Therefore, an olive oil (yellow or green) can be extra virgin or virgin (top qualities), or refined (eg, olive oil and olive pomace oil), or even lampante (refined, but not edible). However, it is important to note that an extra virgin olive oil produced and conserved in the same conditions (same olives cultivars, geographical area, seasonality, extraction plant, storage condition of olives and oil) is expected to have a reproducible colour year-on-year. For this reason, the colour, if correctly defined and evaluated, could be an index of specificity for typical productions and could be included as a quality attribute in the Single Document of a PDO (protected designation of origin).
Q: Does the process of winterisation of olive oil affect the compounds known for health benefits (phenolic compounds, etc) and the quality or shelf life of the oil?
A: Some olive oil producers winterise their olive oil so that during the winter months it does not become solidified on cellar shelves. The winterisation step is typically applied in refined seed oils to reduce waxes and long-chain saturated triglycerides. However, it is not commonly applied in virgin olive oil. Winterisation involves cooling the oil (5-8°C) to allow crystallisation in 24 to 48 hours. The separation of the two phases is done via filtration or centrifugation. If the winterisation was applied to virgin olive oil, which is not usually the case, a minor change would be expected in the content of phenols (and in their corresponding contribution to shelf life) derived from water removal in the filtration process.
Q: It has been proven that olives grown in hotter climates have higher wax contents than those from colder climates; what effect/benefits does the wax content have on the oil?
A: Waxes are present on the fruit skin (epicarp) with the function to protect the inside of the fruit from the rain and limit the excessive evaporation/transpiration of water. Wax extraction and its absorption into the oil is more efficient when solvents are used; however, a limited amount of wax can be extracted by the oil itself when using mechanical methods of extraction.
In hot climates, olive fruits can arrive at the mill at rather high temperatures, which makes the wax more prone to be extracted by the oil. Mechanical extraction of oil from olives, when high temperatures or drastic conditions are applied, can also promote the extraction of wax, but a higher or lower content of wax has no benefit on the oil quality.
Q: Why do tyrosol derivatives have to be quantified in the calculation of olive oil polyphenols content to support the health claim provisioned in the EC Reg. 432/2012?
A: Tyrosol, in free and complex forms, is absorbed by humans upon olive oil consumption. The complex tyrosol forms are partially hydrolysed in the gastrointestinal tract and the colon, giving rise to free tyrosol. Tyrosol can be converted in vivo to hydroxytyrosol.
Tyrosol and its metabolites bind to low‑density lipoproteins (LDL), suggesting a possible protective effect on their oxidation. Despite the lack of in vivo data, cell-mediated oxidation experiments of LDL1 showed that tyrosol provided a 40 percent inhibition, whereas it could protect Caucasian colon adenocarcinoma (Caco)-2 cells from injury induced by oxidised LDL.2 Therefore, tyrosol inclusion in a health claim is scientifically supported and meaningful.
Q: Is it true that the more bitter the virgin olive oil, the better the quality?
A: Bitterness and pungency have been related to specific phenolic compounds in virgin olive oils. Although several studies in literature pointed out that these minor compounds play an important role in human health, protecting the blood lipids from oxidation (EC Reg. 432/2012), it is well known that the rejection of bitterness and pungency is a natural reaction for consumers. Phenolic compounds also help maintain the overall quality of virgin olive oils during their storage. This highlights the need for further efforts to disseminate to consumers the positive meaning of bitterness and pungency perceived in virgin olive oil.
Q: Why is olive oil sometimes cloudy – is it a defect or does it mean it’s more ecological/organic?
A: There are two reasons for the cloudiness of olive oil. One could be that part of the major components of the oil (triglycerides) moved to a solid state due to cold temperatures during the storage of the oil pallet before bottles were taken and put on the supermarket shelf. This phenomenon is reversible within a rather short time after exposure at room temperature.
Equally, if the olive oil is not filtered, some cloudiness can be expected due to the presence of tiny particles of organic material (olive flesh), as well as emulsified water in the bottle.
Neither of these circumstances which lead to cloudiness indicate low (or high) product quality.
Q: Is there an interest in vegetable oils obtained by co-milling olives with other products?
A: Vegetable oils obtained by co-milling olives with other products are interesting from a technological, nutritional and sensory point of view. These oils obtained solely by mechanical extraction can show interesting sensory profiles, due to the presence of olfactory, tactile or tasting active compounds derived from fruits, spices and by-products (lemon, capsicum, tomato peels and seeds). The nutritional and health properties are linked with their content in active lipophilic compounds (eg, lycopene from tomato peels and seeds). The mechanical extraction uses olive oil as the sole solvent and any other chemicals are not required, thus achieving a fully sustainable green process.
There is particular interest in developing natural and sustainable products, which also offer an array of choice in terms of flavouring, and the haute cuisine arena has shown enthusiasm for these new oils, with a view to fostering and enlarging the knowledge and consumer demand around virgin olive oils.
Q: How can we make olive oil production more environmentally friendly?
A: There are several technologies to recover phenolic compounds from the olive vegetation waters – a by-product of olive oil production. The olive vegetation water treatments are typically based on membrane filtration (ultrafiltration, nanofiltration and reversed osmosis) and/or the phenolic absorption using active resins that reduce the environmental impact of the vegetation waters, while at the same time, producing a phenolic extract.
The phenolic extract, characterised by various levels of purity, can be used in food processing as an ingredient with antioxidant and antimicrobial properties, or to produce functional food enriched with bioactive phenols.
This article was authored by a range of experts, including Professor Tullia Gallina Toschi (Alma Mater Studiorum – Università di Bologna, IT), Dr Diego Luis García González (CSIC – Instituto de La Grasa, SP), Professor Alessandra Bendini (Alma Mater Studiorum – Università di Bologna), Professor Maria Tsimidou (Aristotle University of Thessaloniki, GR), Dr Florence Lacoste (ITERG, FR), Professor Maurizio Servili (University of Perugia, IT), Dr Wenceslao Moreda (CSIC – Instituto de La Grasa, SP), Professor Lanfranco Conte (President of the Italian Society for Fats and Oils Researches), and Professor Paul Brereton (Queen’s University Belfast, UK) who was responsible the overall concept of OLEUM’s Question of the Month and the OLEUM Network. Dr Tassos Koidis (Queen’s University Belfast, UK) curated the questions and answer list in this article and coordinates the OLEUM Network where these questions were originally posted.
For more information about olive oil, visit: www.oleumproject.eu
This article was developed in the context of the project OLEUM ‘Advanced solutions for assuring authenticity and quality of olive oil at global scale’, funded by the European Commission (EC) within the Horizon 2020 Programme (2014–2020, GA no. 635690). The information expressed in this article reflects the authors’ views; the EC is not liable for the information contained herein.
- Di Benedetto, et al. 2007, Νutr. Metabol. Cardiovasc. Dis., 17, 535
- Giovannini, et al. 1999, J. Nutr., 129, 1269