Determination of Olive Oil Purity and Degree of Oxidation Using the LAMBDA XLS

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.
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