Riboflavin and lumichrome in Dalmatian sage honey and other unifloral honeys determined by LC–DAD technique

Riboflavin (vitamin B2) and its metabolite lumichrome were quantified in 117 samples from 11 unifloral honeys types (Arbutus unedo L., Asphodelus microcarpus Salzm. et Viv., Citrus spp., Eucalyptus spp., Hedysarum coronarium L., Castanea sativa L. honeydew, Mentha spp., Paliurus spina-christi., Salix spp., Salvia officinalis L., Satureja spp.). The quantification of these two compounds was performed by LC–DAD method which does not require sample purification. The proposed method in our study has low limits of detection and quantification, very good linearity in a large concentration range and very good precision. It allows simultaneous determination of 5-hydroxymethylfurfural (HMF) and known chemical biomarkers of unifloral honeys such as abscisic acid diastereomers, homogentisic acid, methyl syringate and kynurenic acid. No statistical correlation was observed between riboflavin and lumichrome content. Although, the concentration of vitamin B2 in honey may be too low (<6.1 mg/kg) to generate interest in the field of nutrition, the presence of its main metabolite lumichrome may be useful to determine the botanical origin of certain unifloral honeys. In fact, the analysis of 11 unifloral honey types showed that Dalmatian sage (S. officinalis L.) honey is characterised by unusual high levels of lumichrome (20.2 ± 2.6 mg/kg). The botanical origin of lumichrome from sage flower was assessed by analysing bee-stomach extracts. Other analytical parameters, such as total phenols, antioxidant and antiradical activities, HMF and diastase activity were studied in Dalmatian sage honey.