Pollen is a unique raw material because it is exposed to the outdoor environment before and during collection. Therefore, pollen can be potentially impacted by moisture and airborne components present outdoors. They include both ubiquitous biological and chemical contaminants. The potential impact of chemical contaminants in pollen is not discussed in this post.
Proper pollen collection is essential to produce allergen extracts. Pollen collection is tedious and requires a high level of specialization. A few large pollen collection entities own land to cultivate the desired plants for pollen collection under conditions that minimize exposure to man-made pollutants. However, this is an emerging strategy, which often does not allow for the collection of sufficient amounts of pollen necessary for the production of pollen allergen extracts. Many small family-owned pollen collection entities also obtain pollen for the production of pollen extracts.
After the pollen used for the production of allergenic extracts has been collected, it is dried to prevent potential microbial growth. Subsequently, their identity and purity are evaluated. Qualified individuals should perform the pollen identification and purity assessments in appropriate laboratories.
It is essential to perform all activities associated with pollen used for the production of pollen extracts, including identification and purity assessments, in dedicated areas of allergen manufacturing companies where other types of raw materials are not present. Otherwise, cross-contamination with other allergenic products might occur.
Microscopic analysis is performed to verify pollen identify and assess its purity. Currently, pollen purity assessments include counting and identifying biological components contaminating the pollen. However, this method of evaluating pollen purity does not consider either the potential clinical relevance of specific contaminants or their relative volume compared to that of the pollen in the final sample. While the potential clinical relevance of many pollen contaminants is unknown, volumetric counting instead of particle counting could provide a better estimation of the amount of foreign biological materials contained in pollen. However, standardized and approved methods to perform this evaluation are lacking.
Microscopic pollen analysis also can provide valuable information regarding pollen quality for the production of pollen extracts. The biological components that typically contaminate pollen include plant parts, foreign pollen, fungal structures, and other biological agents.
The pollen collected for the production of allergen extracts must meet particular purity specifications. Specifications for the maximum allowed concentrations of biological contaminants in pollen are typically internally proposed by allergen manufacturing companies based on the likelihood of achieving a particular purity level after cleaning pollen. These specifications are not based on any potential health effects upon exposure to the contaminants because those effects are unknown.
The presence of biological contaminants in pollen is impossible to avoid, difficult to evaluate, and the interpretation of the associated purity data is very subjective. However, if the evaluation of pollen purity to prepare allergen extracts is properly performed and interpreted, it can benefit the allergen manufacturing companies that produce such extracts. For example, the presence of a large number of plant parts and a variety of miscellaneous fungal spores generally indicates that the pollen is not sufficiently clean, and that additional activities to remove biological contaminants are necessary. To the contrary, the presence of large amounts of one single spore type, hyphae, and/or sporulating structures indicates that fungi have actively infested the pollen. This pollen should be discarded for the production of pollen extracts.
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The image below describes our proposal to prepare a guidance document to assist the individuals and organizations involved in the evaluation of pollen purity to prepare allergen extracts. Please click the image to see it enlarged.