Composição química e atividade antioxidante do pólen coletado pela abelha sem ferrão: Melipona seminigra Cockerell, 1919

Abstract

Stingless bees have gained attention because their importance as pollinators of a wide range of native plant species and because they represent an important income source for meliponicultors. In order to contribute to the knowledge of the chemical composition and antioxidant activity of pollen collected by the stingless bee Melipona seminigra Cockerell, 1919 (uruçú-boca-de-renda), an economical specie in the Amazon region, two samples were collected during two distinguished weather season in the Brazilian Amazon, dry (august 2008, 50 mm) and rainy (april 2008, 300 mm) season. The centesimal composition analysis showed that both samples have a similar nutritional value and all values are in accord to the recommended by the Brazilian Ministery of Agriculture, but carbohydrate contents, which were ca 10 % above. In both samples of pollen, the main botanical source was Miconia dispar (Melastomataceae) (rainy season: 53.19% and dry season: 95.60%) followed by pollen of different Myrtaceae species (rainy: 25.64% and dry 0.96%) and Mimosa pudica pollen (Fabaceae; rainy: 16.81% and dry: 3.44%). Aqueous and ethanolic extracts from samples collected in the two different seasons were prepared and the ethanolic extracts were fractionated by liquid-liquid partition into hexanes, ethyl acetate and hydroalcoholic fractions. The antioxidant activity of the extracts and fractions was determined by two different methods: DPPH· radical scavenging assay and the ferric reducing antioxidant power assay. In both cases, the ethanolic extracts were more active than the aqueous ones. The fractions were also assayed and the ethyl acetate fractions were the most active ones. The total phenolics contents as determined by the Folin-Ciocalteu assay have confirmed that the phenolic compounds were concentrated into these fractions. Fingerprinting analysis by RPHPLC of purified fractions obtained by solid phase extraction (RP-SPE) of ethanolic extracts of each characteristic seasonal period showed similar compositions. The phenylpropanoid, p-coumaric, and the flavonoids myricetin, quercetin and naringenin could be identified with the help of coelution method with authentic commercial standards. The main component of the fraction obtained by RP-SPE was purified by semi-preparative RP-HPLC and was identified by 1H NMR data as quercitrin (quercetin 3-O-rhamnopyranoside).