Manuka honey adulteration detection based on near-infrared spectroscopy combined with aquaphotomics

The syrup-blended adulteration of Manuka honey was detected using near-infrared (NIR) spectroscopy combined with aquaphotomics. Manuka honey was adulterated with five different syrups (corn syrup, sucrose syrup, high fructose corn syrup, beet syrup, and rice syrup) in degrees from 10% to 50% for NIR spectra collection. Spectral variance analysis, PCA analysis, and partial least square regression (PLSR) model regression vector analysis were then performed for the spectral region of 1300-1800 nm. Finally, 12 characteristic bands were selected according to the results of analysis, and the aquagrams constructed on the basis of these wavelengths were used for aquaphotomic evaluation. The evaluation results showed that Manuka honey dominated at long-wavelength regions, indicating that more water molecules with strong hydrogen bonds and more structured water molecules are present in Manuka honey compared with sugar syrups. On the other hand, sugar syrups dominated at short-wavelength regions, indicating that sugar syrups mainly contain unstructured free water molecules with few or no hydrogen bonds. Furthermore, as the degree of adulteration increased, the number of structured water molecules, which facilitate molecular interactions, in Manuka honey decreased. The experimental results demonstrated that the detection of syrup-adulterated Manuka honey using NIR spectroscopy combined with aquaphotomics is practical.