Study On The Degradation Of Edible Fungi Endogenous Formaldehyde And Its Transformation Into Thioproline

In recent years,more and more people pay attention to the problem of food safety.Edible fungi is the sixth largest planting industry in China,its yield and variety are the highest in the world.At the beginning of this century,Japan and the European Union had made a strict detection limit on the amount of Letinous edodes formaldehyde to our country’s exports.The recent emergence of the "Pleurotus ostreatus formaldehyde incident" caused a great impact on the edible fungi industry.This paper mainly optimized the extraction methods of edible fungi endogenous formaldehyde,censused the content of endogenous formaldehyde in different growth stages of edible fungi and the changes of endogenous formaldehyde content during storage;established a method for the determination of thioproline in Letinous edodes by solid phase extraction-hydrophilic interaction chromatography;It was the first time to track and detect the content of thioproline produced by the fresh letinous edodes treated by L-cysteine,further to explore on the conversion of endogenous formaldehyde of Letinous edodes treated by L-cysteine and the related quality analysis.Specific research results are as follows:(1)The pretreatment conditions for extraction of endogenous formaldehyde from edible fungi were optimized.Taking Letinous edodes as an example,derived pH,derived temperature and derived time were optimized.The results showed that:the react of formaldehyde and 2,4-dinitrophenylhydrazine was stable at pH 5.0,the derived effect was best at 80℃ for 10 min derived time.To Typsizygus marmoreus,Flammulina velutipes,Agrocybe chaxingu,Auricularia polytricha,Auricularia auricular,Pleurotus eryngii do spiked recoveries rate were found all above 85%,suitable for the detection of endogenous formaldehyde of the edible fungus.(2)Detecting different growth stages of endogenous formaldehyde content of edible fungi,the results show that,with the growing up of Letinous edodes,endogenous formaldehyde content increased from 3.07 μg/g to 5.16 μg/g gradually,the others were below 1.0 μg/g.Through the different gas packaging storage and different temperatures storage,it can be found that,the endogenous formaldehyde,GGT specific enzyme activity and C-S lyase specific enzyme activity of Letinous edodes showed a rising trend with storage time extension,they were positively correlated.in addition,they were significantly higher at oxygen storage than that of carbon and nitrogen storage,10 ℃ storage is significantly higher than 4℃ storage,which showed that the production of endogenous formaldehyde of Letinous edodes was related to GGT enzyme activity,C-S lyase enzyme activity.However,the other edible fungi endogenous formaldehyde contents were no related to GGT enzyme activity and C-S lyase enzyme activity in different gas packaging storage and different temperature storage.In the process of storage,all edible fungi except Letinous edodes endogenous formaldehyde contents were no higher than 1.0 μg/g,which was much lower than that Letinous edodes.(3)A simple and sensitive method for the accurate determination of thioproline in Lentinus edodes fruit bodies is described.Optimized chromatographic conditions were that the sample was analyzed on a column of Inertsil HILIC(4.6x250 mm,5 μm),using a mixture of acetonitrile-0.1%phosphoric acid solution(85:15,v/v)at 30℃using a flow rate of 0.8 mL/min at 193 nm detection wavelength.Samples were dissolved by methanol-water(70:30,v/v),purified by MAX anionic solid phase extraction column,and eluted by methanol-1.0%formic acid(90:10,v/v).The experimental results showed that there were a good linear relationship(r2>0.9998)in the range of 2～100μg/mL.The recoveries were between 96.3%～101.7%,and the relative standard deviations(RSDs)were 1.3%～4.8%(n=3).The limits of detection and the limits of quantification were 0.76 μg/g and 2.31 μg/g respectively.This method is suitable for the determination of thioproline in Letinous edodes with characteristics of simplicity,quickness,without derivatization and high rate of recovery.For further characterization,we used liquid chromatography-mass spectrometry to detect Letinous edodes samples treated L-cysteine can be found the absorption peak of thioproline.The establishment of this method will lay the foundation for the study of the transformation of Letinous edodes endogenous formaldehyde.(4)Study on Letinous edodes treated by L-cysteine(40mM),we can found that:during storage,the growth of endogenous formaldehyde content of treatment group was significantly lower than that of the control group;the control did not detected thioproline,treatment group detected thioproline and with prolonged storage time,the content of thioproline was increased gradually.It can be inferred that the endogenous formaldehyde produced by Letinous edodes has a chemical reaction with L-cysteine,producing the beneficial substances for human body-thioproline.In addition,the changes in the quality of Letinous edodes treated by L-cysteine found that:Lcysteine have a inhibitory effect on Letinous edodes’s polyphenol oxidase and browning degree,it can play a preservation effect.Therefore,L-cysteine has a good application prospect for the control of endogenous formaldehyde of Letinous edodes.