Studies On Composition Of Sugar And Acid In Different Citrus Cultivars And Relationship Between Composition And Non-Enzymatic Browning

Study was carried out on the difference of quality changes during storage of Guoqing No.1 (C.unshiu), Owari, jincheng (C.sinensis) ,sour orange (C.aurantium) and grapefruit (C.paradisi) .Meanwhile, it was discussed that factors affecting nonenzymatic browning of juice and controlling in Jincheng orange juice. Rheological properties of concentrated orange juice and doff-pectic concentrated orange juice were determined at different temperatures and different concentrations. The major results are as follows:1. Determination of saccharides and organic acid in orange juice by HPLC was developed.Saccharides were extracted from samples with water by oscillation and isolated by SPE with Sep-Pak-C₁₈ cartridge.Sucrose,glucose and fructose were separated on a Agilent Zorbax Carbohydrate column(4.6×250mm, 5μm),with 80% acetonitrile solution as mobile phase, temperature 25±2℃, RID.The relative standard deviations were 0.83-1.71%, the recoveries were 95-105%.By general tests on chromatographic separating conditions, the optimal chromatographic separating condition was established: sinochrom ODS-BP column (4.6x250mm, 5μm) was used at 25℃,mobile phase was 3%CH₃OH-H₃PO₄solution of pH2.6,mobile rate was 0.5mL/min,detection wavelength was at 210nm with DAD,injecting volume was 10μL. The relative standard deviations were l.ll%-4.78%, the recoveries were96%-105%.Determination of ascorbic acid in orange juice by HPLC with 0.1% oxalic acid as mobile phase , sinochrom ODS-BP column (4.6×250mm, 5μm) was used at 25℃, mobile rate was 0.8mL/min,detection wavelength was at 254nm,injecting volume was 10μL. The relative standard deviation was1.640%, the recoveries were96%-105%.2. Significant difference was between decomposed rate, the ratio of juice and the ratio of weightlessness of the fruit of 6 citrus cultivars. Sweet orange had lower decomposed rate, lower the ratio of weightlessness, and higher ratio of juice. Grapefruit took second place. While, Satsuma mandarin had higher decomposed rate, higher the ratio of weightlessness, and lower ratio of juice.3. Sugar and acid contents were investigated in 6 citrus cultivars. Sucrose accounted for about 37%-55% of the total sugar, fructose contents and glucose contents were close, and citric acid for about 70% of the total acid contents in fruits; in addition, the ascorbic acid contents were more than 0.47%.difference between soluble solids, total sugar, total acid and brix to acid ratio of the fruit of each cultivar resulted in different flavor. During storage of fruits, sugar contents rose at the first 10days, and decreased in latter days, acid contents decreased gradually, while brix to acid ratio rose gradually.4. Factors affecting NEB of juice and controlling were discussed.During storage of orange juice, pH value decreases. When pH value is2-3, lower the pH value is, greater the brown becomes. When pH value is4-6, higher the pH value is, greater the brown becomes. During storage of orange juice,the changes of 5-HMF follows zero order kinetics while the changes of brown pigment follows first order kinetics.Activation energy values of 9.2801 kJ/molå’Œ18.1337 kJ/mol are abstained for 5-HMF and brown pigment, respectively.Reducing sugar can accelerate NEB of orange juice; the effect of fructose is higher than glucose. Sucrose can inhibit NEB of orange juice. Cu²⁺,Fe³⁺ and Fe²⁺ can accelerate NEB of orange juice evidently;Mn²⁺ and Zn²⁺ have slight effect on NEB of orange juice; Al³⁺, Sn²⁺ and Ca²⁺ can inhibit NEB of orange juice. Ascorbic acid and citric acid can all inhibit NEB of orange juice; the optimal concentration is 0.03% and 0.5%, respectively. 1% and 2% lysine and glycin can accelerate NEB of orange juice. 1% asparagines can inhibit nonenzymatic brown of orange juice. 5. Concentrated orange juice was pseudoplastic fluid and doff-pectic concentrated orange juice was Newtonian fluid. By regression analysis, both orange juice viscosity could be described by an Arrhenius type equationη=Koexp (Ea/RT) within the range of temperatures and concentrations.The change in their viscosity of both orange juice with temperature can be described by an Index type equationη=Kexp(AC).Within the range of temperature 10-60℃and concentration 25-50°Brix, the combined effect of temperature and concentration on the viscosity of concentrated orange juice can described by an equationη=7.199×10^-5 (2.272/T+0.170C, within the range of temperature 20-50℃and concentration 20～60°Brix, The combined effect of temperature and concentration on the viscosity of doff-pectic concentrated orange juice can described by an equationη=6.814×10^-5 (2.117/T+0.598C).