Electro-membrane filtration for the selective isolation of bioactive peptides from an αs2-casein hydrolysate

For the isolation of the ingredients required for functional foods and nutraceuticals generally membrane filtration has too low a selectivity and chromatography is (too) expensive. Electro-membrane filtration (EMF) seems to be a breakthrough technology for the isolation of charged nutraceutical ingredients from natural sources. EMF combines the separation mechanisms of membrane filtration and electrophoresis. In this study, positively charged peptides with antimicrobial activity were isolated from an αs2-casein hydrolysate using batch-wise EMF. αs2-Casein f(183-207), a peptide with strong antimicrobial activity, predominated in the isolated product and was enriched from 7.5% of the total protein components in the feed to 25% in the permeate product. With conventional membrane diafiltration using the same membrane (GR60PP), isolation of this and other charged bioactive peptides could not be achieved. The economics of EMF are mainly governed by the energy costs and the capital investment, which is affected by the flux of the desired peptide. A maximum average transport rate of αs2-casein f(183-207) during batch-wise EMF of 1.2 g/m2 · h was achieved. Results indicate that an increase in the hydrolysate (feed) concentration, the applied potential difference and the conductivity of the permeate and electrode solutions, and a reduction in the conductivity of the feed result in a higher transport rate of αs2-casein f(183-207). This is in line with the expectation that the transport rate is improved when the concentration, the electrical field strength, or the electrophoretic mobility is increased, provided that the electrophoretic transport predominates. The expected energy consumption of the EMF process per gram of peptide transported was reduced by approximately 50% by applying a low overall potential difference and by processing desalinated hydrolysate. Considerable improvements in transport rate, energy efficiency, and process economics seem to be attainable by additional optimization of the process parameters and the EMF module design

Ag-functionalized carbon molecular-sieve membranes based on polyelectrolyte/polyimide blend precursors

We prepared dense flat-sheet Ag-functionalized carbon molecular-sieve (CMS) membranes from blends of P84 co-polyimide and a sulfonated poly(ether ether ketone) with a Ag+ counterion (AgSPEEK). These blends offer the possibility of producing new functionalized precursor structures, which were previously not possible, such as integrally skinned asymmetric hollow fibers. Membranes prepared at a pyrolysis end temperature of 800 °C showed a maximum permeability for all tested gases at a Ag content of approximately 2.5 wt.-% (He permeability PHe = 465 Barrer (1 Barrer = 7.5 × 10-18 m2 s-1 Pa-1), PCO2 = 366 Barrer, PO2 = 91.8 Barrer, PN2 = 10.3 Barrer). The maximum achieved selectivity for O2 over N2 with CMS membranes based on these blends was O2/N2 = 13.5 (Ag content: 4.5 wt.-%, PO2 = 52.7 Barrer). The CO2 over N2 selectivity reached a value of 48.9 (Ag content: 4.5 wt.-%, PCO2 = 191 Barrer). These observations are explained by the formation of selective bypasses around Ag nanoclusters in the CMS matrix.\u

Evapoporometry adaptation to determine the lumen-side pore-size distribution (PSD) of hollow fiber and tubular membranes

Determining the pore-size distribution (PSD) of ultrafiltration membranes is crucial in assessing their properties. Evapoporometry (EP) characterizes the PSD based on evaporating a volatile wetting liquid from the membrane pores that permits determining the pore diameter using the Kelvin equation. EP has been applied in prior studies to determining the PSD for flat sheet and the outer surface of hollow fiber (HF) membranes. This paper adapts EP to characterizing the PSD on the lumen side of HF membranes. This required sealing the HFs to ensure that evaporation occurred only from the lumen side. A model was developed to determine the required membrane sample and test-cell dimensions. EP characterization based on remeasurements of a PES/PVP single-bore HF gave mass-based and flow-based average pore diameters of 106.2±1.6 nm and 157.8±4.3 nm, respectively, the latter of which was closer to the flow-based average pore diameter of 140 nm determined by liquid-displacement porometry. No pores were found larger than 300 nm, which was consistent with the known rejection properties. EP characterization based on remeasurement of a PES multi-bore HF gave mass-based and number-based average pore diameters of 26.6±0.6 nm and 14.0 nm, respectively, with 90% of the pores being smaller than 20 nm, which was consistent with the known rejection properties. This study underscores the importance of understanding the basis for the PSDs obtained using different characterization methods and viewing the PSD in the form most useful to assess the relevant properties for a particular application.NRF (Natl Research Foundation, S’pore)MOE (Min. of Education, S’pore)EDB (Economic Devt. Board, S’pore

Thinking the future of membranes: Perspectives for advanced and new membrane materials and manufacturing processes

The state-of-the-art of membrane technology is characterized by a number of mature applications such as sterile filtration, hemodialysis, water purification and gas separation, as well as many more niche applications of successful membrane-based separation and processing of fluid mixtures. The membrane industry is currently employing a portfolio of established materials, mostly standard polymers or inorganic materials (not originally developed for membranes), and easily scalable manufacturing processes such as phase inversion, interfacial polymerization and coating. Innovations in membranes and their manufacturing processes must meet the desired intrinsic properties that determine selectivity and flux, for specific applications. However, tunable and stable performance, as well as sustainability over the entire life cycle of membrane products are becoming increasingly important. Membrane manufacturers are progressively required to share the carbon footprint of their membrane modules with their customers. Environmental awareness among the world's population is a growing phenomenon and finds its reflection in product development and manufacturing processes. In membrane technology one can see initial steps in this direction with the replacement of hazardous solvents, the utilization of renewable materials for membrane production and the reuse of membrane modules. Other examples include increasing the stability of organic membrane polymers and lowering the cost of inorganic membranes. In a long-term perspective, many more developments in materials science will be required for making new, advanced membranes. These include "tools" such as self-assembly or micro- and nano-fabrication, and "building blocks", e.g. tailored block copolymers or 1D, 2D and 3D materials. Such membranes must be fabricated in a simpler manner and be more versatile than existing ones. In this perspective paper, a vision of such LEGO (R)-like membranes with precisely adjustable properties will be illustrated with, where possible, examples that already demonstrate feasibility. These include the possibility to switch properties using an external stimulus, adapting a membrane's selectivity to a given separation, or providing the ability to assemble, disassemble and reassemble the membrane on a suitable support as scaffold, in situ, in place and on-demand. Overall, it is foreseen that the scope of future membrane applications will become much wider, based on improved existing membrane materials and manufacturing processes, as well as the combination of novel, tailor-made "building blocks" and "tools" for the fabrication of next-generation membranes tuned to specific applications

Native protein recovery from potato fruit juice by ultrafiltration

Potato fruit juice, i.e. the stream resulting after the extraction of the starch from the potato, contains up to 2.5% [w/w] of proteins that are potentially valuable for the food market. However, today the recovery of protein from the potato fruit juice with reverse osmosis membranes results in a protein concentrate that is not suitable for human consumption. The described research shows that the use of ultrafiltration with additional diafiltration is able to produce a higher quality protein. Tests with the produced protein show that the quality depends on the rate of diafiltration used and that the product has functional properties that are equal or better than the compared commercial food product that are currently used