Probiotics Biofilm-Integrated Electrospun Nanofiber Membranes: A New Starter Culture for Fermented Milk Production.

Electrospun nanofiber membranes are widely investigated in the past few decades as candidates for tissue engineering, which can mimic natural extracellular matrix (ECM) and improve cell adhesion, proliferation, and expression on nanofiber membranes. However, the formation of bacterial biofilms on nanofiber membranes and application of the biofilm-integrated nanofiber membranes remain largely unknown. Here, electrospun cellulose acetate nanofiber membranes are first utilized as scaffold materials for Lactobacillus plantarum ( L. plantarum) biofilm formation. Nanofiber membranes proved to be an excellent scaffold for bacteria biofilm with high stability, where biofilms were interlocked with nanofibers forming a cohesive structure. In comparison with planktonic bacteria, L. plantarum biofilms on nanofiber membranes show excellent gastrointestinal resistance. Instead of decreasing, the number of viable cells increased after 3 h digestion in vitro. The L. plantarum biofilm-integrated nanofiber membranes were used as reusable starter cultures for fermented milk production showing excellent fermentative ability and higher survival of L. plantarum during shelf life. The viable cells in fermented milk remained at 11 log CFU/g throughout the reusable batches, which is far above the required value of 7 log CFU/g in commercial products. In addition, the produced fermented milk possesses shorter fermentation time and higher survival of probiotics during shelf life. The results suggest electrospun nanofiber membranes are ideal scaffold materials for bacteria biofilms immobilization in biotechnology and fermentation engineering, which broaden the potential use of electrospun nanofiber membranes in microbiology and strengthen the application of biofilms in fermentation engineering.

Multilayer affinity adsorption of albumin on polymer brushes modified membranes in a continuous-flow system.

Polymer brushes modified surfaces have been widely used for protein immobilization and isolation. Modification of membranes with polymer brushes increases the surface concentration of affinity ligands used for protein binding. Albumin is one of the transporting proteins and shows a high affinity to bile acids. In this work, the modified membranes with cholic acid-containing polymer brushes can be facilely prepared by the immobilization of cholic acid on the poly(2-hydroxyethyl methacrylate) grafted microporous polypropylene membranes (MPPMs) for affinity adsorption of albumin. ATR/FT-IR and X-ray photoelectron spectroscopy were used to characterize the chemical composition of the modified membranes. Water contact angle measurements were used to analyze the hydrophilic/hydrophobic properties of the membrane surface. The modified MPPMs show a high affinity to albumin and have little non-specific adsorption of hemoglobin. The dynamic binding capacity of albumin in the continous-flow system increases with the cycle number and feed rate as the binding degree of cholic acid is moderate. The highest binding capacity of affinity membranes is about 52.49 g/m2 membrane, which is about 24 times more than the monolayer binding capacity. These results reveal proteins could be captured in multilayers by the polymer brushes containing affinity ligands similar to the polymer brushes containing ion-exchange groups, which open up the potential of the polymer brushes containing affinity ligands in protein or another components separation. And the cholic acid containing polymer brushes modified membranes has the promising potential for albumin separation and purification rapidly from serum or fermented solution in medical diagnosis and bioseparation.

Hydrophilic modification of PVDF microfiltration membranes by adsorption of facial amphiphile cholic acid.

Amphiphilic molecules have been widely used in surface modification of polymeric materials. Bile acids are natural biological compounds and possess special facial amphiphilic structure with a unusual distribution of hydrophobic and hydrophilic regions. Based on the facial amphiphilicity, cholic acid (CA), one of the bile acids, was utilized for the hydrophilic modification of poly(vinylidene fluoride) (PVDF) microfiltration membranes via the hydrophobic interactions between the hydrophobic face of CA and the membrane surfaces. Ethanol, methanol, and water were respectively used as solvent during CA adsorption procedure. Their polarity affects the CA adsorption amount, as similar to CA concentration and adsorption time. There are no changes on the membrane surface morphology after CA adsorption. The hydrophilicity of PVDF membranes is greatly enhanced and the water drops permeates into the CA modified membranes quickly after modification. All these factors benefit to the permeation flux of membrane for water. When CA concentration is higher than 0.088 M, the water permeation flux is doubled as compared with the nascent PVDF membrane and shows a good stability during filtration procedure. These results reveal the promising potential of facial amphiphilic bile acids for the surface modification of polymeric materials.