Serum Protein Removal From Skim Milk Using Polymeric Spiral-Wound Microfiltration Membranes

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There is interest in membrane fractionation of milk to create novel products with wideranging use in food and non-food applications. Various pressure-driven membrane processes are utilized by the dairy industry to create novel food ingredients, including microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO), in order of decreasing pore size. Microfiltration of skim milk to fractionate casein (CN) and serum proteins (SP) is the newest application of filtration to dairy fluids. Removing SP from skim milk using MF creates a micellar CN concentrate (MCC) that has unique functional properties and can be used as a new ingredient in with unique functional properties food product development. Two primary MF membrane materials and configurations are currently used for SP removal from skim milk, tubular ceramic and polymeric spiral-wound (SW) membranes with pore sizes ranging from 0.1 to 0.5 [mu]m. As with most membrane processes on complex fluids, fouling and flux decline are monitored by the processor to ensure optimal system efficiency. Ceramic membranes, which have been studied more than SW membranes, achieve theoretical SP removal and achieve high flux (e.g., 54 kg/m2 per h). Polymeric SW MF membrane use for SP removal has b een studied less than ceramic membranes, but they are lower cost and can contain more membrane surface area per unit floor space than ceramic membranes, making them an attractive alternative that warrants further study. The first objective of our research was to determine the process necessary to create a 95% SP reduced MCC using a 0.3 [mu]m polyvinylidene fluoride (PVDF) polymeric SW MF at 50°C and compare the efficiency of the SW process to theoretical values and to a 0.1 [mu]m ceramic uniform transmembrane pressure (UTP) MF membrane process. A three-stage, 3.00x concentration factor, MF diafiltration (i.e., dilute with filtered water) process was employed and SP removal at each stage was quantified. Permeate flux was low and increased, 14.4, 22.1, 32.6 kg/m2 per h, from stage 1 to 3, respectively. Skim SP removal for stage 1 to 3 w ere 38.6, 20.8, and 10.9%, respectively, and were cumulatively lower than theoretical, 70.3 vs. 97.0%. It was estimated an additional 5 stages (i.e., a total of 8) would be necessary to achieve 95% removal of SP with polymeric SW membranes. Research to improve SP removal from skim milk using PVDF SW MF membranes would allow more efficient and cost effective production of MCC. Casein in skim milk is the primary foulant of PVDF SW MF membranes. Previously, we observed that flux was higher when the concentration of CN in feed material was low er (i.e., low CF). The second objective of our research was to determine the impact of CF, 3.00, 2.25 and 1.50x on the removal of SP from skim milk during PVDF SW MF at 50°C using a 0.3 [mu]m pore size membrane. Flux increased, 12.8, 15.3, and 19.0 kg/m2 per h, with decreasing CF. However, SP removal also decreased, 35.6, 24.3, and 10.6%, as CF decreased from 3.00 to 2.25, and 1.50x, respectively, which was unexpected. The rate of SP removal per unit membrane surface area was relatively constant, 0.036, 0.039, and 0.039 kg/m2 per h, among CF. These results led us to believe that the rate at which the concentration of solute near the membrane surface changes during startup is a significant factor in the deposition of foulant on the membrane surface and the foulant changes SP rejection. At low CF, the rate of concentration change and foulant layer formation is slower, which could cause more pore plugging by casein micelles and restrict passage of SP but not solvent (i.e., water) than at high CF. Controlling the startup procedure and foulant deposition onto the membrane could lead to more efficient removal of SP from skim milk using polymeric SW MF membranes.

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Microfiltration; Milk Serum Protein; Spiral-Wound Membrane


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Union Local


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Barbano, David Mark

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Bauman, Dale Elton

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Food Science and Technology

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M.S., Food Science and Technology

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Master of Science

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dissertation or thesis

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