Effect of storage on oxidative quality and stability of extruded astaxanthin-coated fish feed pellets

• Astaxanthin is protected against degradation in the pellet core structure.
• Astaxanthin demonstrates important self-protective properties.
• The pellet structure can be considered as delivery systems for the coating.
• Surface/core ratio has a significant effect on the self-protective properties.

This study examined the stability of extruded and astaxanthin-coated fish feed pellets during storage in a light box at 28 °C and 620 lx. Seven groups of fish feed pellets were vacuum coated with fish oil that contained levels of astaxanthin ranging from 0 to 100 ppm. To equalize differences in the conditions for the fish feed pellets inside the light box, the samples were systematically circled during the experimental storage period of 183 days. The degradation of astaxanthin was monitored using multi-spectral images, captured 28 times in the course of the storage period. Additionally, samples were collected at storage day 8, 15, 22, 92 and 183 for chemical determination of the astaxanthin concentration. The degradation of astaxanthin was shown to primarily be affected by light and limited to occur at the surface of the fish feed pellets, whereas the astaxanthin embedded in the core of the pellets was comparatively protected against degradation. Furthermore, the initial concentrations of astaxanthin influenced the degradation per se, signifying self-protective properties of astaxanthin.