The present invention relates to a method for removal of saturated fat and contaminations from edible oils that are obtained from an organic raw material. In particular, the invention relates to a method by which saturated fat and contaminations are precipitated from organic oils and then perform a complete purification thereof by the use of an electric field.

Background of the invention

In raw materials used in the preparation of food products contaminations caused by the increased use of pesticides and other chemicals which accumulate in the environment represent an increasing problem. Oils intended for use in food products for human and animal consumption often contains toxic components, such as heavy metals, polychlorinated biphenyls (PCB), dioxins, flame retardants, and similar, which must be removed from the oil before the use thereof.

Sathivel, S. et al. "Adsorption of FFA in Crude Catfish Oil onto Chitosan, Activated Carbon, and Activated Earth: A Kinetics Study", Journal of American Oil Chemist's Society, 2004, Vol. 81, No. 4, pp. 493-496, has investigated the effect of chitosan, activated carbon and activated earth in the removal of free fatty acids from oils obtained from fish offals. It was found that chitosan was the most effective of the three investigated absorbents.

Maes. J. et al. "Removal of Dioxins and PCB from Fish Oil by Activated Carbon and Its Influence on the Nutritional Quality of the Oil", Journal of American Oil Chemist's Society, 2005, Vol. 82, No. 8, pp. 593-597, has investigated the removal of dioxins and PCB from fish oil when using activated carbon as an absorbent.

PCT NO2008/000238, belonging to the present applicant, discloses how to remove or reduce the amount of heavy metals and organic contaminations from marine oils by the use of chitosan.

It is often desirable to reduce the level of saturated fat in oils of marine and vegetable origin. It has now been shown that chitosan is very well suited also in this respect.

That chitosan binds to fat is well known. It is worth noting chitosan in contact with for instance mineral oil creates one hard lump. Therefore, it is very surprising that it is possible to remove saturated fat and contaminations from oils by the use of chitosan.

The object of the present invention is a method for removal of contaminations and saturated fat from oils of vegetable and marine origin by the use of at least one absorbent, and subsequently removal of formed precipitations mechanically and/or by the use of an electric field.

Summary of the invention

The present invention relates to a method for the removal of saturated fat and contaminations from marine and vegetable oils, comprising the steps:

1) mixing intimately a first absorbent agent comprising chitosan and a second absorbent agent comprising activated carbon into the oil to obtain a

homogenous suspension,

2) allowing the oil suspension to rest until most of the formed precipitations have sedimented before separating the sedimented layer from the oil, and

3) performing purification of the oil phase.

In an embodiment of the invention the final step of purification of the remaining oil phase, which contains mieroparticles of chitosan with absorbed substances, is performed by exposing the oil phase to an electric field between a cathode and anode in the reaction vessel to obtain that all remaining suspended substances are deposited on the anode, which field is obtained by direct current with a voltage in the range from about 0.1 to about 500 volt between the cathode and anode,.

The invention also relates to a purified oil obtained by the present method.

Brief description of figures

Figure 1 show schematically an example of a vessel suitable for use by the method of the present invention, which vessel may also be provided by a heating jacket for temperature control .

Figure 2 shows the same vessel provided with a mixing device.

Figure 3 shows the vessel provided with an electrode.

Figure 4 shows the vessel with the anode lifted out of the vessel for being cleaned.

Detailed description of the invention

The present invention relates to a method for obtaining organic oils that are free of contaminants, and simultaneously reduce the content of saturated fat by the use of at least one absorbent which forms precipitates comprising contaminants and saturated fat, and then remove all rests of precipitations by exposing the oil to an electric field generated with direct current.

The term "free of contaminants" is used herein to indicate that the content of foreign and potentially unhealthy compounds is well below the threshold values set by health authorities. The term "precipitation" is used herein to designate the combination of precipitated contaminants and saturated fat.

Suitable oils for purification according to the invention comprise edible oils of vegetable and marine origin.

In the purification of organic oils it is used at least one absorbent, preferably a first and a second absorbent, and optionally also auxiliary substances.

As the first absorbent is used chitosan, optionally together with carrageenan, alginates and chondroitine glycol, or mixtures thereof.

The preparation of chitosan is well known and described in detail in the literature, for instance ki EP 1,412,391 B l . Chitosan may be prepared from chitin which can be found in the shell of marine shellfishes. Chitin is a natural polymer containing acyl moieties (-CH3-CO-) which can be converted to a desired extent by treating the chitin with alkaline water and thus obtain chitosan. Depending on the conditions by the preparation of chitosan, a desired degree of the acetylation can be obtained, that is to say that not all acyl groups necessarily will be converted. In this way it is obtained a polymer chain consisting of randomly distributed chitosan and chitin monomers. The fraction of chitin is typically below 0.25. Chitin is insoluble in water, while chitosan is water soluble at acidic conditions, i.e. at pH below 7.

Depending on the conditions of preparation the polymer chain will get different lengths. Therefore, chitosan is often characterized by the viscosity of an aqueous solution of chitosan. Typically, 1 percent by weight of chitosan is dissolved in 1 percent by weight of acetic acid, and the intrinsic viscosity ([η j) of the solution is determined. From this follows that chitosan may have different properties depending on the degree of the acetylation, the distribution of chitin monomer units, chain lengths, cleavage products, and similar.

All types of commercially available chitosan may be used in the present invention, also salts and glucose amides of chitosan, and hydrolyzed chitosan. The chitosan may have a degree of acetylation from high to low, and the whole range of viscosities.

In principle the chitosan could be mixed directly into the oil, but since chitosan is not soluble in oils it is more suitable to use a chitosan-containing "purification" liquid. A typical purification liquid is prepared by dissolving chitosan in acidic water. All types of suitable acids may be used for this, preferably hydrochloric acid, acetic acid or hydroxyl acetic acid, most preferred hydroxyl acetic acid (glycolic acid). To keep the chitosan dissolved the purification liquid must have an acidic pH, i.e. pH must be below 6.5-7.

The purification liquid may have various compositions and still give acceptable results. As the purification liquid may be used an aqueous solution containing from about 0.1 percent by weight to about 10 percent by weight of chitosan and sufficiently of a strong acid to keep the chitosan dissolved. In principle there is no lower limit for the content of chitosan; however, for an acceptable effect the amount should be at least 0.1 percent by weight. The upper limit is determined by the solubility of chitosan in the purification liquid. Preferably the purification liquid comprises about 1 percent by weight of chitosan and about 1 percent by weight of an acid, such as glycolic acid. Experimentations in an industrial scale shows that the use of such a purification liquid can remove about 70-80% of the content of saturated fat in the oil which shall be purified.

Experimentations have shown that the efficiency of the "purification" liquid can be improved further if the solution in addition to chitosan also contains silica, bentonite, lime, coral sand, diatomaceous earth, calcium carbonate, carrageenan or ion exchangers, or a mixture thereof.

To remove the saturated a particularly suitable purification liquid contains in addition to about 1 percent by weight of chitosan and about 1 percent by weight acid, also about 0.5 percent by weight of carrageenan and about 0.5 percent by weight of silica.

As soon as the first absorbent has been suspended in the oil, the second absorbent may be added. As the second absorbent is preferably used activated carbon as particles, and preferably as powder, optionally together with bentonite,

diatomaceous earth, lime, calcium carbonate, coral sand or ion exchangers, or a mixture thereof.

The addition of activated carbon will result in that chitosan with absorbed substances coalesce into greater particles which will precipitate more easily. This reveals a surprising synergistic effect between chitosan and activated carbon. In this way the contaminations can easily be removed from the reaction mixture. The amount of activated carbon used in the purification is not critical; but should be kept as low as possible for practical and economy reasons.

During the addition of the first and second absorbents the oil mixture is stirred vigorously to obtain an intimate blending, followed by a short gentle stirring. The solution is then allowed to rest. The contaminations and saturated fat are now bound to the absorbents and form particles which will precipitate and then sediment as a layer on the bottom of the reaction vessel.

The above described purification liquid containing chitosan is mixed into the oil first, then activated carbon. It is also possible to first add the activated carbon to the oil. and then the purification liquid. Another option is to add activated carbon to the purification liquid before this is added to the oil. The invention is not restricted to adding the absorbent in any certain sequence.

The sediment can be drawn off through a valve in the bottom of the vessel. This procedure is suitable for efficient removal of greater amounts of contaminations. When the bottom layer has been drawn off through the valve in the bottom of the reaction vessel, the remaining oil will contain minor amounts of suspended substances. The reason is that not all precipitated substances will sediment to a bottom layer. Remaining contaminations can be removed in a traditional way by the use of a filtering device and/or a centrifuge. However, it has surprisingly been shown that the suspended substances can be removed in a simple way by subjecting the oil to an electric field generated with direct current. This method is an optional or supplemental method for removing the remaining amounts of suspended substances which exist in the form of microparticles in the oil. By this method a total removal of all suspended substances is obtained. This process may start at any stage of the purification method as soon as the blending procedure has been terminated and after that the oil has come to rest. This process is preferably started after that the bottom layer has been removed mechanically. Optionally, all sedimented substances can be removed by the use of an electric field generated with direct current without performing any mechanical removal; however, this is considered being somewhat unpractical.

For the removal of precipitated substances by the use of an electric field, it can be used a reaction vessel provided with a negatively charged electrode and a positively charged electrode. Analogous to electrolysis the negatively charged electrode will be termed cathode and the positively charged electrode anode. The jacket of the reaction vessel can be the cathode. The anode is immersed in the oil in the centre of the vessel. The applied direct current voltage between the electrodes is typically be in the range from about 0.1 to about 500 volt.

To obtain electric conductivity in the oil it may be suitable to add to the oil phase a diluted salt solution in an amount of about 0.1 percent by weight of the oil. However, this feature is not compulsory. The optional salt can be any salt giving electric conductivity. Preferably sodium chloride or ferric chloride is used. The salt solution can be added under stirring at any stage in the process. The ferric chloride will bind to chitosan and will deposit together with chitosan on the anode.

The oil phase containing suspended microparticles is exposed to the electric field in a period of time from about 10 seconds to many hours, depending on the conditions.

Chitosan has a negative charge and the precipitated or suspended substances thereon will therefore have a negative surface charge and will be attracted to the anode and deposit thereon. When a deposited layer of appropriate thickness has been formed on the anode, the anode is taken out of the vessel and cleaned. Deposited substances may often adhere firmly and have to be removed by the use of a mechanically device.

The anode is manufactured from a suitable electric conducting material, for example a metal alloy. The anode can be of any suitable shape, such as one or more rods, plates, wire nettings, etc. The process of removing the particles by the use of an electric field may in principle begin as soon as the first step of the decontamination method has been initiated. Optionally, this may be a separate method step performed after that the mixture which shall be purified has been allowed to rest, or after that most of the bottom layer has been drawn off or removed by any other means.

The collected waste must be disposed of in a depot approved by governmental autliorities for disposal of environmental hazardous waste. All contaminated substances separated in the method, such as the bottom layer drawn off or collected by filtering, or removed mechanically from the anode, may be evaporated to dryness. During the evaporation the chitosan will bind all contaminating substances and prevent them from evaporation. Chitosan will function in this way up to about 300 °C. The evaporation method can for example be per formed up to about 200 °C. At the end of the

evaporation method the remaining material is only solid substances which in fact are contaminations concentrated to the smallest possible volume.

A preferred embodiment of the method will now be described in more detail by reference to the figures.

A suitable reaction vessel for use in the method according to the invention is shown in figure 1. The reaction vessel may be of any suitable size. The reaction vessel may often be provided with an outside heating jacket to obtain that the temperature in the oil in the vessel is kept constant. A suitable stirring device having controllable speed is used for efficient blending, as shown in figure 2. The oil is filled in the reaction vessel and under gentle stirring brought to a temperature preferably in the range of 10 to 70 °C, more preferred in a range from 20 to 50 °C, typically about 40 °C. All steps in the purification method are preferably performed at about the same temperature.

The purification liquid solution is then added to the oil under vigorous stirring until an intimate blending with the oil has been obtained.

The purification liquid is added to the oil in an amount corresponding to from about 0.001 percent by weight to about 10 percent by weight of chitosan, preferably from about 0.1 percent by weight to about 0.5 percent by weight of chitosan, more preferred about 1 percent by weight, typically about 0.1 percent by weight, based on the weight of the oil which shall be purified.

After that the purification liquid has been added to the oil, activated carbon is added. Activated carbon may also be dispersed in the purification liquid and then add this slurry. An option is also to combine the activated carbon with the oil before adding the purification liquid. Activated carbon is preferably used in the form of a powder or fine particles.

When the purification liquid and the activated carbon have been added to the oil, it will change its colour from a transparent, yellow colour to a turbid, obscure yellow-white colour. This indicates that the contaminations have been absorbed by the chitosan and are present as a suspension of microparticles in the oil. The oil is then allowed to rest while maintaining the temperature in the oil.

Operation parameters such as stirring speed, the period of time for each step, etc, will depend on the used equipment, and the type of oil and the amount of contaminations and saturated fat in the oil. A person skilled in the art will be able to easily decide on actual parameters by routine experimentation.

The particles suspended in the oil will sediment and form a bottom layer which can be drawn off through a valve in the bottom of the reaction vessel. The oil is then filtered to remove remaining suspended particles and possible solid substances. As an alternative to filtering, the microparticles in the oil may be removed by the use of an electric field, as described above. In that case the reaction vessel is provided with an anode, as schematically shown in figure 3. When this method has been finished, the anode is lifted out of the reaction vessel as schematically shown in figure 4. and the anode is cleaned.

If there is a possibility of oxidation of oil, the entire purification process according to the invention, or parts thereof, may be performed in an inert atmosphere.

To control and ensure a good quality of the purified oil, as a routine a sample is drawn from each lot and analyzed. The final product is then fed to a suitable container for storing or shipment to the market.

The final product is a clear, pure oil free of objectionable flavours, heavy metals, contaminations and saturated fat.

Industrial applicability

The present invention is a method for removing saturated fat and

contaminations from organic oils by the use of chitosan to obtain precipitation of particles. The method is simple, cost efficient and suitable for industrial applicability. The invention can be used for industrial decontamination of all types of marine and vegetable oils.

Examples

The invention will now be explained in more detail in the following examples; however, these examples shall not be interpreted as any restriction of the scope of the invention.

Example 1

To determine the obtainable extent of decontamination of a marine oil by the use of the present invention, an experiment was performed with shark oil. Shark oil is a commodity and the provided batch of shark oil was analyzed. The total amount of contaminations, defined as the total amount of dioxins, furans and dioxin-resembling PCB, was found to be 67 picograms of contaminations per gram of oil.

The shark oil was filled into a reactor vessel equipped with a heating jacket and a stirring device. The oil was heated to about 40 °C under gentle stirring and kept at this temperature during the entire decontamination method.

A premade 1% aqueous solution of chitosan was poured into the oil under vigorous stirring, in an amount of about 2 g of chitosan per kg of oil. As soon as a homogenous mixture was obtained, the stirring was reduced to a gentle stirring. The oil now changed color from a transparent yellow to a turbid off- white/yellow color. The activated carbon powder was then strewn onto the oil under vigorous stirring. As soon as the carbon powder had been mixed into the oil, the stirring was reduced to a gentle stirring for a few minutes, and the oil was then allowed to rest. The formed solids were allowed to sediment, and then the supernatant oil was collected by the use of a pumping device and conveyed to a storing bank. The oil was analyzed for contaminations.

The procedure was repeated, except that the activated carbon was used as a powder.

To determine the effect of chitosan, the purification liquid was replaced with a hydrochloric acid solution in such an amount that the pH was adjusted to pH 5 and pH 3, respectively, and activated carbon was not added.

Example 2

Salmon oil, which is a commodity, was provided and analyzed. The total amount of contaminations, defined as the total amount of dioxins, furans and dioxin- resembling PCB, was found to be 9.9 picograms of contaminations per gram of oil.

The salmon oil was purified in the same way as disclosed in example 1 by the use of activated carbon in the form of powder or pellets.

The results obtained in examples 1 and 2 are presented in table 1. The results reveal that the purification of the oils with the use of a chitosan-containing purification liquid and activated carbon gives the clearly best result. Table 1

Example 3

A vegetable oil was stored at about 1 °C. The oil became turbid and a bottom layer of saturated was observed.

The same oil was heated to about 40 °C and a purification liquid consisting of about 1 wt% of chitosan, about 1 wt% of glycolic acid, about 0.5 wt% of carrageen and about 0.5 wt% of silica was combined with the oil. Activated carbon powder was added to this mixture in an amount in the range from about 0.1 to 10 grams of activated added under continuous stirring. The stirring was then terminated, and the mixture was allowed to rest and cooled down to ambient temperature. A bottom layer consisting of contaminations and saturated fat was obtained. The sedimented layer was drawn off through a valve in the bottom of the vessel.

The supernatant oil was then subjected to a method of particle precipitation method. To the oil was added about 0.1 wt% of aqueous sodium chloride. An electrode in the form of a metal plate was positioned in the centre of the vessel. A direct current voltage was applied between the wall of the vessel serving as a negative electrode (cathode) and the electrode in the centre of the vessel serving as a positive electrode (anode). On the anode a layer grew steadily thicker. The method was allowed to run as long as the anode layer increased in thickness. It lasted from 10 minutes to 10 days until the increase in thickness stopped. The anode was then lifted out of the oil in the vessel and the created layer was removed mechanically.

The purified oil was then stored at about 1 °C. The oil remained clear and no bottom layer sedimented. Analyzes of the oil revealed that contaminations and

5 saturated fat were absent.

Even if the present invention has been described and exemplified above with a minor selection of marine oils, a person skilled in the art will realize that the present invention can be used for the purification of all types of marine and vegetable oils. Thus, the invention shall not be construed to be restricted to the specific types of oils j o exemplified, but will encompass all equivalent embodiments. Modifications and

variations of the present method will be obvious to a person skilled in the art within the scope of the invention defined by the following claims.

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