Abstract: Objective: The aim of this study was to address the effect of rosemary extract and ascorbic acid separately and in combination on redness (a* value) and lipid oxidation in prepared chicken steak for the purpose of delaying discoloration and lipid oxidation during its storage. Methods: The concentrations of rosemary extract and ascorbic acid in the marinade were optimized using one-factor-at-a-time method and response surface methodology based on central composite design. The responses were a* value and thiobarbituric acid reactive substances (TBARS) value. Results: The addition of rosemary extract and ascorbic acid had significant influences on both a* and TBARS values. The coefficients of determination (R2) of the two quadratic polynomial regression models were found to be 0.932 0 and 0.886 3, respectively, and lack-of-fit test revealed a non-significant value for the models (P > 0.05), indicating that the models appropriately explain the variability of the observed responses. The linear term of rosemary extract (P < 0.05) and the linear and quadratic terms of ascorbic acid (P < 0.01) significantly influenced a* value, and the linear term of rosemary extract (P < 0.01) and the quadratic term of ascorbic acid (P < 0.05) significantly influenced TBARS value. Conclusion: The highest a* value and the lowest TBARS value were simultaneously obtained by the addition of rosemary extract at 0.198 g/kg and ascorbic acid at 0.255 g/kg. After 50 d storage, a* and TBARS values were experimentally measured as 21.88 and 0.59 mg/kg, which were consistent with the fitted results.

Key words: rosemary extract, ascorbic acid, discoloration, lipid oxidation, prepared chicken steak, central composite design