Effect of plant extracts on lipid and protein oxidation of mackerel (Scomber scombrus) mince during frozen storage

The effects of different plant extracts [green tea extract (GTE), grape seed extract (GSE), and pomegranate rind extract (PRE)] at a level of 100 ppm equivalent phenolics and butylated hydroxytoluene (BHT) on the changes in quality of fish (Scomber scombrus) mince during 6 months frozen storage at −18 ± 1 °C were investigated. During storage, significant oxidative reactions in both the lipids and proteins were observed with the increase in thiobarbituric acid reactive substances (TBARS) and carbonyls and decrease in sulphydryl groups and protein solubility. BHT and PRE effectively inhibited lipid oxidation as lower peroxide and TBARS values were observed. Moreover, antioxidants added to minced fish significantly reduced protein oxidation compared to control without any antioxidant. The minced fish containing PRE had lower carbonyl and higher sulphydryl contents, but no significant differences for carbonyl and sulphydry contents were observed among antioxidant sources. Protein solubility decreased with increase in storage period. The loss of protein solubility was higher in control samples than in antioxidant treated ones. Among antioxidant sources, PRE was an excellent antioxidant toward both lipid and protein oxidations. Therefore, it could be a potential source of natural antioxidants in minced fish during frozen storage.