Abstract

Bee bread (BB) is a fermented mixture of plant pollen, honey, and bee saliva that worker bees use as food for larvae, and for young bees to produce royal jelly. In the present study, five BB samples, collected from Apis mellifera iberiensis hives located in different apiaries near Bragança, in the northeast region of Portugal, and one BB commercial sample were characterized by high-performance liquid chromatography coupled to a diode array detector and electrospray mass spectrometry (HPLC-DAD-ESI/MS) in terms of phenolic compounds, such as flavonoid glycoside derivatives. Furthermore, the samples were screened, using in vitro assays, against different human tumor cell lines, MCF-7 (breast adenocarcinoma), NCI-H460 (non-small cell lung cancer), HeLa (cervical carcinoma) and HepG2 (hepatocellular carcinoma), and also against non-tumor liver cells (porcine liver cells, PLP2). The main phenolic compounds found were flavonol derivatives, mainly quercetin, kaempferol, myricetin, isorhamnetin and herbacetrin glycoside derivatives. Thirty-two compounds were identified in the six BB samples, presenting BB1 and BB3 with the highest contents (6802 and 6480 µg/g extract, respectively) and the highest number of identified compounds. Two isorhamnetin glycoside derivatives, isrohamnetin-O-hexosyl-O-rutinoside and isorhamnetin-O-pentosyl-hexoside, were the most abundant compounds present in BB1; on the other hand, quercetin-3-O-rhamnoside was the most abundant flavonol in BB3. However, it was not possible to establish a correlation between the flavonoids and the observed low to moderate cytotoxicity (ranging from >400 to 68 µg/mL), in which HeLa and NCI-H460 cell lines were the most susceptible to the inhibition. To the authors’ knowledge, this is the first report characterizing glycosidic flavonoids in BB samples, contributing to the chemical knowledge of this less explored bee product.

Highlights

  • The nutritional requirements of honeybees, Apis mellifera, are met by the collection of pollen, nectar, and water

  • Ethanolic extracts were screened against tumor cell lines

  • Five Bee bread (BB) samples, collected from Apis mellifera iberiensis hives located in different apiaries near Bragança, in the northeast region of Portugal, and one sample of commercial BB

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Summary

Introduction

The nutritional requirements of honeybees, Apis mellifera, are met by the collection of pollen, nectar, and water. Pollen collected by bees is mixed with a small amount of honey and saliva, and packed into the cells of the honeycomb where it undergoes a chemical change to form a product called bee bread [2]. This mixture undergoes different chemical processes due to the action of distinct enzymes from glandular secretions, microorganisms, moisture and temperature (35–36 ◦ C chamber temperature offspring), allowing the transformation, improvement and preservation of the stored pollen, which is called bee bread after two weeks of initial storage [3,4]. Ethanolic extracts were screened against tumor cell lines (human glioblastoma cell line U87MG)

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