Quality control and analysis of foods and beverages cover the ability to assess sensory attributes, nutritional components, and chemical compositions of ingredients, contaminants, and more. UV-Visible spectroscopy is often used to obtain quick, inexpensive, easy-to-use analysis, especially for beverages, thin liquids, and oils, as well as sticky and thick liquids, like honey. One quality attribute of honey that can be of concern to consumers is color.
The World Health Organization adopted standards for honey (last amended in 2022) which note that “Honey sold as such shall not have added to it any food ingredient, nor shall any other additions be made other than honey. Honey shall not have any objectionable matter, flavour, aroma, or taint absorbed from foreign matter during its processing and storage.”
In addition, the US Department of Agriculture (USDA) grades the quality of extracted honey, and has designated color standards ranging from Water White to Extra White, White, Extra Light Amber, Light Amber, Amber, and Dark Amber. (You can find the table of color designations and the Pfund color grader scale on page 5 of the United States Standards for Grades of Extracted Honey.)
The Importance of Color
The color of honey is closely linked to its botanical origin and is a very important parameter to measure. It indicates its floral source (the flower from which the bees gather nectar to make honey), the mineral content, and can provide information about storage conditions.
The color of five different honey samples was determined by measuring their absorption using a UV-Vis spectrophotometer. From these measurements, the honey samples were further categorized by color based on where they fell on the Pfund scale.
The samples were transferred directly into 1.0 cm cuvettes, with care taken to not introduce bubbles into the samples. Deionized water was used as a blank. The honey color can be determined in the Pfund scale by measuring the absorbance at 560 nm and multiplying by a factor of 3.15. Based on these measurement, the purchased honey samples represented a range of colors from White to Light Amber. See Table 2.
Through these simple and quick measurements, the color of honey samples can be easily analyzed. By its nature, this information can tells us a great deal about the honey source, its mineral content, and can indicate if an unwanted byproduct was formed during storage.
UV-Vis Spectrophotometer Principles
UV-Visible spectroscopy is a well-established analytical technique used in the food and beverage industry for testing in the quality control stages. UV-Visible spectroscopy measures the absorption or reflectance of light in the ultraviolet and /or visible region of the spectrum.
In the most basic terms, spectrophotometers enable photometric comparisons of relative light intensities across the ultraviolet and visible spectrums. Directing a controlled, constant intensity light source (halogen, deuterium, xenon) across the spectrum or at a specific wavelength through a sample easily can confirm known or calculate unknown characteristics of the sample. The incident light (I0) can be redirected backward as reflection, suffer an energy loss as absorption, and pass through transparent or translucent samples as transmission. (Read more about UV-Vis spectrophotometers.)
The power of UV-Vis spectroscopy is that it quantitatively analyzes light absorbing chemical species and excels at measuring chemical composition, assessing physical and sensory parameters, and ensuring authenticity. Analytical chemistry has relied heavily on this technique and has had widespread use among scientists working on food and beverage development from concept to research & development and through commercialization.
For more details, watch the webinar: UV-Vis Spectroscopy Techniques in Food and Beverage Analysis.
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