105 Czech J. Food Sci., 34, 2016 (2): 105–110 Food Chemistry and Safety doi: 10.17221/320/2015-CJFS In recent years, the search for naturally occurring molecules that can act as antioxidants has become one of the fastest growing fields of study in food chemistry worldwide (Gil-Chavez et al. 2013) because of the increase in the number of oxidative stress-related diseases (Joudalová & Réblová 2012). The unbal- ance between free radicals and antioxidants is one of the primary causative agents, and improving the antioxidant status will decrease the risks of developing several types of illnesses (J oudalová & Réblová 2012). Analyses such as the serum total antioxidant capacity (TAC) indicate the cumulative effect of all antioxidants in blood (Prior & Cao 1999). High TAC values may suggest greater protection against oxidative stress-related diseases; however, it may also be part of an adaptation process to an increase in oxidative stress at early stages (Prior & Cao 1999) of DNA and protein damage due to the production of radicals; by-products in lipid peroxidation, mainly malondialdehyde (MDA) is an example. Low levels of serum MDA are frequently linked to low prob- abilities of developing diseases that are associated with oxidative stress (Niedernhofer et al. 2003). Meanwhile, one of the most frequently studied components of marine products is collagen, which is a stromal protein. Since collagen shows resistance to hydrolysis, working with a digestible protein such as gelatine is preferable. Gelatine is a soluble protein whose functionality is observed in both the native form of the protein and its hydrolysates. They have been proved to have antioxidant, antihypertensive, and anticancer activities, among many other charac- teristics (Alemán et al. 2011). The main by-product from jumbo squid that has been studied is the skin; however, fns and arms, which are also considered discards, are rich in collagen and other proteins (Tor- res-Arreola et al. 2008). In the literature, there is scarce information about the functional properties of Squid By-product Gelatines: Effect on Oxidative Stress Biomarkers in Healthy Rats Jesús Enrique CHAN-HIGUERA 1 , Rosario Maribel ROBLES-SáNCHEZ 1 , Armando BURGOS-HERNáNDEZ 1 , Enrique MáRQUEZ-RíOS 1 , Carlos Arturo VELáZQUEZ-CONTRERAS 2 and Josafat Marina EZQUERRA-BRAUER 1 1 Department of Food Research and Graduate Program and 2 Department of Chemical and Biological Sciences, University of Sonora, Hermosillo, Sonora, Mexico Abstract Chan-Higuera J.E., Robles-Sánchez R.M., Burgos-Hernández A., Márquez-Ríos E., Velázquez- Contreras C.A., Ezquerra-Brauer J.M. (2016): Squid by-product gelatines: Effect on oxidative stress biomarkers in healthy rats. Czech J. Food Sci., 34: 105–110. Gelatines from three different jumbo squid ( Dosidicus gigas) by-products (fins, arms, and skin) were compared based on their chemical and biochemical properties (amino acid composition, molecular weight distribution, and in vitro digestibility), antioxidant capacity (ABTS + and ORAC assays) and effect on oxidative stress biomarkers (serum an- tioxidant capacity (TAC) and serum malondialdehyde levels (MDA)) in healthy rats. Gelatine from the skin showed the highest polar and imino amino acid contents and a higher proline hydroxylation degree. Gelatine β-component was not detected in either fins or arms. These differences may explain the higher in vitro digestibility and higher an- tioxidant capacity (before and after digestibility) of the skin gelatine. Fin gelatines decreased TAC-ORAC values. All obtained gelatines decreased the MDA levels. Jumbo squid gelatine, administered during feeding, may help decrease a breakdown product of spontaneous lipid peroxidation in serum. Keywords: colagen derivates; Dosidicus gigas; antioxidant capacity; in vitro assays