Study on stability testing of the ethanolic extract of Benjakul remedy on antioxidant activities and total phenolic content

Introduction: Benjakul is a Thai Traditional medicine preparation in The National Essential Drug Lists of Thailand. It is used for improvement of general health and wellbeing. It is composed of five plants: Piper retrofractum fruit, Piper sarmentosum root, Piper ribessoides stem, Plumbago indica root, and Zingiber officinale rhizome. There is no report about the stability of the antioxidant activities of the ethanolic extract of Benjakul and determination of total phenolic content. Objective was to investigate the stability of the ethanolic extract of Benjakul by determination its antioxidant activity and total phenolic content. Method: Benjakul preparations were extracted with 95% ethanol. The extracts were stored under accelerated storage conditions at 45°C and 75% relative humidity (RH) for 4 months and keeping at days 0, 15, 30, 60, 90 and 120 respectively. At the end of the storage, the extracts were tested for antioxidant activities by 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay, 3-ethylbenzothiazoline-6-sulphonic acid (ABTS) cation radical scavenging assay and also determination of total phenolic content using Folin-Ciocalteu’s reagent. Result: The results from DPPH radical scavenging assay showed that the EC 50 values of the extracts at days 0, 15, 30, 60, 90 and 120 were 17.24 ± 0.48 - 17.70 ± 0.67 μg/ml. The results from the ABTS assay showed the EC 50 of the samples as 28.71 ± 1.00 - 33.17 ± 0.26 μg/ml. The antioxidant activities from both assays showed no significant difference at different storage times (p > 0.05). In addition, the total phenolic content showed as 72.43 - 77.42 mgGAE/g extract and no significant difference at different storage times with day 0 (p > 0.05). Discussion and Conclusion:  The ethanolic extract of Benjakul was stable over 2 years, because of no significant difference of its antioxidant activities and total phenolic content at various time comparison with day 0 under the accelerated storage conditions. Key words: Stability, Benjakul, Antioxidant activities, Total phenolic compound