Pollen is unique: A comparison of existing methods for analyzing protein and lipid content in pollen

Flowering plants vary in the quantity and quality of resources they provide to pollinators. The resources contained in pollen from certain plant species can be more effective in improving colony growth and mitigating bee health problems than others. Therefore, assessing the nutritional content of bee-collected pollen is a priority to inform the decision-making processes related to selecting pollinator-attracting plants for land management and creating artificial pollen substitutes for supplementary feeding. Current literature on pollen protein and lipid contents in pollen ranges from ~10%-60% protein and 2%-20% lipid. The high variation is due to the unique physical nature of pollen, differences in methods used to analyze proteins and lipids, and sheer diversity of pollen types. In this study, we review the pros and limitations to some of the commonly used methods to assess pollen protein and lipid content. Using Brassica and Rosa pollen, we compared the protein and lipid results of these pollen types using these methods. Since pollen contains an exine to protect the pollen’s cytoplasm containing proteins and lipids, we also developed a modified protocol to fracture the pollen’s exine and fully extract the nutrients contained within the pollen grains. Using this modified protocol, we obtained higher protein and lipid values in pollen compared to using traditional analytical methods. These results will help standardize methods for analyzing pollen nutrients and improve understanding on pollinator nutritional needs.