12 Quality Assurance
Inspired by the laser fluorescence results, we made similar measurements
using an Ocean Insight back-thinned CCD-array spectrometer
and a 365 nm LED for fluorescence excitation.
Fluorescence spectra were measured for several types of honey purchased
from a local grocery store. Honey varieties included clover honey,
golden blossom honey, orange blossom honey and organic honey, ranging
in price from about $0.45/oz. to nearly $1.00/oz. All samples were produced
in the U.S. except for the organic brand, which came from Brazil.Undiluted
honey was pipetted into a disposable cuvette and placed into a sample holder
with the excitation and emission fibers arranged at 90 degrees. The fluorescence
spectra measured for the honey samples (measurement time was kept
constant for all samples) are shown in Figure 1. Differences in fluorescence
intensity and subtle differences in spectral shape are observed for all samples.
The broad fluorescence peak observed between 400-700 nm in each
spectrum results from the presence of flavonoids (antioxidant compounds) in
the sample. Variations in the shape of these fluorescence spectra are primarily
attributed to differences in the flavonoid composition of the nectar used to
make the honey. Note that the small peak at 365 nm is not fluorescence from
the honey but excitation energy that is scattered into the spectrometer by the
undiluted, optically dense honey samples.
The flavonoids that dominate the fluorescence spectra for honey
(Figure 1) are polyphenols. These plant metabolites determine the color, aroma
and flavor of the honey, and provide antioxidant and other health benefits.
The unique fluorescence spectrum for each honey sample illustrates the
power and sensitivity of fluorescence spectroscopy for characterizing honey.
The measurements we conducted focused on the fluorescence of a small
set of pure honey samples using a single excitation wavelength. Additional
measurements (like those done in Egypt and at other research labs around
the globe) could easily be done using the vast array of modular spectroscopy
components available. Measurements could be expanded to use a range of
LEDs for fluorescence excitation to find the optimal excitation wavelength for
the detection of honey adulterants. Also, Ocean Insight Vis-NIR spectrometers
and classification models have been used for honey discrimination.
In either case, through the use of modular spectroscopy components,
measurements could be taken out of the laboratory setting to test
honey quality during bottling or at the point of sale to authenticate that
the honey is 100% pure.
1 Ruoff, Karoui, et al. “Authentication of the Botanical Origin of Honey by
Front-Face Fluorescence Spectroscopy. A Preliminary Study,” Journal of
Agriculture and Food Chemistry, April 2005.
2 El-Bialee, Rania, et al. “Discrimination of Honey Adulteration Using
Laser Technique,” Australian Journal of Basic and Applied Sciences,
7(11) Sept 2013, Pages: 132-138
W www.oceaninsight.com M firstname.lastname@example.org
US +1 727-733-2447 EUROPE +31 26-3190500 ASIA +86 21-6295-6600
Figure 1: Fluorescence of pure honey with 365 nm excitation. The spectra are dominated by fluorescence response due to
the flavonoids present in the honey.