Preliminarily Study on Hydroxyproline Content of Purple-spotted Bigeye (<i>Priacanthus tayenus</i>) Scaly Skin and Its Gelatine Quality

The investigation of alternative raw materials for gelatine production from fishery industry by-products has gained attention due to the increasing demand for gelatine and the importance for sustainable practices. This study aims to determine the optimal hydrochloric acid (HCl) concentration for mineral removal during pre-treatment, assess hydroxyproline content at various processing stages and characterise the resultant gelatine. The methodology involved pre-treatment of the materials with 0.1 M sodium hydroxide (NaOH) to remove non-collagen proteins, followed by mineral extraction using varying HCl concentrations (0.25, 0.5, 0.75 and 1 M). The process included swelling in 0.2% citric acid for 12 h and gelatine extraction at 65°C for 7 h. The results indicated that 0.25 M HCl was most effective for mineral removal. The hydroxyproline analysis showed an insignificant increase (0.088 mg/mL-0.103 mg/mL) from the pre-treatment stage to the final gelatine product. The physicochemical properties of the liquid gelatine, including yield (6.5 ± 0.39%), pH (6.55 ± 0.11), and gel bloom strength (174 ± 8.54 blooms) conformed to Gelatin Manufacturers Institute of America (GMIA). Functional groups confirmed the presence of gelatine-specific, such as amides A, B, I, II and III. The molecular profile is comparable to commercial gelatine, with α1 chains at 130 kDa, α2 chains at 115 kDa, and β chains at 235 kDa. The gelatine derived from the scaly skin of purple-spotted bigeye exhibits promising attributes, aligning with commercial standards and highlights the potential of fishery by-products as a sustainable and halal source of gelatine.