Fish products and Byproducts Technology

Unit 10 - Fish By- products

10.2. Shark leather
Skin from fish and other aquatic animals offer a potential source of leather in the countries where climatic conditions and topography do not allow raising of goats and sheep’s. Few such countries are Japan, Vietnam Thailand, Korea, Norway, Sweden etc. Skins of shark can be processed into fine leather suitable for manufacture of fancy items. The main component of skin is collagen. Collagen constitutes about 90% of all nitrogenous matter of the skin. Leather tanned from Indian shark skin is about one and half times superior to that from cow hides in strength and durability. Shark skin has a protective coating of a calcareous deposit known as “shagreen”. It can be used as a suitable raw material for manufacture of suitcases, shoes, belts, vanity bags etc.
Both demersal as well as pelagic varieties are suitable for the leather production

Process
There are following operations for making of leather from shark skin

• Curing of skin: The skin is removed from shark body and cured with salt by spreading it with flesh side or skin may also be preserved by sun drying in tropical countries like India. More care is necessary for removal of skin from body of fish.
• Washing and soaking: skins are washed and soaked which plumps up skin and hides restoring them into their original texture and consistency.
• Liming: liming is done to remove epidermis layer using calcium hydroxide which attacks epidermal proteins exclusively but dermal layer containing collagen is not affected by liming
• Bating: bating is carried out with trypsin which hydrolyses elastin protein of the skin.
• Tanning: basically there are two principal types of tanning which includes vegetable tannage and mineral tannage. Vegetable tannage gives heavy leather while mineral tannage gives soft and pliable leather. Mineral tannage is preferred for shark skin where active ingredients are tannin which areglucosides of polyphenol.
• Drying: using tunnel drier preferably at slow rate.
• Finishing operations: lubrication of fibre with fat - liquor colouring and shading by combination of dyes

Removal of shagreen is necessary as it makes the leather rough.