Chitosan-based biodegradable coatings for securing nutrients in extruded fish feed pellets

The aim of this study was to evaluate the effect of a biodegradable chitosan-based coating on the quality parameters of sinking fish feed. The feed pellets had a diameter of 5 mm and were coated with 1 % and 2 % chitosan. Coated and uncoated (control) pellets were evaluated for their dimensions (length, diameter), weight, sinking velocity, floatability, hardness and water absorption index. Vitamin C loss during sinking in artificial sea water was kinetically modelled using Fick's 2nd law. The coatings reduced the loss of vitamin C when the pellets were immersed in seawater, the diffusion coefficients for vitamin C loss were calculated to 1.10×10 −10 , 4.50×10 −11 , and 1.20×10 – 11 m 2 /s for uncoated pellets, pellets coated with 1 % and 2 % chitosan, respectively. In addition, the chitosan coating led to a significant decrease in the water solubility index, to 26.87 %, 11.53 % and 9.91 % for control samples and pellets coated with 1 % and 2 % chitosan, respectively. However, chitosan coating increased the water activity of the pellets and resulted in a darker colour compared to the control pellets (lower lightness). The research demonstrated that the application of chitosan as a biodegradable coating may significantly reduce nutrient loss in water during sinking without affecting the main physical and mechanical properties of the pellets.