APPLICATION NOTE UV/Vis Spectroscopy Author: Jorge Puente PerkinElmer Espana SL Tres Cantos, Madrid, Spain Determination of Olive Oil Purity and Degree of Oxidation using the LAMBDA XLS Introduction Olive oil is well established in the food industry. Demand continues to grow not only because of its distinct flavor, but also because of an increased awareness of its health benefits. In fact, the FDA allows producers of olive oil to place a health claim on their products because there is some scientific evidence to support a risk reduction of coronary heart disease by consuming a higher proportion of monounsaturated fat in one’s diet. This is significant because olive oil is considerably rich in monounsaturated fats, most notably oleic acid. It is therefore of interest to producers to know the quality of the oil, its state of preservation, and changes brought about in it by technological processes. The quality of the olive oil is studied by measuring the characteristics of the absorption bands between 200 and 300 nm. These are frequencies related to conjugated diene and triene systems. A low absorption in this region is indicative of a high-quality extra virgin olive oil, whereas adulterated/refined oils show a greater level of absorptions in this region. Instrumentation The PerkinElmer LAMBDA™ XLS UV/Vis spectrophotometer, shown in Figure 1, is a standalone, robust scanning spectrophotometer with no moving parts and a unique Xenon® Lamp Source (XLS) with a typical lifetime of five years. The LAMBDA XLS is equipped with a large LCD screen making running methods and viewing data easier. Results can be printed, stored, or exported into Microsoft® Excel® for use on your personal computer. Table 1. Measured and Permitted K Values of Commercial Olive Oils. Measured K Values Olive Oil Sample Type K232 K266 K270 K274 Delta K Extra Virgin - Sample 1 1.897 0.151 0.148 0.135 0.005 Extra Virgin - Sample 2 1.717 0.201 0.189 0.173 0.002 Virgin - Sample 3 1.436 0.240 0.248 0.223 0.016 Olive Oil - Sample 4 3.000 0.640 0.832 0.458 0.283 Method Olive oil samples were diluted in iso-octane (2,2,4trimethylpentane). All samples were measured in matched, synthetic fused silica cuvettes (10 mm is the recommended pathlength) running a solvent blank as a reference. Absorption measurements for purity determination were made at 232, 266, 270 and 274 nm. K values were calculated according to the equation shown in Figure 2. The purity of olive oil can be determined from three parameters: • K232 absorbance at 232 nm • K270 absorbance at 270 nm • Delta K (Figure 3) The LAMBDA XLS was used to collect UV data from four different label graded commercial olive oil samples. Results The results collected using the LAMBDA XLS for the four different graded olive oils are shown in Table 1. Figure 1. LAMBDA XLS UV/Vis spectrophotometer. Kλ = Absλ D = Dilution gr/L DxL L = cuvette pathlength Figure 2. K equation for λ nm. Conclusion The LAMBDA XLS is a reliable and cost effective system appropriate for keeping up with regulations around the standard method for measuring olive oil purity using a UV spectrophotometric technique. Delta K = K270 – K266 + K274 2 Figure 3. Delta K equation. PerkinElmer, Inc. 940 Winter Street Waltham, MA 02451 USA P: (800) 762-4000 or (+1) 203-925-4602 www.perkinelmer.com For a complete listing of our global offices, visit www.perkinelmer.com/ContactUs Copyright ©2008-2014, PerkinElmer, Inc. All rights reserved. PerkinElmer® is a registered trademark of PerkinElmer, Inc. All other trademarks are the property of their respective owners. 008298C_01