| This paper mainly studied removing astringency, protecting color, clarification and concentration technologies of blueberry juice, and discussed the change of physical parameters of concentrated blueberry juice.Gelatin was applied to remove tannin in blueberry juice. The experimental results showed that the adsorption of tannic acid by gelatin accorded with the second level dynamics equation, and its isotherm fitted Langmuir adsorption equation meaning single molecule layer adsorption. The optimal condition for gelatin to adsorb tannin was the dosage of gelatin 1.2 g/L, adsorption temperature 30 ℃, and adsorption time 30 min. The amount of gelatin adsorption was 421.2 mg/g, the rate of tannin removal was 56.16%, and a small amount of other nutrients was adsorbed.Citric acid, L- lysine, trehalose and ascorbic acid were used for protecting the color of blueberry juice. The research showed that four color protecting agents could improve blueberry juice browning during storage. The citric acid was the best color fixative. When the blueberry juice adding 0.6%(g/g) of citric acid was storing for 7 days, its browning rate was 13%, and its anthocyanin residual rate was 83.41%. Compared with blueberry juice not adding any color protecting agent, browning rate dropped 8.97% and anthocyanin residual rate rose 18.34%. When the blueberry juice without adding any color protecting agent was storing for 7 days, its anthocyanin degradation reaction followed first-order dynamics reaction kinetics. When the blueberry juice adding 0.6%(g/g) of citric acid was storing for 7 days, its anthocyanin degradation also followed the first-order dynamics reaction kinetics. Its degradation rate constant under different temperatures(5, 18, 30 and 40 ℃) was decreased by 30.28%, 37.65%, 42.19% and 46.51% respectively, and its half life was increased by 43.43%, 60.41%, 73.02% and 86.85% respectively. Its activation energy of anthocyanin degradation was 35.26 KJ/mol, smaller than 40.74 KJ/mol of blueberry without adding citric acid. This showed that anthocyanin degradation in blueberry juice with citric acid was less affected by the temperature.Chitosan solution was used for clarifying blueberry juice, and the process was optimized by using response surface method. The optimal condition was the dosage of chitosan solution 0.09 g/L, the temperature 36 ℃ and pH 3.63. After blueberry juice was clarified by chitosan solution, clarification degree of blueberry juice was 88%. Total sugar, total acid, vitamin C and soluble solid were slightly decreased. Protein, total phenol and pectin that caused the turbidity of blueberry juice were reduced greatly.Vacuum evaporation and freeze-drying were applied to study concentration process of blueberry juice. The result showed that freeze-drying had an obvious advantage in keeping total content of aroma, the relative content of every component and the nutrition in blueberry juice. Frozen concentrated blueberry juice retained 85.94% of all the aroma components in the original juice. The relative content of total aroma components and main characteristic aroma components decreased significantly in blueberry juice of vacuum evaporation concentration under 40 ℃, and the juice only retained 67.05% of all the aroma components in the original juice. Frozen concentration juice retained 88.47% of anthocyanin content and 82.31% of ascorbic acid content, however vacuum evaporation concentrated juice only retained 77.54% of anthocyanin content and 71.58% of ascorbic acid content. Therefore freeze drying method was the best concentration process.We found the effect of temperature on the viscosity could be described by Arrhenius equation: η=K0exp(Ea/RT), the effect of soluble solid content could be described by exponential function: η=Kexp(AC), and the combined effect of concentration and temperature on the viscosity could be described by η=0.3034e-0.0728Cexp(6491.7e0.0284C/RT) through the study on physical parameters of frozen concentration juice. |
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