Abstract: Alkylperoxyl radicals derived from the thermal decomposition of 2,2’-azobis(2-amidinopropane)dihydrochloride (AAPH) at different concentrations were used to oxidize myofibrillar protein from grass carp (Ctenopharyngodon idellus), the thermal stability, surface hydrophobicity, zeta potential, turbidity and average particle size of grass carp myofibrillar protein were determined, and the endogenous fluorescence spectrum and atomic force microscope observation were carried out, and the effect of oxidative modification by alkylperoxyl radicals on its heat-induced aggregation behavior was investigated. The results showed that oxidative modification with low concentration (≤ 1.0 mmol/L) of AAPH enhanced the thermal stability of myofibrillar protein, while the opposite effect was observed with high concentration of AAPH (5.0 mmol/L). With the increase in heating temperature, the surface hydrophobicity, zeta potetial, and turbidity of myofibrillar protein in the control and AAPH-treated groups increased first and then decreased. The intrinsic fluorescence intensity declined with increasing temperature, and a red shift of the fluorescence peak was observed, which was more obvious at higher degree of oxidization. The mean particle size of thermal aggregates increased gradually with increasing temperature in the control and 0.2 mmol/L AAPH-treated groups, while it increased first and then decreased in the 1.0 mmol/L and 5.0 mmol/L AAPH-treated groups. The results of atomic force microscopy (AFM) demonstrated that the particle size of thermal aggregates increased with increasing temperature, and the particle size of the control group was relatively smaller and evenly distributed, while the particle size of the oxidized groups was varying and unevenly distributed. Higher degree of oxidization resulted in bigger particle size and smaller number of particles. This study indicated that alkylperoxyl radical could significantly affect the heat-induced denaturation and aggregation of myofibrillar protein from grass carp, and change the morphological characteristics of thermal aggregates.

Key words: grass carp; myofibrillar protein; alkylperoxyl radical; protein oxidation; heat-induced aggregation