Turning fishery waste into aquafeed additives: Enhancing shrimp enzymes immobilization in alginate-based particles using electrohydrodynamic atomization

Alternative protein ingredients are gradually replacing fish meal in aquafeeds. However, farmed animals often struggle to digest the provided feed, which leads to inefficient nutrient assimilation. This results in a high feed conversion ratio and in water quality deterioration. Fish waste-derived proteases show great potential as bioactive ingredients to enhance protein digestibility. To achieve this, a suitable carrier is essential to include exogenous proteases in the fish feed formulation. Therefore, this research aimed to immobilize a shrimp enzyme extract into different alginate-based microcapsules through electrodynamic atomization and compare their structural and functional properties. Morphology, physicochemical and thermal properties, and in vitro protein release were evaluated for the following microcapsules made from various materials: alginate (A), alginatechitosan (AC), alginate-bentonite (AB), alginate-bentonite previously subjected to a sonication treatment (ABs), and a combination of all materials (ABsC or ABC). The average sizes ranged from 360 to 790 mu m (wet) and 260-516 mu m (freeze-dried), confirming the expected differences, with larger sizes for those including chitosan and bentonite. ABsC proved to be the most suitable system for immobilizing exogenous proteases, as these particles exhibited high encapsulation efficiency in both wet and freeze-dried versions and displayed controlled protein release under typical conditions of the proximal intestine. This was further confirmed through an in vivo trial. Two bioassays were conducted with tilapia (Oreochromis niloticus) (n = 42, 2.6 +/- 0.58 g) to evaluate the distribution of ABsC-rodamine labeled particles in digestive organs and digestive enzyme activity. ABsC remained in the intestine for over 7 h, and a significant increase in total proteolytic activity was observed 60 min after feeding. These findings suggest that ABsC microcapsules could serve as effective carriers for exogenous proteases in feeds for aquaculture.