Comparative stability of arbutin in Arctostaphylos uva‐ursi by a new comprehensive stability‐indicating HPLC method

Introduction Arbutin is a phenol glucoside found in high concentrations in bearberry leaves and associated with the antimicrobial activity of the plant. Hydroquinone can also be found in leaves or be formed by degradation of arbutin. Lengthy exposure to free hydroquinone is associated with induction of toxicity in different organs. Objective To develop and validate a stability‐indicating method by high‐performance liquid chromatography diode array detector (HPLC‐DAD) for simultaneous quantification of arbutin and hydroquinone in bearberry leaves and perform a comprehensive forced degradation study comparing synthetic arbutin and the arbutin in bearberry leaves. Methods Separation was performed using a C18 column, mobile phase with water–methanol (95:5), flow rate 1.0 mL/min and detection at 280 nm. Bearberry leaves were assayed and a forced degradation study of arbutin was performed in different conditions. Results The method complied with all required validation parameters. Contents varied from 1.19 to 4.15% (w/w) of arbutin and from 0.022 to 0.604% (w/w) of hydroquinone. Synthetic arbutin was susceptible to acid hydrolysis and oxidative degradation, forming hydroquinone as the main degradation product. The same study using bearberry leaves showed that constituents of the plant matrix may act as antioxidants, reducing the oxidative degradation of arbutin, however acid hydrolysis of arbutin occurred in higher intensity. Conclusion Analysis of bearberry leaves evidenced high variation in arbutin and hydroquinone levels, demonstrating the need for standardisation and control. The stability profiles of synthetic arbutin and the arbutin in bearberry leaves were considerably different and the results may be useful for determining the most appropriate conditions for extraction and production of bearberry‐based formulations. The analysis of different samples of bearberry leaves by a new stability‐indicating HPLC method evidenced high variation in arbutin and hydroquinone levels, demonstrating the need for standardization of these contents. The stability of arbutin under different forced degradation conditions was evaluated both isolated and in bearberry leaves. Isolated arbutin showed to be labile to acid hydrolysis and oxidation, however the bearberry matrix prevented its oxidative degradation.