Extraction and characterization of collagen from rabbit skin: partial characterization Extracción y caracterización de colágeno de piel de conejo: caracterización parcial Miguel Angel Martínez-Ortiz, Alma Delia Hernández-Fuentes, Diana J. Pimentel-González, Rafael G. Campos-Montiel, Apolonio Vargas-Torres and Gabriel Aguirre-Álvarez* Centro de Investigación en Ciencia y Tecnología de los Alimentos, Instituto de Ciencias Agropecuarias, Universidad Autónoma del Estado de Hidalgo, Av. Universidad Km 1, Rancho Universitario, C.P. 43600 Tulancingo, Hidalgo, México (Received 6 March 2014; final version received 16 July 2014) Extraction and characterization of collagen were carried out in rabbit skins as a new alternative for collagen type I. Acetic acid and pepsin were for the extraction of soluble and insoluble collagen, respectively. The enzymatic treatment yielded higher amount of collagen (71%). The average pH value was 6.3, no matter what the method of extraction was. Denaturation temperature of collagen was found at 36°C approximately in two different techniques: Rheometer and Differential Scanning Calorimetry (DSC). Despite the amount of collagen in solution was low, its viscosity was high because of the hydrodynamic behaviour of collagen molecules. Sodium dodecyl sulphate polyacrylamide gel electrophoresis results showed three different bands that reflected two alpha-chains and one beta-chain with molecular weights of 102, 118 and 220 kDa, respectively. Determination of hydroxyproline gave evidence that the extracted material was collagen. It was concluded that rabbit skin could be an alternative source for the extraction of collagen. Keywords: collagen; rabbit skin; extraction; thermal analysis Se realizó la extracción y caracterización de colágeno en pieles de conejo como una nueva alternativa para colágeno tipo I. Se usaron ácido acético y pepsina para la extracción de colágeno soluble e insoluble respectivamente. El tratamiento enzimático fue el que rindió alta cantidad de colágeno (71%). El pH promedio fue de 6,3 sin importar cuál fue el método de extracción. La temperatura de desnaturalización del colágeno se encontró a 36°C aproximadamente mediante dos diferentes técnicas: Reometría y DSC. A pesar de que la cantidad de colágeno en la solución fue bajo, su viscosidad fue alta debido a el comportamiento hidrodinámico de las moléculas. Los resultados de SDS–PAGE mostraron tres diferentes bandas en las que se reflejaron dos cadenas alfa y una cadena beta con pesos moleculares de 102, 118 and 220 kDa respectivamente. La determinación del contenido de hidroxiprolina dio evidencia de que el material extraído fue colágeno. Se concluyó que la piel de conejo podría ser una alternativa de materia prima para la extracción de colágeno. Palabras claves: Colágeno; conejo piel; extracción; análisis térmicos Introduction Collagen is a product highly demanded and used in the cosmetic, pharmaceutics and food industry due to its molecular properties. This fibrous protein can be obtained from different sources and it is the main component of skins, bones and tendons (Ahmad & Benjakul, 2010; Delvin, 2004; Huang, Shiau, Chen, & Huang, 2011; Jongjareonrak, Benjakul, Visessanguan, Nagai, & Tanaka, 2005; Yan, Li, Zhao, & Qin, 2012). At least 29 different types of collagen with a singular amino acid sequence, structure and func- tion have been identified (Li et al., 2013; Liu, Liang, Regenstein, & Zhou, 2012). Collagen is a biopolymer composed of two alpha- 1 chains and one alpha-2 chain. It is composed of a third part of glycine, and it does not contain tryptophan and lower amounts of tyrosine and histidine (Huang et al., 2011; Kittiphattanabawon, Benjakul, Visessanguan, Nagai, & Tanaka, 2005; Muyonga, Cole, & Duodu, 2004; Schrieber & Gareis, 2007). Collagen is a unique triple helix structure conformed for three polypeptide chains, and it is conformed in quaternary structures. In this structure, it can be found ordered macroscopic ultra structures. Its molecular characteristics obey to the constant repetition of glycine followed by proline and hydroxyproline. The primary structure of collagen type I has a single chain with 1014 amino acids approximately with a molecular weight around 100,000 g mol -1 (Brinckmann, Notbohm, & Müler, 2005; Chien, 1975; Fathima, Madhan, Rao, Nair, & Ramasami, 2004; Nalinanon, Benjakul, Kishimura, & Osako, 2011). The main sources of collagen come from skins and bones of bovine and porcine animals. However, some diseases such as bovine spongiform encephalopathy and foot and mouth disease as well as religious issues had lead the researchers and collagen users to find different sources of collagen (Jongjareonrak et al., 2005; Nalinanon, Benjakul, Visessanguan, & Kishimura, 2007). On the other side, Mexican producers of rabbit meat face a problem related to the proper disposal of by-products such as rabbit skins. The main aim of this project was to use this organic residue as a raw material for the extraction of collagen. Materials New Zealand rabbit skins with 40–50% of water content were used in this experiment. They were obtained from Tulancingo, Hidalgo. Acetic acid reactive grade (99% purity), sodium chlor- ide reactive grade, porcine digestive protease (Pepsin), dialysis membrane tubing with 6–8 kDa molecular weight cut-off, phos- phorous pentoxide (98.5% purity) from Sigma-Aldrich, hydro- chloric acid solution at 50% (v/v), cooper sulphate 0.05 M, sodium hydroxide 1.25 M, hydrogen peroxide at 6%, sulphuric acid 0.9 M and 4-dimethylaminobenzaldehyde at 5%. *Corresponding author. Email: aguirre@uaeh.edu.mx CyTA – Journal of Food, 2015 Vol. 13, No. 2, 253–258, http://dx.doi.org/10.1080/19476337.2014.946451 © 2014 Taylor & Francis Downloaded by [Uni Autonoma del Estado de Hidalgo] at 10:15 25 August 2015