Research And Application Of Freeze Concentration In Orange Juice

The study applied freeze concentration which is a non-thermal concentration methods based on the phase equilibrium between ice and water. During the process water became ice and the concentration of solution increased. Compared with evaporating and reverse osmosis concentration, freeze concentration has its advantage, the loss of volatile aromatic component and the sensitive components such as enzyme and pigments are very little. So it would be significant to improve the quality of orange concentrate.There are two kinds of Freeze concentration, including progressive crystallization and suspension crystallization. When applying progressive crystallization, it is easy to form thick ice on the cold wall but thermal conductivity of ice is limited, ice growth rate is very slow, so it is difficult to be carried out in large scale production. The solute and fibre is easy to be trapped in the ice and difficult to be separated from each other. Suspension crystallization forms lots of ice crystal in solution, The surface area of ice crystal per unit mass is large, The pure ice crystal can be formed and the final concentration could be high, so suspension crystallization is better than progressive crystallization in industry. The research includes:(1) During the freeze concentration, choosing right initial freeze temperature and controlling the ice growing velocity is important to keep ice crystal' s purity. The temperature of coolant, between -2.5～-3℃, is suitable to freeze orange juice as a freezing temperature at the beginning and the concentration of solute trapped in ice was less than 0.5%.(2) Heat conductivity of suspension crystallization is better than progressive crystallization. Compared with the ice crystal got from these two methods at the temperature of -2. 5℃, -3℃and -3.5℃, the ice crystal got from suspension crystallization contained less solute than that from progressive crystallization. (3) The growth of kinetics of ice crystals was developed, the model showed that the growth rate of ice is proportional to the mass of ice. According to (dm₁)/dt=km₁{1-(m₁)/(m_1,max)}, an initial valueβ₀ was supposes as the unkown coefficientβ₀ Adopts Runge-Kutta method to numerically solve the differential equation and searching method to get the coefficient K₁=0.7183/hr, k₁=1.4 in the first concentration; K₂=0.6181/hr, k₂=1.3 in the second concentration.(4) Through two stage of freeze concentration, the concentration of orange juice reached 34.2°Bx. at the first stage, the juice can be concentrated from the initial concentration of 13°Bx to 26.4°Bx, the concentration of melted ice crystal is 1.5%; while at the second stage, the concentration of juice was concentrated from the initial 20.8°Bx to 34.2°Bx, the concentration of melted ice crystal is 1.75% at last.(5) The freeze depression curve of the orange juice was also studied. The result showed that the freeze depression curve is linear relationship in the range of experiment. The freezing point temperature of initial orange juice(13°Bx) is -1.4103℃and the final concentrated orange juice(34.2°Bx) is -4. 7655℃.(6) Compared with the viscosity of sugar solution, orange juice filtrated and orange juice unfiltrated, the result showed that the lower the viscosity is, the better result of freeze concentration will be, which means the higher concentration of juice and the lower concentration of melted ice crystal will be.(7) The separation method of concentrated juice from ice crystal was also studied, the best way to separate the concentrated from ice crystal is to combine washing tower and presser.