Refining of vegetable oil

Details Refining of vegetable oil Refining of vegetable oil

1999-12-21

2001-06-26

Paden, Carolyn (Department: 1761)

Food or edible material: processes, compositions, and products

Inhibiting chemical or physical change of food by contact...

Treating liquid material

C426S417000, C426S601000, C554S008000, C554S009000

Reexamination Certificate

active

06251460

ABSTRACT:

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 >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 ≦1 wt. %. Fine virgin olive oil is allowed to have a free fatty acid content of ≦2.0 wt. %. Semi-fine or regular virgin olive oil is allowed to have a free fatty acid content of ≦3.3 wt. %. When a virgin oil has an acidity of >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 <0.5 wt. %. For complying with same provisions the content of wax esters must be <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° 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 >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° C. for two hours.
Caustic refining results in a colourless, transparent and bland olive oil. The content of wax esters is <350 ppm. The oil contains <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° 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° 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 >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° 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° C. and at a pressure of 3 mbar the stripping time should be less than 30 minutes. 5 to 25 m
3
of steam is used per kg of oil. Preferably, the stripping is carried out at a temperature of about 240° 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° C., preferably at 80-95° C., most preferably at 90° 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
−
is present in the oil. When sodium hydroxide is chosen as the lye, it is added in an amou

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