A preliminary study on the characterisation of honey by near infrared spectroscopy

Near infrared (NIR) spectra were measured, at five temperatures, for 48 samples of honey, from a variety of geographical and botanical sources, and the data was used to explore the possibility of using NIR spectroscopy for testing label claims concerning the geographical and botanical source of honey being offered for sale to the public. Three spectra were obtained at each temperature and a blank spectrum was also recorded to check on the state of the system. Thus a total of 16 spectra were collected for each sample, and the complete experiment amounted to 768 spectra each containing 700 data points. These data were compressed by selection and principal component analysis so that they could be used in a canonical variates analysis (CVA) program. There were sufficient numbers of honeys from four botanical sources, acacia, chestnut, heather and rapeseed, to make use of CVA. Acacia and rapeseed formed clusters that were well separated from chestnut and heather clusters, which were partially overlapped. Mahalanobis distance (MD) calculations were used to test group membership in a cross-validation experiment in which each of the 28 members of groups was left out of the calibration calculations, one at a time. When using 10 principal components (PCs) as the input variables, 19 of the honeys were assigned to the correct group while two honeys were incorrectly assigned to another group. When using 15 PCs, the number of correct assignments reduced to 13 but there were no incorrect assignments. There were 20 honeys which did not belong to the four test groups. When these were tested for group membership at 10 PCs, 10 were incorrectly assigned to a group. This reduced to two errors at 15 PCs. Tests on the country of origin were inconclusive. These results demonstrate that the successful characterisation of the botanical source of a honey may be obtained by NIR spectroscopy. Further work with larger numbers of samples and groups will be required to realise this potential.