The dried pellet and supernatant were measure by Kjeldahl method Put the samples into digestion tube, add catalyst tablet and 15 ml of sulfuric acid (H2SO4). Start the digestion machine at 400 °C for 2 h and cool down before go to next step. Run on distillation program with 25 ml of boric acid in 250 ml flasks. (เพิ่มตาราง Distillation program ). Titrate with 0.01 N HCl at the end of titration point (pink color, pH 4.6). Calculate the nitrogen content following: