Quantification of mulberrin and morusin in mulberry and other food plants via stable isotope dilution analysis using LC-MS/MS

Mulberry (Morus) is an important food and medicinal plant primarily used in sericulture. It is rich in prenylated flavonoids like morusin and mulberrin, which have shown promising bioactivities in vitro and in vivo but so far rely on HPLC methods for their quantification in plant material. Hence, a more sensitive LC-MS/MS stable isotope dilution assay for morusin and mulberrin was developed and validated. The analytes were quantified in 17 plant samples, with up to three plant compartments investigated (branches, leaves, fruits). The highest amounts were found in branches of a German mulberry tree (43 μg/g morusin, 910 μg/g mulberrin). Limits of detection reached 0.02 μg/g for morusin and 0.06 μg/g for mulberrin, which is significantly lower than existing methods, allowing for the detection and quantification of the analytes in leaves and fruits of mulberry, as well as common snowball (Viburnum opulus), a common food and medicine plant.