Abstract
This piece of research evaluates the presence of protease inhibitors in the macroalga Ulva ohnoi and provides an initial overview of their mode of action. The ability of Ulva protease inhibitors to inhibit digestive proteases of three marine fish species, as well as their capacity to hamper the hydrolysis of a reference protein by those fish proteases, were assessed. In addition, thermal stability and the mode of inhibition on trypsin and chymotrypsin were also studied. Dose-response inhibition curves and in vitro protein hydrolysis assays revealed a noticeable inhibition of fish enzymes when Ulva concentration increased in the assay. The thermal treatment of Ulva reduced markedly the inhibitory effect on fish digestive protease. Finally, Lineweaver–Burk plots indicated that trypsin and chymotrypsin inhibition consisted of a mixed-type inhibition mechanism in which the inhibitory effect depends on Ulva concentration. Overall, the results confirmed the presence of protease inhibitors in Ulva, though heat treatment was enough for inactivating these compounds.
Highlights
Anti-nutritional factors (ANFs) can be defined as substances that, by themselves or through their metabolic products, can exert negative effects on food utilization and interfere with the normal growth, reproduction and health of fish [1]
The results confirmed the presence of protease inhibitor in crude
It was found that the amount of Ulva able to cause the inhibition of 50% digestive protease activity (IC50 ) ranged from 0.6 to 0.9 mg Ulva per unit of proteolytic activity (UA)
Summary
Anti-nutritional factors (ANFs) can be defined as substances that, by themselves or through their metabolic products, can exert negative effects on food utilization and interfere with the normal growth, reproduction and health of fish [1]. From a nutritional point of view, the presence of these compounds in diets is responsible for the deleterious effects on the absorption of nutrients and micronutrients, which may interfere with the normal functioning of certain organs [2]. This fact is one of the most important issues derived from using novel dietary ingredients in aquaculture, as well as one of the main drawbacks that limits their practical application in formulated feeds [3,4]. Some species of the genus Ulva have been successfully evaluated as a dietary ingredient in some farmed fish species, such as gilthead seabream (Sparus aurata) [9,10], Senegalese sole (Solea senegalensis) [8,11] or seabass (Dicentrarchus labrax) [12], with promising results in terms of growth, survival and nutrient utilization
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