Antioxidant activity measurement of oleoresin from rosemary and sage

•Commercial rosemary and sage extracts were tested for antioxidant activity.•Photochemiluminescence (PCL), DPPH assay and Rancimat test were performed.•All the methods provided correlated results of antioxidant activity.•PCL provided rapid and sensitive measurement of antioxidant capacity of extracts.•Phenolic diterpenes were the major compounds identified in extracts by UPLC–MS/MS.

The antioxidant activity of oleoresin from rosemary (Rosmarinus officinalis L.) (ROSM) and sage (Salvia officinalis L.) (SAG) was evaluated using photochemiluminescent method (PCL assay), spectrophotometric method based on 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay and Rancimat test. Using PCL assay, the antioxidant content of lipid (ACL) soluble compound in the extracts was quantified (μmol Trolox equivalents/g extract). Rancimat test was used to evaluate the induction period (IP) of sunflower oil blended with ROSM and SAG at 500 and 1000 mg/kg under elevated temperature (110 °C). The IP was used to determine the oxidative stability index (OSI) and percentage antioxidant activity (%AA). In addition, the phenolic characterization of extracts was performed using ultra performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) which suggested that phenolic diterpenes could be the major antioxidant compounds. The EC50 value obtained from PCL and DPPH assays were significantly correlated (r = 0.997, p < 0.01). The SAG showed significantly (p < 0.05) higher antioxidant activity than ROSM in all the tested methods. The OSI and %AA of ROSM and SAG blended oil was significantly higher (p < 0.05) than the control sunflower oil sample. In conclusion, the PCL and Rancimat test were successfully used for direct and dependable monitoring of antioxidant activity and intended as the alternative to DPPH assay for industrial application.