Abstract
Abstract Bee pollen, one of the economic bee products, is widely known as a nutritional food with many bioactivities that depend on many such factors as bee species, plant source and biogeography. For this study, bee pollen was collected from Apis mellifera, harvested from the flowers of mimosa (Mimosa pigra L.) in the Chiang Mai province, Thailand. The sample was extracted in methanol (MeOH) and then sequentially partitioned with hexane, dichloromethane (DCM) and MeOH in order to isolate compounds depending on their polarities. The obtained extracts were then tested for their antioxidant and anti-tyrosinase activities through 1,1-diphyenyl-2-picrylhydrazyl (DPPH) assay and for/through inhibition of mushroom tyrosinase extract, respectively. The DCM partitioned extract of mimosa flower bee pollen (DCMMBP) provided the highest antioxidant activity, with an effective concentration at 50% (EC50) of 192.1 μg/mL, and was further fractionated by silica gel 60 column chromatography and Sephadex LH20 size exclusion chromatography. All fractions were tested for their antioxidant activity and analyzed for the chemical structure through nuclear magnetic resonance (NMR). The most active fraction (EC50 of 121.3 μg/mL) was a mixture of compounds, but the isolated flavonoid, naringenin, had a negligible antioxidant activity. In contrast, all three partitioned extracts and pooled fractions after silica gel 60 column chromatography provided no anti-tyrosinase activity (IC50 of > 500 μg/mL) and a very low percentage of tyrosinase inhibition (0–2.99 ± 3.18%), compared to kojic acid (IC50 of 8.58 μg/mL and tyrosinase inhibition of 74.2 ± 1.25%).
Highlights
Bee pollen, mixture of pollen mixed with a small amount of nectar or even honey, varies depending on the biogeographic origin, plant species, bee species and the season (Negrão & Orsi, 2018)
The three partitioned extracts were tested for their tyrosinase inhibitory activity, with the obtained inhibitory concentration at 50% (IC50) values shown in Tab. 1 in comparison with that for kojic acid as the standard reference
The botanical origin was confirmed under scanning electron microscope (SEM), where the morphology in the mimosa bee pollen was the same as that reported for mimosa floral pollen (Caccavari, 2002; El Ghazali et al, 1997)
Summary
Mixture of pollen mixed with a small amount of nectar or even honey (brought from the hive), varies depending on the biogeographic (regional) origin, plant species, bee species and the season (Negrão & Orsi, 2018). Over-production of melanin can occur, which can cause socially undesirable such aesthetics, as dark-looking skin and freckles, as well as more serious effects like melisma and malignant melanoma. Both the antioxidant and anti-tyrosinase activities are widely accepted to be indicators of anti-melanogenesis. The phenolic extracts of bee pollen harvested from rape flowers contained a high content of rutin and exhibited high in vitro antioxidant and mushroom tyrosinase inhibitory activities (Sun et al, 2017). The aim of the study was the testing of antioxidant and anti-tyrosinase activity of monofloral bee pollen of Mimosa pigra L. harvested in Thailand
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