Structural Characterisation of Deposit Layer during Milk Protein Microfiltration by Means of In-Situ MRI and Compositional Analysis

Abstract

Milk protein fractionation by microfiltration membranes is an established but still growing field in dairy technology. Even under cross-flow conditions, this filtration process is impaired by the formation of a deposit by the retained protein fraction, mainly casein micelles. Due to deposition formation and consequently increased overall filtration resistance, the mass flow of the smaller whey protein fraction declines within the first few minutes of filtration. Currently, there are only a handful of analytical techniques available for the direct observation of deposit formation with opaque feed media and membranes. Here, we report on the ongoing development of a non-invasive and non-destructive method based on magnetic resonance imaging (MRI), and its application to characterise deposit layer formation during milk protein fractionation in ceramic hollow fibre membranes as a function of filtration pressure and temperature, temporally and spatially resolved. In addition, the chemical composition of the deposit was analysed by reversed phase high pressure liquid chromatography (RP-HPLC). We correlate the structural information gained by in-situ MRI with the protein amount and composition of the deposit layer obtained by RP-HPLC. We show that the combination of in-situ MRI and chemical analysis by RP-HPLC has the potential to allow for a better scientific understanding of the pressure and temperature dependence of deposit layer formation.

Build-up and relaxation of membrane fouling deposits produced during crossflow ultrafiltration of casein micelle dispersions at 12 °C and 42 °C probed by in situ SAXS

“…The influence of temperature on fouling layer structure and properties is studied very rarely, only data for skim milk filtration are available. For example [79], concluded from in situ MRI analysis of dead-end filtration of skim milk that deposit obtained at 45 • C (and mostly composed of casein micelles) is denser (i.e. more concentrated) than that obtained at 22 • C. This is in accordance with data presented in Fig.…”

“…The importance of swelling for deposit erosion (Fig. 10) also suggests that external fouling could be more efficiently removed by not applying TMP when rinsing the membrane (this idea has already been voiced [77][78][79], also in the milk filtration literature [8]). This is because applied TMP counteracts the osmotic swelling pressure and reduces the swelling.…”

“…Refs. [48][49][50]70,71,79]). It corresponded to wall shear stress τ w ≈ 0.2 Pa (at 12 • C) and 0.1 Pa (at 42 • C).…”

Comparative Assessment of Tubular Ceramic, Spiral Wound, and Hollow Fiber Membrane Microfiltration Module Systems for Milk Protein Fractionation

“…The deposit formation of retained matter is an issue in all membrane systems, as reported for HFM [ 15 , 16 , 17 , 18 , 19 ], CTM [ 1 , 6 , 7 ], and SWM [ 9 , 11 ]; however, at different levels due to the different flow channel configurations. Deposit formation strongly impairs flux and the desired high whey protein mass flow, which is a key aspect in milk protein fractionation [ 7 ].…”

“…In previous studies, we have reported on MF-based milk protein fractionation by HFM [ 16 , 17 , 18 , 19 ], however with another perspective on fundamental aspects of deposit formation; therefore, small lab scale modules have been utilized. We also demonstrated that the length dependency in HFM is equal to that of CTM, and that the length-dependent pressure drop is responsible for inhomogeneous fouling along the HFM [ 19 ].…”