Design of active double-layer gel coatings based on furcellaran-gelatin and aqueous butterfly pea (Clitoria ternatea) flower extract for prolonging the shelf-life of salmon (Salmo salar)

Abstract

In the paper, a method for producing innovative and active biopolymer double-layer coatings with a matrix based on furcellaran (FUR) and gelatin obtained from salmon skins (GEL) is presented, as well as an aqueous extract of clitoria flower (Clitoria ternatea) (BP). The first layer was based on an innovative combination of gelatin and furcellaran, enriched with an aqueous extract of clitoria flowers, characterized by antibacterial properties. The second layer was a pure combination of these two polymers, designed to provide protection against undesirable external factors. Hydrogels with different contents (1; 1.5; 2%) of the clitoria flower extract (1BP, 2BP, 3BP) inhibited the growth of gram-positive bacteria, and demonstrated antioxidant activity at the level of 1.80 mM Trolox/mg (FRAP method) and 47.57% (DPPH method). The analysed coatings in the applied deformation conditions showed properties typical of gels, with dominance of elastic properties over viscous ones. The shape of the flow curves of the analysed gels is typical for shear thinning non-Newtonian fluids, for which the apparent viscosity decreases with increasing shear rate. The influence of using hydrogels as active coatings on the quality of salmon fillets (Salmo salar) during their refrigerated storage was assessed. It was found that the coating with added clitoria extract had an inhibitory effect on the development of microorganisms during the whole storage period of the fish. The obtained active coatings show significant high applicative potential, however, further research should be carried out using other model food products.