Law Of Occurrence And Development Of Dew Condensation During Storage Of Soybean And Its Influence On Quality

In this subject,Chinese soybeans and American soybeans with a moisture content of12±0.5%were taken as research objects.The temperature of grains of the spring and summer,summer and autumn alternated,autumn and winter,winter and spring alternates were simulated in a specially-made experimental simulation silo with a wall surface that can be heated and cooled,stored under the conditions of setting the temperature difference of the warehouse wall as 20?,15?and 10?respectively,the critical parameters of soybean condensation,the heat transfer law of grain piles during the condensation process,and the influence of condensation on soybean quality were studied,and the process of soybean condensation and the characteristics of heat transfer in grain piles,the relationship between soybean quality changes and temperature difference and moisture were explored.The main conclusions are as follows:1.The temperature difference had a significant effect on the dew condensation time of the soybean grain pile(P<0.05),the larger the temperature difference,the shorter the time to dew condensation.The condensation time was 19.17?22.41 h at a temperature difference of 20?,and the condensation time was 22.42?29.54 h at a temperature difference of 15?,and the condensation time was 30.59?39.88 h at a temperature difference of 10?;when dew,the moisture content of soybeans increased by more than 1.5%;under the same conditions,the time for American soybeans to reach dew condensation was 3.25 h later than Chinese soybeans on average;the critical temperature and humidity of dew condensation was related to the temperature and humidity of the grain pile when entering the warehouse.The critical time of soybean dew condensation in the alternate period of spring and summer,summer and autumn was 26.97 h,which was shorter than the 32.58 h in the alternate period of autumn and winter,winter and spring;During the alternate period of spring and summer,summer and autumn,the critical temperature of soybean condensation was 21.69?and the critical relative humidity was 73.00%,which was higher than 8.43?and 71.72%during the alternate period of autumn and winter,winter and spring.When the local temperature of the grain pile dropped by 5 to 8°C within 40 hours,condensation was prone to occur,and the grain management personnel must enter the warehouse in time to check the condensation on the grain pile.2.During the dew condensation process,the greater the temperature difference,the more obvious the temperature,humidity,and moisture changes in each part of the grain pile.Under a temperature difference of 20°C,the temperature of all parts of the grain pile near the hot and cold walls was basically stable after storing Chinese soybeans for 2 days;the average temperature rise rate near the hot wall was 0.35°C/h,and the average temperature drop near the cold wall was 0.36°C/h;The water content of the upper,middle and lower layers near the hot wall continued to decrease,and dropped to 9.77%,8.01%,and 7.16%respectively within 30 d,the moisture content of the lower layer dropped the most,and the moisture content of soybeans(near the upper layer of the cold wall)at the condensation site continued to increase in the early period(0?9 d)to 33.41%,the volatility rised in the middle and late periods(9?30 d)of condensation,and the moisture rised to36.99%in 30 d.The relative humidity near the hot wall gradually decreased,and the relative humidity near the cold wall first decreased and then increased,and there were a minimum point of relative humidity.The temperature,humidity and moisture changed in various parts of the soybean grain pile in the American soybeans were similar to those of Chinese soybeans.There was a closed air circulation inside the grain pile.The direction of the air circulation was from the high temperature lower layer of the grain pile to the high temperature upper layer to the low temperature upper layer to the low temperature lower layer.The air circulation inside the grain pile transferred the moisture in the high temperature part to the low temperature part.At the same time,the energy inside the grain pile was transferred in the form of a slightly inclined vertical surface.3.Condensation had a significant impact on soybean quality(P<0.05).When dew condensation occurred at a temperature difference of 20?,the quality of Chinese soybeans changed the most,and the storage stability was poor.After 6 days of storage,the moisture of soybeans rised to more than 20%,L^*value,a^*value,b^*value,germination rate,crude fatty acid value,peroxide value changed drastically.After 30 days of storage,the color of soybean kernels darkened,the L^*value dropped by 16.82%,the a^*value dropped by30.35%,and the b^*value dropped by 52.54%;the germination rate dropped to 2%,and the germination ability was almost lost;the crude fat content was not Significant change(P>0.05),the crude fatty acid value and peroxide value rose to 8.53 mg/g and 2.32mmol/kg respectively,which had reached the severely unsuitable state in the soybean storage quality judgment standard;the functional properties of protein had changed,water retention decreased by 51.49%,oil retention increased by 40.33%,emulsification stability decreased by 38.13%,and emulsification activity increased by 9.14%.The quality changes of American soybeans with condensation at a temperature difference of 20°C were similar,but the magnitude of the change was smaller than that of Chinese soybeans,after 30 days of storage,the crude fatty acid value increased to 1.25 mg/g,which was still suitable for storage in the soybean storage quality judgment standard.The quality changes of Chinese soybeans and American soybeans that dew condensation at a temperature difference of 10?were small.4.During the dew condensation process,the greater the temperature difference,the faster the moisture content of soybeans increased,and the more obvious the changes in the low-field NMR relaxation map of soybean seeds.When the dew condensation occurred at a temperature difference of 20°C(20?40°C)and 10°C(10?20°C),there were only T₂₁ peaks characterizing“bound water”and T₂₃ peaks characterizing“oil”in the Chinese soybean grains,during the dew condensation process,the area of the T₂₁ peak increased,and it was divided into two relaxation peaks at 6 d and 24 d of storage,namely the T₂₁ peak and the T₂₂ peak that characterized“weakly bound water”.The T₂₃ peak area did not change significantly(P>0.05);At 30 d,the sum of the T₂₁ peak and T₂₂ peak areas under the two temperature differences gradually increased,reaching 2.45 and 1.90 times the sum of the initial peak areas,respectively,the sum of the T₂₁ peak and T₂₂ peak areas was significantly positively correlated with the water content(P<0.01),the correlation coefficients were0.992,0.995,respectively.During the dew condensation process,the low-field NMR relaxation map of American soybean seeds was similar to that of Chinese soybeans,but the variation range was smaller than that of Chinese soybeans.Under the above two temperature differences,there were two relaxation peaks of T₂₁ and T₂₂ after storage for 18 d and 30 d;When stored for 30 d,the peak time of T₂₁ and T₂₂ peaks of American soybeans was lower than that of Chinese soybeans,and the bound water and weakly bound water were more stable than Chinese soybeans.Correlation analysis of each quality index of two soybeans and water content and the sum of(T₂₁+T₂₂)peak area showed that soybean color,germination rate,crude fatty acid value,peroxide value,water holding capacity and moisture had a high correlation,these indicators can be used as sensitive indicators in the process of soybean dew condensation.