Various agents can be used to promote protein stability, such as cryoprotectants, protease inhibitors, phosphatase inhibitors, antimicrobial agents, reducing agents, chelating agents, and detergents. These additives may help to enhance the shelf life of the proteins. However, the question of whether to add or not should be carefully considered depending on the experimental need. For example, high viscosity may compromise sample quality as well as downstream experimental results. While helping to prevent disulfide bond formation, reducing agents also inhibit other redox reactions which may be of interest.  Similarly, the inclusion of protease inhibitors for proteins to be used with cell cultures or in living systems would not be advisable.