Sericin
Also searched as: silk gum, silk glue, sericine, gum silk
The water-soluble, serine-rich glycoprotein gum that coats and binds the two fibroin strands of a raw silk filament and is largely removed during degumming.
In detail
A raw silk filament is two fibroin brins wrapped in layers of sericin. The gum glues the filament into the cocoon structure and makes raw silk stiffer and less lustrous than finished silk. Sericin is hydrophilic because many of its amino acids carry polar side groups, especially serine, aspartic acid and glycine residues, and it dissolves in hot water, particularly with soap, alkali or enzymes. Degumming exploits this solubility, removing most of the sericin to reveal the softer, brighter fibroin beneath. Because sericin is a large fraction of cocoon mass, its removal has a major effect on yarn weight.
The science and numbers
Sericin makes up roughly 20 to 30% of Bombyx mori cocoon mass. It is encoded by several genes, including Ser1, Ser2 and Ser3, whose alternative splicing produces a family of polypeptides ranging from about 20 to 400 kDa; Ser1 is a single-copy gene of about 23 kb with nine exons. Its 18 amino acids are dominated by residues with hydroxyl, carboxyl and amino side groups, and serine commonly accounts for around 30% of the total, which explains both the name and the protein's strong affinity for water. Conventional soap and detergent degumming partially hydrolyzes sericin and lowers its molecular weight, so protein recovered from degumming wastewater is more degraded than sericin extracted under milder conditions.
A practical example
A weaver weighs a skein of raw silk, degums it in a hot soap bath, dries it and weighs it again, recording a loss of roughly a quarter of the original mass. Most of that loss is sericin. Another skein is only partly degummed, leaving some gum in place, and it keeps a crisper, firmer hand. The exercise shows that degumming is a controllable finishing choice rather than an all-or-nothing step.
What to distinguish
Sericin content varies with silkworm strain and with how it is measured, so percentages differ between studies. The extraction method also changes the recovered protein: hot water, soap, alkali and enzymes hydrolyze sericin to different degrees, which is why sericin sold for cosmetic or biomedical use is not one uniform material. Residual sericin on a silk yarn is not a defect in itself, and marketing claims about its skin benefits need separate evidence.
Origins and history
The name comes from the Latin sericum, silk, a word linked in classical sources to the Seres, the name Greek and Roman writers gave to the people of the eastern silk-producing lands. Removing the gum from raw silk is an old practice wherever silk was worked, but interest in sericin as a material in its own right is recent. Research since the late 2000s has studied it for cosmetic and biomedical uses, often proposing recovery from degumming effluent that was historically discarded.
Related terms
Sources & further reading
- BioMed Research International (Wiley): Silkworm sericin, properties and biomedical applications (Kunz et al., 2016)
- Frontiers in Bioengineering and Biotechnology: Silk sericin and its biomedical applications, extraction methods and genetic insights (Ser1 to Ser6)
- ScienceDirect: Sericin coats of silk fibres, a degumming waste or future material?
- Progress in Polymer Science (ScienceDirect): Natural protective glue protein, sericin bioengineered by silkworms
Technical references reviewed 2026-09-22. Examples are illustrative. Industry organizations and manufacturers describe their own fields; their references are not independent product endorsements. Figures are approximate and depend on the stated test conditions.