Abstract
Propolis, a sticky bee hive product collected from resinous plant sources by Apis mellifera bees, exhibits a wide range of biological and pharmacological properties, primarily attributed to its rich composition of bioactive constituents, including phenolic acids, esters, and flavonoids. In this study, the antioxidant properties of 76 liquid propolis solutions from 18 different countries were investigated based on their dry matter, total phenolic and total flavonoid contents, antioxidant capacities, and phenolic profiles. The antioxidant activities of propolis from various geographic regions, including Latvia, Croatia, New Zealand, San Marino, Russia, France, Romania, Italy, Estonia, Brazil, Belgium, Germany, Slovenia, Japan, the United States of America (USA), the United Arab Emirates (UAE), Spain, and Korea, were compared. Total phenolic and flavonoid contents, as well as total antioxidant capacity (Cupric Reducing Antioxidant Capacity-CUPRAC method), were analyzed by spectrophotometry, and the major constituents were investigated by liquid chromatography-mass spectrometry (LC-MS/MS). Antioxidant test results indicated that 29 products scored below 10 mg Trolox equivalent (TE)/mL, and only 14 were scored above 100 mg TE/mL. The results showed that the total phenolic content of the samples ranged from 0.1 to 107.5 mg Gallic acid equivalent (GAE)/mL, while total flavonoid content varied between 0.1 and 174.5 mg Catechin equivalent (CE)/mL. Based on the CUPRAC assay, total antioxidant capacity values ranged from 0.1 to 492.3 mg TE/mL. Among the 76 analyzed samples, nine products exhibited antioxidant capacity values exceeding 150 mg TE/mL. In all of these samples, phenolic profiling confirmed the presence of propolis, and the analytical results were consistent with the information declared on the product labels. Hence, this study provides a comprehensive, real-market evaluation of commercial propolis products by integrating spectrophotometric assays with LC-MS-based targeted metabolomics profiling, highlighting formulation- and product type-driven differences in phenolic composition and antioxidant capacity beyond geographical origin.