From Grove to Table: Analyzing Key Polyphenols in Olives and Olive-Based Products
ABSTRACT
Olea spp., commonly known as the olive, is a plant genus comprising approximately 30 species, primarily distributed across Africa and the Mediterranean region. Around 2,600 varieties of olive have been recognized, with many cultivars selectively bred for table olive processing or olive oil production. Olives and olive-derived products are essential components of the Mediterranean diet, which has been shown to reduce the risk of cardiovascular diseases, diabetes, and cancer.
The polyphenols found in olives are partially responsible for the many recognized pharmacological properties of olive-based products, such as their antioxidant, antiviral, and immune-modulating effects. This paper will briefly discuss the analytical methods developed and offered by Eurofins Craft Technologies (ECT), designed to quantify several polyphenols found in both raw olives and refined olive products. These include 3,4-dihydroxyphenylglycol (DHPG), hydroxytyrosol, tyrosol, verbascoside, and oleuropein. Collectively, these compounds are referred to as Valuable Olive Polyphenols (VOPs).
I. Demands for olive products testing
Olive leaves and fruits (drupes and flesh) are rich sources of Valuable Olive Polyphenols (VOPs). Olive leaves contain approximately 6-14% oleuropein (an ester of hydroxytyrosol and ellagic acid) and up to 25% hydroxytyrosol. Commercially available oleuropein and hydroxytyrosol are often sold in the form of olive-leaf capsules, powders, or liquid extracts. Prolonged consumption of hydroxytyrosol and oleuropein (as a hydroxytyrosol precursor) can help lower plasma glucose levels and improve insulin resistance, while oleuropein may significantly reduce reactive oxygen species induced by cytokines.1
Olive leaf extracts offer numerous health benefits, particularly for individuals with diabetes, as they may help prevent neural damage, alleviate diabetic neuropathic pain, and reduce heat hyperalgesia. Verbascoside, DHPG, and tyrosol, though present in lower concentrations, can be converted into hydroxytyrosol and exhibit antioxidant properties, with DHPG being a potent antioxidant. Additionally, verbascoside (also known as acteoside) has been found to promote dopamine biosynthesis and may provide some antidepressant effects.
Increasing consumer demand for natural antioxidants, whether through diet or supplements, has led to a need for testing VOPs in both raw olives and refined olive products. VOP contents and characteristics are dependent on a variety of factors including harvest season, storage and processing conditions, and olive varieties therefore it is essential to accurately measure these concentrations in raw products for effective downstream processing. To meet this need, the scientists at Eurofins Craft Technologies have developed and validated two high-performance liquid chromatography (HPLC) methods for analyzing specific olive phenolics in raw olives and refined olive-based products, including olive leaf powder, olive concentrates or pomace juice, olive oil, olive oil margarine, and olive oil based mayonnaise.
II. Validated Methods For Olive Product Testing at Eurofins Craft Technologies
Both methods developed at Eurofins Craft Technologies provide high-resolution separation of olive phenolics, effectively analyzing both the complex matrix of raw olives (Figure 2) and the simpler matrix of olive-based refined products.
Our rigorous validation procedures demonstrated adequate accuracy and precision for both the complex matrix of raw olives and the simpler matrices of refined products (Table 1).
It is important to note that the concentration of VOPs are heavily influenced by various factors, including the plant parts (leaf, drupes – flesh or pit), harvest timing, storage conditions, and processing methods. Olive leaves are rich in hydroxytyrosol and oleuropein, while olive flesh contains these two compounds along with DHPG, tyrosol, and verbascoside in lower concentrations. Olive seeds, on the other hand, are abundant in hydroxytyrosol and tyrosol.
As fruit ripening progresses, oleuropein in the flesh decreases, while the concentrations of hydroxytyrosol, tyrosol, and verbascoside increase. Storage conditions have a significant impact on VOPs concentrations. For instance, DHPG is eliminated during alkaline (sodium hydroxide) treatment in table olive processing but is retained if olives are naturally brined without lye. In the case of olive leaves, drying at high temperatures can drastically alter the oleuropein content and antioxidant properties compared to air-drying or freeze-drying. Additionally, freeze-thawing of olive leaves (and possibly flesh) has been shown to negatively affect verbascoside levels while increasing hydroxytyrosol content, likely due to the release of compartmentalized glycosidases.
Processing methods also play a major role in determining VOPs content. In the "debittering" process for table olives, which involves alkaline treatment, oleuropein concentration decreases while hydroxytyrosol levels rise compared to fresh drupes. Olive oil, by contrast, contains much lower total polyphenols, around 0.3% – 1.5% of the olive fruit, with most VOPs remaining in the pomace after oil extraction. The oil fraction itself contains oleuropein as the primary VOPs, while hydroxytyrosol, tyrosol, and verbascoside are released into the olive-milling wastewater (OMWW).
Given the transient nature of VOPs, it is essential to estimate their content in both raw ingredients and refined products, as well as to track changes over time. VOPs testing at Eurofins Craft Technologies provides clients with product research, process optimization, all while ensuring product integrity.
AUTHOR BIO
Dr. Truc Mai is a scientist at Eurofins Craft Technologies (ECT), where she specializes in advancing the company's botanical portfolio and special testing services. Dr. Mai holds a BSc in Biotechnology from Vietnam National University, a Master’s in Biology from John Carroll University (OH), and a Ph.D. in Molecular Biology from New Mexico State University (NM).
With over a decade of experience in biological research, biotechnology, and separation sciences, Dr. Mai has made significant contributions to the development of innovative solutions at ECT, particularly in the areas of botanical research and advanced testing techniques. Her extensive background in molecular biology and biotechnology has enabled her to drive impactful advancements within the organization, particularly in the intersection of biology and applied science.
