Chemical profile and antioxidant activity of geopropolis from Melipona subnitida collected inside and outside the nest

Melipona subnitida (“jandaíra”) is a species of stingless bee endemic to the Caatinga, a dry forest in the northeastern Brazilian semi-arid. Propolis is a product containing beeswax and plant resin. It contains compounds that can be able to prevent health problems by protecting cells against damage by oxidative agents. M. subnitida produces geopropolis, a mixture of propolis with soil. Samples of geopropolis of M. subnitida, one of inside and another outside of the nest from a hive in the municipality of Mossoró (northeastern Brazil) were analyzed by HPLC-PDA-ESI-MS/MS and their antioxidant activity evaluated by the DPPH and β-carotene/linoleic acid methods. Both samples exhibited similar chemical profile, characterized by 26 phenolic compounds, however, the compounds detected were more abundant in sample collected from inside of the nest. They were tentatively characterized as galloyl hexoses, coumaroyl-O-galloyl-hexoses, cinnamoyl-O-galloyl-hexoses, coumaroyl- and cinnamoyl- galloyl hexoses, phenylpropanoyl-O-benzoyl hexoses, flavanones and ellagitannins. Flavonoids, galloyl hexoses, coumaroyl-O-galloyl-hexosides, cinnamoyl-O-galloyl-hexosides and coumaroyl-cinnamoyl-galloyl hexosides were reported previously in this genus, however ellagitannins and phenylpropanoyl-O-benzoyl hexoses are reported for the first time. Comparing the antioxidant activity of the geopropolis samples from inside and outside of the nest, the latter was higher than the former.

亮足无刺蜂（Melipona subnitida，俗称jandaíra）是一种特有于巴西东北部半干旱旱生林卡廷加（Caatinga）的无刺蜂物种。蜂胶（Propolis）是一类由蜂蜡与植物树脂组成的产物，其含有的成分可通过保护细胞免受氧化因子损伤，进而预防健康问题。亮足无刺蜂可产生土栖蜂胶（geopropolis）——即蜂胶与土壤的混合物。研究人员采用高效液相色谱-光电二极管阵列-电喷雾串联质谱（HPLC-PDA-ESI-MS/MS），对采自巴西东北部莫索罗市某蜂箱的巢内与巢外土栖蜂胶样本进行了分析，并通过1,1-二苯基-2-三硝基苯肼（DPPH）法与β-胡萝卜素/亚油酸法评估了其抗氧化活性。两组样本的化学指纹图谱相似，均含有26种酚类化合物，但巢内样本中的化合物丰度更高。研究人员初步将这些化合物鉴定为没食子酰己糖类、香豆酰-O-没食子酰己糖类、肉桂酰-O-没食子酰己糖类、香豆酰基与肉桂酰基没食子酰己糖类、苯丙酰基-O-苯甲酰己糖类、黄烷酮类以及鞣花单宁类。此前该无刺蜂属中已有黄酮类、没食子酰己糖类、香豆酰-O-没食子酰己糖苷类、肉桂酰-O-没食子酰己糖苷类以及香豆酰-肉桂酰-没食子酰己糖苷类的相关报道，但鞣花单宁类与苯丙酰基-O-苯甲酰己糖类为该属首次报道。对比两组巢内外土栖蜂胶样本的抗氧化活性发现，巢外样本的抗氧化活性高于巢内样本。