Tuna (Thunnus spp.) and tuna-like species are significant sources of food and thus play a very important role in the economy of many countries. More than 48 species of tuna swarm the Atlantic, Indian, and Pacific Oceans, and the Mediterranean Sea. The annual global production of tuna has undergone a marked increase from less than 0.6 million metric tons in 1950 to almost 4.5 million metric tons in 2007. Tuna generally is processed as raw fish flesh and marketed as loins/steaks or as a canned food. In the tuna canning process, only about one-third of the whole fish is used. Thus, the canning industry generates as much as 70% solid wastes from original fish materials. This waste consists of muscle (after loins are taken), viscera, gills, dark flesh/muscle, head, bone, and skin. Conventionally, these protein-rich by-products from the tuna industry are processed into low market value products, such as fish meal and fertilizer. However, a promising alternative use of these by-products is as functional food ingredients. Fish protein hydrolysate (FPH), which is obtained through hydrolysis of tuna waste, can be used as an ingredient in food industries to provide functional effects such as whipping, gelling, and texturing properties. Recently, FPH was found to be a potential source of antioxidants (such as peptides with anticancer properties), antianemia compounds, and components for use in microbial growth media. This article is intended to summarize the existing knowledge about FPH, highlight some pertinent information related to the tuna fishing industry, and provide a new outlook on the production and applications of FPH.

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The goal of this study was to optimize enzymatic hydrolysis of the dark flesh of skipjack tuna (Katsuwonus pelamis). Alcalase 2.4 L was used as the hydrolytic enzyme at various concentrations (1, 1.5, 2, 2.5 and 3% w/w) at pHs from 6 to 10, temperatures from 35 to 75°C and times of 2 to 6 h. The experiment was performed following a five-level second-order central composite design with six replications at the center points. The high coefficients of determination for degree of hydrolysis (R2 = 0.8909) and free tryptophan content (R2 = 0.9732) indicate the suitability of the design for predicting the responses. The optimum hydrolytic conditions predicted by the response surface methodology were 2% Alcalase at pH 8.86 and 65.4°C for 5.74 h. These conditions resulted in an experimental degree of hydrolysis of 20.74% and free tryptophan content of 102.23 mg kg-1

The goal of this study was to optimize enzymatic hydrolysis of the dark flesh of skipjack tuna (Katsuwonus pelamis). Protamex® was concentrations (1%, 1.5%, 2%, 2.5% 40 to 60 o C and times of 2 to 6 h. The experiment was performed following a five second-order central composite design w coefficients of determination for degree of hydrolysis (R2 = 0.9674) and free tryptophan content (R2 = 0.9426) indicate the suitability of the design for predicting the responses. The optimum hydrolytic conditions predicted by the response surface methodology were 3% Protamex® at pH 6.57 and 58 °C for 4 h. These conditions resulted in an experimental degree The goal of this study was to optimize enzymatic hydrolysis of the dark flesh of skipjack tuna (Katsuwonus pelamis). Protamex® was used as the hydrolytic enzyme at various centrations (1%, 1.5%, 2%, 2.5% and 3% w/w) at pHs from 6.5 to 8. Protamex® at pH 6.57 and 58 °C for 4 h. These conditions resulted in an experimental degree free tryptophan.