Quality assessment of marketed food supplements and herbal tea products of olive leaf in Turkey

Abstract

In this study, qualitative and quantitative analysis of commercially available food supplements composed of olive leaf extract and herbal tea products containing olive leaf were evaluated by High-Performance Thin-Layer Chromatography (HPTLC) and a newly developed and validated High-Performance Liquid Chromatographic (HPLC) method for their quality assessment. In addition, leaves of two varieties of Olea europaea L. (var. europaea and var. sylvestris) grown in Turkey which were assigned as reference plant materials and their chemical compositions were also comparatively analyzed by HPTLC. Then HPTLC fingerprints of reference plant materials were compared to the marketed olive leaf samples. For quantification of oleuropein and luteolin 7-O-glucoside (L7G) contents in the samples, a simple and fast HPLC method was developed and validated. Consequently, in water and hydroalcoholic extracts of O. europaea var. europaea leaves, oleuropein contents were found to be 15.89% (w/w) and 15.84% (w/w), while L7G contents were 0.75% and 1.23%, respectively. For the reference materials, oleuropein in O. europaea L. var. sylvestris leaves was found to be 12.77% (w/w, in water extract) and 12.36%(w/w, in hydroalcoholic extract), while the concentration of L7G was 0.51% (w/w) and 0.83% (w/w) in water and hydroalcoholic extracts, respectively. Qualitative analysis of the commercial products revealed that fraud was detected in three of eight olive leaf herbal tea bag brands and two of ten olive leaf food supplements. These samples were found either devoid of oleuropein or they had different HPTLC fingerprint profiles than the reference samples.