Yvette Mattley, PhD

As a premium-priced, all natural product, honey is sometimes adulterated with substances such as sugar syrup, molasses, starch, and water to fool the consumer with a finished product that is less than pure. Detecting adulterated honey is a challenge due to natural variations in composition arising from nectar differences. Additional variability is added via processing and storage conditions. 

	As research has demonstrated, fluorescence measurements are ideal for a rapid screening of honey samples because fluorescence is nondestructive and simple to perform. Little to no sample preparation is necessary and testing does not require complicated instrumentation or highly trained personnel.

-FL spectrometer and a 365 nm LED as the fluorescence excitation source. Fluorescence spectra were measured for several different types of honey, including clover honey, golden blossom honey, orange blossom honey, and organic honey.

	Undiluted honey was pipetted into a disposable cuvette and placed in a 4-way cuvette 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 the samples) are shown in Figure 1. Differences in fluorescence intensity and subtle differences in spectral shape are observed for all of the samples.


	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.

	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 attributed to differences in the flavonoid composition of the nectar used in the honey. 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 shown in Figure 1 are polyphenols. These plant metabolites determine the color, aroma, and flavor of the honey, and provide antioxidant and other health benefits. The fluorescence spectrum for each honey sample illustrates the 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 could be performed by mixing and matching our modular spectroscopy components. For example, we could use a range of LEDs for fluorescence excitation to find the optimal excitation wavelength for the detection of honey adulterants.

	Regardless of our approach, through the use of modular spectroscopy components, measurements can 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 pure.


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The flavonoids that dominate the fluorescence spectra for honey shown in Figure 1 are polyphenols. These plant metabolites determine the color, aroma, and flavor of the honey, and provide antioxidant and other health benefits. The fluorescence spectrum for each honey sample illustrates the sensitivity of fluorescence spectroscopy for characterizing honey.

Fluorescence Spectroscopy Detects Adulterated Honey

Although most often associated with Christmas, multicolored holiday lights are used year-round as an appealing decorative accent. Today, LED lights are as ubiquitous as incandescent lights, with manufacturers touting their low power requirements, high efficiency, and bright color. But how do LEDs compare with incandescent decorative lights? Here's what we discovered when measuring the relative irradiance of several multicolored light strings.

Experiment Materials and Spectrometer Setup

	We tested one string of 20 multicolored incandescent lights and two strings of multicolored LED lights - one was a new, 10-light string and the other was a slightly used, 20-light string. The incandescent lights were purchased at a local pharmacy for about $4 and the newer LEDs for $5 (for half as many lights). All the lights were manufactured in China.

	Our measurement setup comprised a spectrometer (200–1025 nm), an integrating sphere, an optical fiber, and spectroscopy software. We used a radiometrically calibrated light source as the reference and measured the incandescent lights and newer LED lights straight from their packaging and the older LEDs on a "tree" fashioned out of laboratory clamps and fittings.

	The incandescent lights that we measured had broadband spectra with very strong intensity in the shortwave NIR region >700 nm (Figure 1). The light at these wavelengths produces heat, which makes the bulb warm during operation.


	Figure 1: In incandescent lights, heat results from the spectral output at wavelengths >700 nm.

	The LED light strings that we measured had narrowband emission with no intensity in the shortwave NIR region >700 nm, which allows the bulbs to remain cool to the touch even after long periods of operation. In addition to producing less heat, the LEDs are more energy efficient than incandescent lights.

	Generally, the LEDs produced brighter colors than the incandescent lights, especially in the blue and green bulbs (Figure 2).


	Figure 2: The LED bulbs had strong output for the colors tested, especially at blue and green wavelengths.

What Can Relative Irradiance Measurements Reveal?

	The spectrometer setup used for these measurements showed good results for the incandescent and LED lights tested, providing some insight into the differences between the two types. Variability in performance between the LED strings also was observed. Our experiment suggested that the LEDs perform very well spectrally, although to make an assessment of cost effectiveness versus incandescent lights would require additional testing and analysis.


	830 Douglas Avenue, Dunedin, FL 34698
	tel. +1 (727) 733-2447, fax +1 (727) 733-3962
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Although most often associated with Christmas, multicolored holiday lights are used year-round as an appealing decorative accent.

Author | Yvette Mattley, PhD

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