**María Blanco 1,2,\*, José Antonio Vázquez 1,3, Ricardo I. Pérez-Martín 1,2 and Carmen G. Sotelo 1,2**


Received: 29 November 2018; Accepted: 27 December 2018; Published: 9 January 2019

**Abstract:** The small-spotted catshark is one of the most abundant elasmobranchs in the Northeastern Atlantic Ocean. Although its landings are devoted for human consumption, in general this species has low commercial value with high discard rates, reaching 100% in some European fisheries. The eduction of post-harvest losses (discards and by-products) by promotion of a full use of fishing captures is one of the main goals of EU fishing policies. As marine collagens are increasingly used as alternatives to mammalian collagens for cosmetics, tissue engineering, etc., fish skins represent an excellent and abundant source for obtaining this biomolecule. The aim of this study was to analyze the influence of chemical treatment concentration, temperature and time on the extractability of skin collagen from this species. Two experimental designs, one for each of the main stages of the process, were performed by means of Response Surface Methodology (RSM). The combined effect of NaOH concentration, time and temperature on the amount of collagen recovered in the first stage of the collagen extraction procedure was studied. Then, skins treated under optimal NaOH conditions were subjected to a second experimental design, to study the combined effect of AcOH concentration, time and temperature on the collagen recovery by means of yield, amino acid content and SDS-PAGE characterization. Values of independent variables maximizing collagen recovery were 4 ◦C, 2 h and 0.1 M NaOH (pre-treatment) and 25 ◦C, 34 h and 1 M AcOH (collagen extraction).

**Keywords:** fish discards; fish by-products; collagen; cosmetic applications; experimental designs; response surface methodology
