Tyrosinase inhibition and free radical scavenging activities of bee pollen from western honeybee Apis mellifera

Abstract

Bee pollen is one of bee products. It is the mixture of flower pollen, nectar, and bee secretion. It is produced by workers in the genus of Apis. The major chemical compositions of bee pollen are protein, essential amino acids, sugar, fat, nucleic acid, and fiber. Minor chemical compositions are minerals, vitamins, saturated/unsaturated fatty acids, polyphenol, and flavonoid. These compounds make bee pollen exhibit a wide range of bioactivities including anti-inflammatory, antioxidant, antibacterial, and antifungal activities. In this work, bee pollen of A. mellifera was studied. Tea flower (Camellia sinensis (L.) Kuntze) and mimosa flower (Mimosa pigra L.) were collected from Chiang Mai province and sunflower (Helianthus annuus L.) bee pollen was collected from Lopburi province, Thailand. All samples were extracted by methanol. Next, they were partitioned by hexane, dichloromethane, and methanol in order to isolate compounds depending on their polarities. The obtained partitioned extracts were tested for the free radical scavenging and antityrosinase activities. For the free radical scavenging activity by DPPH assay, dichloromethane partitioned extract of mimosa flower bee pollen (DCMMBP) provided the highest free radical scavenging activity at EC50 value of 192.07 μg/mL. Then, it was further purified by silica gel 60 column chromatography and size exclusion chromatography. All fractions were tested for the free radical scavenging activity and analysed for a chemical structure by nuclear magnetic resonance (NMR). The most active mixture had the EC50 value of 121.29 μg/mL. Additionally, a pure compound was found to be naringenin, belonging to flavonoid group. Naringenin was obtained in small amount and had low free radical scavenging activity. For the tyrosinase inhibitory activity, it was tested by a biochemical reaction of an extract on mushroom tyrosinase. The result showed that dichloromethane partitioned extract of sunflower bee pollen provided the highest mushroom tyrosinase inhibitory activity at IC50 value of 159.39 μg/mL. Thus, it was further purified by silica gel column chromatography and HPLC. All fractions were tested for antityrosinase activity and analysed a chemical structure of active fractions by NMR. The active mixtures were predicted to be spermidine derivatives which provided the highest tyrosinase inhibitory activity at IC50 value of 6.65 μg/mL. It could be concluded that the free radical scavenging and antityrosinase agents were rich in mimosa flower and sunflower bee pollen, respectively.