A Study On Correlation Between Volatile Organic Compounds And Ochratoxin A In Aspergillus Carbonarius

Ochratoxin A(OTA),ochratoxin B(OTB),ochratoxin a(OTa)and Mellein are secondary metabolites produced mainly by Aspergillus species.Due to their similar structures,OTB,OTa and Mellein are proposed to be part of the OTA biosynthetic pathway.However,the biosynthetic pathway of OTA has not been fully elucidated biochemically or genetically.Therefore,in this study was to establish a reliable,efficient and sensitive high-performance liquid chromatography coupled with electrospray ionization and triple quadrupole mass spectrometry(LC-ESI-MS/MS)method for detecting multiple ochratoxins(OTA,OT?,OTB and Mellein)in vitro cultures.Performance was tested in terms of accuracy,selectivity and repeatability.Besides,the kinetics of these ochratoxins in during A.carbonarius and A.ochraceus strains growth period were also analysis to provide relevant information for OTA biosynthetic pathway.The results showed that A.carbonarius produced OTa,OTB and OTA;and during 7 days growth period,OTA and OTB showed the same variety tendency,accumulating from the 2nd incubation day,at the 3rd day reached the highest level,and then decreased.However,OTa increased along with the whole cultivate period;specially,when the OTA decreased dramatically the OTa rapid accumulated.While for A.ochraceus,it produced OTB,OTA and Mellein;also the variety tendency of OTA and OTB were similar accumulating from the 3rd day,and increasing sharply in the 6th day.The Mellein produced in the 2nd day and the 3rd day reached the highest level and then decreased,when the Mellein decreased dramatically the OTA and OTB accumulated rapidly.There have been numerous studies on ochratoxin metabolism and hazard evaluation for dried vine fruit,but multi-ochratoxin analysis is seldom.Therefore,a method was developed for the determination of OTA,OT?,OTB and Mellein in dried vine fruit.Methanol-1%sodium bicarbonate extraction solution(6:4,v/v)was determined to be the most efficient.Solid-phase extraction(SPE)was performed as a clean-up step prior to HPLC-MS/MS analysis to reduce matrix effects.Thirty commercial dried vine fruit samples were collected from Xingjiang and analysised the ochratoxins,10 were contaminated with ochratoxins;in addition,OTB,OTa and Mellein were also detected in different samples.Microbial volatile organic compounds(VOCs)are one of the natural organic compounds produced by filamentous fungi,and these VOCs basically possess low molecular weight.The VOC profile and composition varies along with the growth,generation,and decline of fungi.A reliable,efficient and sensitive headspace-solid phase microextraction-gas chromatography mass spectrometry(HS-SPME-GC-MS)method for VOCs detection was developed.Apply this method to identify the VOCs in three A.carbonarius strains under incubation period.These three strain origined from different sources,one from grape and other two from dried vine fruits.Results showed that 33 VOCs were detected in these strains.These VOCs included 1 ketone,1 aldehyde,2 alcohols,6 esters,11 sesquiterpenes,11 hydrocarbons,and 1 cyclic dicarboxylic anhydride.Furthermore,we applied principal component analysis(PCA),using the identified volatile compounds as variables,to differentiate A.carbonarius strains and visualize the content change of these volatile metabolites during the fungi growth.Sesquiterpenes were the mainly biomarker for different original sources of A.carbonarius.Ester metabolites synthesised at the beginning of the growth period,whereas the hydrocarbon compounds appeared to be dramatically yielded along with the incubation period extension.The VOC metabolites have been reported to show the close relationship with the mycotoxin production.Specific VOCs have been applied to the early food mycotoxin detection.In this study,we choose the mainly ochratoxingenic strain-A.carbonarius as the target strain,detected the OTA and VOCs verify regularity during a 7-day incubation period.Partial least squares regression(PLSR)analysis was used to develop the model to predict the correlation between the volatile metabolites and the OTA accumulaiton.This analysis indicated that C-8 alcohols,ketones,and trans-nerolidol showed a close relation with the OTA.This study could provide useful information on predicting OTA accumulation in grapes and dried vine fruits by detecting specific VOCs.