The influence of temperature and time on the antioxidant activity and color parameters of dog-rose (Rosa canina) ethanolic extract

Abstract

This paper presents the study of the stability of antioxidant activity and color of the 50 % ethanolic extract of dog-rose (Rosa canina) from the Republic of Moldova with the main objective to test a food dye of natural origin. The extract was submitted to: -2 °C for 12 hours; 4 °C for 12 hours; 40 °C for 15 minutes, 60 °C for 15 minutes, 80 °C for 15 minutes and 100 °C for 2 minutes, after which the antioxidant activity and the color (CIELab) parameters were measured. Three sets of extracts were kept for 2 weeks at -2 °C; 4 °C and 25 - 30 °C and afterwards the parameters mentioned above were measured once again. Moreover, the total content of polyphenols was determined by Folin-Ciocalteu method. The results were expressed in mg gallic acid equivalents per liter. The antioxidant activity was determined using the method based on the interaction with the ABTS radical, the results being expressed in mmol trolox equivalent per liter. Thermal treatments have not influenced antioxidant activity, but have significantly affected the extract by increasing its luminosity and changing the red/green parameter towards more red tones, while storage at -2 °C caused the decrease of yellowness. Storage at 4 °C was found to be optimal for the preservation of the antioxidant activity.