Optimization Of Extraction Method For Volatile Compound From Coriander And Study On The Regulation Mechanism Of Exogenous Methyl Jasmonate

Coriander is a well-known seasoning vegetable with unique aroma and natural nutritional value in its leaves.It is currently widely cultivated and consumed in China.Previous studies mainly focused on the yield and basic nutritional quality of coriander,but there were few reports on the regulation of volatile flavor compounds in coriander leaves during cultivation.Volatile compounds are important chemical components of coriander,which not only endows coriander special fragrance,but also has a series of biological activities such as antioxidant,antimicrobial,hypnotic and antimutagenic.This study systematically optimized the headspace solid-phase microextraction（HS-SPME）conditions for volatile compounds in the leaves of"Sijidayouye"coriander.On this basis,the dynamic changes of volatile compounds in coriander leaves at 0h（CK）,6h,12h,24h and 48h after methyl jasmonate（MeJA）treatment were investigated.Combined with metabonomics and transcriptomics,the regulation mechanism of MeJA on the synthesis of main volatile compounds in coriander leaves was preliminarily clarified.The research results are as follows:（1）The extraction conditions of volatile compounds by HS-SPME from coriander leaves were optimized.The extraction conditions of volatile compounds from coriander leaves were optimized by single factor test,Plackett-Burman design,steepest climb test and Box-Behnken response surface design.The optimized HS-SPME conditions were as follows:50/30μm DVB/CAR/PDMS extraction fiber,1.0 g coriander sample,0.5 g CaCl₂,heating temperature 64℃,equilibrium time 10min,extraction time 43 min,and desorption time 5 min.The method was simple,accurate and reproducible,and was suitable for extraction,qualitative and quantitative analysis of volatile compounds from coriander leaves.（2）Exogenous application of MeJA could regulate the volatiles of coriander leaves.By concentration comparison,0.25%volume concentration of MeJA was determined to be the appropriate concentration for regulating the volatiles in coriander leaves.The total number and content of volatiles increased first and then decreased with the extension of MeJA treatment time,and the contents of most substances reached the highest at 24h after MeJA treatment.A total of 93 volatile compounds were identified from coriander,including 35 aldehydes,13 alcohols,8 terpenes,15hydrocarbons,11 esters and 11 other components.Aldehydes are the category with the highest number and content,mainly consisting of medium to long chain fatty aldehydes ranging from C10 to C18.The higher content components include（E）-2-tetradecenal,（Z）-9-hexadecenal,2-dodecenal,（E）-2-hexadecenal,（E）-2-decenal,and（E）-2-tridecenal.（3）The characteristic aroma intensity of coriander was significantly improved after MeJA treatment.27 volatile compounds were selected as the characteristic odor components（OAVs≥1）,which contributed to the flavor of coriander.Citrusy and fatty aromas were relatively strong fragrances in coriander leaves,and the effect of MeJA treatment was the most obvious for 24h.Multivariate statistical analysis showed that the metabolic profile of volatiles in coriander was significantly affected by MeJA treatment,and the response of volatiles to MeJA was time-specific.Electronic nose analysis showed that the aroma fingerprints of different groups of samples were similar,and the difference was mainly reflected in the response intensity of W5S sensor（nitrogen oxide）and W2W sensor（aroma component）.MeJA treatment could enhance the response signals of most sensors.（4）Metabolomics analysis showed that MeJA affected related precursors of volatiles synthesis in coriander leaves.A total of 916 components were detected,which were mainly phenolic acids,lipids,flavonoids,amino acids and their derivatives,most of which were precursors to the synthesis of volatile compounds from coriander.A total of 339 different metabolites were screened in 4 comparison groups（0h vs 6h,0h vs 12h,0h vs 24h,0h vs 48h）,which were significantly enriched in lysine degradation,tryptophan metabolism,ascorbic acid and uronic acid metabolism,and plant hormone signal transduction,etc.（5）Transcriptomics analysis showed that MeJA mainly affected the metabolic pathways of jasmonic acid and fatty acids.A total of 10314 DEGs were detected in the 4 comparison groups,and the largest number of DEGs（7043）was enriched in 0h vs 6h.The pathways of KEGG enrichment includeα-linolenic acid metabolism,unsaturated fatty acid biosynthesis,plant hormone signal transduction,fatty acid metabolism,linoleic acid metabolism,fatty acid degradation,etc.GO analysis significantly enriched jasmonic acid metabolism,jasmonic acid biosynthesis,jasmonate-mediated signaling pathway regulation,response to jasmonic acid,fatty acid biosynthesis,unsaturated fatty acid biosynthesis,unsaturated fatty acid metabolism,fatty acid derivative metabolism and lipid catabolism process.（6）MeJA treatment affected the expression level of genes,activity of enzyme and content of metabolites in jasmonic acid synthesis,jasmonic acid signal transduction and fatty acid synthesis pathways.Transcriptomics and metabolomics results showed that after MeJA treatment,related genes and metabolites in jasmonic acid synthesis,jasmonic acid signal transduction and fatty acid synthesis pathways were significantly regulated,showing a trend of first increasing and then decreasing,which was basically consistent with the results of qRT-PCR and absolute quantitative verification of metabolites.In jasmonic acid synthesis and signal transduction pathways,the expression levels of most genes reached the highest after 6h treatment with MeJA,including CsPLA2G,CsAOS,CsAOC,CsOPR,CsOPCL1,CsACOX,CsACAA1 and CsJAR1.The enzyme activity reached its maximum at 6h（AOS,AOC,OPR and JAR1）and 12h（LOX）.The content of JA and JA-Ile reached its maximum at 6h and 12h after MeJA treatment,respectively.In the fatty acid synthesis pathway,gene expression levels reached the highest at 6h（CsACC,CsFabH,CsFabG,CsFabI,CsFAB2 and CsFATA）,12h（CsFabF）and 24h（CsFabD and CsFATB）,respectively.The related enzyme activities reached the maximum at 6h（FabG,FabI and FAB2）and12h（ACC,FabF and FAT）,respectively.The contents of fatty acids,including linolenic acid,linoleic acid,palmitic acid and oleic acid,showed a trend of constant increase or first increase and then decrease within 48h after MeJA treatment.It is a direct precursor to the synthesis of main volatiles（medium and long chain fatty aldehydes）in coriander leaves.