Study On Local Heating Of Imported Soybean During Storage

In this subject,the american soybean was taken as the research object,the law and quality change of local heating by local moisture and impurity accumulation during storage have been systematically simulated and studied.The method of local embedding was used to embed soybean with different mass（120kg,60kg,30kg,15kg and 7kg）with different water content（16%,18%,20%）,and soybean with different impurity content（50%,30%）under the same mass in the middle and lower part of normal soybean under safe water in the simulated warehouse（1.5 m×0.95 m×1.2 m）.The temperature of soybean was monitored by the temperature measuring cable in the warehouse,The local heating condition and heat transfer law of imported soybean during storage were studied.Meanwhile,the variety of microorganism causing the heating and the change of soybean quality were discussed,and the microstructure of soybean cotyledons under different heating conditions was observed and analyzed.The results are as follows:1 The moisture content of soybean was an important factor affecting fever.The moisture content and the quality of embedded soybean had significant effects on the range of heat diffusion（P<0.05）.Low initial grain temperature could effectively limit fever.The initial grain temperature was 21～26℃,the embedding weight was 120kg,60kg,30kg,15kg,and the moisture content was 20%.The soybean began to heat after 1 d,1 d,2 d and 3 d of storage,and reached the highest temperature after 11 d,11 d,13 d and 13 d of storage,which were52.1℃,43.2℃,41.4℃and 29.1℃respectively.When the initial grain temperature was 16～18℃,the embedding weight was 120kg,60kg,30kg and 15kg respectively,and the moisture content was 18%,the heating time was delayed by 4～5 days and the maximum temperature was reduced by 20℃compared with 20%moisture content.Soybean with different moisture content were not heating when the embedding weight was 7kg.When the initial grain temperature was 16～17℃,the highest temperature was 20.1℃only when the weight of soybean was 120kg.The high impurity content of soybeans is also easy to cause local heating.The initial grain temperature was 14℃,and 120kg soybean with 50%impurity content was embedded.After8 days of storage,it began to heat.and the highest temperature was 18.2℃.When the initial grain temperature was 13℃,120kg soybean with 30%impurity content was embedded,no heating occurred.When soybean is locally heated,the spreading speed of heat and the spreading degree of heating range have obvious directionality.The vertical upward heat diffusion should be paid more attention.The heat of soybean with different moisture content and embedding quality is easy to transfer upward,and the diffusion range of heating area in vertical direction is 1～2times of that in horizontal direction.Compared with the soybean with 16%moisture content,the maximum vertical and horizontal diffusion areas of 120kg soybean with 20%moisture content increased by 4 and 5.8 times,respectively;compared with 15kg soybean,the maximum vertical and horizontal diffusion areas of 120kg soybean with 20%moisture content increased by 3 and 2.87 times,respectively.2 High moisture content soybean can accelerate the growth of microorganisms,and the effect of high impurity on microorganisms is not obvious.Low moisture content,low grain temperature and low oxygen can limit the growth of microorganisms.The total number of fungi colonies increased from 0.48×104 cfu/g to 1.37×106 cfu/g after 3 days,which was higher than the original sample by 2 orders of magnitude.After 9 days storage,the total number of fungi colony decreased to 1.4×105 cfu/g when the heating temperature reached 47.2℃.15kg soybean with 20%moisture content was mildly mildewed after 3 days storage,and severely mildewed after 15 days storage.However,120kg soybean with 16%moisture content was mildly mildewed after 48 days storage.120kg soybean with 50%impurity content was embedded,the initial grain temperature was 14℃,and there was no mild mildew during the whole storage period of 54 days.Through the high-throughput sequencing of soybean,the results showed that different degrees of fever,the corresponding colony types and dominant bacteria were also different.Aspergillus is always the dominant species in the two states of high temperature and medium temperature.The highest heating temperature of 120kg soybean with 20%moisture content can reach 52.1℃,which belongs to high temperature.In the later stage of storage,some facultative anaerobes,yeasts and anaerobes are mainly produced.The highest heating temperature of 15kg soybean with 20%moisture content can reach 29℃,which belongs to moderate temperature.Aspergillus species propagated in large numbers with the extension of time;there were three unique yeast species in the late stage of high temperature and heat storage compared with the early stage,but there was no significant difference in the whole storage period of medium temperature and heat storage.aflatoxin B₁ and ochratoxin A were not detected in two kinds of embedded soybean.3 During storage,high moisture content soybeans,regardless of the embedding quality,will cause quality deterioratio;low moisture content soybeans have little effect on the quality.High temperature heating has a greater impact on quality,after 9 days of storage,the temperature reached 47.2℃,and the germination rate dropped to 0.After 21 days of storage,the color of soybean was dark brown,and the crude fatty acid value rose to 5.26 mg·g^-1,which had reached a serious state of not suitable for storage.High temperature caused protein thermal denaturation,resulting in the decrease of moisture holding capacity of protein by 1.09 g·g^-1,and the increase of oil holding capacity by 0.78 g·g^-1,after 54 days of storage,the germination rate of soybean with 16%moisture content decreased to 67%,the color became dark,the crude fatty acid value increased to 1.86 mg·g^-1,which was still suitable for storage,the moisture holding capacity of protein decreased by 0.18 g·g^-1,and the oil holding capacity increased by0.16 g·g^-1,the range of quality changes were small.The moisture content of soybean with 50%impurity was 11.8%,and the quality of the stored grain did not change significantly due to the low temperature.4 High temperature and mildew damage the cell structure of soybean cotyledons,resulting in the loss of nutritional value of soybean.The tissue structure of cotyledons was observed by scanning electron microscope.The results showed that the tissue structure of cotyledons was damaged and shrunk,the tissue gap was enlarged,the structure was loose,and the damaged area was increased.The structure of cotyledon cells was observed by transmission electron microscope.High temperature resulted in the increase of membrane permeability,plasmolysis,protoplasm leakage in vitro,flocculent protein in vivo and cell deformation.The growth of mold degrades the cytoplasm,resulting in the decomposition of cell structure and protein body,deformation of protein body and separation of plasma membrane and cell wall.