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This project aims to obtain and characterize protein hydrolysates from the solid residues (dark muscle) and effluents (cooking water) generated from the processing of yellowfin tuna (Thunnus albacares) and evaluate their potential to be applied as organic fertilizer in farming. From the studied viscera (stomach, pyloric blind, liver, pancreas, and intestine), it was found that the pyloric blind of the tuna digestive system represents an adequate source of alkaline proteases that act on the dark muscle of tuna and cooking water, at pH optimum of 10.5 and temperature of 50 °C. The results of SDS-PAGE electrophoresis and enzymatic inhibition indicate that the proteolytic activity exhibited by the enzymatic extract of the pyloric blind of tuna is mainly due to serine protease enzymes, especially trypsin type, and it showed a proteolytic activity similar to that of a commercial protease coming from Bacillus sp. It is possible to use these enzymes in processes that require pH values between 8 and 11 and mild temperatures conditions (30-50°C). The cooking water showed a low yield and high ash content, which may decrease the protein hydrolysates' nutritional quality and functional properties.

Fresh wastes of Mexican headshell shrimp (Litopenaeus vannamei), blue crab (Callinectes bellicosus), and Mexican brown crab (Callinectes sapidus) exoskeletons were autoclaved, dried, and grounded at a particle size of 150 µm. Macerated samples were diluted to ethyl acetate, acetone, cyclohexane, isopropyl alcohol, hexane, heptane, and a combination of hexane-acetone-ethanol-toluene solvents. High-Performance Liquid Chromatography analysis determined the astaxanthin amount in every organic solvent extract. Acetone was the most efficient solvent: 114 µg/g (L. vannamei), 39 µg/g (C. bellicosus), and 44 µg/g (C. sapidus); the mixture of hexane-acetone-ethanol-toluene resulted a idoneus solvent when was used on crab exoskeletons: 39 µg/g (C. bellicosus) and 51 µg/g (C. sapidus). The astaxanthin characterization was performed without saponification, in L. vannamei chromatograms, the amount of trans astaxanthin was 6.23 µg/g (5.47 % of total area), in C. bellicosus was 26.13 µg/g (67 % of total area) and in C. sapidus was 28.42 µg/g (64.6 % of total area).