Study On The Dynamic Changes Of Volatile Compounds In Brown Rice Damaged By Stored Grain Pests

Rice is one of the main grains in China,especially in Northeast China.At present,about 50 million tons of grain are dispatched through "North Grain South transportation" every year in China,most of which are transported by container.In fact,the grain circulation process is a combination of storage and transportation.It also needs to control pests,molds and other factors to ensure the quality and safety of grain in the circulation process.Due to the influence of the circulation mode,it is impossible to investigate the internal environment of the container in the process of transportation.Therefore,according to the change of the grain pile in the container,it is the most important thing for the grain circulation process to formulate the appropriate control plan.Solid phase microextraction(SPME)technology has been widely concerned in recent years.This technology can solve the problem of sample preparation in the process of field investigation.It is a relatively convenient and rapid detection technology,which can provide new ideas for pest detection technology in the process of grain circulation.In this experiment,the brown rice infected by the red flour beetle(Tribolium castaneum(Herbst))and the rusty grain beetle(Cryptoleste ferrugineus(Stephens))was used to simulate the dynamic changes of the internal ecological environment of grain piles during grain circulation,and the volatile compounds of brown rice were extracted and identified by HS/DI-SPME-GC-MS.The Principal Component Analysis(PCA),Orthogonal Partial Least Squares-Discriminant Analysis(OPLS-DA)and Hierarchical Cluster Analysis were used to find characteristic volatile compounds from brown rice,so as to accurately identify the species,quantity and time of the pests in brown rice through the changes of the compounds,so as to guide the formulation of the pest control plan in the process of transportation.Finally,the metabonomics method was used to study the metabolic pathway of volatile compounds in brown rice infected with different pest species and population density,to understand the relationship between the compounds expressed differently in brown rice and insect infestation,so as to apply them to pest prewarning and search for new biomarkers.The main conclusions are as follows:(1)The method of HS/DI-SPME-GC-MS applied to the detection of volatile compounds in brown rice was preliminarily established,and optimized the extraction conditions for this method,including extraction temperature,extraction time,equilibrium time,sample quantity and resolution time.HS/DI-SPME-GC-MS was used to detect the changes of volatile compounds with brown rice during simulated storage and transportation period,and the stability and accuracy of the optimized HS/DI-SPME were verified.It was proved that HS/DI-SPMEGC-MS has the potential to be used in the detection of brown rice during grain storage and transportation.(2)The effects of the red flour beetle population density(0,5,50)and the rusty grain beetle population density(0,10,100)on volatile compounds with brown rice were studied.According to the method of multivariate statistical analysis,compared the brown rice samples infested by different quantity pests with brown rice samples uninfested by pests,the infestation of two pests with different population density had a significant impact on the volatile compounds of brown rice.18,8,7 and 14 characteristic volatile compounds were screened out respectively,which can distinguish the population density of two pests.(3)The effect of population density of pests on metabolism pathway of brown rice was analyzed by metabonomics.The selected characteristic compounds were enriched by metabonomics,and the different characteristic volatile compounds were enriched to 8,6,3 and 7 metabolism pathways respectively,and most of them are related to fatty acid metabolism,which indicates that the infection of different insect species or the same insect species with different insect population density has an important effect on lipid substances in brown rice.(4)The effects of infection time(1 week,2 weeks,3 weeks,4 weeks)on the volatile compounds of brown rice were studied.The analysis of PCA model and OPLS-DA model showed that the volatile compounds of brown rice samples infected by two pests at different times were significantly different.The results of hierarchical clustering showed that the volatile compounds content in brown rice would show a reverse trend with the extension of infection time,especially in the brown rice infected by red flour beetle(Tribolium castaneum(Herbst)).This experiment optimized the method of HS/DI-SPME,explored the feasibility of HS/DISPME-GC-MS to detect pests in the process of grain circulation,provided the scientific basis for the fast inspection technology of pests in the process of grain transportation,identified the volatile compounds in brown rice treated with different factors.The volatile compounds in brown rice were identified by multivariate statistical methods,and the effects of pest species and population density on brown rice were analyzed from the perspective of metabonomics,which provided a theoretical basis for the establishment of grain resistance mechanism between grains and pests.