The National Agriculture and Food Research Organization (NARO) in Japan maintains 27 native European strains of the domesticated silkworms (Bombyx mori). Many of them are distinguished by their flesh color, oval cocoon shape, high yarn volume, and thick cocoon filament. Among the native European varieties, “Cévennes White” is a white cocoon that is not commonly found. This cocoon has relatively thick filaments that are shallowly wrung-out and bale-shaped. Court costumes from the French Rococo era were restored using “Cévennes White.” Several features of the court costume, such as whiteness, lightness, three-dimensional shape, and softness, are attributed to “Cévennes White.” Therefore, to examine the whiteness of “Cévennes White,” we first measured cocoon color with a colorimeter. The results showed that “Cévennes White” had a lower yellowness index as well as less whiteness than the Chinese or Japanese white cocoon strains. In addition, the silk proteins of “Cévennes White” exhibited a strong blue fluorescence, as revealed by a three-dimensional fluorescence analysis performed using a fluorescence spectrophotometer.

The multi-band progressive type of cocoon drying machine is a hot air-drying method commonly used for cocoon drying. It is recommended that a hot air-drying temperature at 115 ˚C be used in contact with the cocoon. Thereafter, the finishing temperature should be gradually reduced to 60 ˚C. However, in this study, the harvested cocoons were dried at 60 ˚C for 24 hours because high temperature treatment usually causes the fluorescent color to disappear. Therefore, we considered introducing an air-heated decompression dryer, which is used in the production of dried persimmon, “Ichida-gaki,” to improve the efficiency of cocoon drying. The results of drying white cocoons using an air-heated decompression dryer showed that the yellow index was significantly low, and the discoloration caused by heat was suppressed to a considerable extent. Furthermore, the result of drying green fluorescent cocoons, which are genetically modified silkworms, using the air-heated decompression dryer showed that discoloration was prevented to a considerable extent. Regarding constant drying at 60 ˚C, low temperature drying without decompression required 24 hours of drying, whereas decompression drying reduced the drying time to 14 hours; this is expected to improve the cocoon processing efficiency.

A mechanism affecting the initial stage of thermal decomposition of Bombyx mori silkworm silk in an un-degummed state was elucidated using thermogravimetry (TG) and temperature programmed desorption – mass spectrometry (TPD-MS) for silk samples of three kinds, in which the amount of sericin relative to fibroin increased in the order of raw silk, silk floss, and sericin cocoon. Thermal decomposition occurred along with weight loss consistently at 170 °C in all three samples. Considering the TPD-MS results indicating simultaneously observed onset of H₂O evolution, the initial thermal decomposition was attributed to dehydration of serine (Ser) and asparatic acid (Asp) side-chains, which are predominant in sericin. The evolved H₂O can induce amide-bond hydrolysis, triggering main-chain decomposition. The progress of main-chain decomposition was monitored via TPD-MS by measuring the evolution of CO₂ and NH₃. Both the extent of the previously described H₂O evolution and the extent of amide-bond hydrolysis by the evolved H₂O affected the thermal decomposition rate during the initial stage. Such a decomposition rate was evaluated from the TG weight loss rate. The Ser and Asp residue contents increase along with the sericin ratio. This increase leads to accelerated H₂O evolution and amide-bond hydrolysis, resulting in a steeper decline gradient in the TG curve.

Silk sericin, derived from the domesticated silkworm Bombyx mori, exhibits a highly hydrophilic nature due to its rich content of hydrophilic amino acids. This property, along with its excellent film-forming ability in its native high-molecular-weight state, suggests its potential use as an additional skin barrier. High-molecular-weight sericin (HS) can be efficiently sourced from the Sericin Hope strain, which produces cocoons composed exclusively of sericin. This study investigates the potential of HS as a skin protector. For safety, calcium chloride (CaCl₂), a neutral salt, was used to dissolve the Sericin Hope cocoon shells to extract HS. The extracted sericin was then stabilized with glycerol in fluid formulations. A centrifugation method was employed to desalt excess CaCl₂, offering a simpler and faster alternative to conventional dialysis. When a moisturizing cream containing the desalted high-molecular-weight sericin/glycerol composition (HSG) was applied to human skin, it significantly suppressed transepidermal water loss (TEWL) compared to a placebo cream without HSG. This suppression of TEWL underscores HSG’s ability to prevent water transpiration from human skin. The study concludes that HSG could serve as a useful skin protectant to support the skin barrier.

Silk is a natural fiber with excellent mechanical properties. However, the development of higher strength silk is anticipated to expand its applications. The F₁-hybrid of the high-strength silk thread producing silkworm strain MC502 developed through selective breeding and standard silkworm strain J137 exhibits retention of high-strength characteristics of MC502, with markedly better raw silk yield compared to MC502. However, the feeding response of artificial diet and mounting efficiency, which are important for practical use, have not been evaluated. Therefore, we investigated the feeding response of artificial diet and mounting efficiency, in MC502×J137 and J137×MC502. Because both strains ate an artificial diet for general strains of silkworm and reached second instar development, they can use artificial diet rearing during young instars of silkworms: the current mainstream sericultural practice. Furthermore, the mounting efficiency of MC502×J137 and J137×MC502 was better than that of the standard strain, J137×C146. These results demonstrate that no important difficulties exist to hinder the practical use of the F₁-hybrid of MC502 and J137.

Kuwana et al., (2014) reported the breaking stress and breaking strain of spider silk (C515-SpA1x2) respectively as 13.5% and 42.5% higher than those of native silk (C515). However, C515-SpA1x2 produced around 10 years ago exhibited a marked decrease in its tensile properties. After several treatments applied to silk, moisture was observed to play a role in the change of tensile properties of C515-SpA1x2. Furthermore, after immersion in 99.5% ethanol, the difference in slope between C515 and C515-SpA1x2 in the plastic deformation region widened. Both treatments were regarded as strongly affecting the amorphous region. This result indicates that the spider proteins are expressed disproportionately in the amorphous region.