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- Olive (Olea europaea)
- Mediterranean Diet
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Date:
08-29-2014 | HC# 041412-503
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Re: Review of the History, Chemistry, and Potential Health Benefits of Olive and Olive Oil
Uylaşer V, Yildiz G.
The historical development and nutritional importance of olive and olive oil
constituted an important part of the Mediterranean diet. Crit Rev Food Sci Nutr. 2014;54(8):1092-1101.
The olive (Olea europaea) has been regarded as a symbol of peace and has
played an important role in many ancient civilizations. The origins of the
olive tree have been traced back to 3150-1200 BCE in the Mediterranean region including
Turkey, Syria, Lebanon, Palestine, and
Israel. The primary direction of cultivation and trade of olive trees expanded
westward to Turkey, Egypt, Greece, Italy, Northern Africa, and eventually to Southern
France. Although there are around 600 species in the olive oil family
(Oleaceae), this review focuses mostly on O.
europaea, the only cultivated species.
Based on reports from 2011, it has been found
that most of the olive trees are used for olive oil production (90%) and the
rest are harvested for table olives. Moreover, about 81% of olive oil
production comes from European countries, followed by North Africa (11%), the
Near East (7%), and the Americas (1%). Furthermore, the majority of table olives
come from European countries (34.1%). In the past, olive oil was primarily used
as a lamp fuel (from late 19th to 20th century), whereas in
the 21st century, olives are more valued for their dietary and
nutritional qualities.
Olives are single-seeded fruits (drupes) that
vary in size, shape, oil content, and flavor. Table olives are harvested in
mid-autumn, whereas olives used for oil production are harvested when they turn
black in the late autumn or winter. Oleuropein is the bitter component of
olives that require these fruits to be processed before consumption. The most
common processing methods used to make the fruits more palatable include the
following: the Californian processing methods, the Spanish processing method, a
natural fermentation/brine method, and the Greek processing method. Some of
these methods involve fermenting, washing, brining, adding sodium hydroxide,
adding iron-salt, and/or air oxidizing the olives.
Olives
Olive and olive oil consumption are
associated with nutritional and medicinal effects, which may be attributed to
phenolics, and to a lesser extent to the tocopherols and monounsaturated fats.
Phenolics function as antioxidants, which provide health benefits and aid in
food preservation. Phenolic content varies depending on the processing method
(e.g., fermentation), cultivar type, irrigation methods, and the degree of
maturation. Some of the phenolics identified in table olives include tyrosol,
hydroxytyrosol, oleanolic acid, and most predominantly, oleuropein. In
addition, numerous other polyphenolics have been identified in olives. As olive
fruits mature, oleuropein and the total phenolic content generally decrease,
whereas tyrosol and hydroxytyrosol increase. The antioxidant activity of olives
are dependent on the structure of the phenolics (hydroxytyrosol has higher
activity than tyrosol), the color of the olive (black olives have more
antioxidant activity than green olives), the type of olive cultivar, as well as
the harvest season. In terms of medicinal uses, olives have been used to protect
against cardiovascular and gastrointestinal disorders. Olives have also been
shown to have beneficial effects on conditions such as cancer, constipation,
diabetes, rheumatism, and have exhibited antimicrobial activities.
Olive oil
Edible olive oils are categorized into six
different types of grades: extra virgin olive oil (acidity up to 0.8% with oleic acid), virgin
olive oil (acidity up to 2.0%), refined olive oil (less alpha-tocopherol and squalene
than virgin olive oil), olive oil (a mixture of refined and virgin olive oil),
refined residue olive oil (same triglyceride composition as virgin olive oil with
less phenolics but with more oleanolic acid and erythrodiol), and olive residue
oil (a blend of refined residue oil and virgin olive oil).
Virgin olive oil consists of two major
fractions, with the larger fraction consisting of triacylglycerols (mostly
oleic acid and some linoleic acid) and the smaller fraction consisting of
compounds such as tocopherols, sterols, triterpenic dialcohols, and phenolics.
Similarly to table olives, the phenolic content of olive oil varies depending
on many factors including extraction and separation techniques. Most of the
phenolic content of virgin olive oil consists of tyrosol, hydroxytyrosol, and
their secoiridoid derivatives (e.g., oleuropein). These phenolic compounds are
important for the stability of the oil, antioxidant effects, and may contribute
to anti-inflammatory and antiatherosclerotic effects.
The cardiovascular benefits of olive oil are
usually attributed to the high level of monounsaturated fatty acids; however,
other phytochemical components probably also contribute to these effects. Some
of the biologically active components of olive oil also include phenols,
alpha-tocopherol, and squalene. As with phenolics, the fatty acid content of
olive oil depends on a number of factors (e.g., cultivar, climate). The most
prominent fatty acids in olive oil include the monounsaturated oleic and
palmitoleic acids, as well as the polyunsaturated linoleic and linolenic acids.
Out of these fatty acids, oleic acid generally has the highest concentration in
olive oil. The fatty acid profile of olive oil determines the quality of the
oil and is also used to classify the oil (e.g., can determine cultivar
differences).
Both table olives and olive oil are important
products of the Mediterranean region and are one of the major
foods that are linked to the health benefits of the Mediterranean diet. The
authors describe numerous factors that may contribute to the phytochemical
diversity of olive products. Such information is important because some of
these differences may have an impact on their purported health benefits.
—Laura M. Bystrom, PhD
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