Business owners, consumers helped by NMR measurements of polyphenols

Olive oil is known to have health benefits, from reducing the risk of heart disease and diabetes to providing anti-inflammatory and cognitive benefits. What is less well known, however, is that the health benefits vary greatly depending on the specifics of the particular olive oil. That’s why consumers who want the health benefits of olive oil could use some guidance when they face dozens of options at the store.

Based on an analysis of scientific studies, the European Food Safety Authority (EFSA) concluded five years ago that the “consumption of olive oil polyphenols contributes to the protection of blood lipids from oxidative damage.” The higher the polyphenol level, the greater the health benefits. Importantly, the processing involved in producing pure, regular or light olive oil destroys the crucial phenols. Only true extra virgin olive oils (EVOO) retain important polyphenols, such as oleacein and oleocanthal. Even among EVOOs, levels vary greatly.

As consumers become savvier shoppers, olive oil producers are increasingly interested in touting the specifics of the oil they make. To avoid misleading labels, some countries set minimum oleocanthal and oleacein requirements for an oil to be termed EVOO. Early harvest EVOOs, which boast some of the highest polyphenol levels, must meet additional standards, including having the olives picked by dates determined based on geography and climate.

Recently, business leaders from the Halkidiki region of Greece asked experts in the Laboratory of Pharmacognosy and Natural Products Chemistry at the University of Athens to measure the polyphenol levels in the region’s current early harvest olive oil. The university employed a method first described in the paper, “Direct Measurement of Oleocanthal and Oleacein Levels in Olive Oil by Quantitative H-1 NMR. Establishment of a New Index for the Characterization of Extra Virgin Olive Oils.” The research, by Evangelia Karkoula, Angeliki Skantzari, Eleni Melliou and Prokopios Magiatis, was published in the Journal of Agricultural and Food Chemistry on November 2, 2012.

When the researchers began, they set out to develop a fast and accurate method of measuring the olive oil content of oleocanthal and oleacein. Because these polyphenols react with water and methanol, commonly used chromatographic methods were problematic. The researchers created a new way to extract polyphenols from olive oil without using any reacting solvents. Then they directly measured oleocanthal and oleacein levels using q1H NMR. They recorded the spectra using a Bruker Avance 600.

The results illustrated that oleocanthal and oleacein levels are highest in oils made from olives harvested early in the season. While most EVOOs are labeled with the date by which the oil is best consumed, few have information about when the olives were harvested. The basic rule of thumb is that olive oil with a slightly bitter taste and greenish hue, sold in a container that shields the oil from light, is more likely to have higher levels of oleocanthal and oleacein. While that basic rule might be somewhat helpful, actual data about polyphenol content is more useful, and useful information was exactly what the olive oil makers from Halkidiki wanted.

To gather data, scientists at the University of Athens laboratory used the q1H NMR methods demonstrated in the pivotal 2012 paper. They found that the average polyphenol content in early harvest Halkidiki olive oil was 495 mg/kg, significantly higher than the international average of 330 mg/kg. With data in hand, producers are making the case to consumers that Halkidiki early harvest olive oil has high nutritional value.

Given the variation in health benefits, as well as differences in price and availability, consumers benefit from knowing the polyphenol content of various olive oils. An NMR-based method, along with increasingly widespread and strict labeling requirements, will help consumers when they find themselves looking at shelves stocked with olive oil offerings.

For more information:

Olive oil as medicine: the effect on blood lipids and lipoproteins Mary Flynn, PhD, RD, LDN and Selina Wang, PhD, March 2015, UC Davis Olive Center at the Robert Mondavi Institute

Baiano A TC, Viggiani I, Nobile MAD. Effects of cultivars and location on quality, phenolic content and antioxidant activity of extra-virgin olive oils. J Am Oil Chem Soc 2013;90:103-111

Hernáez A, Fernández-Castillejo S, Farrás M, et al. Olive oil polyphenols enhance high-density lipoprotein function in humans: a randomized controlled trial. Arterioscler Thromb Vasc Biol 2014;34:2115-9.