The Determination Of Low-molecule Mass Aldehydes In Foods

Low molecular mass aldehydes(LMMAs)are a group of important compounds,which widely existed in various foods.Many LMMAs have high volatility and low odor threshold value,leading to different food flavors and textures.When the concentration of LMMAs exceeds a certain levle,it will cause adverse effects to human health.Therefore,it is of great significance for LMMAs analysis in food samples.However,the analysis of LMMAs are often hindered by the intrinsic properties of aldehydes,such as high hydrophilicity,volativity and lack of chromophores or fluorophores.In this thesis,we developed a novel pre-column derivatization method to detect LMMAs in foods,using a synthetic fluorescent reagent 4-hydroxylaminopropyl-7-methoxylcoumarin(HAMC).Compared with existing method,our method was simple,ease of automation and of high sensitivity and selectivity.,making it an ideal candidate for LMMAs detection in different food samples.Using this method,we succesfully analyzed LMMAs in honey,coffe and juices.The correlation of LMMAs and food storage conditions as well as processing methods were investigated.The main work of this paper is as follows:(1)We investigated the properties of the new fluorescent reagent HAMC and used HAMC to derivatize aldehydes.The derivatization conditions were optimized and a simple derivatization method based on nitrone formation was developed.Combining this method with high performance liquid chromatography-fluorecence detection(HPLC-FLD),three furanic aldehydes,including furfural(F),5-methylfurfural(MF),5-hydroxymethyl furfural(HMF),were qualitatively and quantitative analyzed.The derivatization carried out in aqueous condition at room temperature within 30 min with high efficiencies.The following HPLC-FLD analysis avoids complicated sample pretreatment and lengthy extraction steps.Compare with other conventional method,our method also overcomes the problem of product isomerization,making the chromatogram simple and increasing the overall detection sensitivity.It has been successfully used for the determination of furfural in honey and coffee samples.(2)HAMC was further applied to the analysis of 13 aldehydes,including aliphatic aldehydes(C1-C10)and furfurals(F,MF,HMF).A baseline separation of 13 aldehydes peaks was realized on a C18 column,and the detection limit was as low as 0.08 nm.In order to investigate the effect of juice storage conditions on LMMAs,four fresh juices(orange juice,grape juice,apple juice,kiwifruit juice)under different storage conditions were analyzed.It was found that for all the juice samples stored under 45~oC for 7 days,the concentration of HMF showed obvious increasements,indicating that HMF could be used as a reliable indicator of the freshness of juice products.Finally,the types and processing degree of different kinds of orange juice drinks were distinguished by aldehyde analysis.The principal components analysis of aldehydes in orange juice,concentrated orange juice and non-natural orange juice drinks were analyzed.It was found that formaldehyde and acetaldehyde could cluster different kinds of juice and provide evidence for the identification of orange juice varieties.(3)HAMC derivatization can improve the ionization efficiencies of aldehydes and produce the characteristic ion fragments(m/z 231).Therefore,we did a comparison investigation of LMMAs detection using HPLC-FLD methods versus ultra-performance liquid chromatography-mass spectrometry(UPLC-MS)method.The results of HPLC-FLD detection showed that there were C1,C2,HMF in red wine samples.Only phenylpropanal was found by UPLC-MS detection using pre-ion scanning mode,which can be explained by the matrix effects due the the complexity of the wine sample.We suggested that other enrichment or purification methods,such as solid phase extraction(SPE)may be the solution for UPLC-MS detection using HAMC derivatization method.