Swelling Behavior and Mechanical Stability of Composite Fibers Prepared from Casein Micelles and Calcium Alginate

Milk casein micelles are natural nanocarriers for poorly soluble calcium phosphate and can be used to stabilize and functionalize composite structures due to their excellent gelling properties. This study shows that alginate and native casein micelles can be processed into stable composite fibers by extrusion in a calcium-rich coagulation bath. The influence of micellar casein content on the swelling of fibers in decalcifying media is analyzed and the effects of the treatment on the mechanical properties are investigated. Pure alginate fibers swell strongly in trisodium citrate solutions due to calcium removal, whereas alginate-casein interactions in composite fibers significantly reduce this strong swelling. In acidic solutions such as citric acid and glucono-δ-lactone, pure alginate fibers become softer and lose strength. If the amount of micellar casein in the fiber is increased, it can be observed that the swelling capacity decreases during the acid treatment, but the extensibility increases significantly in mechanical tests after the treatment. However, citric acid also stabilizes the fiber structure through hydrogen bonding and makes the fibers more flexible, which leads to a greater reduction in swelling and allows for higher breaking strains, compared to glucono-δ-lactone.