Page 417 - Biosystems Engineering

394 Cha pte r F o u r tee n

Olive oil’s yield and commercial quality are substantially equiva-
lent among the three different extraction systems, whereas character-
istics and quantities of the by-products change significantly.
In the traditional system, the effluent is essentially constituted by
the water deriving from the olives, also called “vegetation water.”
In the three-phase system, to facilitate the separation of the oil by
decanter, potable water (in quantities equal to around 50 percent of
the original olive weight) is added to the olive paste before thermo-
mixing. For this reason, three-phase systems produce the largest vol-
umes of wastewaters.
The two-phase system appeared on the market in the early 1990s.
It is based on a technological improvement of the decanter that directly
separates the oil form olives without the addition of water. This system
practically does not produce liquid effluent but only one liquid–solid
mixed residue remains after industrial process. Nevertheless, the
two-phase pomace is more difficult to handle due higher moisture.
Environmental impact of olive oil production is considerable;
actually, about 5 to 7 million tons of olive mill effluent is produced
yearly. Olive mill wastewaters have a very high polluting level
because they are rich in organic substances. In fact, their chemical
oxygen demand (COD) and biological oxygen demand (BOD5) are
100 to 200 gL and 20 to 100 gL , respectively (Belice et al. 1990).
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On the other hand, olive mill by-products are a rich source of bio-
active olive polyphenols. In fact, the wastewaters are characterized
by a high content of polyphenols, ranging from 0.5 to 24 gL –1
(De Leonardis et al. 2009). Polyphenol level of the olive pomaces is
very variable, according to industrial procedures of oil extraction.
In particular, phenolic compounds are around 1.2 percent for press
process, 0.5 percent for the three-phase process, and 2.4 percent for
the two-phase process.
Finally, also olive leaves contain polyphenols in quantities vari-
able from 1.4 to 6.4 g 100 g of dry matter (Ryan et al. 2001; De Leonardis
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et al. 2007).

14.3 Nature of Olive Polyphenols
At least 30 different phenolic substances are identified in olives and
in their derived products (Montedoro et al. 1993). Although olive
polyphenols have been studied extensively, their qualitative and
quantitative compositions still vary too much because the data are
strongly affected by the analytical techniques applied and by the sol-
vent used to extract the phenols. At present, there is no worldwide
accepted official analytical method. Generally, in virgin olive oil, the
total phenols, extracted by different percentage concentrations of
methanol and water solution, are measured using the Folin–Ciocalteu
spectrophotometric method and are expressed as caffeic acid or gallic
acid in milligrams per kilogram of oil (ppm) .