Stability of n-3 fatty acids in fish particles during processing by impingement jet

Abstract

Impingement jet systems have been identified as an alternative to conventional drying and freezing methods. Due to a high gas-particle relative velocity, which enhance heat transfer, product quality is improved. Surface heat transfer coefficients, drying and freezing times of fish particles (mackerel, Trachurus murphyi) were determined under several operation conditions (gas velocity and temperature, particle geometry, material load) using impingement jet. Heat transfer coefficients were estimated in the range of 100–300 W/m 2 K and a correlation of Nusselt and Reynolds numbers were established. Drying and freezing time was significantly influenced by gas temperature and particle geometry. The susceptibility of n-3 fatty acids of fish particles to oxidation during drying and freezing was determined by GC analyses of methyl esters of fatty acids, and results were compared with those obtained by alternative conventional methods. As freezing and drying time increased, n-3 fatty acids losses increased. This suggests that a lower gas temperature with short freezing time would yield a higher quality of fish particle (i.e. with minimal n-3 fatty acids losses) and a higher gas temperature with short drying time would yield a higher quality of product.