Effect of temperature on the antioxidant activity of phenolic acids

Abstract

The effect of temperature on the antioxidant activity of phenolic acids (gallic, gentisic, protocatechuic, syringic, vanillic, ferulic, caffeic, and sinapic; 0.5 mmol/kg) was studied in pork lard, using an Oxipres apparatus, at a temperature range of 90°C to 150°C. The antioxidant activity of all studied compounds decreased with increasing working temperature, whereas a linear relationship (P < 0.01) existed between temperature and the antioxidant activity in all cases. However, the relative rate of the antioxidant activity decrease with increasing temperature (i.e. in comparison with the activity at 90°C) was not the same for all studied phenolic acids. Easily oxidisable phenolic acids (i.e. gallic, gentisic, protocatechuic, and caffeic) showed a slower decrease in antioxidant activity with increasing temperature (in comparison with their activity at 90°C) than the less oxidisable ones (i.e. syringic, ferulic and sinapic acids, and especially vanillic acid). Consequently, only gallic, gentisic, protocatechuic, and caffeic acids showed a significant antioxidant activity at 150°C and vanillic acid was active only at 90°C.