Detection of olive oil adulteration by low-field NMR relaxometry and UV-Vis spectroscopy upon mixing olive oil with various edible oils

S Ok

doi:10.3989/gya.0678161

Abstract

Adulteration of olive oil using unhealthy substitutes is considered a threat for public health. Low-field (LF) proton (1H) nuclear magnetic resonance (NMR) relaxometry and ultra-violet (UV) visible spectroscopy are used to detect adulteration of olive oil. Three different olive oil with different oleoyl acyl contents were mixed with almond, castor, corn, and sesame oils with three volumetric ratios, respectively. In addition, Arbequina olive oil was mixed with canola, flax, grape seed, peanut, soybean, and sunflower seed oils with three volumetric ratios. Transverse magnetization relaxation time (T2) curves were fitted with bi-exponential decaying functions. T2 times of each mixture of olive oils and castor oils, and olive oils and corn oils changed systematically as a function of volumetric ratio. To detect the adulteration in the mixtures with almond and sesame oils, both LF 1H NMR relaxometry and UV-Vis spectroscopy were needed, where UV-Vis-spectroscopy detected the adulteration qualitatively. In the mixtures of Arbequina olive oil and flax, peanut, soybean, and sunflower seed oils, both T21 and T22 values became longer systematically as the content of the olive oil was decreased. The unique UV-Vis maximum absorbance of flax oil at 320.0 nm shows the adulteration of olive oil qualitatively.

Highlights

Olive oil is a “natural fruit juice” obtained from the fruit of Olea europea L. by mechanical or physical procedures (Zamora et al 2001)
The detection of olive oil adulteration was shown by LF 1H nuclear magnetic resonance (NMR) relaxometry and UV-Vis spectroscopy upon blending three olive oil samples having different oleoyl acyl contents with various edible oils
When the three olive oil samples were mixed with castor oil, both T21 and T22 values became shorter as the volumetric ratio of olive oil to castor oil was changed from 2:1 to 1:1, and even further to 1:2

Summary

Introduction

Olive oil is a “natural fruit juice” obtained from the fruit of Olea europea L. by mechanical or physical procedures (Zamora et al 2001). The consumption of olive oil has increased recently due to its sensory qualities such as taste and health benefits, namely the reduction of risk factors and prevention of the occurrences of chronic diseases like diabetes and obesity (Rohman and Che Man, 2010; Yang and Irudayaraj, 2001; Mendes et al, 2015). In addition to the increase in olive oil consumption, there are malpractices in olive oil production including adulteration. Olive oil is usually adulterated by blending with either pomace olive oil or other cheap edible oils including corn, peanut, and sunflower oils. Such malpractice causes threats and challenges to the suppliers and the health of the ultimate consumers (Gurdeniz and Ozen, 2009; Lizhi et al, 2010). It is essential to develop viable techniques for detecting adulterated edible oils

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