Fish products and Byproducts Technology

Unit 10 - Fish By- products

10.3. Fish glue
Fish gelatin and fish glue are more or less same and can be prepared from fish skin and fish head. If required, fish skin can be preserved by salting and drying before processing into glue however, fish head should be processed fresh.

Process
Glue from fish skin : Skin whether fresh or salted is washed and soaked in fresh water for the periods in the range of 1- 18 hrs depending on the condition of the material (fresh or salted). Washed skins are immersed in 0.2% caustic soda solution to open the fibre bundles and remove cementing materials. It is then neutralised with HCl and washed again in cold running water. Swollen skin is then transferred to steam jacketed double bottomed kettle covered with an equal weight of water and is heated with steam. Small quantities of acetic acid also may be added to the mixture to hasten the hydrolysis of the stock into glue and to act as a catalyst. Cooking is continued for about 8 hrs and the glue liquid is drawn off from the bottom of the cooker. The second run is made in a similar manner which is then concentrated in open heated pans at atmospheric pressure until the solid content reaches to 50- 55 % and cooled. Sometimes small quantities of volatile essential oils may be added to preserve the glue and to mask the fishy odour.
Glue from fish head: It should be processed fresh with addition of some bleaching agents like sulphurous acid during cooking of the skin some glacial acetic acid is added which softens the head bones.

Uses

• Can be used in furniture
• Box making
• Sizing agent
• Can be used in special cements
• Photo engraving plate manufacture
• Book binding and small repair work etc