sericin
noun
ser·i·cin ˈser-ə-sən 
: a gelatinous protein that cements the two fibroin filaments in a silk fiber
Example Sentences
Recent Examples on the Web The formula features the brand's silk protein, which is a blend of sericin and fibroin. 
Sarah Han, Allure, 14 June 2022 This luxurious ingredient contains two proteins — sericin and fibroin — that can benefit skin health, according to Morgan Rabach, M.D., a clinical assistant professor of dermatology at Mount Sinai in New York City. Jennifer Hussein, Allure, 1 Mar. 2022 Next, the cocoons are boiled to dissolve the sericin, the gummy substance holding the cocoon together, so the thread can be easily unwound. Jennifer Billock, Smithsonian, 12 Apr. 2017
Sarah Han, Allure, 14 June 2022 This luxurious ingredient contains two proteins — sericin and fibroin — that can benefit skin health, according to Morgan Rabach, M.D., a clinical assistant professor of dermatology at Mount Sinai in New York City. Jennifer Hussein, Allure, 1 Mar. 2022 Next, the cocoons are boiled to dissolve the sericin, the gummy substance holding the cocoon together, so the thread can be easily unwound. Jennifer Billock, Smithsonian, 12 Apr. 2017 Word History
Etymology
International Scientific Vocabulary, from Latin sericum silk
First Known Use
1859, in the meaning defined above