Study On The Technologies Of Kumquat Juice Concentrating Process

Kumquat-a Hong Branch,citrus subfamily, the citrus family, kumquat species-isone of the characteristic fruits in Fujian. The kumquat is rich in pectin, which,togetherwith such macromolecules as fiber, suspends in the sticky kumquat slurry afterbeating, leading to the instability of juice and relatively lower juice yield; thenon-enzymatic browning of kumquat juice, affecting its color and flavor color andflavor impact, is easy to be found during processing, which results in the decline ofthe quality of kumquat juice. How to break the bottleneck of the kumquat juiceconcentrating processing technology is the key to the development of the kumquatjuice industrialization. The key techniques of kumquat juice concentrating processingwere studied in this paper. the results showed as the following:1. On the basis of single factor experiments, the effect of cellulase enzymatic,acid protease, pectinase with different enzyme concentration, enzymolysistemperature and enzymolysis time on the juice yield and and suspension stability ofkumquat was studied by taking orthogonal experimental design, according to wichthe optimal composite enzymatic hydrolysis parameters of kumquat juice weredetermined. The results showed as the following: cellulase, protease and pectinaserespectively increased the juice yield and the suspension stability of kumquat indifferent degree; the optimal process parameters were: cellulase of3000U/Kg pulp,pectinase of25U/Kg pulp enzymolysis time of30min, enzymolysis temperature of50℃, on the condition of which the juice yield was83%, together with bettersuspension stability.2The effect of the antioxidants-ascorbic acid, citric acid, L-cysteine–on theinhibition of non-enzymatic browning of the kumquat juice were studied. Theresults showed that these three antioxidants could inhibit non-enzymatic browning ofthe kumquat juice, declining its red-green index,a, in a different degree, together withsimilar changing trend of the yellow-blue index, b, and of browning degree accordingto the change of antioxidants addition which means that there is a certain corelationbetween them. Compared with the single antioxidant,composit antioxidant had abetter effect on inhibiting non-enzymatic browning of the kumquat juice, and theoptimal composite antioxidant combination is: adding0.05%of L-cysteine, citric aciddosage of0.15%and vitamin C dosage of0.1%.3. The relationship between the concentration of kumquat juice and the viscosity of kumquat juice, between the temperature and viscosity during the concentrationprocess were studied, according to which the rheological properties of concentratedkumquat juice were decided, together with the establishment of the condenseddynamic model.The results showed the concentrated kumquat juice belonged topseudoplastic non-Newtonian fluid, that with the increase of temperature, theviscosity of concentrated kumquat juice decreased, that with the rise ofconcentration of kumquat juice, the viscosity of concentrated kumquat juice increased,that by regression analysis, the mathematical model equation of the combined effectsof the temperature and concentration on the viscosity of kumquat juice wasdeduced.The mathematical model equation is η=3.050×exp(22.572/RT+0.115C),whose scopp of application is: temperature of20-60℃and the concentration of30-60°Brix.4. The vacuum concentration process of kumquat juice was studied.The optimumparameters are: speed of100r/min, temperature65℃, vacuum degree of-0.095Mpa.The frozen concentrating end of kumquat juice was28.3°Brix. The effect offreeze concentration, vacuum concentration, atmospheric concentration on the contentof physical and chemical composition of the liquid intermediary kumquat juicereconstituted from certain concentration (total acid, total sugar, vitamin C) and on thedifferent sensory indicators were compared in this paper as well.The results showedthe quality of kumquat juice by atmospheric concentration was inferior to vacuumconcentration, that color, aroma, flavor, turbidity and the main component of kumquatjuice processed by frozen concentration was slightly better than the vacuumconcentration. Given the heavy energy consumption of equipment for freozenconcentration and its lower efficiency, though freozn concentration could keep soundthe flavor of kumquat juice. the application of the frozen concentration in theindustrial production is still limited. So it is more appropriate to adopt vacuumconcentration for producing concentrated kumquat juice.5. By measuring the ability of scavenging DPPH free radical,of scavengingHydroxyl Radical and of total antioxidant capacity, polyphenol content, colordifference, Vtamin C content of different concentration restored kumquat juice, theeffect of vacuum concentration process on the physical and chemical quality ofrestored kumquat juice was studied. The results showed with the increase ofconcentration, the ability of scavenging DPPH free radical,of scavenging Hydroxyl Radical and of total antioxidant capacity of restored kumquat juice decreased at firstand then increased, declinging later again, that the changing trend of polyphenolcontent, of the browning degree was similar as well, which indicated that theantioxidant activity of restored kumquat juice may mainly controlled by thepolyphenol content.