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 amount 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.
There are three main methods used to collect pollen from wind-pollinated plants; first, the water-set; second, the vacuum; and third, the cut/dry/sieve. Many pollen species can be collected using either method.
The three collection methods have advantages and disadvantages. The main advantage of the water-set method is that it results in very clean pollen. To the contrary, it is very labor intensive and often the resulting pollen is impacted by high moisture and subsequent microbial growth.
The main advantage of the vacuum and the cut/dry/sieve methods is that are relatively simple to perform. Their main caveat is that the resulting pollen often contains high levels of biological contaminants.
Following collection, pollen is dried to reduce moisture content and prevent microbial growth. Subsequently, the naturally present plant parts, fungal spores, insect fragments, and foreign pollen grains are removed. The two primary methods to clean pollen are mechanical gradation sieving and air classification, both described below.
Mechanical gradation sieving is the simplest and most widely used method because such sieving with various micron-sized meshes can remove biologic contaminants. The air classification method can separate particles that differ in both weight and size, resulting in very clean pollen for the production of pollen extracts. Though, air classification machines are expensive and often disrupt pollen, making its quality difficult to assess because some cytoplasmic material containing allergens can be lost during the cleaning process.
Proper understanding regarding pollen collection to produce allergen extracts is essential for allergen manufacturers and clinicians who use pollen allergen extracts.