TECHNICAL AND ECONOMIC FEASIBILITY OF A NON-CONVENTIONAL METHOD FOR CONCENTRATING ORANGE JUICE
The objective of this study was to develop and evaluate an improved method for concentrating orange juice. It was postualted that the juice concentrate quality could be improved if the heat load experienced by the juice during concentration was minimized. A method was developed which used a semi-permeable membrane to separate the juice into serum and pulp fractions. The serum was free of enzymes and microorganisms and was concentrated in a TASTE evaporator. Microorganisms and enzymes in the pulp fraction could have been inactivated with conventional heat exchangers but were not. The resulting recombined concentrate was less heat treated than conventionally prepared concentrate.
Single-strength orange juice was processed by ultrafiltration through a hollow-fiber polysulfone membrane.Suspended solids were removed at a 3:1 volumetric permeate to retentate ratio. The serum was concentrated to 80 degrees Brix in a pilot scale TASTE evaporator. A suitable heat exchanger was not available for pasteurizing the pulp. Concentrated serum was recombined with raw pilp to yield a final 50 degrees Brix product. Evaporator performance and essence recovery were compared to conventional concentration. Ascorbic acid retention and non-enzymatic browning in the concentrated serum was compared to that observed in whole concentrate prepared by conventional evaporation.
Evaporator water removal capacity and steam economy were similar when concentrating either whole juice or serum. Only aqueous phase essence compounds were recovered when concentrating the serum. No essence oil was recovered. When concentrating whole juice, most compounds (including essence oil) were recovered by the essence unit. Ascorbic acid losses during concentration of the serum averaged 1.2%. Browning index increases averaged 4%. The browning index was significantly less than that observed during the concentration of whole juice.
The economics of the membrane/evaporator concentration process were not favorable when compared to conventional evaporation. Processing costs were estimated at 15% higher than evaporation alone. Thrity to 40% increases in storage, refrigeration and shipping costs were expected because the product was 50 Brix rather than 65 Brix. However, the process does offer the possibility of improved concentrate quality and the concentrated serum holds potential for use in new types of citrus products.