Int Aquat Res (2010) 2: 173-181 (Special Issue of AquaMedit 2010 Conference, Greece) ISSN 2008-4935 Available online at www.intelaquares.com International Aquatic Research Optimization of enzymatic hydrolysis of yellowfin tuna Thunnus albacares viscera using Neutrase Ali Motamedzadegan 1* , Bahareh Davarniam 2 , Gholamhassan Asadi 2 , Abdolmohammad Abedian 3 , Mahmoudreza Ovissipour 4 1 Department of Food Science, Sari Agricultural Sciences and Natural Resources University, Sari, Iran. PO Box: 578 2 Department of Food Science and Technology, Science and Research Branch of Tehran, Islamic Azad University,Tehran, Iran 3 Department of Fisheries, Faculty of Natural Resources and Marine Sciences, Tarbiat Modares University, Iran 4 Department of Fisheries, Gorgan Agricultural Sciences and Natural Resources University, Gorgan, Iran ــــــــــــــــــــــــــــــــــــــــــــــــــــ ـــــــ ـــــــــــــــــــــــــــــــــــــــــــــ ـــــــــ ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ Abstract Enzymatic hydrolysis of yellowfin tuna visceral protein using Neutrase was studied by response surface methodology using factorial design. Degree of hydrolysis (DH; %) has been estimated as a response surface to the hydrolysis conditions (enzyme activity, reaction temperature, and reaction time). R 2 of 0.91 for the mathematical model indicated that 91% of the variability within the range of values studied could be explained by the model. Lack-of-fit test revealed a non-significant value for the model, indicating that the regression equation was adequate for predicting the degree of hydrolysis under any combination of the variables (P < 0.05). Enzyme activity of 39.61 AU/kg protein, temperature of 53° C, and hydrolysis time of 141min were found to be the optimal conditions to reach 30% degree of hydrolysis. The tuna visceral protein hydrolysates had relatively high protein (74.56%), and low lipid (1.86%) content. The chemical score of the hydrolysate indicated that it fulfils adult human nutritional requirements except methionine. Lysine and methionine were the first and the second limiting amino acid in that order. Phenylalanine was predominant amino acid in the hydrolysates with respect to common carp requirement. Keywords: Fish protein hydrolysate, Tuna visceral protein, Neutrase, Optimization, RSM ــــــــــــــ ــــــــــــــــــــــــــــــــــــــــــــ ـــــــ ـــــــــــــــــ ـــــــــ ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ Introduction Recognition of the limited biological resources and increasing environmental pollution have emphasized the need for better and more value-added utilization of the under-utilized fish and the by-products from the fishing industries (Geurard et al. 2002). Commercially viable means for totally utilizing aquatic animals and using them as food have not been successful. More than 100 million tons of fish per year are being harvested (FAO 2006); close to the maximum sustainable yields, of which 29.5% is transformed into fishmeal (Kristinsson and Rasco 2000a). More than 15% of the harvested biomass is considered processing waste, and is not used for human consumption. Nowadays, industries are no longer permitted to discard their wastes directly to the environment. This results in refining costs for the materials before discarding. Enzyme utilization to hydrolyze food proteins is a * Corresponding author. Email: amotgan@yahoo.com. Tel: +98-151-3822749, Fax: +98-151-3822577. © 2010, IAU, Tonekabon, IAR-10-1155.