Bee pollen is collected by foraging honey bees (Apis sp. including A. mellifera) and stingless bees . It is a combination of principally floral pollen mixed with some nectar or honey, enzymes, wax and bee secretion. The pollen mixture is transported as a small pellet in the pollen basket of the forager’s hind legs to the bee hive where it is stored and used as a food source for the bee larvae . Bee pollen can be considered nutritional, since it contains essential substances, such as carbohydrates, proteins, amino acids, lipids, vitamins, mineral substances and trace elements , but its typically low concentration in individual flowers makes it not worthwhile as a mainstay food supply for mammals and most large animals.
The main bioactive compounds reported from bee pollen are phenolic compounds, and specifically quercetin, kaempferol, caffeic acid  and naringenin . In addition, the chemical composition of bee pollen depends mainly on which plants are used as pollen sources by the collecting bees, and so are likely to vary according to pollen availability within the foraging colonies range as well as by pollen (flower) selection by the bee species. Thus, bee pollen would be expected to show regional, seasonal and bee species specific variations; consequentially, the chemical composition and bioactivity are likely to vary accordingly. For example, bee pollen in one study site in Brazil was found to mainly be comprised of the pollen from Scoparia dulcis L. and Senna obtusifolia L. and had the main bioactive chemical components of p-hydroxycinnamic acid, dihydroquercetin, isorhamnetin, luteolin and quercetin . That from another site in Portugal was mainly derived from Salix atrocinerea, Erica Australia
Raphanus raphanistrum and Eucalyptus globules, with the different principal bioactive chemical components of kaempferol-3-neohesperidoside, quercetin-3-rhamnoside, myricetin-3-galactoside, kaempferol-3-sophoroside, quercetin-3-sophoroside, tricetin, myricetin and luteolin .
Globally bee pollen has been reported to provide a diverse array of bioactivities, such as antiproliferative, anti-allergic, antibiotic, antidiarrheic and antioxidant activities [8–10]. In addition, Eraslan et al.  reported that bee pollen, in which the dominant pollen was from Brassica napus L., could detoxify propoxur, a broad spectrum carbamate insecticide, in experimental rats. Note, however, that was well as the differences between bee pollen samples, the active compounds reported will also reflect variations in the actual bioactivities screened for and in the methodology utilized for screening for them as well as variations in the extraction and enrichment of the compounds.
Free radicals are compounds or an ion that has an electron donor and a molecule of oxygen, such as O∙
-, HO∙, ROO∙, H2O2, in the center of the structure . The most common free radicals in biological systems are reactive oxygen species (ROS), and these serve as a connection among signals inside the cells involved in stress responses, cell proliferation, aging and cancer . An excess amount of free radicals can cause damage or death to cells and can lead to many diseases, such as cancer, cataract formation, age-related and muscular degeneration, atherosclerosis, cardiac ischemia, Parkinson’s disease, gastrointestinal disturbance, aging and rheumatoid arthritis [14–16]. In addition, too high a free radical level inside the body has been shown to affect low density lipoprotein (LDL) and to induce protein and DNA damage . Thus, finding new suitable antioxidant agents is still important.
Antioxidant agents have been successfully isolated directly from plants, such as flavonoids, quercetrin (quercetin-3-O-rhamnoside), rutin (quercetin-3-O-rutinoside) and quercetin from Solidago microglossa , methyl 3,5-dicaffeoyl quinate and 3-O-feruloylquinic acid from Kalopanax pictus , and flavanones and hydroxycinnamic acid derivatives (polymethoxyflavones and furocoumarin) from citrus fruits in Cyprus .
Besides directly from plants, antioxidant agents can also be obtained or found in bee pollen, a source of mainly plant origin. For example, Silva et al.  showed that the chemical constituents in the bee pollen of the stingless bee, Melipona subnitida, in Brazil had free radical scavenging activity. The bee pollen was largely collected from the pollen of Mimosa gemmalata (a plant in the Mimosaceae family) and a plant in the Fabaceae family. Seven active compounds were found, namely naringenin, isorhamnetin, D-manitol, β-sitosterol, tricetin, selagin and 8-methoxiherbacetin. These anti-oxidant chemical constituents have also been found in the bee pollen from A. mellifera .
In addition, the bioactivities of bee pollen have been reported to depend on the geographic region, harvesting period and seasons, as expected and outlined above. Leja et al.  reported that the total antioxidant activity, expressed as the percentage of the inhibition of lipid peroxidation, varied significantly among different pollen types. Bee pollen from Pyrus communis, Malus domestica, Taraxacum officinale, Aesculus hippocastanum, Robinia pseudoacacia, Phacelia tanacetifolia and Sinapis alba provided a total antioxidant activity of greater than 60%. Moreover, other external factors, such as the solvent used in the extraction, and the extraction and pollen storage methods also play an important role in the bioactivities obtained and reported. For example, Negri et al.  reported that the methanol extract of untreated bee pollen, bee pollen frozen at −18 °C and bee pollen frozen and then dried presented a significantly different antioxidant activity, with that prepared from pollen that was frozen and then dried being the most active. However, whether this reflects changes in the relative extraction efficiencies or changes in the actual chemical composition, such as from susceptibility to biotic chemical reactions, like enzymic modification, or abiotic ones like oxidation and photodegradation, is unknown.
That the bioactive chemical constituents in bee pollen could be an alternative source for free radical scavenging activity led to our interest in studying the bee pollen of A. mellifera in Nan, Thailand. The sample was collected in Nan province because of the unique or typical geography and botanical diversity of the region and so potential diversity of pollen available for bees. However, the region also has commercial agriculture including nearby monoculture corn (Zea mays L.) fields which turned out to be significant. Nevertheless, the bee pollen was collected and sequentially extracted with three solvents of decreasing polarity before using bioactivity guided fractionation to yield pure bioactive components. These pure active compounds were then analyzed for their formula structure by NMR. The origin of the pollen in the bee pollen was evaluated by morphology using light and scanning electron microscopy (SEM). The nutritional components in bee pollen were also assayed in order to promote its consumption. The benefit of this work might be that new active anti-oxidant compounds could be obtained and might be developed to be an anti-oxidant agent useful in the pharmaceutical industry. Finally, this may help promote the bee industry in Thailand and so bring an increased income to bee farmers.