Study On Critical Point And Quality Change Of Heating And Mildew In Storage Wheat

This project was based on Henan common hard wheat harvested in 2017,and the moisture content of wheat was adjusted to 16%,18%,20% and 22%,the storage temperature was normal temperature(15-25?)and high temperature(25-35?),respectively,wheat was placed in a simulated storage experiment with a capacity of 1000 kg.To study the occurrence of heatinig and mildew under different storage conditions,determine the changes of grain temperature,total number of mold colonies,grain quality,rheological properties and microstructure during storage,find the critical point of heating and mildew,the quality change was corresponding to heating and mildew process,to provide theoretical basis and guidance for the actual storage of wheat.(1)Under high temperature storage(25-35?),wheat with moisture content of 16%,18%,20% and 22% had heating phenomenon for only 6 d,3 d,3 d and 3 d,respectively,the highest grain temperature during storage was 44°C,51°C,53°C and54°C.At room temperature(15-25°C),the time of heating of wheat grain piles with moisture content of 18%,20% and 22% was 27 d,12 d and 5 d,respectively,and the highest grain temperature was30°C,48°C and 48°C;during the storage of wheat grain with a moisture content of 16%(110d),there was no heating phenomenon,and the highest grain temperature was only 26°C.Wheat grain piles with moisture content of 16%,18%,20% and 22% can significantly delay the occurrence of heating when stored at room temperature,which is delayed by 104 d,24 d,9 d and 2 d,respectively.The highest grain temperature was lowered by 18°C,21°C,5°C and6°C,respectively.(2)At room temperature(15-25°C),the critical points for the start of mild mildew in wheat grain piles with moisture content of 16%,18%,20% and 22% were 33 d,24 d,6 d and6 d.The critical points of mildew are 60 d,33 d,9 d and 9 d,the critical points of severe mildew are 93 d,36 d,12 d and 12 d;During storage at high temperature(25-35°C),the critical points for the mild mildew with the moisture content of 16%,18%,20% and 22%were undetected,3 d,6 d and undetected,and the critical point of moderate mildew were 12 d,6 d,9 d and 3 d,the critical points of severe mildew were undetected,12 d,12 d and 9 d.Wheat with the same moisture content can delay the degree of mildew during storage at roomtemperature.The critical point of moderate mildew in the storage of wheat grain with same moisture content can be delayed by 48 d,27 d,0 d and 6 d.(3)The quality of the wheat during the process of heating and mildew was obviously deteriorated,and the quality of the middle-layer wheat grain pile decreased significantly faster than the upper and lower layers.Germination rate and gluten water absorption showed a downward trend.At the end of storage(severe mildew),the germination rate decreased from about 95% to about 10%,and the gluten water absorption was less than 180%,which was unsuitable for storage.The falling number was increased at first then decreased.The germination rate can be used as one of the sensitive indicators for determining the heating and mildew process of wheat.The change of gluten water absorption in this experiment is not obvious,due to the storage period is short,and it will not reach the unsuitable state until the wheat is severely mildewed.After the wheat was heated and mildewed,the rheological properties of the dough changed to some extent.The specific performance is that the weakening degree of the wheat dough of each moisture content is increasing.At the end of the storage period,stored at the room temperature is about 100 FU,and about 140 FU at the high temperature.The elongation,tensile resistance,stretching ratio and stabilization time are all increased first.At the end of storage the trend of decline is that the stability time of wheat dough in the room temperature environment is about 4 minutes,and the high temperature environment is about 8 minutes,which indicates that the dough strength is deteriorated during storage,and the toughness and ductility of the dough are improved first and then deteriorated;The peak viscosity of the wheat grain pile with 20% moisture content increased from the initial 2277.3 cP to 3630.7 cP,the retrogradation value increased from 1249.0 cP to 1710.3 cP,and the attenuation value increased from 987.0 cP to 1501.7 cP.The increase indicates that the amylose content increases after the heated and mildewed,the stability of the cold paste deteriorates,and it is easy to retrogradate..(4)The microstructure of endosperm and embryo cells in wheat grains with different heating and mildew stages changed significantly.Scanning electron microscopy showed that the microstructure of wheat grain endosperm had little effect on the degree of binding of starch and protein matrix during the heating period.The main change was that the small grainstarch began to fall off leaving obvious pits.The starch granules were further detached and damaged during the mildew period,and the starch content decreased.Thereby the amylopectin content is reduced,which is consistent with the change of starch gelatinization properties;the protein matrix is severely damaged,leaving a large number of fragments,and the protein matrix is loosely bound to the starch.Transmission electron microscopy showed that the wheat embryo cell structure was strong in the early stage of heating,and the mitochondria accumulated in the vicinity of the cell membrane to provide energy for the cells;the embryo cells were rich in organelles;the organelles in the mildew stage were mixed with the cytoplasm,and it was difficult to identify the structure of nucleus and mitochondria.;the cell wall toughness is reduced,the cell morphology cannot be maintained,the cell gap is continuously increased,and the vitality is gradually lost.(5)According to the results of the critical point study on the heating and mildew of wheat with different moisture content,it is recommended to ensure the safe storage conditions of wheat under the condition that the mild mildew is not met: at room temperature(15-25°C)the safe storage periods with the moisture content of 16%,18 %,20% and 22% were 33 d,24 d,6d and 5 d respectively;wheat with a moisture content of 16% at high temperature(25-35°C)could only be stored safely for 6 d,moisture content higher than 16% can only be stored safely for 3 days.Therefore,in the case of high temperature(25-35°C)environment during storage of wheat with moisture content higher than 16%,it is very easy to have heating and mildew in a short period of time,and must be treated as soon as possible to avoid loss.