*2.1. Hydroxyproline and Collagen Content of Raw Materials*

The quantification of total collagen content from hydroxyproline (Hyp) was determined as per the earlier method [15]. In general, the PSC had a high content of Hyp than ASC, similarly the collagen content was also high in PSC. The hydroxyproline and collagen contents of PSC and ASC were about 120 and 106.36 mg/g and, 896.738 and 793.49 mg/g, respectively (Figure 1). The present result was in accordance with the hydroxyproline content of collagen from silvertip shark (113 and 105 mg/g) and brownbanded bamboo shark (103.71 mg/g) [1,16]. The hydroxyproline content may depend on the seasonal variations and body temperature of the fish species.

**Figure 1.** Hydroxyproline and collagen content of blue shark skin collagen. ASC-Acid soluble collagen, PSC-Pepsin soluble collagen. \* *p* < 0.05 vs. ASC.
