Identification of pollen taxa by different microscopy techniques.

Matej Pospiech,Simona Ljasovská,Pavel Štarha,Pavel Hrabec,Zdeňka Javůrková,Bohuslava Tremlová,Josef Bednář,Filippo Giarratana

doi:10.1371/journal.pone.0256808

Matej Pospiech, Simona Ljasovská + Show 6 more

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https://doi.org/10.1371/journal.pone.0256808

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Abstract

Melissopalynology is an important analytical method to identify botanical origin of honey. Pollen grain recognition is commonly performed by visual inspection by a trained person. An alternative method for visual inspection is automated pollen analysis based on the image analysis technique. Image analysis transfers visual information to mathematical descriptions. In this work, the suitability of three microscopic techniques for automatic analysis of pollen grains was studied. 2D and 3D morphological characteristics, textural and colour features, and extended depth of focus characteristics were used for the pollen discrimination. In this study, 7 botanical taxa and a total of 2482 pollen grains were evaluated. The highest correct classification rate of 93.05% was achieved using the phase contrast microscopy, followed by the dark field microscopy reaching 91.02%, and finally by the light field microscopy reaching 88.88%. The most significant discriminant characteristics were morphological (2D and 3D) and colour characteristics. Our results confirm the potential of using automatic pollen analysis to discriminate pollen taxa in honey. This work provides the basis for further research where the taxa dataset will be increased, and new descriptors will be studied.

Highlights

Pollen is a natural component of honey, but due to its specific shape characteristics, it is successfully used as a method to identify the geographical and botanical origin of honey, or to determine a single-species honey
The differences between pollen taxa were confirmed for microscopic methods used
Morphometric, volumetric, and colorimetric descriptors were mostly relevant for the discrimination with diverse variability for microscopic methods. 3D descriptors classified pollen taxa mostly in dark field, colour descriptors mostly in phase contrast

Summary

Introduction

Pollen is a natural component of honey, but due to its specific shape characteristics, it is successfully used as a method to identify the geographical and botanical origin of honey, or to determine a single-species honey. This issue is studied by the scientific branch called mellisopalynology. Honey analysis is based on visual inspection according to international standards of the International Honey Committee and this technique was described in detail in the work by Von Der Ohe et al [1] This method of evaluation is prone to be affected by subjective errors in analyses [1,2].

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