This disclosure relates to methods for the prevention of the reduction of disulfide bonds in a polypeptide expressed in a recombinant host cell, comprising, following fermentation, adding phosphate to a harvest solution of the recombinant host cell, wherein the disulfide bond in the polypeptide remains non-reduced.本揭露係有關一種防止重組宿主細胞中所表現多肽中之雙硫鍵還原之方法,其包括在發酵後,添加磷酸鹽至重組宿主細胞之收集溶液中,其中多肽中之雙硫鍵保持未還原。