Masayoshi Yamazaki

Purification and Identification of Flavonoids from the Yellow Green Cocoon Shell (Sasamayu) of the Silkworm, Bombyx mori

Three quercetin glycosides, quercetin 5-O-β-D-glucoside, quercetin 7-O-β-D-glucoside, and quercetin 4′-O-β-D-glucoside, and two kaempferol glycosides, kaempferol 5-O-β-D-glucoside and kaempferol 7-O-β-D-glucoside, along with their aglycones, quercetin and kaempferol, were isolated from an ethanolic extract of Sasamayu cocoon shells. The chemical structures were characterized by chemical and spectroscopic methods including UV spectrometry and HPLC-ESI-MS. The five flavonol glycosides of the shell are different structurally from those of the leaves of mulberry (Morus alba). It was suggested that potent antioxidative activity in the cocoon is mainly due to flavonoid compounds since free radical scavenging activity was found in the cocoon flavonoids identified here.

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 AC-SP were compared with those of alkali-degraded sericin powder (AL-SP) and hot-water degraded sericin powder (HW-SP). Based on an SEM analysis, AC-SP showed a thin film structure of 10–100 μm with good dispersity while AL-SP and HW-SP had a much larger thin film structure (<500 μm). The extract of AC-SP 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 AC-SP was a trypsin inhibitor complex powder and that the release of CSTI-IV from AC-SP 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.

Properties of an Emulsion Prepared from Silk Sericin and Vitamin E

An emulsion (SR-EM) was prepared from vitamin E and aqueous sericin solution obtained from cocoons of Bombyx mori. Properties such as emulsifying degree, heat stability and radical scavenging activity of SR-EM were compared with those of CS-EM and AL-EM, vitamin E emulsions prepared from casein and bovine serum albumin, respectively. The degree of emulsifying for SR-EM was three times higher than that for CS-EM. CS-EM and AL-EM were a heat-stable emulsion, whereas SR-EM was a heat-labile emulsion because absorbance spectra changed exclusively in SR-EM after treated from 115 to 127deg. These results indicated that the oil-water interface of SR-EM was unstable under the high pressure-high temperature treatments compared to those of CS-EM and AL-EM. Each emulsion showed lower radical scavenging activity than a vitamin E solution,suggesting that the interaction of vitamin E and a radical molecule may be interfered by a protective protein colloid. SR-EM and CS-EM were more stable in 60% ethanol solution at ambient temperature than AL-EM because the radical scavenging activity of SR-EM and CS-EM was some 50% lower than that of AL-EM.