Natural foods are becoming more and more well-liked by the general population in today's globe as a result of the realization that they can help with disease prevention and treatment [1,2]. Polyphenols and flavonoids, which have the capacity to scavenge free radicals, are abundant in bee pollen and bee bread. Phenolic acids and flavonoids are probably the most studied classes of phenolic compounds. The ability of phenolic compounds, which are found naturally in plants, to successfully protect the body from free radicals is well established [3]. The beneficial properties of these substances include antioxidant, anticarcinogenic, antimicrobial, antiapoptotic, anti-atherosclerosis, anti-inflammation, cardiovascular protection, anti-aging, they also have an impact on the enhancement of endothelial function, inhibition of angiogenesis or even cell proliferation activity. The choice of solvent is one of the key factors leading to the selective extraction of secondary metabolites [4]. Solvents (extrahents) containing hydroxyl groups in their structure can form intramolecular hydrogen bonds with the hydroxyl groups of phenolic compounds, thereby increasing their solubility [5]. This research aims to compare the levels of bioactive compounds in samples of bee bread and bee pollen stored under different conditions, using different solvent concentrations for extraction.
Dried and frozen samples of bee bread and bee pollen were investigated in this study. The samples were collected in §southern Lithuania, in the Lazdijai region, in July 2022. Extraction of bee bread and bee pollen was performed by the maceration method. Three different concentrations of extrahent were used: 70, 50, and 30% methanol. The total amount of phenolic compounds, flavonoids, and antiradical activity was evaluated using spectrophotometric methods [6]. The results were expressed in mg of rutin equivalents (RE) in 1 g of the sample.
The results showed that freezing had no significant effect on phenolic compounds, flavonoids, and antiradical activity in the bee bread. The content of tested parameters statistically ($p \le 0.05$) increased by using a higher concentration of methanol. The total phenolic compounds varied from 42.11 mg RE/g to 93.62 mg RE/g, the flavonoids from 19.03 mg RE/g to 39.04 mg RE/g, and antiradical activity from 22.61 mg RE/g to 67.37 mg RE/g in the samples of bee bread. The highest levels of bioactive compounds were obtained at a methanol concentration of 70%. Nonetheless, both freezing and extrahent concentration had a significant impact on phenolic compounds content in bee pollen. In the extracts from dried material obtained using 70% methanol, the content of phenolic compounds was 99.95 mg RE/g, while in frozen – 83.85 mg RE/g. In 30% methanol extracts, phenolic compounds in dried material were 1.5 times higher than in the frozen bee pollen.
In conclusion, the highest amounts of the biologically active compounds were obtained using 70% methanol concentration. Freezing had no significant effect on the bioactive compounds in bee bread but had a compelling effect on bee pollen phenolic compounds. It is believable that different extrahents or even their mixtures may possess different both quantitative and qualitative extraction capabilities of biologically active compounds. The results also may be depended on the plant material, in our case on the botanical origin of bee bread or bee pollen. It would be recommended to optimize extraction solvent before the work with new plant material.