Inclined-film vacuum evaporation of fruit juices

Abstract

Juice from Citrus reticulata Blanco was extracted and preheated at 80°C to reduce enzyme activity and microorganisms load before feeding to an inclined-film vacuum evaporator. The evaporator consisted of an evaporating chambor which was in an inclined position of 60° from the vertical line, a hot-wator heater, a food tank, two condensers, and two concentrated-juice tanks. In the evaporating chamber, juice was causod to flow onto an inclined heated plate and overflow a wire as thin film along the plate. The heated plate, beneath which hot water circulatod by a centrifugal pump, was maintained to bo covered with the juice all the time in order to obtain continuous evaporation, Vacuum was also applied by two vacuum pumps during the evaporation. The concentrated juice flowed under gravitational force to the concentrated juice tanks attached to the end of the evaporating chamber, while the water vapor evaporated from the juice passed through the condensers to the condensate tanks. The relationship between initial and final mass flow-ratos, the physical properties of fruit juice, the plate inclination, the vacuum applied, and the hot-water temperature was derived there tically and expressod as: (P0 4/3 – P2 4/3) = 0.925 (Ts - Tv) (P2k3 g cos G )1/3 The feed flow rate and the temperatures of hot water used Here varied in the experiment. The evaporation ratios were determined. Titratable acidity, vitamin C content, pH, Brix of juice before and after processing were determined. The storage keepability, color, and appearance of concentrated juice were also studied. The experimental results agreed reasonably well with the theoretically derived equation. The evaporation ratios were rather low. The concentrated-juice developed unacceptable flavor and taste with acceptable color, and the vitamin C content was untitratable. The keepability would be possible with the aid of some preservatives, The precipitation of juice was still found with just noticeable change of color.