Characterization of sericin powder prepared from citric acid-degraded sericin polypeptides of the silkworm, Bombyx mori

Acid-degraded sericin powder (AC-SP) was prepared from aqueous solution containing citric acid-degraded sericin polypeptides of Bombyx mori. The morphological and biochemical properties of AGSP were compared with those of alkali-degraded sericin powder (AL-SP) and hot-water degraded sericin powder (HW-SP). Based on an SEM analysis, AGSP showed a thin film structure of 10-100 mum with good dispersity while AL-SP and HW-SP had a much larger thin film structure (<500 mu m). The extract of AGSP showed stronger trypsin inhibitor activity due to cocoon shell trypsin inhibitor (CSTI-IV) than that of HW-SP. The extract of AL-SP showed no CSTI-IV activity. It was found that AGSP was a trypsin inhibitor complex powder and that the release of CSTI-IV from AGSP depended on pH and ion strength. Similar powder materials were obtained when such organic acids as tartaric acid and succinic acid were used. These results suggest that the acid-degraded sericin polypeptides work as a protein matrix to which CSTI-IV may bind ionically.