Refining of vegetable oil

The present invention relates to a process for refining high acidity vegetable oil that includes PA0 a) stripping an optionally bleached vegetable oil with steam at a temperature of 120 to 250.degree. C. and a pressure of 0.7 to 5 mbar for 1 to 60 minutes; PA0 b) treating the oil obtained with lye; PA0 c) bleaching the oil obtained; PA0 d) stripping the bleached oil obtained with steam at a temperature of 120-250.degree. C. and a pressure of 0.7-5 mbar for 5-120 minutes. The resulting oil is bland, transparent and colorless. Refined olive oil is suited for blending with a virgin olive oil or to be used as an ingredient for the preparation of spreads, mayonnaises, tomato sauces and salad oils.

The present invention is concerned with a novel process for refining crude
 vegetable oil, particularly olive oil, and with a novel olive oil which
 contains 0.001-0.15 ppm of chlorophyll and &gt;0.2 wt. % of fatty acids.
 Olive oil as a salad oil and a frying oil is appreciated for its delicious
 taste not only in the traditional olive oil consuming countries, the
 Mediterranean area, but to an increasing extent also in Western Europe and
 the USA.
 Traditionally, olive oil is prepared by harvesting the olive fruits and
 subjecting these to malaxation: crushing and kneading the olives so that a
 mash is obtained containing the whole content of the olive fruit including
 an aqueous phase, an oil phase and solid remains of the olive fruits. The
 liquid part is quickly separated in an aqueous phase and an oil phase by
 decanting. The oil phase is further cleared from solid residues by
 filtration resulting into a first cold pressed olive oil, generally
 referred to as virgin olive oil.
 Virgin olive oils are placed into several quality categories. Extra virgin
 olive oil should have an absolutely perfect flavour and odour and a free
 fatty acid content in terms of oleic acid of .ltoreq.1 wt. %. Fine virgin
 olive oil is allowed to have a free fatty acid content of .ltoreq.2.0 wt.
 %. Semi-fine or regular virgin olive oil is allowed to have a free fatty
 acid content of .ltoreq.3.3 wt. %. When a virgin oil has an acidity of
 &gt;3.3 wt. % it is denoted as Lampante oil. Besides its high acidity
 Lampante oil also shows bad smell and off-flavour. It is therefore
 relatively cheap and is only suitable for consumption after refining.
 The undesired substances which are removed from the olive oil by refining
 comprise free fatty acids, oleanolic acid, pigments and off-flavour
 components.
 Generally, legal provisions require the free fatty acids amount in
 commercial refined olive oil to be &lt;0.5 wt. %. For complying with same
 provisions the content of wax esters must be &lt;350 ppm. During a
 deodorisation treatment the olive oil is exposed to high temperatures
 during a relatively long time. Free fatty acids will react with fatty
 alcohols when both are present in Lampante oil under formation of
 undesired wax esters. Therefore high contents of free fatty acids in crude
 olive oil may contribute to formation of wax esters during the refining
 process.
 Oleanolic acid is undesired because it may cause turbidity when olive oil
 is cooled to temperatures below ambient temperature. Removal of this
 component results in a transparent oil.
 The pigments carotene and chlorophyll are harmless and tasteless, but are
 removed because a colourless olive oil is desired for many applications.
 The usual processes for olive oil refining are physical refining and
 caustic refining. Physical refining avoids exposing the oil to alkaline
 chemicals and suffers less from the oil losses which make caustic refining
 more expensive. Caustic refining, on the other hand is necessary when a
 colourless oil, free from chlorophyll is desired.
 Physical refining comprises the following steps:
 1) washing the crude olive oil with water which is substantially free from
 iron, copper, zinc and calcium ions, followed by centrifuging to separate
 the water phase from the oil phase;
 2) bleaching the washed olive oil with standard bleaching earth, followed
 by filtration;
 3) stripping the bleached olive oil with steam at 3 mbar and 250.degree. C.
 for two hours.
 The content of wax esters in physically refined olive oil may be up to 400
 ppm.
 Although carotene is completely removed by physical refining, the refined
 olive oil is still coloured because it contains &gt;0.5 ppm, usually 0.6-0.8
 ppm of chlorophyll.
 Caustic refining comprises the following steps:
 1) washing the crude olive oil with water which is substantially free from
 iron, copper, zinc and calcium ions, followed by centrifuging to separate
 the water phase from the oil phase;
 2) treating the washed olive oil with a stoechiometric excess of lye;
 3) washing the deacidified olive oil with water;
 4) bleaching the washed olive oil with standard bleaching earth, followed
 by filtration;
 5) stripping the bleached olive oil with steam at 3 mbar and 250.degree. C.
 for two hours.
 Caustic refining results in a colourless, transparent and bland olive oil.
 The content of wax esters is &lt;350 ppm. The oil contains &lt;0.1 wt. % of free
 fatty acids, because for neutralization an excess of lye is used. The
 neutralized fatty acids form a soap which strongly promotes the
 neutralized olive oil to be emulsified in the aqueous phase. Subsequently
 the aqueous soap phase is discarded with the emulsified olive oil. On
 account of great oil losses, the efficiency of caustic refining is poor.
 SUMMARY OF THE INVENTION
 The present invention provides an efficient and economical process for
 refining of vegetable oil. By a sophisticated combination of refining
 steps the drawbacks of the conventional refining processes of vegetable
 oil with a high acidity have been overcome. The invented process comprises
 the successive steps of:
 stripping an, optionally bleached, vegetable oil with an inert gas at a
 temperature of 120-250.degree. C. and a pressure of 0.7 to 5 mbar for 1-60
 minutes, preferably 1-30 minutes;
 treating the stripped oil with lye;
 bleaching the oil obtained in the previous step;
 stripping the bleached oil with an inert gas at a temperature of
 120-250.degree. C. and a pressure of 0.7-5 mbar for 5-120 minutes.
 The process is generally suited for vegetable oils which need a refining
 treatment, particularly for high acidity oils, which have a high fatty
 acids content such as special types of crude olive oil.
 The refined olive oil which is delivered by the process is novel by its
 characteristic contents of chlorophyll and free fatty acids. The
 composition of olive oil according to the invention is characterised by
 the novel combination of 0.001-0.15 ppm of chlorophyll and &gt;0.2 wt. % of
 free fatty acids.
 DETAILS OF THE INVENTION
 Before the first stripping treatment the oil to be refined may be subjected
 to an optional bleaching treatment. The bleaching treatment removes
 already some of the chlorophyll. A standard bleaching earth is suitable,
 but, preferably, a non-activated bleaching earth is used.
 The amount of bleaching earth is 0.1 tot 2 wt. %, preferably 0.25 wt. %,
 based on the weight of the vegetable oil. Both optionally added phosphoric
 acid as well as the bleaching earth serve to remove iron and/or copper
 compounds. A suited amount of phosphoric acid (50% aqueous solution) is
 0.02 to 0.3 wt. %.
 The crude vegetable oil is washed several times with water, which is
 substantially free from iron, copper, zinc and calcium ions. By
 centrifuging oil and water are suitably separated.
 The washed vegetable oil is subjected to an initial mild stripping
 treatment with an inert gas, preferably with steam at a temperature of 120
 to 250.degree. C. and a pressure of 0.7 to 5 mbar and for a time which
 depends on the stripping temperature. However, the treatment should be
 relatively short: less than 60 minutes and preferably less than 30
 minutes, to ensure that no substantial amount of wax esters is formed. For
 instance, at a temperature of 240.degree. C. and at a pressure of 3 mbar
 the stripping time should be less than 30 minutes. 5 to 25 m.sup.3 of
 steam is used per kg of oil. Preferably, the stripping is carried out at a
 temperature of about 240.degree. C. and a pressure of about 2 mbar.
 This first stripping treatment removes at least a part of the fatty
 alcohols, oleanolic acid, pigments and volatile substances and a major
 amount of the free fatty acids. A typical reduction from 6 wt. % down to 1
 wt. % prevents in the next lye treatment substantial oil losses.
 The stripped vegetable oil is subjected to a treatment with lye, which
 generally takes places in a stirred tank under intensive agitation and at
 70-100.degree. C., preferably at 80-95.degree. C., most preferably at
 90.degree. C. Preferably, lye is added in just enough amount to make the
 oil colourless. More preferably, so much lye is added that 50-250 mmol of
 OH.sup.- is present in the oil. When sodium hydroxide is chosen as the
 lye, it is added in an amount of 0.2-1% (calculated as wt. % dry NaOH on
 oil), preferably in the form of a 5 N lye solution. The lye treatment
 effectively removes pigments and oleanolic acid is removed in the same
 time. Since the lye is used in such small amount, only very little fatty
 acid soap is formed.
 The lye is washed from the oil with water which is substantially free from
 iron, copper, zinc and calcium ions.
 The lye treatment is followed by a bleaching treatment. In this step any
 remaining metals are removed and the amount of pigments and decomposition
 products is further decreased. For bleaching conditions see the first
 (optional) bleaching treatment above.
 The next, final treatment comprises stripping the bleached oil with inert
 gas, preferably with steam. The conditions are chosen such that all
 remains of pigments and all volatile substances are removed. The
 conditions with respect to time and temperature can be kept so moderate
 that the content of wax esters remains relatively low.
 The process according to the invention is suited for efficiently and
 economically deacidifying oils with a free fatty acid content up to 15 wt.
 %. It is particularly suited for coloured oils, such as olive oil and palm
 oil. The term olive oil in the context of this specification comprises all
 oils derived from olives, including oils such as Lampante oil or olive
 residue oil (extraction oil, also denoted as ORO) Generally, these acidic,
 often coloured oils show a free fatty acid contents &gt;3 wt. %.
 The present process delivers a colourless and transparent oil, having a 450
 nm absorbency of &lt;0.01. It contains less than 350 ppm wax esters and is
 characterized by a chlorophyll content of 0.001-0.15 ppm. The amount of
 free fatty acids, however, is characteristic for physically refined olive
 oil and is generally more than the upper limit of 0.1 wt. % resulting from
 caustic refining.
 In the olive oil according to the invention the allowed amount of free
 fatty acids is at least 0.2 wt. %, preferably at least 0.3 wt. %, more
 preferably at least 0.4 wt. %, still more preferably at least 0.5 wt. %,
 still more preferably at least 0.6 wt. %. The costs of the final stripping
 step of the process are lower when the remaining amount of fatty acids is
 higher.
 The invention provides a process with mild stripping conditions and low
 exposure to alkaline chemicals. Nevertheless a bland, colourless olive oil
 is obtained with an acceptable fatty acid content.
 The colour of olive oil can be determined by UV spectroscopy. The UV-peaks
 between 400 and 700 nm in crude Lampante denote the presence of
 chlorophyll and carotenoid compounds. These peaks have disappeared in
 olive oil which has been refined according to the present invention.
 The obtained oil is bland and has a taste which is so stable that, when
 kept nine months under proper storage conditions, no change in taste can
 be detected.
 A refined Lampante oil obtained by the present process is allowed to be
 denoted as "pure olive oil". Generally, it is marketed as a blend with
 non-refined virgin olive oil. Such blends, generally, contain 80-98 wt. %
 of the refined olive oil. The 0.2-15 ppm of chlorophyll present in such
 blends originate from the added virgin olive oil.
 The refined olive oil may be incorporated also in food compositions which
 usually contain a substantial amount of fat, often 40 wt. % or more. The
 odourless and colourless oil is especially suited for the manufacture of
 spreads such as margarine. The fat phase of spreads used for buttering
 bread contain a liquid oil. The invented refined olive oil is particularly
 suited to serve as liquid oil for spread manufacture. It is also suited
 for the manufacture of mayonnaise, dressings, tomato sauces and salad
 oils. Usually in these food compositions 5 to 100 wt. % of the refined
 olive oil is incorporated.
 In the present specification weight percentages are calculated on the oil
 phase, unless specified otherwise.
 The invention is illustrated by the following example.

EXAMPLE
 Crude Lampante oil containing 5 wt. % of free fatty acids is stirred with
 0.08 wt. % of phosphoric acid (50% aqueous solution) for 15 minutes.
 Thereafter 0.25 wt. % of Volcansil.TM. bleaching earth is added and the
 mixture is stirred at 80.degree. C. under atmospheric pressure for 20
 minutes. Then the pressure is lowered and the bleaching process is
 continued under vacuum and at a water content of 0.1 wt. % for another 20
 minutes. The bleaching earth is removed from the bleached oil by
 filtration.
 The oil is stripped with steam at 245.degree. C. under a pressure of 3 mbar
 for 10 minutes.
 The stripped oil is treated with lye by intensive stirring at 90.degree. C.
 for 15 minutes. 3 wt. % of 5N lye is used. The treated oil is washed twice
 with water which is substantially free from iron, copper, zinc and calcium
 ions and then centrifuged.
 The washed oil is bleached with 0.25 wt. % of Volcansil.TM. bleaching earth
 under atmospheric pressure.
 The bleached oil is finally stripped with steam at 200.degree. C. under a
 pressure of 3 mbar for 120 minutes.
 A colourless, transparent and bland oil is obtained possessing a free fatty
 acid content of 0.25 wt. % and 200 ppm of wax esters.