Extraction of acid-soluble and pepsin-soluble collagens from common carp scales (Cyprinus carpio) and determination of their characteristics

Collagen is the most abundant and important structural protein in the connective tissue of animals, the production of which is of great importance in the fields of medicine, cosmetics and food. Due to religious restrictions as well as common diseases between livestock and humans, today collagen extraction has turned to other sources, especially aquatic sources. Therefore, the aim of this study was to extract collagen by conventional acidic and enzymatic methods from common carp scales and determine its characteristics in order to make optimal use of this waste to produce valuable products and find alternatives to collagen obtained from land animals. 

Acid-soluble collagen (ASC) and pepsin-soluble collagen (PSC) were extracted from common carp scales (Cyprinus carpio) and their properties were determined. Common carp scales were prepared with the use of 0.5 M acetic acid and pepsin enzyme. Finally, the extracted collagens were lyophilized and after calculating the extraction efficiencies, their characteristics were determined by electrophoresis tests, UV spectroscopy, X-ray diffraction and isoelectric point determination.  

The results showed that the extraction efficiencies of ASC and PSC were 1.9% and 2.96% (based on dry weight), respectively, which means digestion with pepsin could increase collagen efficiency up to 1.54 times. The results of SDS-PAGE analysis showed that both ASC and PSC are type I collagen and are composed of α1, α2 and β in the (α1) 2α2 chain structure; the isoelectric point of collagens was in the pH range of 5-6. The maximum absorption peak of the UV spectrum of collagen was observed at 235 nm. Although pepsin enzyme (1% dry weight of scales) increases efficiency without significant changes in collagen native structure, but its use for mass production of type I collagen in Iran is not recommended unless self-sufficiency and reduction of pepsin price achieved, while collagen extraction by acidic method is very simple and research to design a production line for this method is recommended. Common carp scales have the potential to be used as an alternative source of collagen in the food and health-pharmaceutical industries. These results can provide a solution to control the waste of the aquatic processing industry in creating environmental pollution, as well as producing a high value-added product from common carp scales.