Detection Of Volatiles In Stored Grain And Stored Grain Insect With Solid Phase Microextraction-GAS Chromatography Mass Spectrometry (SPME-GCMS)

Stored grain insects are endemic to grain industries throughout the world. The detection and quantification of stored grain insects in stationary or moving grain masses and other agricultural products has proved a difficult task. The volatiles of stored grain and stored grain insects, which are identified through chemical signals, could demonstrate the presence of insects.Rhizopertha dominica (Fbricius) and Tribolium castaneum (Herbst) are very important insect of stored grains worldwide. The quality and change in quality of stored wheat and flour are critical for human beings because they are among the top list of people’s diet. In the present study, the volatiles from wheat, flour, R. dominica, T. castaneum, wheat infested by R.domnica and flour infested by T.castaneum were separated and identified. Head space solid phase microextraction (HS-SPME) coupled with gas chromatography and mass spectrometry (GC-MS) techniques were used to analyse the volatile chemicals. The main results are shown as follow:1. Optimised the techniques of HS-SPME coupled with GC and confirmed detection method in analyze volatiles from stored grain insects and their hosts. The results showed that 50/30 μm PDMS/CAR/DVB fiber,24 h sample sealing time,4 h fibre extraction time and 5 min desorption time, tempreture rise programme and non polar column were suitable for detect the volatiles of stored grain and stored grain insects.2.The optimized HS-SPME coupled with GC-MS techniques were used to analyse the headspace volatile organic compounds (VOCs) of healthy wheat, R. dominica and wheat plus R. dominica respectively. The two important compounds Cyclopentanecarboxylic acid, pentyl ester and 2-Thiophenecarboxylic, octyl ester were detected in the R. dominica sample but in quite low amount, meanwhile, they can be identified in the wheat plus R. dominica sample with a very high amount. So, these compounds can be used as the indicators of the healthy wheat, that’s mean, if these compounds were detected in the healthy wheat, we can make the conclusion that the wheat was infested by R. dominica already.3.The volatile organic compounds (VOCs) on the headspace of health wheat, R. dominica and wheat plus R. dominica were analyzed by the optimised HS-SPME coupled with GC-MS techniques used both polar column and non polar column. A total of 41,20 and 46 volatiles were identified from wheat, R. dominica and wheat plus R. dominica respectively. The volatiles are mainly carbonyl chemical compounds such as aldehydes, ketones, alcohols and other chemical compounds. Most of VOCs are non-polar compounds, such as Heptane,2-Triophenecarboxylic acid, octyl ester and 3-Methyl-2-Butanol. However, there are some polar compounds like Acetone,2-Pentanol and 1-Hexanol were detected by polar column but in quite low amount.4. The optimized HS-SPME coupled with GC-MS techniques were used to extract and identify the volatiles of stored wheat flour, T. castaneum and T. castaneum infested flour respectively.2-methyl-p-Benzoquinone,1-Hexadecene and 4-ethyl-1,3-Benzanediol were the obvious compounds in T, castaneum but they can’t be detected in T. castaneum infested flour. The result showed that VOCs of T. castaneum infested flour almost same as the healthy flour. Although there are some unique compounds presented in T. castaneum infested flour, but the signal of these special compounds are not obviously compared with other compounds contained in it.5.The VOCs on the headspace of flour, T. castaneum and T. castaneum infested flour were analyzed by the optimised HS-SPME coupled with GC-MS techniques used both polar column and non polar column. A total of 43,41 and 54 volatiles were identified from wheat flour, Tribolium castaneum and T. castaneum infested flour respectively. Both polar column and non-polar column can detect most of important compounds of these three samples. Like Hexane, Pentanol, Hexanal and D-Limonene of wheat flour; 1-Tridecene,1-Pentadecene,4-Ethyl-1,3-benzanediol and (Z)6-Pentadecen-1-ol of T. castaneum; Hexane, Pentano, Hexanal, D-Limonene,1-Pentanol and of T. castaneum infested flour. However, there are some special polarity compounds were only detected by polar column or non-polar column, such as Octane, Acetone and 1-Hexanol were only detected by polar column from wheat flour; 2-Methyl-p-benzoquinone and 2-Methyl-1,3-benzenediol were only detected by non-polar column from T. castaneum; 1-Pentanol and Hexanoic acid were only detected by polar column from T. castaneum infested flour. Anyway, most of these special compounds were detected in quite low amount.The techniques of headspace solid phase micro-extraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS) were optimized by this experiment, and we used the optimized techniques to analysis volatile organic chemicals of wheat, R. dominica, wheat plus R. dominica flour, T. castaneum and T. castaneum infested flour respectively. A new efficient and simple method to diagnostic R. dominica in wheat was established. The knowledge gained in this study provides a scientific basis for further study about the chemical communication and host locating mechanism in stored grain and stored grain insects.