Identification Of Aroma Active Compounds Of Citrus Juices And Aroma Variation During Processing And Storage

Aroma has long been known to be one of the most important quality attributes of citrus juices.Encompassing the central task of characteristic aroma component of citrus juice,the ten citrus juices from three cultivars planted in Song zi and Yi chang region of Hubei province in China were chose in this paper.The volatile compounds and aroma active components of ten citrus juices were identified by SPME-GC-MS and GC-Olfactometry.The aroma constituents of Jinchen fruits at different harvested time were studied.Comparison of aroma components were extensively investigated in squeezed juice,pasteurized juice and irradiated juice from Jinchen fruit and aroma variation of aseptic juice during storage.Furthermore,the electronic nose was applied to discriminate the overall aroma of different citrus juices and monitor aroma change during sour orange juice processing.The results could be benefit to evaluate aroma quality of citrus juice and provide important information about citrus processing and products quality improving.Through the studies above,conclusions were made as follows:1.Isolation the volatile compounds from citrus juicesThe volatile compounds of Jinchen orange juice were extracted by simultaneous distillation-extraction,head-space technique,solvent extraction and solid phase microextraction.The solid phase microextraction was the valid method to isolate volatile compounds.The optimum extraction condition was:6ml orange juice with 0.36g/mL NaCl, extracting 40min after equilibrium 15 min at 40℃by DVB/CAR/PDMS50/30μm fiber.2.Analysis of volatile compounds and physical and chemical propertiesThe volatile components in ten citrus juices were analyzed by headspace solid phase microextraction(HS-SPME) combined with GC-MS.The results showed that there were 43,47 and 46 aroma components in three Mandarin juices(Guoqing 1,Miyagawa Wase, Owari),respectively.In five orange juices(Jinchen sweet orange,Hamulin sweet orange, Newhall navel,Blood orange,Sour orange),54,57,52,54 and 44 volatile compounds were detected,as well as 45 and 39 volatiles in two grapefruit juice(White grapefruit and Pink grapefruit).Moreover,the difference of the radio of soluble solids and total acids,VC content, sugar content,and organic acid content were observed among the different citrus juices.3.Analysis of the aroma active compounds in citrus juices The GC-O method was performed to identify the aroma active compounds of ten citrus juices.The mandarin juice,Guoqing 1,Miyagawa Wase and Owari were characterized by 21,17,27 odorants,respectively,while the white and pink grapefruit juices,were characterized by 20 and 21 odorants.In five orange juices,such as Jinchen sweet orange,Hamulin sweet orange,Newhall navel,Blood orange,Sour orange, 30,30,26,34,30 odorants were found,respectively.The kinds of odor compounds of blood orange was highest while white grapefruit juice was least in all samples..There were some aroma active compounds not detected by GC-MS.Vanillin was confirmed to be the aroma active compound of three mandarin juice isolated by solvent extraction.The flavor profile showed that the herbaceous/green note formed the main odor note of the overall aroma of Guoqing 1 and Owari,and the main perceived note of Miyagawa Wase was the wood/leg odor.The floral note was the main perceived note in Jinchen sweet orange,Hamlin sweet orange,Newhall navel,and Sour orange.The profile of sour orange was completely different from the four sweet orange juices.Four sweet orange juices had a similar distribution of the odor note.The white grapefruit and pink grapefruit mainly presented fruity odor and wood/leaf odor,respectively.Considering the aroma components and chemical and physical properties,Jinchen is the feasible fruit for processing.Sour orange juice,grapefruit juice and mandarin juice could be added to orange juice to improve their odor and taste.4.Comparison of volatile compounds in Jinchen fruit at different harvested timeThe volatile compounds of Jinchen fruit harvested on Oct.1st,Nov.1st,Dec 1st,Dec. 30th were analyzed.The results showed that the peak area of total volatile compounds and aroma active compounds such as limonene and linalool increased with the fruits development.The total peak areas reached highest in fruits harvested on Dec.1st and reduced in the fruits from Dec.30th5.Change of aroma compounds in Jinchen orange juice after squeezing, pasteurization and irradiation.The volatile compounds analysis of hand extracted juice,mechanically extracted juice and peel oil were performed.The fresh Jinchen juices were treated with pasteurization and irradiation with three different doses.According to the results,total peak areas of volatile compounds in hand extracted juice were lower than mechanically extracted juice and decreased 27.64%after pasteurization.The irradiated juices with three different dose treatments were found at higher peak area than pasteurized juice.Total of 51 volatile compounds identified in mechanically extracted juice,as well as 54 in hand juice,47 in pasteurized juice.Meanwhile,there were 51,54 and 47 active aroma compounds identified in those three different juices.Major group odor of mechanical extracted juice presented higher than hand extracted juice except fatty note. The overall aroma of hand juice changed after pasteurization due to decrease of fruity note,floral note,citrusy note,herbaceous note,piney note and increase of wood/leaf note, and fatty note.In peel oil extracts,a total of 32 compounds were identified in the volatile fraction and 22 aroma active compounds were perceived.Linalool,α-pinene,and decanal with the greatest aroma intensity gave the predominant contribution to peel-oil odor.6.Change of aroma compounds of Jinchen juice during storageThe Jinchen orange juice treated with pasteurization and irradiation stored in 4℃for 60d,D-limonene decreased throughout the whole storage,meanwhile,linalool, 4-terpinenol,α-terpineol,6-methyl-5-hepten-2-one,andα-pinene showed the increasing trend and then declined.7.Research of electronic nose for citrus juicesThe electronic nose was applied to discriminate the overall aroma of different citrus juices and monitor aroma change of sour orange juice during processing.The electronic signal was linear with different reconstituted concentrated juice.The 55°Brix reconstituted concentrated juice was chosen as unknown sample to discriminate the concentration.The discriminate result is 57.95 and RSD is 5%.