Comparative Methods to Evaluate the Antioxidant Capacity of Propolis: An Attempt to Explain the Differences

Abstract

Propolis is a natural product produced by bees that contains a complex mixture of compounds, including phenolic compounds and flavonoids. These compounds contribute to its biological activities, such as antioxidant capacity. This study analysed the pollen profile, total phenolic content (TPC), antioxidant properties, and phenolic compound profile of four propolis samples from Portugal. The total phenolic compounds in the samples were determined by six different techniques: four different Folin–Ciocalteu (F-C) methods, spectrophotometry (SPECT), and voltammetry (SWV). Of the six methods, SPECT allowed the highest quantification, while SWV achieved the lowest. The mean TPC values for these methods were 422 ± 98 and 47 ± 11 mg GAE/g sample, respectively. Antioxidant capacity was determined by four different methods: DPPH, FRAP, original ferrocyanide (OFec), and modified ferrocyanide (MFec). The MFec method gave the highest antioxidant capacity for all samples, followed by the DPPH method. The study also investigated the correlation between TPC and antioxidant capacity with the presence of hydroxybenzoic acid (HBA), hydroxycinnamic acid (HCA), and flavonoids (FLAV) in propolis samples. The results showed that the concentrations of specific compounds in propolis samples can significantly impact their antioxidant capacity and TPC quantification. Analysis of the profile of phenolic compounds by the UHPLC-DAD-ESI-MS technique identified chrysin, caffeic acid isoprenyl ester, pinocembrin, galangin, pinobanksin-3-O-acetate, and caffeic acid phenyl ester as the major compounds in the four propolis samples. In conclusion, this study shows the importance of the choice of method for determining TPC and antioxidant activity in samples and the contribution of HBA and HCA content to their quantification.

Comparison of the Chemical Composition and Antioxidant Properties of Propolis from Urban Apiaries

“…It has been shown that the high content of some flavonoids, such as quercetin, kaempferol, and galangin, affects the high antioxidant activity of propolis extracts [ 31 , 32 ]. The antioxidant capacity of flavonoids is mainly related to their chemical structure and, as with phenolic acids, is based on the O-H bond dissociation energy value [ 33 ].…”

“…Some authors conclude that the FRAP method has limitations and needs to be modified. The fact that it is based on an aqueous solution (acetate buffer) limits the method to hydrophilic substances, while some components of propolis with antioxidant properties (e.g., terpenes) are hydrophobic [ 33 ].…”

Examination of Raw Samples and Ethanol Extracts of Gerês Propolis Collected in Different Years

“…After analyzing the quality parameters of G19-G22 unprocessed samples and assessing the chemical characteristics of the respective ethanol extracts, we shifted our focus to propolis' biological features, namely its antimicrobial and antioxidant capacities. According to Sheng et al [47], a natural product can be classified as a possible natural antioxidant if it exhibits DPPH• and ABTS• radical scavenging capacities, and previous studies reported Portuguese propolis on numerous occasions as a natural product with a high antioxidant capacity [18,25,48]. Falcão et al [21] described that ethanol extracts of propolis samples collected from Portuguese northern and coastal regions displayed EC 50 values ranging from 10 to 30 µg/mL, values notably and significantly lower compared to those reported for samples from other areas of Portugal.…”