Animal-free caseins by precision fermentation: technical challenges and perspectives

Caseins, the major milk proteins, assemble into micelles that provide the structural basis for many of the functional and nutritional properties of dairy products. While recombinant DNA technology has enabled the efficient microbial production of some whey proteins, the expression of caseins has proven considerably more challenging. Their susceptibility to proteolysis, tendency to self-associate, and post-translational modifications complicate their heterologous production. This review summarizes the current state of microbial casein expression in different host systems. Particular attention is given to secretory casein production, which offers advantages for downstream processing but appears difficult to achieve efficiently. Strategies including protease deletion, kinase co-expression, and the use of phosphomimetic casein variants are discussed as potential avenues to improve yields and functionality. Together, these insights highlight both the promise and the remaining hurdles for producing recombinant caseins suitable for food applications through precision fermentation. Looking ahead, advances in host engineering, secretion efficiency, scalability of the fermentation and the downstream processing, and protein functionality will be essential to enable industrial-scale production, facilitating the implementation of recombinant caseins as a viable ingredient for alternative dairy products.