Imaging of bee honey sugar crystals by second-harmonic generation microscopy

Bee honey is an exceptionally nutritious food with unique chemical and mineral contents. This report introduces the use of the second-harmonic generation (SHG) microscopy for imaging honey sugar crystals' morphology as an alternative for its authentication process. The crystals and their boundaries are clearly observed with SHG compared with bright-field microscopy, where the liquid honey avoids the visualization of a sharp image. Four different honey samples of Mexico's various floral origins and geographical regions are analyzed in our study. These samples are representative of the diversity and valuable quality of bee honey production. The SHG image information is complemented with Raman spectroscopy (RS) analysis, since this optical technique is widely used to validate the bee's honey composition stated by its floral origin. We relate the SHG imaging of honey crystals with the well-defined fructose and glucose peaks measured by RS. Size measurement is introduced using the crystal´s length ratio to differentiate its floral origin. From our observations, we can state that SHG is a promising and suitable technique to provide a sort of optical fingerprint based on the floral origin of bee honey.