https://www.sciencedirect.com/science/article/am/pii/S0376738821009819

A critical review and commentary on recent progress of additive manufacturing and its impact on membrane technology

Caseins (αS1, αS2, β and κ) are the main protein fraction of bovine milk. Together with nanoclusters of amorphous calcium phosphate (CaP) and divalent cations, they combine to form a polydisperse distribution of particles called casein micelles. A casein micelle model is proposed which is consistent with the way in which intrinsically disordered proteins interact through predominantly polar, short, linear, motifs. Using the model, an expression is derived for the size distribution of casein micelles formed when caseins bind to the CaP nanoclusters and the complexes further associate with each other and the remaining mixture of free caseins. The result is a refined coat-core model in which the core is formed mainly by the nanocluster complexes and the coat is formed exclusively by the free caseins. Example calculations of the size distribution and surface composition of an average bovine milk are compared with experiment. The average size, size distribution and surface composition of the micelles is shown to depend on the affinity of the nanocluster complexes for each other in competition with their affinity for free caseins, and on the concentrations of free caseins, calcium ions and other salts in the continuous phase.

A quantitative calcium phosphate nanocluster model of the casein micelle: the average size, size distribution and surface properties

Effect of changes in ionic composition induced by different diafiltration media on deposited layer properties and separation efficiency in milk protein fractionation by microfiltration

Casein as the major protein of milk is a promising protein source for biopolymer fibers. Current casein-based fibers are fabricated by dissolving caseins in alkaline media and wet spinning in a coagulation bath containing harsh chemicals. In milk, casein is present in so-called casein micelles (CMs). Based on the rennet-induced aggregation, we developed a process that can be applied for the spinning of micellar casein fibers in a sustainable way without the use of harsh chemicals. Fabricated fibers show a surface with a characteristic microstructure, which can also be detected embedded in a network structure inside the fiber. The fibers are stable under acidic and neutral conditions and decompose in alkaline media down to aggregates with sizes comparable to the characteristic microstructure. The so far reached tensile properties of the micellar fiber are between low and mid double-digit percentage range compared to casein azlons.

/pdf/a-regenerated-fiber-from-rennet-treated-casein-micelles-41vc4qo1l1.pdf

A regenerated fiber from rennet-treated casein micelles

Single particle tracking as a new tool to characterise the rennet coagulation process

Calcium effect on the swelling behaviour and stability of casein microparticles

Regenerated fibers from rennet-treated casein micelles can be produced with a defined width and homogeneous surface morphology using a two-substance nozzle integrated in a spinning setup. Extrusion is carried out under standard conditions in a coagulation buffer with 100 × 10−3 m CaCl2 at 60 °C. Electron microscopic images of dried fibers show a fine structure consisting of µm-sized strands running parallel to the fiber axis and radially outward. Confocal fluorescence microscopy lifetime images show that the strands are rich in free calcium, which is released upon swelling in deionized water and diffuses out of the fiber. Fibers made with only 50 × 10−3 m calcium chloride swell at a higher rate to larger equilibrium swelling values because of fewer stabilizing calcium bridges. In HCl, initial swelling of the fibers is followed by deswelling to a defined equilibrium state with a densely packed casein matrix, as indicated by fluorescence microscopy images. Because of the large number of dissolved calcium contacts and the residual charges on the casein, swelling in HCl occurs very quickly. Elastic contributions of the network and released ions lead to deswelling of the fiber, which occurs fastest for those with 100 × 10−3 m CaCl2 due to the high proportion of free ions. 

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/mame.202200272

Fine Structure and Swelling Properties of Fibers from Regenerated Rennet‐treated Casein Micelles

Filter cake formation is the predominant phenomenon limiting the filtration performance of membrane separation processes. However, the filter cake’s behavior at the particle scale, which determines its overall cake behavior, has only recently come into the focus of scientists, leaving open questions about its formation and filtration behavior. The present study contributes to the fundamental understanding of soft filter cakes by analyzing the influence of the porous membrane’s morphology on crystal formation and the compaction behavior of soft filter cakes under filtration conditions. Microfluidic chips with nanolithographic imprinted filter templates were used to trigger the formation of crystalline colloidal filter cakes formed by soft microgels. The soft filter cakes were observed via confocal laser scanning microscopy (CLSM) under dead-end filtration conditions. Colloidal crystal formation in the cake, as well as their compaction behavior, were analyzed by optical visualization and pressure data. For the first time, we show that exposing the soft cake to a crystalline filter template promotes the formation of colloidal crystallites and that soft cakes experience gradient compression during filtration.

/pdf/templating-the-morphology-of-soft-microgel-assemblies-using-4wcfvit47m.pdf

Sebastian Thill

Papers

Single particle tracking as a new tool to characterise the rennet coagulation process

A regenerated fiber from rennet-treated casein micelles

Calcium effect on the swelling behaviour and stability of casein microparticles

Fine Structure and Swelling Properties of Fibers from Regenerated Rennet‐treated Casein Micelles

Templating the morphology of soft microgel assemblies using a nanolithographic 3D-printed membrane