ORIGINAL ARTICLE Physicochemical Characterization of Protein Hydrolysates Produced by Autolysis of Jumbo Squid (Dosidicus gigas) Byproducts Joe Luis Arias-Moscoso & Amir Maldonado-Arce & Ofelia Rouzaud-Sandez & Enrique Márquez-Ríos & Wilfrido Torres-Arreola & Hisila Santacruz-Ortega & Martha Gabriela Gaxiola-Cortés & Josafat Marina Ezquerra-Brauer Received: 11 February 2014 /Accepted: 13 October 2014 # Springer Science+Business Media New York 2014 Abstract The physicochemical characteristics of protein hy- drolysates of jumbo squid (Dosidicus gigas) byproducts (JSBP) produced by endogenous proteases at two different pH values (5.0 and 7.0) were studied using destructive and nondestructive methods. Reaction mixture samples were col- lected at different interval times during hydrolysis to monitor changes in the level of hydrolysis (DH) using the OPA meth- od, the protein peptide molecular masses (MM), and SDS- PAGE. The DH increased from 3.5 to 11.2 % at pH 5.0 and from 4.8 to 17.5 % at pH 7.0. Both pH treatments exhibited similar degradation patterns with progressive proteolysis and, after 120 min of hydrolysis, yielded hydrolysates that contained MM <45 kDa proteins. It was detected lower hy- drophobic amino acid exposure for the protein hydrolysates prepared at pH 5.0 compared with the hydrolysates at pH 7.0. In several wavebands, higher wavenumbers were observed in the FT-IR spectra for the pH 5.0 hydrolysates. Nine different equivalent protons were observed in the NMR spectra for both hydrolysates; these protons might belong to amino acid side chains. SEM showed substantially lower particle size for the JSBPs after hydrolysis at pH 7.0. The hydrolysate zeta poten- tials were -29.4 mV at pH 7.0 and -10.5 mV at pH 5.0. The pH 5.0 hydrolysates exhibited lower endothermic resistance and hydrophobicity (SoANS) compared with the pH 7.0 hy- drolysates. This biophysical characterization enhances the understanding of jumbo squid byproduct hydrolysate physio- chemical properties, which will aid in determining the proper use of these hydrolysates. Keywords Autohydrolysis . Squid . Byproducts . Biophysical properties Introduction Protein hydrolysates are a mixture of amino acids prepared by hydrolyzing a protein using acid or alkali conditions or en- zymes [1]. These products have extensive applications in food, medicine, feed and industrial products [2]. Either chem- ical (using acids or bases) or biological (using proteases) means can be used to generate the hydrolysates [1]. Among these options, protease hydrolysis is most promising for de- velopment because it yields products with high functional and nutritive value [3]. Fish protein hydrolysates are particularly notable for their high nutritive value and functional properties [4], and they have been extensively studied since the 1960s [1]. The high nutritive value and functional properties of fish hydrolysates have spawned a new industry that produces different products for diverse industries (food, feed, and medicine, among others) [5]. Moreover, during the typical seafood cleaning and dressing process, high quantities of protein are discarded, J. L. Arias-Moscoso : O. Rouzaud-Sandez : E. Márquez-Ríos : W. Torres-Arreola : J. M. Ezquerra-Brauer (*) Departamento de Investigación y Posgrado en Alimentos, Universidad de Sonora, Hermosillo, México e-mail: ezquerra@guayacan.uson.mx A. Maldonado-Arce Departamento de Física, Universidad de Sonora, Hermosillo, México H. Santacruz-Ortega Departamento de Investigación en Polímeros y Materiales, Universidad de Sonora, Hermosillo, México M. G. Gaxiola-Cortés Departamento de Manejo de Zonas Costeras, Unidad Multidisciplinaria de Docencia e Investigación del SISAL, Universidad Nacional Autónoma de México, Mexico, Mexico Food Biophysics DOI 10.1007/s11483-014-9374-z