Aldehyde formation in frozen mackerel (Scomber scombrus) in the presence and absence of instant green tea.

The effect of frozen storage on lipid peroxidation in Atlantic mackerel (Scomber scombrus) stored for up to 26 weeks at -10 or -80°C (control), with and without green tea antioxidants, was investigated. Hydroperoxides (PV) and aldehydes (TBARS) were measured by HPLC and LC-MS and hexanal by GC. There was an increase in peroxide value which was associated with an increase in aldehydes, followed by hexanal increase with storage time and at a higher temperature of -10°C compared with samples stored at -80°C. Although TBARS is a common assay used to follow malondialdehyde formation, other aldehyde products can also react with thiobarbituric acid to give the red chromogen. Analysis of aldehyde-TBA adducts by LC-MS confirmed the presence of malondialdehyde and, in particular, we report the production of gluteraldehyde for the first time in stored frozen fish. Green tea (at 250ppm) substantially slowed down the oxidation process, whereas at 500ppm it was less effective.