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Partial characterization of the digestive enzymes of Pacific bluefin tuna <Emphasis Type="Italic">Thunnus orientalis</Emphasis> under culture conditions
Authors:Ana Matus de la Parra  Antonio Rosas  Juan Pablo Lazo  Maria Teresa Viana
Institution:(1) Departamento de Ecología y Biología Animal, Facultad de Ciencias, Universidad de Vigo, 36310 Vigo, Pontevedra, Spain;(2) Programa de Maestría y Doctorado en Oceanografía Costera, Facultad de Ciencias Marinas, Universidad Autónoma de Baja California (UABC), Ensenada, BC, Mexico;(3) Centro de Investigaciones Científicas de Educación Superior de Ensenada (CICESE), Km 107 carretera Tij-Eda, 22860 Ensenada, BC, Mexico;(4) Instituto de Investigaciones Oceanológicas, Universidad Autónoma de Baja California, Km 107 carretera Tij-Eda, 22860 Ensenada, BC, Mexico
Abstract:The digestive enzyme activities of Pacific bluefin tuna Thunnus orientalis were evaluated for specific activity and characterized for pH and temperature optima in crude extracts of stomach, caecal mass, and proximal, middle and distal intestine. A higher level of alkaline proteolytic activity was detected in the caecal mass than in the proximal intestine. Total alkaline proteases, trypsin, chymotrypsin and leucine aminopeptidase (LAP) were tested. The temperature and pH analyses showed that proteolytic activity as well as lipase were maximal in the alkaline range, with a maximum at pH 9.0 and at temperatures between 35 and 60°C, except for the pepsin, which showed maximum activity at the same temperatures but in the acid range (pH 3.0). The α-amylase activity showed a broader range in activity, both for pH and temperature, with higher activity over the alkaline pH values and higher temperature. The lipase activity seems to be nondependent on bile salts under our assay conditions, resulting in a significant activity reduction in the presence of bile salts. This knowledge will allow the development of a gastrointestinal model (everted intestine) where food or feed will be hydrolysed with the fish’s own enzymes, a project that is being undertaken in our laboratory as a contribution to the development of novel diets for tuna fish.
Keywords:Bile salts  Digestive enzymes  Pacific bluefin tuna  Pancreatic lipase            Thunnus orientalis
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