Overall, all these fundamental experimental studies highlight the critical role of the hydroxyl group in ensuring adequate hydrogen bonding interactions between sugar and protein. Such an interaction requires the binding of sugar to protein in a stoichiometric manner as there might be a limited number of binding sites on the surface of protein molecules that may form hydrogen bonds with stabilization. Therefore, it is expected that a saturation level will be reached if all binding sites are used, and a further increase in sugarto-protein ratio will not further improve protein stability. Such saturation levels have been observed in several studies. For example, Cleland and Carpenter et al. demonstrated that the concentration range of sugars, including sucrose and trehalose, to maximize the native state of the formulations of recombinant humanized monoclonal antibody HER2 is 60-100 mM. Further increase of sugar concentration can only mitigate the rate of protein aggregation slightly. Similarly, a molar ratio of trehalose and recombinant humanized monoclonal antibody anti-IgE (rhuMAbE25) in the range of 300:1 to 500:1 was reported able to maximize the stability of the spray-dried recombinant antibody. However, if the stability data is replotted in the log scale, a linear correlation was still observed between the stability of rhuMab HER2 and sucrose concentration. Therefore, it is still debatable whether the saturation refers to no additional improvement or is because of the sensitivity of plotting to differentiate the degradation rate.