Microencapsulation of fish oil derived from fish industry side streams to improve stability, efficiency and bioaccessibility of omega-3 fatty acids

Fish processing side streams can be valorized by extracting polyunsaturated fatty acids (PUFA), mainly long-chain omega-3 fatty acids, docosahexaenoic (DHA) and eicosapentaenoic acid (EPA). However, PUFA are prone to oxidation, resulting in undesirable odors and tastes. This study focuses on encapsulation efficiency (EE), oxidation stability, and in vitro bioaccessibility of fish oil-filled powders, produced via freeze-drying. Fish oil, rich in DHA and EPA, extracted from sea bass filleting side streams was used to create nanoemulsions with different biopolymer wall materials, including sodium caseinate, maltodextrin, modified starch, chitosan, and carboxymethyl cellulose (CMC). The impact of homogenization process (1- or 2-step), and wall material on EE, in vitro bioaccessibility, and oxidation stability of microencapsulated fish oil powders was evaluated after a 2-month storage at 25 °C, at an environment of 43 % and 75 % relative humidity (RH). Results showed that emulsions produced with 1-step homogenization had larger droplet sizes (>2150 nm) and lower EE (40.8–69.0 depending on wall material), while 2-step homogenization resulted in 29.7 % higher yields and lower emulsion droplet sizes (272 nm), indicating the impact of the second step. In the case of 2-step homogenization, a mixture of sodium caseinate and maltodextrin achieved a moderate EE of 51.6 %, while combinations of maltodextrin with CMC, modified starch, and chitosan showed much higher yields (82.4 %, 81.0 %, 80.0 %, respectively), due to enhanced matrix-forming capability provided by protein-polysaccharide interactions. The use of these biopolymers significantly enhanced omega-3 in vitro bioaccessibility, particularly maltodextrin and CMC (29.6 %) and chitosan (27.1 %), compared to non-encapsulated fish oil (15.5 %), whereas maltodextrin with modified starch did not show a beneficial effect (9.0 %), possibly due to excessive structural rigidity limiting release. Freeze-drying combined with 2-step homogenization proved effective in preserving omega-3 quality and improving in vitro bioaccessibility. • Freeze-dried nanoemulsions, preserve fish oil stability for 56 d at 25 °C and 43 % RH • Encapsulation efficiency reaches 82.4 % with maltodextrin and CMC mixtures • Two-step homogenization yields encapsulation efficiency of higher than 70 % • Maltodextrin with CMC boosts bioaccessibility of omega-3 fatty acids to 29.64 % • Freeze-drying inhibits lipid oxidation, maintaining stability at 43 % RH and 25 °C