Two methods were compared for purification of the non-hydrolyzable residue and the acid-precipitable fraction from hydrolyzate, which contained contaminating protein. The first method was based on hydrolysis with 2% alkaline protease from Bacillus licheniformis (Subtilisin type VIII, Sigma) [33]. The reaction was conducted at pH 9.6 (0.5 M NaHCO3 buffer) 37 ◦C, with gentle shaking for 24 h. The solution was centrifuged (11 000 rpm, 5 min, 5 ◦C) and both the insoluble part and the supernatant were recovered. The supernatant was acidified to pH 2.5 with HCl, and a precipitate was obtained.