 39.90% m.c.during drying process were studied at different air temperatures and speeds.In addition,the moisture changes and mildew of peanut pods,kernels and shells with nearly 6% m.c were studied under different relative humidity and storage temperature.The main results in the paper are as follows:(1)The initial moisture content of peanut pods,kernel and shell of normal peanut(Kainong 172)were 46.51,43.71,53.00%,respectively.When the air speed was 0.3 m/s and the air temperatures were 45,40,35 and 30 °C,the drying time for the peanut pods whose moisture content were less than 10% m.c was 24,28,38 and 44 h,respectively.Besides,the corresponding moisture change speeds of peanut pods,kernels and shells were1.53,1.31,0.97 and 0.83 %/h,1.37,1.18,0.87 and 0.75 %/h,1.90,1.61,1.20 and 1.04 %/h,respectively.When the air speed was 0.7 m/s and the air temperature were 45,40,35 and30 °C,the drying time of peanut pods was 21,25,35,40 h,respectively,and the corresponding moisture change speeds of peanut pods,kernels and shells were 1.74,1.47,1.05 and 0.92 %/h,1.51,1.32,0.95 and 0.83 %/h,2.18,1.82,1.29 and 1.14 %/h.,respectively.During the drying process of wet peanuts,it can be divided into ? stages based on the moisture content.When the air speed was 0.3 m/s and air temperatures were45,40,35 and 30 °C,the moisture change speed of peanut pods in stages?,?and ? was4.21,1.57 and 0.98 %/h,3.52,1.19 and 0.98 %/h,2.75,1.00 and 0.80 %/h,1.87,0.92 and0.60 %/h,respectively;the moisture change speed of peanut kernels in stages?,? and? was 1.03,1.63 and 1.19 %/h,0.86,1.26 and 1.08 %/h,0.67,1.01 and 0.72 %/h,0.64,0.78 and 0.72 %/h,respectively.When the air speed was 0.7 m/s and the air temperatures were 45,40,35 and 30 °C,the moisture change speed of peanut pods in stages ?,? and? was 10.32,1.67 and 1.07 %/h,9.51,1.23 and 1.05 %/h,7.44,1.10 and 0.86 %/h,1.98,1.03 and 0.61 %/h,respectively;the moisture change speed of peanut kernels in stages ?,? and ? was 2.67,1.65 and 1.22 %/h,1.12,1.44 and 1.21 %/h,1.01,1.06 and 0.78 %/h,0.85,0.87 and 0.75 %/h,respectively.The results showed that the drying rate of the peanuts decreased with air temperature and air speed increased.The drying rate of peanut shells was higher than that of peanut pods and kernels.The variation range of air temperature on the drying rate of peanut pods could reach up to 28%,while the air speed was only 12%.Changes in moisture content in the?stage of peanut pods and peanut kernels were mainly affected by air speed.The influence of the air change speed on the above?stage reduced with lower wind temperature.It should be avoided to improve drying efficiency by the way of wind speed increasing in the late phase of peanut drying.With air temperature rised(30 °C to 45 °C),the increase amplitude of moisture change rate in peanut pods added first and then decreased at the inflection point of wind temperature of 40 °C.When the drying efficiency is improved by increasing temperature in the drying process of wet peanut,the heating range should be determined reasonably to avoid a small increase in drying efficiency after a large increase in drying energy consumption,which will cause a waste of energy.(2)The initial moisture content of peanut pods,kernels and shells of high-oleic peanut(Kainong 1760)were 39.90,38.65,45.17%,respectively.The drying time for the peanut pods whose moisture content were less than 10% m.c was 18,24,29 and 38 h at the air speed of 0.3 m/s and the air temperature of 45,40,35 and 30 °C,respectively.Besides,the corresponding moisture change speeds of peanut pods,kernels and shells were 1.71,1.25,1.03 and 0.79 %/h,1.54,1.17,0.97 and 0.73 %/h,2.06,1.59,1.26 and 0.98 %/h,respectively.When the air speed of 0.7 m/s and the air temperature were 45,40,35,and30 °C,the drying time of peanut pods was 15,19,25 and 34 h,respectively;and the corresponding moisture change speeds of peanut pods,kernels and shells were 2.00,1.61,1.23 and 0.88 %/h,1.85,1.51,1.17 and 0.82 %/h,2.51,1.95,1.48 and 1.08 %/h,respectively.When the air speed of 0.3 m/s and the air temperature of 45,40,35 and 30°C,the moisture change speed of peanut pods in stages?,? and ? was 5.10,0.85 and1.53 %/h,1.56,1.24 and 1.09 %/h,1.05,1.01 and 0.93 %/h,0.96,0.65 and 0.63 %/h,respectively;the moisture change speed of peanut kernels in stages?,? and ? was1.85,1.29 and 1.75 %/h,0.92,1.33 and 1.29 %/h,0.65,1.28 and 1.21 %/h,0.50,0.96 and0.88 %/h,respectively.When the air speed was 0.7 m/s and the air temperatures were 45,40,35 and 30 °C,the moisture change speed of peanut pods in stages ?,? and ? was9.79,1.05 and 1.83 %/h,2.30,1.26 and 1.42 %/h,1.20,1.15 and 1.18 %/h,1.18,0.77 and0.81 %/h,respectively;the moisture change speed of peanut kernels in stages ?,? and? was 2.61,1.48 and 1.83 %/h,1.01,1.97 and 1.68 %/h,0.67,1.86 and 1.32 %/h,0.60,0.98 and 0.95 %/h,respectively.The results showed that different varieties of peanuts had different drying characteristics.High-oleic peanuts had lower drying time than normal peanuts,and the drying rate was higher than normal peanuts.The variation range of moisture change speed of high-oleic acid peanut pods caused by air speed change was higher than normal peanut pods.With the air temperature dropped from 45 °C to 30 °C,the drying rate of normal peanut pods in the ? stage decreased with the decrease of air temperature,and the drying rate of high-oleic peanut pods in the ? stage increased first and then decreased at the inflection point of wind temperature of 40 °C.In the drying process of high-oleic wet peanut,the air temperature should be lower than 40 °C in ?stage to avoid adverse effect on peanut drying.(3)During storage of dried peanuts,the moisture content of peanut pods(nearly 6%m.c.)reached to 9.18% m.c.after 16 days without moldy at 20 °C and 70% RH;the moisture content rose to 8.47% after 17 days at 25 °C,it is stable without mildew;the moisture content increased to a stable value of 7.95% without moldy after 16 days at 30 °C.At the condition of 80% RH,the moisture content of peanut pods reached to 10% m.c.in10 days at 20 °C,then reached to 11.27% m.c.and been mildew after another 4 days;the moisture content of the peanuts increased to 9.82% m.c.and mildew emerged at 25 °C;the moisture content of the peanuts rose to 9.50% m.c.and mildew appeared after 13 days at30 °C.At the condition of 90% RH,the moisture content of the peanut increased to 10%m.c.after 5 d,then increased to 12.75% m.c.with another 3 d and appeared mildew at20 °C;the moisture content of the peanuts increased to 10% m.c.in 5 days,and to 10.71%m.c.after another 2 days with mildew at 25 °C;the moisture content of the peanuts increased to 9.54% m.c.after 7 days and mildew aroused at 30 °C.Under the same condition of humidity,the higher temperature was,the lower peanut moisture content was.At 20-30 °C,the moisture content of dried peanut pods at 70% RH did not exceed 10%,without moldy;the moisture content increased rapidly and been moldy within 2 weeks;at the condition of 90% RH,the moisture content exceeded 10% after 5 days and got moldy in8 days.The relative humidity of dry peanut should not exceed 70% RH when the storage temperature is higher than 20 °C. |
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