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Abstract
Flavonoids are regarded as key compounds in bee bread. In this paper, quantitative determination of sum of flavonoids and dominating group of flavonoids were carried out by colorimetric aluminum chloride method. The principle of aluminum chloride colorimetric method is that aluminum chloride forms complexes with flavones and flavanols wherein it reacts with the C-4 keto group and hydroxyl groups of the ring C, and/or ring A and/or ring B. In this work 3 samples of bee bread and 5 extracts were investigated. The total contents of flavonoids in the tested extracts ranged from 10 to 166 mg/L. Our study confirmed that complex of quercetin dihydrate with aluminum chloride had the maximum absorption at 423.8–427.2 nm, namely in the limits for flavanols from 415 to 440 nm, in differential spectra in the range of quercetin concentrations of 2.08–31.2 mg/L (solvent was ethanol 50%). According to literature data, flavanols (galangin, morin, kaempferol, rutin, quercetin, quercitrin and myricetin) have absorption maximum in the range from 415 to 440 nm while flavones (chrysin, apigenin, and luteolin) and glycosides of flavanols – less 415 nm. Our studies demonstrated that the structure of direct spectra of developed extracts was very similar. There was no any absorption maximum. The structure of the differential spectra of all the developed extracts was also very similar. But there was one divergence in the differential spectra: an absorption maximum varies in the range from 406.9 nm to 411.7 nm that indicates different composition of flavonoids in the extracts. Repeatability of the position of an absorption maximum of the extracts is very good at carrying out analyses in the different days. On the base of conducted experiments, we assume that our bee bread samples can contain flavanols mainly in the form of glycosides and flavones as absorption maxima of the extracts in their differential spectra are less than 415 nm.