Racemic synephrine found in Citrus aurantium-listing pre-workout supplements suggests a non-plant-based origin

Multi-ingredient pre-workout supplements (MIPS) contain Citrus aurantium as a source of bioactive amines such as p-synephrine, but concerns regarding the authenticity of ingredients in some supplements as well as adverse effects from consumption have been raised. R-(−)-Synephrine is the predominant enantiomer in Citrus aurantium extracts while synthetic preparations are often racemic. The aims of this study were to develop a screening method to determine the ratio of synephrine enantiomers in pre-workout supplements listing Citrus aurantium and to assess the ingredient authenticity by directly comparing their ratios to that found in Citrus aurantium standardised reference materials (SRMs). Quantification of enantiomers in the supplements and SRMs was achieved using a validated, high-performance liquid chromatography-single quadrupole mass spectrometry (HPLC-UV-QDa) direct enantioseparation method with a cellobiohydrolase (CBH) column (100 × 4.0 mm, 5 μM) and UV detection at 225 nm. Citrus aurantium SRMs were found to have an average enantiomeric ratio of 94:6 (R:S) with total synephrine ranging from 5.7 to 90.2 mg/g. Within the pilot sample of pre-workout supplements tested, only 42% (5/12) had enantiomeric ratios consistent with the SRMs with total synephrine ranging from 0.03 to 91.2 mg/g. For the remaining supplements, four had racemic ratios of synephrine (0.14 to 5.4 mg/g), two lacked any detectable levels of synephrine, and one had solely the S-(+)-enantiomer (0.15 mg/g). These results bring the authenticity of labelling of some pre-workout supplements into question and highlight the need for more stringent labelling regulations and testing for dietary supplements.