Studies On The Aroma Components In Citrus Juice During Key Processing Units

Encompassing the central task of characteristic aroma component of citrus juice andits variation during processing, aroma components were systematically analyzed byintegrated using Gas-Chromatogram and Mass-Spectrum (GC-MS) in this paper. Amethod for the determination of aroma components in citrus juice was developed by usingsolid-phase microextration with different fiber coating and gas chromatography-massspectrometry. In this study, the aroma components of citrus juice were qualitatively andquantitatively analyzed and studied for different varieties before and after pasteurized,lime juice during processing and concentrating. And the physical and chemicalcharacteristic indexes of citrus juice for different cultivars and lime juice duringprocessing and concentrating were elementarily studied. Through the studies above,conclusions were made as follows.1. Optimized the method of HS-SPMEThe method of extracting and analyzing aroma components in citrus juice wasestablished. The optimum extraction condition of HS-SPME-GC-MS isDVB/CAR/PDMS (30/50μm) coated fiber, 6mL juice sample in 15mL vial, equilibratedfor 15 min at 40℃, then extracted for 30min at the same temperature and 36%(m/v) ofadded sodium chloride.2. Aroma components, chemical and physical characters analysis of citrus juice fordifferent cultivars before and after pasteurizationA comparison on the aroma compounds in five cultivars before and afterpasteurization, including Owari(C.unshiu Marc.), Jinchen(C.sinensis Osbeck), Hamlin(C.sinensis Osbeck), Lime (C.aurantium) and Tarocco (C.sinensis Osbeck) wereconducted. 68 and 66 aroma components were identified in unpasteurized and pasteurizedHamlin juice respectively, as well as 65 and 68 in Jinchen juice, 54 and 58 in lime juice,61 and 67 in Tarocco juice, and 40 and 55 in Owari juice, respectively.The characteristic aroma components in pasteurized juices were evoluted. Thechemical and physical characters including soluble/acid, the content of VC, sugar andacid et al, were also changed during pasteurized. The content of aroma components inHamlin juice is more than other four cultivars both before and after pasteurization. Thearoma of mandarin juice was weaker than others. Different characteristics were observedin Hamlin, Jinchen, Owari, Lime and Tarocco. In order to produce citrus juice with betterquality, citrus juice should be confected in a certain proportion in the industriallyproduction process.3. Aroma components, chemical and physical characters analysis of lime juice during key processing unitsThe chemical and physical characters of lime juice were changed by refining,centrifugation and pasteurization. The effect of refining was more important to thecontent of glucose and Vitamin C. The effect of centrifugation was more important tosoluble solid and total acid. The effect of pasteurization was more important to the colorand the content of total sugar.The delicate fresh flavor of citrus juice was easily changed during processing. Thejuice underwent compositional changes that invariably cause an alteration in the originalflavor and aroma of the fresh juice. 52 aroma components in fresh squeezed juice wasidentified and analyzed, as well as 65, 67and 60 aroma components in refined, centrifugaland pasteurized juice. The aroma of fresh squeezed juice was full-bodied. After refining,the contents of alcohols, ketones and other compounds decreased. The effect ofcentrifugation on hydrocarbons, esters and aldehydes was significant that centrifugationdecreased the contents of these compounds. The effect of pasteurization on the totalaroma contents was not obvious compared with the effect of refining and centrifugation.In the pasteurization step, some aroma-active compounds were lost, and some othercompounds were produced simultaneously. A GC-O analysis should be combined toidentify the volatile products that may cause a negative effect in orange juice.4. Aroma components, chemical and physical characters analysis of lime juiceduring concentratingThe total content of aroma compounds in NFC lime juice was 464.932μg·mL^-1, andthat in the reconstituted orange juice (10°Brix) from concentrated to 37.5°Brix, 55°Brixand 63.5°Brix was 13.460μg·mL^-1, 2.242μg·mL^-1 and 2.107μg·mL^-1, respectively. 62aroma components in NFC lime juice was identified and analyzed, as well as 38, 31 and34 aroma components in reconstituted lime juice from concentrated to 37.5°Brix, 55°Brixand 63.5°Brix, respectively.Concentrated lime juice was pseudoplastic fluid. By regression analysis, the limejuice viscosity could be described by an arrhenius type equationη=K₀exp(Ea/RT) withinthe range of temperatures and concentrations. The change with temperature could bedescribed by an index type equationη=Kexp(AC). The combind effect of temperature andconcentration on the viscosity of concentrated orange juice can described by an equationη=3.79×10^-6 exp(3.460/T+0.165C).