I have engineered my yeast to display a molecule, which should selectively modify my endogenously introduced peptide. At the end of the reaction, I centrifuged the yeast cells in the media, containing my peptide. My peptide is expected to be in the supernatant. But, on my occasions, I found out that my peptide sticks to the yeast cell surface. I confirmed this, using flow cytometry. I have used different blocking buffers like 3% BSA in 2X PBS, 3% BSA in 2X PBS + 0.2% Triton, 0.5% PEG in PBS. But, it's not solving the problem.

Any idea on how I can prevent my peptide from sticking to my yeast surface?