Rapid Honey Quality Profiling With Near-Infrared Spectroscopy (NIRS)

Honey mostly consists of two sugars – glucose and fructose – which make up roughly 85 % of its total weight. It also contains sucrose, a disaccharide that is composed of glucose and fructose, and other disaccharides such as turanose and maltose. These are present in concentrations ranging from 0.5 to 3.5 %.¹ Honey’s sugar content is generally measured using high-performance liquid chromatography (HPLC).

The color of honey is a quality attribute that is evaluated by consumers and an important sensory property in the beekeeping market. Worldwide, different types of honey are classified using the Pfund color scale. These parameters of honey quality can be simultaneously measured in as little as a few seconds, with no sample preparation required, by employing near-infrared spectroscopy (NIRS).

Image Credits: Metrohm Middle East FZC

Experimental Equipment

Samples of pure honey were measured using an OMNIS NIR Analyzer Solid (Figure 1). The measurements were all performed in transflection mode (1000–2250 nm), using a 2 mm gap size reflector and 28 mm disposable vials. OMNIS Software was used for all prediction model development and data acquisition.

HPLC was the reference method used to measure the concentration of fructose, glucose, sucrose, turanose, and maltose in honey. A Pfund colorimeter was used to measure color, alongside the Pfund scale, which ranges from 0 to 140 mm (from light-colored honey up to the darkest samples).

Figure 1. The OMNIS NIR Analyzer Solid from Metrohm. Image Credit: Metrohm Middle East FZC

Configuration

OMNIS NIR Analyzer Solid

The OMNIS NIR Analyzer Solid is a near-infrared spectrometer that can be used for both solid and viscous samples. Developed and produced in accordance with Swiss quality standards, it is the NIRS solution for routine analysis across the entire production chain. It applies the latest technologies and integrates into the modern OMNIS Software, resulting in the operability,  speed, and flexible utilization of this spectrometer.

Image Credit: Metrohm Middle East FZC

Small Reflector OMNIS NIR, 2 mm

Reflector with a gap size of 2 mm and an optical path length of 4 mm, used for the transflection measurement of liquids.

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Disposable Vials, 22 mm, Reflection

216 lockable disposable glass vials with a 28 mm diameter for analyzing solids in reflection.

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Result

The acquired NIR spectra of honey samples (Figure 2) were utilized to develop prediction models to quantify fructose, glucose, sucrose, turanose, and maltose content, as well as color. The quality of the prediction models was evaluated using correlation diagrams (Figures 3–8), which show a high correlation between the reference values and the NIR predictions. The respective figures of merit (FOM) display the forecasted prediction precision during routine analysis.

Figure 2. NIR spectra of honey analyzed on OMNIS NIR Analyzer Solid. Image Credit: Metrohm Middle East FZC

Results of Honey Glucose Content

Figure 3. Correlation diagram and the respective figures of merit for the prediction of glucose content in honey. Reference values were obtained with HPLC. Image Credit: Metrohm Middle East FZC

Source: Metrohm Middle East FZC

Results of Honey Fructose Content

Figure 4. Correlation diagram and the respective figures of merit for the prediction of fructose content in honey. Reference values were obtained with HPLC. Image Credit: Metrohm Middle East FZC

Source: Metrohm Middle East FZC

Results of Honey Sucrose Content

Figure 5. Correlation diagram and the respective figures of merit for the prediction of sucrose content in honey. Reference values were obtained with HPLC. Image Credit: Metrohm Middle East FZC

Source: Metrohm Middle East FZC

Results of Honey Maltose Content

Figure 6. Correlation diagram and the respective figures of merit for the prediction of maltose content in honey. Reference values were obtained with HPLC. Image Credit: Metrohm Middle East FZC

Source: Metrohm Middle East FZC

Results of Honey Turanose Content

Figure 7. Correlation diagram and the respective figures of merit for the prediction of turanose content in honey. Reference values were obtained with HPLC. Image Credit: Metrohm Middle East FZC

Source: Metrohm Middle East FZC

Results of Color

Figure 8. Correlation diagram and the respective figures of merit for the prediction of color in honey. Reference values were obtained with a Pfund colorimeter. Image Credit: Metrohm Middle East FZC

Source: Metrohm Middle East FZC

Conclusion

This article has shown how near-infrared spectroscopy can be employed in the quality control of honey. Fructose, glucose, sucrose, turanose, and maltose content can be measured at the same time in just a few seconds, as can the samples’ colors.

Measurements performed with NIR spectroscopy require no sample preparation or solvents, therefore saving users time and funds. Only one analytical technology is required for sample measurement when using NIRS. Table 1 compares it to other conventional methods. Finally, unlike HLPC, NIRS does not necessitate skilled technical operators to perform the measurements.

Table 1. Overview of analytical methods used for the determination of reference values in honey. Source: Metrohm Middle East FZC

Reference

1. Sevgi Kolayli, et al., (2012). CHAPTER 1. Sugars in Honey. Food and nutritional components in focus, (online) pp.3–15. DOI: 10.1039/9781849734929-00003. https://books.rsc.org/books/edited-volume/1813/chapter/2125161/Sugars-in-Honey.

This information has been sourced, reviewed and adapted from materials provided by Metrohm Middle East FZC.

For more information on this source, please visit Metrohm Middle East FZC.