Milk Protein Fractionation by Means of Spiral-Wound Microfiltration Membranes: Effect of the Pressure Adjustment Mode and Temperature on Flux and Protein Permeation.

Martin Hartinger,Joseph Dumpler,Hans-Jürgen Heidebrecht,Simon Schiffer,Ulrich Kulozik

doi:10.3390/foods8060180

Martin Hartinger, Joseph Dumpler + Show 3 more

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https://doi.org/10.3390/foods8060180

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Abstract

Protein fractionation by means of microfiltration (MF) is significantly affected by fouling, especially when spiral-wound membranes (SWMs) are used. We investigated the influence of the mode of transmembrane pressure (ΔpTM) increase to target level and the deposit layer pressure history on the filtration performance during skim milk MF at temperatures of 10 °C and 50 °C. Two filtration protocols were established: No. 1: ΔpTM was set directly to various target values. No. 2: Starting from a low ΔpTM, we increased and subsequently decreased ΔpTM stepwise. The comparison of both protocols tested the effect of the mode of ΔpTM increase to target level. The latter protocol alone tested the effect of the deposit layer history with regard to the ΔpTM. As expected, flux and protein permeation were both found to be functions of the ΔpTM. Further, both measures were independent of the filtration protocol as long as ΔpTM was held at a constant level or, as part of protocol No. 2, ΔpTM was increased. Thus, we can state that the mode of ΔpTM increase to target level does not affect filtration performance in SWM. We found that after completion of a full cycle of stepping ΔpTM up from 0.5 bar to 3.0 bar and back down, flux and deposit layer resistance were not affected by the deposit layer history at 10 °C, but they were at 50 °C. Protein permeation, however, was lower for both 10 °C and 50 °C, when the ΔpTM cycle was completed. The processing history had a significant impact on filtration performance due to remaining structural compression effects in the deposited layer, which occur most notably at higher temperatures. Furthermore, temperatures of 50 °C lead to deposit layer aging, which is probably due to an enhanced crosslinking of particles in the deposit layer. Apart from that, we could show that fouling resistance does not directly correlate with protein permeation during skim milk MF using SWM.

Highlights

Microfiltration (MF) applied for milk protein fractionation has been established as a standard operation in the dairy industry in the last years
From the results reported in literature so far, it seems unclear whether the deposit layer history with regard to the mode of ∆pTM increase, i.e., stepwise or directly to target level, deposit layer aging, and structural alterations has a distinct influence on the MF performance of spiral-wound membranes (SWMs)
Influence of Temperature and Initial ∆pTM on Steady-state Conditions of Flux. It was investigated how the flux evolves with filtration time and how much time is needed to reach steady-state conditions with a constant ∆pTM. This was to ensure that the effect of the intensity of deposit layer formation on filtration performance is not obscured by incomplete equilibration at phase-interface between the deposit layer and the bulk

Summary

Introduction

Microfiltration (MF) applied for milk protein fractionation has been established as a standard operation in the dairy industry in the last years. Foods 2019, 8, 180 membranes, flux and whey protein permeation through the membrane are seriously affected by fouling due to protein deposition. It is known that higher levels of transmembrane pressure (∆pTM ) induce compression of deposited protein layers. What remains unclear is whether, or to what extent, the pressure adjustment scheme, i.e., the mode of ∆pTM adjustment to target level, affects MF flux and protein permeation. A stepwise increase or decrease of ∆pTM creates a different situation in terms of processing history, possibly affecting the deposit’s structural properties. Long-term continuous operations (of around 6–24 h) between two membrane cleaning cycles create aging effects related to the processing history, especially when higher temperatures, i.e., around 50 ◦ C, are compared to lower temperatures, i.e., around 10 ◦ C. It can be expected that structural time-dependent modifications of the deposited layer occur at higher temperatures due to more intense interactions between particles in the deposit layer

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