Extração e caracterização de colágeno e gelatina da pele de jundiá (Rhamdia quelen): uma valorização ao subproduto do pescado

Abstract

Collagen and partially hydrolyzed collagen (gelatin) are products obtained from the connective tissue of animals and are used in many ways in various industrial sectors. The by-products of the fish sector have drawn attention to the production of these materials due to the fact that a part of the population does not consume products originating from mammals, due to sanitary problems involving them and the valorization of the discarded by-product. Thus, the research aimed to extract and characterize acid-soluble collagen (ASC), pepsin-soluble collagen (PSC) and gelatin (GPJ) from silver catfish skin (Rhamdia quelen) (PJ) for which to date data have not yet been found in the literature. Collagen was extracted from PJ by chemical and enzymatic method. First, in PJ, pre-treatment was performed to remove undesirable constituents, using 0.1 M sodium hydroxide, 10% butyl alcohol and 3% hydrogen peroxide, for the removal of non-collagenous proteins, fat and pigments, respectively. Afterwards, it was submitted to the extraction process with 0.7 M acetic acid for 24 hours. The ASC was precipitated in the liquid with 0.8 M sodium chloride, subsequently centrifuged, dialyzed in 0.1 M acetic acid and distilled water, and finally frozen and lyophilized. To obtain the PSC, the extraction residue not solubilized in the liquid was used, submitted to the same process mentioned, but with the addition of 1.5% of pepsin on the initial skin weight. Obtaining GPJ consisted primarily of pre-treatment with 0.2 M sodium hydroxide and 0.1 M acetic acid for skin swelling. Subsequently, GPJ was extracted in distilled water at 45 °C for 9 hours. The analyzes performed for the characterization were chemical composition, hydroxyproline content, yield, Fourier transform infrared spectroscopy (FTIR), gel electrophoresis (SDS-PAGE), differential scanning calorimetry (DSC), determination of pH and color, microscopy scanning electronics (SEM) and some technological properties such as emulsifiers and foamers, in vitro digestibility, solubility and viscosity. For ASC, PSC and GPJ, high protein and hydroxyproline composition were obtained, as well as yields with a proportion of 15.1, 71.3 and 63.9% (on dry basis), respectively. FTIR showed peaks in the amide region commonly found in collagen and gelatin, SDS-PAGE marked bands with high molecular weight and DSC showed high thermal characterization compared to other sources. Scanning Electron Microscopy (SEM) showed dense and non-porous layers in GPJ. As for the technological properties, ASC and PSC showed the ability to be used mainly as an emulsifying property at refrigeration temperature and GPJ showed conditions to provide high viscosity in the products to which it is added. Both samples still showed better solubility in an acidic environment. Therefore, the PJ proved to be a possible source for obtaining collagen and gelatin as an alternative to the traditional ones for cattle and pigs, due to the fact that they present chemical and functional characteristics with a positive effect for the most diverse industrial sectors