Study On Membrane Filtration And Vacuum Concentration Of Hetian Red Grape Juice

This research uses the Hetian Red grape as raw material. First, the optimum conditions of using pectinase for clarification were studied. The second step was to use membrane technology to further clarify and sterilize the juice. Choosing different types of membranes, researches were conducted and the conditions were also optimized. Distillation was then used to concentrate the clarified juice from step two. The compositions of juice of various concentration rations were then measured. This research discovered the technological parameters of Hetian Red grape juice concentration and clarification. The details of these results are as follow:Result of the single factor experiment using pectinase showed that the following conditions of 0.4 g/L -0.6 g/L pectinase , temperature 40℃-50℃, and 120 min -180 min gave the best result with transmittance of 90% or more. This result also showed the absence of pectin, proving that pectin was completely removed during the process of the experience. Using the results of the single factor experiments as a foundation, orthogonal research was conducted to clarify Hetian Red grape juice. The results of this research showed that independently the ideal conditions for clarification are 0.4 g/L pectinase,45℃,over the course of 150 min, in which concentration of pectinase have the greatest effect on the result. Then these conditions combined simultaneously to confirm that these conditions were indeed the best. The resulting juice had a transmittance of 94.5%, furthermore, it had the best retention of nutrients.With different membranes, PTFE, PES, and PAN, research of grape juice filtration was conducted. Out of the initial membranes to clarify the Hetian red grape juice, PTFE was chosen because it provided the best clarification and removal of contaminants. The ideal conditions when using this PTFE membrane is 0.06MPa at 40℃. Under these conditions, the resulting juice had a transmittance of 98.6%,turbidity of 0.95NTU, and no detectable presence of pectinase. This clarification had little effect on the nutrient content, flavor, or odor. After filtration, the membrane was washed with a combined solution of 0.1%NaClO + 2%NaOH at less than 50℃for 40 min, it was restored to 95.2% of its original condition.According to the rising concentration, Hetian Red grape juice also had increasing amount of soluble solids, total sugar content, acid content, and stickiness, while the tendency for the light absorption value was to rise, but the pH continually decreased. When the concentration came to five times that of the original juice, it reached the optimal concentration. At this concentration, soluble solids, total sugar content, acid content, pH, stickiness, light absorption value reached 75.5%,72.1%,2.56%,3.2,1900mpa.s,0.424. respectively. At this point, the color reached a light red color. The juice was uniform, without separating into layers, no pulp, and no strange smell. It had the same flavor and odor as the original grape juice.