Study On Volatile Sulfur Compounds And Aroma Active Volatiles In Mandarin Juice

Mandarin?Citrus reticulata,Blanco?is one of the major cultivars grown worldwide.It is extensively cultivated in China,Turkey,Morocco,and throughout the other citrus growing regions.Mandarins are characterized by their thin-skinned easy-peeling fruit and are popular because of their unique flavor and nutritional value.They are also one of the most tolerant citrus species to the 100%fatal bacteria disease,Huanglongbing,also known as citrus greening.However,almost all mandarin fruits are utilized as fresh fruit and little is processed into commercial juices due to off-flavor problems.Because off-flavors are observed either immediately or during storage,juice production is limited.Unfortunately,the off-flavor has not been fully characterized nor have the precursors responsible for all the flavor changes fully identified.Volatile sulfur compounds?VSCs?are a class of volatile compounds with odor properties,which are widely found in food.Due to the characteristics of low concentration,low sensory threshold,and active chemical properties,the detection of VSCs is facing challenges.In recent years,due to the progress of analytical material collection technology and the improvement of the sensitivity of analytical equipment,the comprehensive detection of VSCs in food has become possible,which also provides an opportunity for an in-depth exploration of food flavor.In this paper,mandarin juice was taken as the research object.The identification and aroma characteristics of VSCs during thermal sterilization,storage,and shelf life,aroma activity volatiles that were systematically studied by GC-MS/PFPD,GC×GC-MS/O and GC-FID/O.S-methyl methionine?MMS?and methionine are important precursors of VSCs.The concentration of MMS and methionine were determined in mandarin juice.The studies on thermal dynamics and light dynamics of precursors helped reveal the degradation mechanism of precursors and the effects of VSCs on mandarin juice.It can provide theoretical guidance for mandarin juice industrialized production,storage,business sales,The main research results are as follows:?1?Identification of VSCs in mandarin juice by static headspace SPME combined with GC-MS/PFPD:Taking 10 varieties of mandarin as research subjects,Identification of VSCs in fresh and heat-treated mandarin juice was achieved using a combination of capillary gas chromatography with two dissimilar columns?Wax and DB-5?and a dual sulfur-specific PFPD and SIM?MS?were determined and quantified accurately for the first time.In this chapter,5 kinds of VSCs were determined:carbonyl sulfur?COS?,H₂S,carbon disulfide?CS₂?,methanethiol?MeSH?,dimethyl sulfide?DMS?.Among them,MeSH is a compound with a strong odor,which was first detected in the heated mandarin juice.The calculation of odor activity value?OAV?showed that only two sulfide compounds,MeSH?OAV=25.5?and DMS?OAV=10.8?,affected the overall flavor of the juice.Moreover,Satsuma varieties formed a cluster and were distinguished from other mandarin varieties through principal component analysis?PCA?of just VSC concentrations The thermal degradation of 6 kinds of non-volatile sulfur precursors was studied.DMSP and MMS can produce DMS.Methionine thermal degradation produce methional?Met?,MeSH,dimethyl disulfide?DMDS?,dimethyl trisulfide?DMTS?,and vitamin C can accelerate the thermal degradation of methionine.Cysteine produced small amounts of H₂S and CS₂.Thiamine produced H₂S and 2-methyl-3-furanthiol.The thermal degradation of glutathione produced H₂S compounds.?2?Study on volatile sulfur compounds and aroma active volatiles in mandarin juice by using GC×GC-MS/O,GC-FID/O,GC-MS/PFPD:On the basis of the previous research,the characterization of VSCs in mandarin juice was studied,first of all,kitaguchi wase?KW?,hashimoto wase?HW?,seedless ponkan?SP?,and xinshengxi No.3 ponkan?XP?,four mandarins were as the research samples.The VSCs in fresh and heated mandarin juice were qualitative and quantitative analysis,a total of seven kinds of VSCs was detected:COS,H₂S,CS₂,MeSH,DMS,Met,p-Menthene-8-thiol.Among them,the time-intensity method?OMSE?can detect H₂S?rotten egg?,MeSH?rotten cabbage?,DMS?cabbage,sulfur?,Met?cooked potato?,p-Menthene-8-thiol?grapefruit?.AEDA also preliminarily identified the most aroma active sulfide in juice as Met and p-Menthene-8-thiol.The concentration of H₂S and p-Menthene-8-thiol decreased and the concentration of MeSH,DMS,CS₂,and Met increased.In addition,a total of 30 volatile non-sulfur active components were identified in four kinds of wide-peel citrus juice before and after thermal sterilization.Through OAVs comparison,the main flavor terpene compounds that contribute a lot to the flavor of citrus juice were identified.The PanelCheck V1.4.2 software was used to evaluate the sensory evaluation ability of the members of the sensory group,and a qualified sensory evaluation group was established.Sensory experiments showed that the flavor of SP and XP was better than that of KW and HW,and heat processing promoted the off-flavor and cooked flavor in the juice and reduced the overall flavor attribute.?3?Headspace fingerprinting to evaluate the changes of VSCs and aroma active volatiles in mandarin juice during storage:Ponkan was selected as the research samples,PET bottled fruit juice was placed at 4?,25?,and 40?for 12weeks,9weeks and 7weeks,respectively.GC-MS/PFPD,GC×GC-MS/O,and GC-FID/O were used for qualitative and quantitative analysis of VSCs in mandarin juice during storage.A total of 11 VSCs were identified:H₂S,MeSH,CS₂,DMS,S-methyl thioacetate?MTA?,ethyl acetate?EMA?,DMDS,2-methyl thiophene?2-MT?,3-methyl thiophene?3-MT?,DMTS,Met.At 4?,25?,and 40?,MVDA technology and VID coefficient were used to screen out 8,9,and10 kinds of VSCs with significant changes in concentration.AEDA found that Met was the most aroma active sulfide during storage.By OAVs calculation,it showed that MeSH,DMS,DMTS,and Met affected the overall flavor of the juice.LC-MS/MS study found the non-volatile sulfur precursor methionine and MMS in the juice were degraded during storage,which promoted the generation of VSCs.In addition,the GC×GC-MS/O respectively determine the aroma active nono-sulfur compounds in ponkan juice.At the end of the storage,24 species,18 species,22 kinds of aroma active compounds?FD?2?,under 4?,25?and 40?.Among them,linalool?Floral?,?-damescenone?fruity,smoky?,and?-ionone?Floral?were the most important non-sulfur aroma active compounds?FD?64?.?4?Headspace fingerprinting to evaluate the changes of VSCs and aroma active volatiles in mandarin juice during shelf-life under light:Ponkan was selected as the research samples,PET bottled fruit juice was illuminated by LED?3024 Lux?and UV?360 nm,25?W/cm²?lights.GC-MS/PFPD was used for qualitative and quantitative analysis of 11VSCs in ponkan fruit juice during light shelf-life,among which 9 of VSCs including MeSH,CS₂,DMDS,2-MT,3-MT,DMTS,Met,MTA,and EMA were detected in ponkan juice for the first time.MVDA technique was used to find that the VIDs of Met in the dark group,LED group,and UV group were 0.79,0.85,and 0.92,respectively.During shelf life,LED and UV lighting promoted the degradation of the photosensitizer riboflavin and accelerated the degradation of methionine and the generation of MeSH,DMTS,and Met compounds.OAV calculation found that the contribution of sulfide to the overall flavor of juice was different:Met>MeSH>DMS>DMTS;Sensory experiments showed that the illumination during shelf life?LED and UV lighting?promoted the deterioration of juice flavor.At the end of the shelf-life 28 species,28 species,30kinds of aroma active compounds?FD?2?,under Dark,UV and LED.Among them,cymene?citrusy?,linalool?Floral?,?-damescenone?fruity,smoky?,and?-ionone?Floral?were the most important non-sulfur aroma active compounds?FD?64?.?5?Thermal and light degradation kinetics of sulfur precursor compounds in mandarin juice:Firstly,the concentration of two important precursors of MMS and methionine in15 varieties of mandarin juice was determined by o-phthaldialdehyde/3-mercaptopropionic acid?OPA-3MPA?method.The concentration of MMS ranged from 0.15 to 3.78?g/mL,and the concentration of methionine in mandarin juice ranged from 0.46 to 5.20?g/mL.Secondly,the thermal degradation of MMS,methionine,and Met were all first-order kinetics.Ea of MMS,Methionine,Met were separately 126904 J/mol·K,55099.26 J/mol·K,and 67371.17 J/mol.An of MMS,Methionine,Met were separately 3.91*10¹⁴,406.25,3079260.4.Photodegradation of methionine and Met also belongs to first-order kinetics.The results showed that the degradation rate of MMS,methionine,and Met in the thermodynamic experiment of ponkan fruit juice was lower than that in the simulation experiment,which may be related to the difference of matrix in the fruit juice.In addition,the result of the illumination verification experiment is similar to that of a simulation experiment.