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

Abstract

Abstract 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 CaCl 2 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 CaCl 2 due to the high proportion of free ions.