The invention discloses a method for adjusting isoelectric points of
collagen II. The method includes the steps of 1), weighing a certain amount of the
collagen II with a three-screws structure and with telopeptide removed, adding 100-1000 times the weight of 0.05-0.5mol / L of an
organic acid solution, allowing to dissolve completely by means of stirring, performing displacement of solution with an
ultrafiltration method, adding an alkaline solution with pH value being 7.5-11 during
ultrafiltration, and continuously performing
ultrafiltration till difference value between a permeate solution pH and the added alkaline solution pH is lower than 0.2; 2), feeding the alkaline solution of the
collagen II to a constant-temperature reaction kettle, controlling the temperature of the solution in the reaction kettle to be 10-40DEG C, continuously adding an acid
aqueous solution to the reaction kettle, controlling total adding amount of
acid anhydride to be 0.01-1 times the weight of the collagen II, and adopting the alkaline solution with the pH value being 12-14 to control pH of the reaction solution to be maintained in pH 7.5-11; 3), adding an acid diluting solution to the solution prepared in the step 2) till flocky precipitate appears in the solution, recording the pH value of the solution during
settling, subjecting the solution to centrifugal treatment and collecting the precipitate; 4), subjecting the precipitate to
freeze drying.