Physical, biochemical, densitometric and spectroscopic techniques for characterization collagen from alternative sources: A review based on the sustainable valorization of aquatic by-products

•Collagen is a versatile polymer and it is present in the fishery and aquiculture waste.•Conventional and non-conventional analysis for the characterization are reviewed.•The method of extraction can alter the collagenous molecule structure.•FTIR, Raman, CD, X-ray diffraction are attractive characterization analysis.•The properties of each collagenous molecule signal viability and type of industrial application. Collagenous biopolymers can be analyzed using physic-chemical, densitometric, and spectroscopic analysis to obtain their main characteristics, aiming at their biotechnological manipulation. Collagen extracted from fishery resources is a product of high added value, with potential use in food, biopharmaceutical and cosmetic industries. Some factors make the use of the polymer from fishery resources promising, such as: high availability; greater ontogenetic distance between fish and humans; absence of sociocultural barriers; and absence of toxicity. The collagen extraction method (acid-soluble, pepsin-soluble, electrodialysis, ultrasound, isoelectric precipitation) will directly influence its properties. Thus, this work aims to provide an overview of the extraction methods, characterization techniques (solubility, zeta potential, viscosity, thermogravimetry, differential scanning calorimetry, SDS-PAGE, densitometry, gel strength, centesimal composition, color, aminogram, hydroxyproline determination, X-ray diffraction, circular dichroism, ultraviolet, Raman, and FTIR spectroscopy), and potential analysis with a focus on aquaculture and fisheries sources, through a compilation of scientific information that can be useful to guide aquatic biotechnology professionals, considered that its properties are similar to collagen extracted from mammals. [Display omitted]