Can a mixture of green and wild propolis extracts have a synergistic antioxidant effect in situ? An oil-in-water emulsion application

This study sought to assess the antioxidant synergism in situ (within a food emulsion) between green (GPE) and brown (BPE) Brazilian propolis extracts. A mixture of GPE and BPE (GPE+BPE) was evaluated in a 59:41 v/v ratio, along with the individual extracts (i.e., GPE and BPE). For comparison, butylated hydroxytoluene (BHT) and a negative control (ethanol) were included. A completely randomized experimental design with a 5 × 5 factorial arrangement was utilized to assess the effectiveness of the five treatments on oxidative stability (evaluated by peroxide value [PV] and thiobarbituric acid reactive substance [TBARS]) of the emulsion stored under accelerated conditions. All antioxidants maintained low levels of oxidation products in the emulsions (primary stage). The mixture (GPE+BPE) enhanced the emulsion’s oxidative stability, exhibiting lower peroxide production (k = 0.0550 meq/L/d) compared to the isolated extracts, which had higher PV formation rates (k = 0.0822 and k = 0.1134 meq/L/d, respectively), thus indicating in situ synergism between the BPE and GPE. Quantitatively, the synergistic antioxidant effect in situ was about 30 %. This study is the first to demonstrate antioxidant synergism in situ between Brazilian propolis extracts, offering stronger evidence that mixed propolis extracts can act more effectively as antioxidants in food.