Effect of Salt Addition Time on the Nutritional Profile of Thunnus obesus Head Soup and the Formation of Micro/Nano-Sized Particle Structure

In order to investigate the effects of salt on the nutrients and tastes profiles of big eye tuna head soup, the typical nutrients and taste substances were analyzed. The formation and the morphology of micro/nanoparticles (MNPs) were studied using an inverted optical microscope, and the interactions among components in MNPs were studied using a laser scanning confocal microscope. The results showed that the nutrients were dissolved to the maximum in the soup when salt was added at 150 min of cooking. Comparatively, much smaller MNPs with a more stable bilayer were formed at the same salt addition time. Meanwhile, Cl(−) was found to permeate throughout the core and Na(+) bonded with glycosylated molecules, which were dispersed around much smaller MNPs. These results suggested that in addition to promoting the migration of nutrients and taste substances, NaCl also participated in the formation and stability of MNPs in fish head soups.