Study On The Changes And Mechanisms Of Flavor Substances In Xiangyang Mustards During The Pickling Process

Xiangyang pickled mustards,which is produced by pickling the root-mustard(Brassica juncea var.Megarrhiza)in salt solution,is a conventional Chinese pickled vegetable products.With its fresh,fragrant,crisp and tender quality,full pickled mustards has became famous all around the Xiangyang City.Mustards’ unique volatile flavor is an important factor which is used to eveulate the quality of the pickled root mustards.However,the research on the formation and changes of flavor compounds in pickled mustards during the pickling processing is limited.There is also little unknown about the the effect of processing technic on the changes of mustards’ flavor compounds.It’s necessary to explore the formation and changes of volatile compounds in mustards during the pickling processing so as to improve the processing technic and decrease the pickling time.In this work,root mustards which pickled with traditional processing technic were used as experimemt material.The changes of volatile compounds in mustards at different pickling stages were analysed with HS-SPME-GC-MS,and the differences of flavor compounds among different pickling stages were analysed with method of principal component analysis(PCA).The changes of mustards quality was systematically described by analyzing such factors: colors,water content,sodium chloride content,total acid content,content of reducing sugar and total sugar,Vitamin C content,Amino nitrogen content,and nitrite content.The determination of total glucosinolates(GLS)content was optimized and the content of total GLS in mustards at different pickled stages was detected.The individual GLS was analysed with HPLC method.The extraction method of myrosinase in mustards was optimized,and the changes of myrosinase activity at different stages was determined.The results were as follows:(1)117 volatile compounds were detected among mustards at 8 different pickling stages,of which 18 aldehydes species,4 alcohols species,11 acids species,32 esters species,6phenols species,6 alkene species,8 isothiocyanates species,5 sulfur-contaning compounds species,4 nitriles species,2 ethers species,21 others species.41 volatile compounds were detected in fresh mustards(0#),29 in the first salting mustards(1#),37 in the second salting mustards,36 in the third salting mustards(3#),40 in the fourth salting mustards(F#),41 in the fisrst pickled mustards(Y#),33 in the third pickled mustards(S#),32 in the fifth pickled mustards(P#).(2)Isothiocyanates(ITC)is a special volatile compounds species in mustards,which can give a acrid taste.The content of ITC in mustards increased during the first salting processing,and drcreased in the following pickling stages.And the content of ITC was0.2412 μmol/g in fresh mustards,increased a little in the first salting stages,decreased a lot from the first salting stages to the second salting stages,marginally shorted during the second salting stages,and shorted in a little range in the last salting stages.(3)Through PCA analysis of volatile compounds data in mustards along with the pickling process,the processing technic can be divided into three phases.The first phase include the stages of fresh,first saliting,second salting,three salting and fourth salting,the second phase include the stages of the first and second pickling,and the three phase include the stages of three pickling,fourth pickling,and fifth pickling.There were a lot of special charactertical volatile compounds among the three phases.And along with the three processing phases,the numbers of volatile compounds rised gradually.The content aldehydes,acids,Sulfur-containing compounds(SCP)increased a lot,with the ITC shorted instead.(4)The mustards was white or green in fresh stages,became dark gradually and pitchy in the last phase.Changes of physicochemical property during the salting processing were as follows: 1)contents water,reducing sugar and total sugar,Vitamin C,amino-nitrogen,were decreased gradually,2)the contents of sodium chloride increased,3)the content of total acid and nitrite increased firstly and the decreased along with the processing.(5)As for the determination of total GLS with the palladium chloride method,the concentration of palladium chloride is 0.01g/m L,the reaction temperature is 25℃,and the reaction time is 6h.The sensitivity of palladium chloride method is 0.02746 mg/m L,and the palladium chloride method is available to determine the content of total GLS given its great precision and accuracy.There was 18.8 mg/g(dry weight)total GLS in fresh mustards,14.91 mg/g in the first salting stages,14.73 mg/g in the second salting stages,11.92 mg/g in the three salting stages,and 6.51 mg/g in the last salting stages.(6)The individual GLS of was analysed by HPLC.There were 16 individual GLS detected in mustards,of which 10 aliphatic GLS,2 aromatic GLS and 4 Indoles GLS.And aliphatic GLS hold a great content among the individual GLS,and decreased gradually.(7)The extraction of mysrosinase in mustards was optimized,and the parameters were as follows: the buffer selected was phosphate buffer(0.2M,p H=7.0),the material-liquid ratio is 1:4,the extraction time is 12 h,and the concentration of EDTA in the buffer is 4m M.Myrosinase activity is 100.01 U in fresh samples,and 35.32 U in the first salting samples,and was inactivated in the following stages.