Olive oil is a rich source of beneficial, monounsaturated fats which are characterised by having a single double bond. As much as 75% of the fatty acids in olive oil consist of oleic acid (sometimes referred to as an omega-9). Of the remaining fats, around 15% are saturated (containing no double bonds) and 10% are polyunsaturated (containing more than one double bond).
Extra virgin olive oil
Extra virgin olive oil is the best quality and comes from the first pressing of the fruit. It retains the fresh, olive aroma and has the highest antioxidant content (vitamin E, carotenoids and polyphenols such as peppery oleocanthal) with less than one per cent acidity. Only around 10 per cent of olive oil is of this premium grade quality. It has a distinctive green hue and often hazes at room temperature.
Virgin olive oil
Virgin olive oil is next best in quality with an acidity level of not more than 1.5 per cent. It is also a premium product as it is not purified, and has a slightly more piquant taste.
Pure olive oil
Pure olive oil is a blend of refined olive oil mixed with virgin oil to provide flavour and a quality suitable for cooking. Although the flavour is less pleasing, this is the most widely sold oil as it is less expensive and also the best for cooking.
As the oil matures, oxidation occurs which detracts from the original flavour. Keep all types of olive oil somewhere cool and dark. Most oils are best used within one year of pressing, so buy from outlets where turnover is high, and avoid large containers (especially those made from tin or aluminium). In fact, buy all oils in small sizes, so you renew them frequently.
Cooking with olive oil
Pure olive oil remains stable at high temperatures and can be heated to 210°C before chemical changes occur and it starts to smoke. Virgin and extra virgin olive oils are less stable due to their higher content of heat-sensitive (but flavourful) components and may cause unwanted smells or taste changes if heated above 180°C. Use pure olive oil for frying and roasting, and virgin or extra virgin olive oils for steaming, lower-temperature braising and salad dressing. Discard any oil that begins to smoke or smell odd during use. Ideally, cooking oils should not be re-used.
Health benefits of olive oil
Olive oil contains plant sterols which reduce absorption of cholesterol within the gut. Oleic acid is also processed in the body to slightly lower levels of total and ‘bad’ oxidised LDL cholesterol while increasing desirable high-density lipoprotein (HDL) cholesterol. These effects are most marked with extra virgin and virgin olive oils.
Studies have found that higher consumption of olive oil is associated with a lower blood pressure in those following a Mediterranean style diet, young women with mild hypertension, healthy males, elderly people with hypertension, and those with type 2 diabetes. Whether these effects are due to the polyphenols, the monounsaturated fats or a combination of the two remains unclear.
More recently, olive oil was shown to protect against a number of neurological conditions, including dementias, multiple sclerosis, Parkinson’s disease and reduced blood flow (cerebral ischaemia) related to ageing.
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