The Modification of Milk Protein Composition through Transgenesis: Progress and Problems

Significant modifications of milk composition have been achieved by the successful high expression of several milk protein-encoding transgenes in animals, mainly mice. Potential changes in milk composition or in the primary structures of milk proteins and their presumed advantageous effects upon the physicochemical, nutritional and technological properties of milk and products derived from it, have been discussed in several reviews. This chapter focuses on some projects in progress to illustrate the actual potential of transgenesis but also the difficulties met in practice with respect to the present knowledge on gene expression and the gene transfer methodology currently available. The transgene can be either a wild-type gene possibly from another species, or an engineered gene encoding a native or a modified milk protein. Milk enriched with a specific inhibitor of either plasmin or plasminogen activator could therefore be attractive for the process industry. Lactose, the most abundant milk sugar plays several key roles.