Patent Grant
10221374
The present application is US national stage of international application PCT/EP2016/061964, which had an international filing date of May 27, 2016 and which was published in English under PCT Article 21(2) on Dec. 1, 2016. Priority is claimed to European application EP 15169311.6, filed on May 27, 2015.
The present invention relates to a process for refining glyceride oil, which uses treating glyceride oil with a liquid comprising a basic quaternary ammonium salt as part of the refining process. The present invention also relates to the use of contacting a glyceride oil with a basic quaternary ammonium salt for preventing or reducing the formation of fatty acid esters of chloropropanol and/or glycidol upon heating the glyceride oil.
There are a plethora of glyceride oils that may be extracted from natural sources for human or animal consumption, or for other domestic and commercial uses, including the production of bio-diesel. Such glyceride oils include, for example, vegetable oils, marine oils and animal fats and oils. Typically, it is necessary for glyceride oils to undergo refining before their use which can vary depending on the particular oil and the associated level and nature of any contamination following extraction and also depending, for instance, on the desired organoleptic properties of the refined oil.
Palm oil, for instance, is a vegetable oil derived primarily from the fruit of oil palms and is composed of a number of fatty acids, including palmitic and oleic acids, which are esterified with glycerol. Palm oil has numerous applications and is commonly associated with use in bio-diesel as well as food preparation or as a food additive, whilst it has also found use as an additive in cosmetics and cleaning products. Crude palm oil is known to contain vitamin E and is also one of the richest natural plant sources of carotenes, associated with pro-vitamin A activities, which has seen palm oil also used as a source of antioxidants.
Palm oil contains a large amount of highly saturated fats, has a high oxidative stability and is naturally low in cholesterol and, partly due to its low cost, is used increasingly in the food industry as a substitute for trans-unsaturated fats in certain processed food products. However, as with other glyceride oils, in order to be rendered edible crude palm oil must undergo a refining process to remove unwanted components. Crude palm oil comprises mono-, di- and tri-glycerides, carotenes, sterols, as well as free fatty acids (FFA), which are not esterified with glycerol. FFA leads to degradation of the oil and an increase in rancidity and is thus one of a number of components that the refining process seeks to remove. Other possible contaminants of glyceride oils, the removal of which has become critically important, are fatty acid esters of chloropropanols and/or glycidol (2,3-epoxy-1-propanol).
Fatty acid esters of chloropropanols and glycidol have been found to accumulate in glyceride oil, particularly refined oil which has been exposed to high temperatures, for example as a result of the refining process. Upon consumption, fatty acid esters of chloropropanols and glycidol are hydrolysed by lipases in the gastrointestinal tract, releasing free chloropropanols and glycidol. Chloropropanols encompass the monochloropropanediols 2-chloro-1,3-propanediol (2-MCPD) and 3-chloro-1,2-propanediol (3-MCPD), and the dichloropropanols 2,3-dichloro-1-propanol (2,3-DCP) and 1,3-dichloro-2-propanol (1,3-DCP).
The most common chloropropanol associated with the consumption of refined edible glyceride oils is 3-MCPD, which has been found to exhibit genotoxic carcinogenic effects in in vitro testing. As a result, the Joint FAO/WHO Expert Committee on Food Additives (JECFA) established a provisional maximum tolerable daily intake (TDI) of 2 μg/kg body weight for 3-MCPD in 2001, which was retained on review of new studies in 2006. Investigations into the potential carcinogenic effects of the other free chloropropanols have also been undertaken (Food Chem Toxicol, 2013, August; 58: 467-478).
Fatty acid esters of chloropropanols are thought to be produced from glycerides via the formation of a cyclic acyloxonium ion followed by ring opening with a chloride ion (Destaillats, F.; Craft, B. D.; Sandoz, L.; Nagy, K.; Food Addit. Contam. 2012b, 29, 29-37), as illustrated below where R is the alkyl chain of a fatty acid and R1═H or C(O)R; 1=2-MCPD ester; and 2=3-MCPD ester.
Water used as a stripping agent for deodorisation was initially suspected of providing a source of chloride, thereby exacerbating the formation of chloropropanol fatty acid esters and glycidyl fatty acid esters. However, this was shown not to be the case (Pudel et al., Eur, J. Lipid Sci. Technol. 2011, 113, 368-373) and it has instead been suggested that the chlorine donor must instead be present in the oil in an oil-soluble form to enable the formation of chloropropanols (Matthäus et al., Eur, J. Lipid Sci. Technol. 2011, 113, 380-386).
Inorganic sources of chloride typically found in glyceride oils include iron[III] chloride (a coagulant in water treatment), KCl or ammonium chloride (used to improve plant growth), and calcium and magnesium chlorides. Meanwhile, organochlorine compounds present in crude glyceride oils can be converted to reactive chlorinated compounds such as hydrogen chloride, for instance as a result of thermal decomposition, which can react with acyl glycerols as illustrated above. The organochlorines may be endogenously produced by plants during maturation (Matthäus, B., Eur. J. Lipid Sci. Technol. 2012, 59, 1333-1334; Nagy, K.; Sandoz, L.; Craft, B. D.; Destaillats, F.; Food Addit. Contam. 2011, 28, 1492-1500; and “Processing Contaminants in Edible Oils-MCPD and Glycidyl Esters”, AOCS Press, 2014, Chapter 1).
The International Life Sciences Institute (ILSI) Europe Report Series entitled “3-MCPD Esters in Food Products” by John Christian Larsen (October 2009) provides an overview of recent opinion with respect to 3-MCPD esters and their contamination in native, unrefined fats and oils, as well as refined fats and oils. Reported therein is an investigation conducted by Chemisches and Veterinäruntersuchungsamt (CVUA, Stuttgart, Germany), which indicated that traces of 3-MCPD esters can be found in some native, unrefined fats and oils. Meanwhile, significant amounts of 3-MCPD esters were found in nearly all refined fats and oils.
Deodorisation was identified as the crucial step in the refining process leading to formation of 3-MCPD esters. However, it was also found that there is some formation as a result of bleaching, for instance with bleaching earth. Furthermore, an acidic pre-treatment of crude oil, for instance with hydrochloric or phosphoric acids as part of degumming was also found to exacerbate 3-MCPD ester formation. The survey classified the refined vegetable oils and fats which were tested as part of the survey according to the level of 3-MCPD found to be ester-bound therein, shown below:
It is also reported that fatty acid esters of glycidol have also been detected in refined glyceride oils. Glycidyl ester (GE) is another known contaminant which has been classified by the International Agency for Research on Cancer (IARC) as “probably carcinogenic to humans” (IARC Group 2A) and their formation, for instance during heat treatment of vegetable fat, has raised additional safety concerns (IARC, 2000). Glycidyl fatty acid esters are thought to derive from the same acyloxonium intermediate from which fatty acid esters of 3-MCPD and 2-MCPD are formed. While 3-MCPD and 2-MCPD are formed by nucleophilic attack of a chloride ion on the acyloxonium, the glycidyl ester is formed by intramolecular nucleophilic attack of a hydroxyl group, as illustrated below (R is the alkyl chain of a fatty acid and R1═H or C(O)R).
This is supported by the above ILSI report which states that, in the absence of sufficient amounts of chloride ions in the crude oil, the reaction ends with glycidyl fatty acid ester formation. In contrast, under the conditions of analysis conducted in the above CVUA investigation, involving addition of sodium chloride, it is reported that glycidol nearly quantitatively reacts to form 3-MCPD. There are strong indications that a significant amount (10 to 60%) of measured bound 3-MCPD does in fact derive from fatty acid esters of glycidol formed as a result of the analysis itself.
Glycidyl fatty acid ester is believed to derive predominantly from diglycideride as a result of such an elimination of a fatty acid promoted by heat (Destaillats, F.; Craft, B. D.; Dubois, M.; Nagy, Food Chem. 2012a, 131, 1391-1398).
As mentioned above, the prevalence of fatty acid esters of chloropropanols and glycidol in glyceride oils increases substantially upon exposure to elevated temperatures and other process conditions associated with refining. Typically, phospholipid-containing glyceride oils such as crude palm oil undergo degumming with aqueous phosphoric acid and/or aqueous citric acid to remove hydratable and non-hydratable lipid components and other unwanted substances before FFA are removed. FFA are removed to improve organoleptic properties and oil stability. Deacidification in conventional processing is either by a chemical route (neutralisation) through the addition of a strong base such as sodium hydroxide (“chemical refining”) or by means of a physical route such as steam stripping (“physical refining”). Edible oil refining also typically includes bleaching (e.g. with bleaching earth or clay) and deodorisation (which may also be used to remove FFA) before the refined glyceride oil is considered fit for commercial use. Several methods have now been proposed in the prior art for the removal of fatty acid esters of chloropropanols and glycidol, or their precursors, from edible glyceride oils as part of the overall refining process.
WO 2011/009843 describes a process for removing ester bound MCPD by stripping vegetable oil or fat with an inert gas, such as nitrogen, during deodorisation instead of steam stripping. The process is performed at temperatures of above 140° C. and below 270° C. and therefore offers no significant energy savings over conventional glyceride oil refining processes.
Eur. J. Lipid Sci. Technol. 2011, 113, 387-392 discloses a method of removal of 3-MCPD fatty acid esters and glycidyl fatty acid esters from palm oil using a calcined zeolite and synthetic magnesium silicate adsorbent. WO 2011/069028 also discloses a process for removing glycidyl fatty acid esters from vegetable oil by contacting with an adsorbent, such as magnesium silicate, silica gel and bleaching clay, before steam refining and deodorizing the oil. Issues with the use of adsorbents include the potential for neutral oil losses and the lack of adsorbent recycle options which can have a significant impact on the economic viability of preparing refined glyceride oil.
It is also known, for instance from U.S. Pat. No. 2,771,480, that ion exchange resins can be used for removing FFA, colour-bodies, gums and flavour materials from glyceride oils by adsorption of these impurities onto ion-exchange resins. WO 2011/009841 describes the use of an ion exchange resin, such as carboxymethyl cellulose, for selectively binding species involved in the formation of MCPD esters, or the esters themselves, during the deodorisation process.
As an alternative, WO 2012/130747 describes a process for removing chlorinated contaminants from crude plant oil by means of a liquid-liquid extraction with a polar solvent solution, for example an acidified ethanol-water solution, which is non-miscible with the plant oil. The polar solvent phase is discarded following the extraction before the oil undergoes further refinement.
Liquid-liquid extraction techniques with polar solvents have previously been disclosed as oil treatments for glyceride oils, for instance for the removal of FFA, operating on the basis of the solubility differences of the contaminant and the oil effecting separation by selective partitioning into a particular solvent phase. Meirelles et al., Recent Patents on Engineering 2007, 1, 95-102, gives an overview of such approaches to the deacidification of vegetable oils. Liquid-liquid extraction methods are generally considered to be advantageous on the basis that they may be performed at room temperature, they do not generate waste products and they benefit from low neutral oil losses. However, Meirelles et al. observe that there are significant capital costs associated with the implementation of a liquid-liquid extraction process and there remain doubts as to the overall benefits. Moreover, the polar solvents used in these liquid-liquid extraction techniques are often capable of also removing mono- and di-glycerides from the oil in addition to FFA, which may not be desirable.
There remains a need for a process for preventing or reducing formation of fatty acid esters of chloropropanols and glycidol in glyceride oil which may be capable of providing high value products whilst maximising energy savings for the overall refining process.
The present invention is based on the surprising discovery that basic quaternary ammonium salts comprising a basic anion can be advantageously utilised for preventing or reducing formation of fatty acid esters chloropropanol and/or glycidol in glyceride oil, which treatment can be readily integrated into a glyceride oil refining process.
In addition, treatment of glyceride oil with a liquid comprising the basic quaternary ammonium salt has been found to at least partially remove pigments and odiferous compounds which are typically removed in a separate bleaching step and a high temperature (for example, 240° C. to 270° C.) deodorization step respectively during conventional refining processes. Treatment with a liquid comprising the quaternary ammonium salt has also been found to at least partially degum glyceride oil.
Treatment of glyceride oil with a liquid comprising the basic quaternary ammonium salt also allows for using lower temperatures and/or shorter time periods in the deodorization step of a glyceride oil refining process and less extensive degumming and/or bleaching may be required, if at all. This has the advantage of reducing energy requirements and materials costs associated with the refining process.
Thus, in a first aspect, the present invention provides a process for refining glyceride oil comprising the steps of:
The term “glyceride oil” used herein refers to an oil or fat which comprises triglycerides as the major component thereof. For example, the triglyceride component may be at least 50 wt. % of the glyceride oil. The glyceride oil may also include mono- and/or di-glycerides. Preferably, the glyceride oil is at least partially obtained from a natural source (for example, a plant, animal or fish/crustacean source) and is also preferably edible. Glyceride oils include vegetable oils, marine oils and animal oils/fats which typically also include phospholipid components in their crude form.
Vegetable oils include all plant, nut and seed oils. Examples of suitable vegetable oils which may be of use in the present invention include: acai oil, almond oil, beech oil, cashew oil, coconut oil, colza oil, corn oil, cottonseed oil, grapefruit seed oil, grape seed oil, hazelnut oil, hemp oil, lemon oil, macadamia oil, mustard oil, olive oil, orange oil, palm oil, peanut oil, pecan oil, pine nut oil, pistachio oil, poppyseed oil, rapeseed oil, rice bran oil, safflower oil, sesame oil, soybean oil, sunflower oil, walnut oil and wheat germ oil. Preferred, vegetable oils are those selected from coconut oil, corn oil, cottonseed oil, groundnut oil, olive oil, palm oil, rapeseed oil, rice bran oil, safflower oil, soybean oil and sunflower oil. Most preferably, the vegetable oil is palm oil.
Suitable marine oils include oils derived from the tissues of oily fish or crustaceans (e.g. krill) and oils derived from algae. Examples of suitable animal oils/fats include pig fat (lard), duck fat, goose fat, tallow oil, and butter.
FFA which may be present in the glyceride oils include monounsaturated, polyunsaturated and saturated FFA. Examples of unsaturated FFA include: myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linoelaidic acid, α-linolenic acid, arachidonic acid, eicosapentaenoic acid, erucic acid and docosahexaenoic acid. Examples of saturated FFA include: caprylic acid, capric acid, undecylic acid, lauric acid, tridecylic acid, myristic acid, palmitic acid, margaric acid, stearic acid, nonadecylic acid, arachidic acid, heneicosylic acid, behenic acid, lignoceric acid and cerotic acid.
Preferably the glyceride oil used in the present invention is a vegetable oil. More preferably, the glyceride oil is a vegetable oil selected from coconut oil, corn oil, cottonseed oil, groundnut oil, olive oil, palm oil, rapeseed oil, rice bran oil, safflower oil, soybean oil and sunflower oil. Most preferably, the vegetable oil is palm oil.
The term “palm oil” used herein includes an oil at least partially derived from a tree of genus Elaeis, forming part of the Arecaceae genera, and including the species Elaeis guineensis (African oil palm) and Elaeis oleifera (American oil palm), or hybrids thereof. Reference to palm oil herein therefore also includes palm kernel oil. The palm oil which is treated in accordance with the process of the invention may be crude or non-crude (i.e. at least partially refined). As such, reference to palm oil herein also includes fractionated palm oil, for example palm oil stearin or palm oil olein fractions.
The term “crude” used herein in reference to glyceride oil is intended to mean glyceride oil which has not undergone refining steps following oil extraction. For example, crude glyceride oil will not have undergone degumming, deacidification, winterisation, bleaching, depigmentation or deodorization. “Refined” used herein in reference to glyceride oil is intended to mean a glyceride oil which has undergone one or more refining steps, such as degumming, deacidification, winterisation, bleaching, depigmentation and/or deodorization.
“Chloropropanol” referred to herein corresponds to chloropropanols derived from glycerol by substituting one or two hydroxyl groups with chlorine and which include: 2-chloro-1,3-propanediol (2-MCPD), 3-chloro-1,2-propanediol (3-MCPD), 2,3-dichloro-1-propanol (2,3-DCP) and 1,3-dichloro-2-propanol (1,3-DCP). Fatty acid esters of chloropropanols referred to herein correspond to the mono- or di-esters of the chloropropanols with a fatty acid. Fatty acid esters of glycidol referred to herein correspond to the ester of glycidol with a fatty acid.
Where reference is made herein to a “salt comprising the quaternary ammonium cation” in step (ii), it is intended to refer to a salt which derives from the quaternary ammonium salt contacted in step (i), at least by virtue of the quaternary ammonium cation present in the salt separated in step (ii). In some examples, the salt comprising the quaternary ammonium cation may also comprise a chloride anion, as would be expected as a result of the original quaternary ammonium salt undergoing anion exchange. In other examples, the glyceride oil contains FFA and the salt comprising the quaternary ammonium cation also comprises an anion of a fatty acid. In further examples, the salt comprising the quaternary ammonium cation comprises the same anion as the quaternary ammonium salt contacted in step (i), in other words the salt separated in step (ii) is the same as the salt contacted in step (i).
The term “quaternary ammonium cation” used herein is intended to refer to a cation containing at least one nitrogen atom carrying a positive electric charge, which nitrogen atom is bonded only to carbon atoms. The nitrogen atom may be saturated, being bonded to four carbon atoms by single bonds, or may be unsaturated, being bonded to two carbon atoms by single bonds and to a third carbon atom by a double bond. Where the nitrogen atom is unsaturated, it may be part of a heteroaromatic ring, such as an imidazolium cation. Where the nitrogen atom is saturated, it may be part of an alicyclic ring, such as a pyrrolidinium or a piperidinium cation. Preferably, the nitrogen atom is bonded to four substituted or unsubstituted C1 to C12 hydrocarbyl groups, which may carry additional substituents at carbon atoms that are not bonded to the nitrogen atom carrying a positive electric charge. The term “hydrocarbyl group” refers to a univalent radical derived from a hydrocarbon and may include alkyl, cycloalkyl, alkenyl, alkynyl, or aryl groups.
The quaternary ammonium salt referred to herein is provided in the form of a liquid comprising the salt. The quaternary ammonium salt is non-volatile and exists only in its ionic form as part of the liquid. The liquid may be a solution of the salt in a suitable solvent. Suitable solvents include polar solvents such as aqueous or alcohol solvents, for example water, methanol or ethanol, or mixtures thereof. Preferably, the solvent is water. The quaternary ammonium salt may be an ionic liquid in which case the liquid contacted in step (i) may consist essentially of the ionic liquid or comprise the ionic liquid and one or more co-solvents. Suitable co-solvents include polar solvents such as aqueous or alcohol co-solvents, for example water, methanol, ethanol, or mixtures thereof.
The term “ionic liquid” as used herein refers to a liquid that is capable of being produced by melting a salt, and when so produced consists solely of ions. An ionic liquid may be formed from a homogeneous substance comprising one species of cation and one species of anion, or it can be composed of more than one species of cation and/or more than one species of anion. Thus, an ionic liquid may be composed of more than one species of cation and one species of anion. An ionic liquid may further be composed of one species of cation, and one or more species of anion. Still further, an ionic liquid may be composed of more than one species of cation and more than one species of anion. The term “ionic liquid” includes compounds having both high melting points and compounds having low melting points, e.g. at or below room temperature. The ionic liquid preferably has a melting point of less than 200° C., more preferably less than 100° C. and most preferably less than 30° C.
Preferably, the quaternary ammonium cation of the quaternary ammonium salt used in contacting step (i) according to the present invention is selected from:
[N(Ra)(Rb)(Rc)(Rd)]+,
wherein Ra, Rb, Rc and Rd are each independently selected from C1 to C8 alkyl, wherein one or more of Ra, Rb, Rc and Rd may optionally be substituted at carbon atoms that are not bonded to the nitrogen atom by one to three groups selected from: C1 to C4 alkoxy, C2 to C8 alkoxyalkoxy, C3 to C6 cycloalkyl, —OH, —SH, —CO2Re, and —OC(O)Re, where Re is C1 to C6 alkyl, for example by one to three —OH groups.
More preferably, the quaternary ammonium cation is selected from:
[N(Ra)(Rb)(Rc)(Rd)]+,
wherein Ra, Rb, Rc and Rd are each independently selected from C1 to C4 alkyl, including methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl and tert-butyl, wherein at least one of Ra, Rb, Rc or Rd is substituted each by a single —OH group. Substituted Ra, Rb, Rb or Rd are preferably 2-hydroxyethyl, 2-hydroxypropyl or 2 hydroxy-2-methylethyl.
Most preferably, the quaternary ammonium cation is choline: (CH3)3N+CH2CH2OH.
The quaternary ammonium salt used in contacting step (i) of the process of the present invention also comprises a basic anion selected from hydroxide, alkoxide, alkylcarbonate, hydrogen carbonate, carbonate, serinate, prolinate, histidinate, threoninate, valinate, asparaginate, taurinate and lysinate.
In an embodiment of the present invention, the basic anion is selected from alkylcarbonate, hydrogen carbonate, carbonate, hydroxide and alkoxide; preferably hydrogen carbonate, alkylcarbonate and carbonate; and more preferably hydrogen carbonate.
Where the basic anion is selected from alkoxide or alkylcarbonate, the alkyl group may be linear or branched and may be substituted or unsubstituted. In one preferred embodiment, the alkyl group is unsubstituted. In another preferred embodiment, the alkyl group is unbranched. In a more preferred embodiment, the alkyl group is unsubstituted and unbranched. The alkyl group may comprise from 1 to 10 carbon atoms, preferably from 1 to 8 carbon atoms and more preferably form 1 to 4 carbon atoms. The alkyl group may thus be selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl and/or decyl. It will be understood that branched alkyl groups such as iso-propyl, iso-butyl, sec-butyl and/or tert-butyl may also be used. Especially preferred are methyl, ethyl, propyl and butyl. In a further preferred embodiment, the alkyl group is selected from methyl and ethyl.
In an embodiment of the present invention, the basic anion is selected from serinate, prolinate, histidinate, threoninate, valinate, asparaginate, taurinate and lysinate, preferably from serinate, lysinate, prolinate, taurinate and threoninate, more preferably from lysinate, prolinate and serinate, most preferably the basic anion is lysinate.
It will be appreciated that in order for glyceride oil obtained directly from the process of the invention to be fit for consumption, the quaternary ammonium salt used for contacting the oil in step (i), as well as the salt comprising the quaternary ammonium cation separated in step (ii), should have little or no toxicity and/or be readily and substantially separable from the treated oil. A quaternary ammonium salt comprising a choline cation is particularly suitable for use with the process of the present invention. Choline is a water soluble essential nutrient grouped with the B-complex vitamins which is a precursor to acetylcholine, involved in numerous physiological functions. Choline has particularly low toxicity and excellent biodegradability, making it an ingredient known in nature that is capable of forming a quaternary ammonium cation which is particularly useful in the process of the present invention.
Thus, in particularly preferred embodiments of the present invention the quaternary ammonium salt is selected from choline bicarbonate: (CH3)3N+CH2CH2OH HOCOO−; choline alkylcarbonate: (CH3)3N+CH2CH2OH ROCOO− where R is an alkyl group; or choline hydroxide: (CH3)3N+CH2CH2OH OH−.
Quaternary ammonium salts comprising a basic anion selected from serinate, prolinate, histidinate, threoninate, valinate, asparaginate, taurinate and lysinate are also particularly suitable in the process of the present invention due to the particularly low toxicity of these amino acid derivatives.
In the most preferred embodiments of the present invention, the quaternary ammonium salt is choline bicarbonate: (CH3)3N+CH2CH2OH HOCOO−.
The quaternary ammonium salt used in contacting step (i), as well as the salt comprising the quaternary ammonium cation separated in step (ii), preferably have low oil solubility and preferentially partition into a non-oil phase, such as an aqueous phase, facilitating their removal from the treated oil. More preferably, the quaternary ammonium salt is immiscible with the oil. By immiscible with the oil it is meant that a glyceride oil saturated with the quaternary ammonium salt contains less than 50 mg/kg, preferably less than 30 mg/kg, more preferably less than 20 mg/kg, most preferably, less than 10 mg/kg, for example, less than 5 mg/kg of quaternary ammonium salt.
The solubility of the quaternary ammonium salt may also be tailored such that the quaternary ammonium salt is either insoluble or soluble in water. By insoluble in water it is meant that the quaternary ammonium salt has a solubility in water of less than 50 mg/kg, preferably, less than 30 mg/kg, more preferably less than 20 mg/kg, most preferably, less than 10 mg/kg, for example, less than 5 mg/kg. Preferably, however, the quaternary ammonium salt is miscible with water.
In preferred embodiments, the quaternary ammonium cation is selected to provide low melting fatty acid salts with linear C12 to C18 fatty acids. Particularly preferred quaternary ammonium cations form salts with such fatty acids having melting points of less than 100° C. Such salts may be conveniently separated during separation step (ii) by liquid-liquid separation techniques discussed below.
Suitably, the contacting step (i) of the process of the present invention is carried out at a temperature of less than 80° C., preferably from 25 to 65° C., more preferably from 35 to 55° C., for example, 40° C. As will be appreciated, where the glyceride oil is semi-solid at room temperature, higher temperatures are preferable such that the glyceride oil is in a liquid form for contacting with the liquid comprising the quaternary ammonium salt. Suitably, the contacting step (i) is carried out at a pressure of from 0.1 MPa to 10 MPa (1 bar to 100 bar).
In some embodiments, the contacting step may be carried out by contacting glyceride oil with the liquid comprising the quaternary ammonium salt in a vessel wherein the resulting mixture is stirred using, for example, a mechanical stirrer, an ultrasonic stirrer, an electromagnetic stirrer or by bubbling an inert gas through the mixture. Alternatively, the contacting step may be carried out by passing a mixture of the glyceride oil and the liquid comprising the quaternary ammonium salt through a static mixer, such as a Sulzer mixer or a Kenics mixer.
Suitably, the liquid comprising the quaternary ammonium salt and the glyceride oil may be contacted in a volume ratio of from 1:40 to 1:300. The contacting step may last from 1 minute to 60 minutes, preferably 2 to 30 minutes, more preferably, 5 to 20 minutes and most preferably, 8 to 15 minutes.
FFA present in the oil may be neutralised upon contact with the quaternary ammonium salt to form a quaternary ammonium fatty acid salt. In preferred embodiments, the amount of quaternary ammonium salt employed in the contacting step is at least stoichiometric with the molar amount of FFA contained in the oil. Preferably, the molar ratio of the quaternary ammonium salt to FFA in the oil is from 1:1 to 10:1, more preferably from 1:1 to 2:1. The content of FFA in the glyceride oil may be determined prior to treatment with quaternary ammonium salt using common titration techniques, of which the person of skill in the art is aware. For instance, titration with sodium hydroxide using phenolphthalein indicator may be used to determine the FFA content of glyceride oil.
In the contacting step (i), a liquid comprising the quaternary ammonium salt is contacted with the glyceride oil. The liquid may comprise a suitable solvent or mixture of solvents as described hereinbefore which is/are compatible with the quaternary ammonium salt and the glyceride oil. A solvent or mixture of solvents may be used to modify the viscosity of the liquid comprising the quaternary ammonium salt as desired. Alternatively, use of a solvent may confer desirable properties on the liquid structure of the liquid based reaction that are particularly suitable for promoting the reaction of the quaternary ammonium salt. As mentioned above, suitable solvents for this purpose include polar solvents, such as water, or alcohols, for example methanol or ethanol.
In preferred embodiments, the liquid comprising the quaternary ammonium salt comprises a solvent, preferably wherein the concentration of quaternary ammonium salt in the liquid is 15 wt. % to 90 wt. %. Preferably the solvent is water, such as deionised water.
Where the basic anion of the quaternary ammonium salt is selected from alkylcarbonate, hydrogen carbonate and carbonate, especially where the basic anion is hydrogen carbonate, it is particularly preferred that the liquid comprising the quaternary ammonium salt comprises a solvent, preferably water, and the concentration of quaternary ammonium salt in the liquid is 50 wt. % to 90 wt. %, preferably from 75 wt. % to 85 wt. %.
Where the basic anion of the quaternary ammonium salt is selected from hydroxide and alkoxide, especially where the basic anion is hydroxide, it is particularly preferred that the liquid comprising the quaternary ammonium salt comprises a solvent, preferably water, and the concentration of quaternary ammonium salt in the liquid is 15 wt. % to 60 wt. %, preferably from 40 wt. % to 50 wt. %.
In the above embodiments where the liquid comprises a solvent, additional co-solvents may also be present. For instance, where water is the solvent, alcohol co-solvent(s) may also be present. In the above embodiments, the concentration of co-solvents in the liquid may, for example, be between 1 wt. % and 40 wt. % of the liquid, preferably between 1 wt. % and 10 wt. %.
Separation of the salt comprising the quaternary ammonium cation in step (ii) of the process, may be carried out by gravity separation (for example, in a settling unit), where the treated glyceride oil is generally the upper phase and the salt comprising the quaternary ammonium cation together with any solvent are incorporated in the lower phase in the settling unit. Separation of the salt comprising the quaternary ammonium cation may also be achieved using, for example, a decanter, a hydrocyclone, an electrostatic coalescer, a centrifuge or a membrane filter press. Preferably, the phases are separated using a centrifuge. Contacting and separation steps may be repeated several times, for example 2 to 4 times.
Where the salt comprising the quaternary ammonium cation separated in step (ii) is a solid which is precipitated after contacting step (i), for instance, following formation of a quaternary ammonium fatty acid salt, the solid salt may be separated from the oil by filtration or centrifugation. Alternatively, a polar solvent as described hereinbefore which is immiscible with the oil phase may be added to solubilise the solid salt, following which the salt-containing phase may be separated from the oil by the methods described above.
Contacting and separation steps may also be carried out together in a counter-current reaction column. The glyceride oil (hereinafter “oil feed stream”) is generally introduced at or near the bottom of the counter-current reaction column and the liquid comprising the quaternary ammonium salt (hereinafter “quaternary ammonium salt feed stream”) at or near the top of the counter-current reaction column. A treated oil phase (hereinafter “product oil stream”) is withdrawn from the top of the column and a phase containing a salt comprising the quaternary ammonium cation and solvent when present (hereinafter “secondary stream”) from at or near the bottom thereof. Preferably, the counter-current reaction column has a sump region for collecting the secondary stream. Preferably, the oil feed stream is introduced to the counter-current reaction column immediately above the sump region. More than one counter-current reaction column may be employed, for example 2 to 6, preferably 2 to 3 columns arranged in series. Preferably, the counter-current reaction column is packed with a structured or a random packing material, for example, glass Raschig rings, thereby increasing the phase boundary surface. Alternatively, the counter-current reaction column may contain a plurality of trays.
In particularly preferred embodiments, contacting and separating steps are carried out together in a centrifugal contact separator, for example, a centrifugal contact separator as described in U.S. Pat. No. 4,959,158, U.S. Pat. No. 5,571,070, U.S. Pat. No. 5,591,340, U.S. Pat. No. 5,762,800, WO 99/12650, and WO 00/29120. Suitable centrifugal contact separators include those supplied by Costner Industries Nevada, Inc. Glyceride oil and the liquid comprising the quaternary ammonium salt may be introduced into an annular mixing zone of the centrifugal contact separator. Preferably, the glyceride oil and the liquid comprising quaternary ammonium salt are introduced as separate feed streams into the annular mixing zone. The glyceride oil and the liquid comprising quaternary ammonium salt are rapidly mixed in the annular mixing zone. The resulting mixture is then passed to a separation zone wherein a centrifugal force is applied to the mixture to produce a clean separation of an oil phase and a secondary phase.
Preferably, a plurality of centrifugal contact separators are used in series, preferably, 2 to 6, for example 2 to 3. Preferably, the oil feed stream is introduced into the first centrifugal contact separator in the series while the liquid comprising the quaternary ammonium salt feed stream is introduced into the last centrifugal contact separator in the series such that oil of progressively decreasing content of, for instance, FFA or free chloride anions is passed from the first through to the last centrifugal contact separator in the series while a quaternary ammonium salt stream of progressively increasing content of, for instance, quaternary ammonium-FFA salt and/or quaternary ammonium chloride content is passed from the last through to the first centrifugal contact separator in the series. Thus, a phase containing a salt comprising the quaternary ammonium cation is removed from the first centrifugal contact separator and the treated oil phase is removed from the last centrifugal contact separator in the series.
If necessary, residual quaternary ammonium salt that is present in the treated glyceride may be recovered by passing the product oil stream through a silica column such that the residual quaternary ammonium salt is adsorbed onto the silica column. The adsorbed quaternary ammonium salt may then be washed off the silica column using a solvent for the quaternary ammonium salt and the quaternary ammonium salt may be recovered by driving off the solvent at reduced pressure.
The treated glyceride oil may also be passed through a coalescer filter for coalescing fine droplets of non-oil phase liquid, for instance liquid comprising a salt of the quaternary ammonium cation, so as to produce a continuous phase and facilitate phase separation. Preferably, the coalescer filter comprises a filter medium made from a material which is easier wetted by the liquid comprising the quaternary ammonium salt than by the glyceride oil, for example a filter medium made from glass fibers or cellulose.
In some embodiments, for example where the quaternary ammonium salt is an ionic liquid, the liquid comprising the quaternary ammonium salt may be provided on a support material. Suitable supports for use in the present invention may be selected from silica, alumina, alumina-silica, carbon, activated carbon or a zeolite. Preferably, the support is silica. The supported form may be provided for contact with the oil as a slurry comprising a suitable solvent, wherein the solvent is as described hereinbefore.
Where supported quaternary ammonium salts are used, contacting and separation steps may also be carried out together by passing the oil through a column packed with a supported quaternary ammonium salt (i.e. a packed bed arrangement). In addition, or alternatively, a fixed-bed arrangement having a plurality of plates and/or trays may be used.
Methods for supporting the quaternary ammonium salt on a support material are well known in the art, such as for example, in US 2002/0169071, US 2002/0198100 and US 2008/0306319. Typically, the quaternary ammonium salt may be physisorbed or chemisorbed on the support material, and preferably physisorbed. In the processes of the present invention, the quaternary ammonium salt may be adsorbed onto the support in a quaternary ammonium salt:support mass ratio of from 10:1 to 1:10, preferably in a quaternary ammonium salt:support mass ratio of from 1:2 to 2:1.
It has been found that the quaternary ammonium salt used in accordance with the present invention is capable of preventing or reducing the formation of fatty acid esters of chloropropanol and glycidyl fatty acid esters in glyceride oils as a result of subsequent refining steps. Several reaction mechanisms are believed to be possible as a result of contacting the oil with a liquid comprising the quaternary ammonium salt, which are discussed in further detail below.
Formation of chloropropanol fatty acid esters and glycidyl fatty acid esters has been found to depend predominantly on: (i) the mono- and di-glyceride content of the glyceride oil; (ii) the chloride content of the glyceride oil; (iii) the proton activity of the glyceride oil; and (iv) the extent of heat exposure during refining. Treatment of glyceride oil with the quaternary ammonium salt in accordance with the present invention has been found not to affect the mono- and di-glyceride content of the oil and thus it is believed that it is the chloride content and proton activity that are reduced, thereby leading to the prevention or reduction of chloropropanol fatty acid ester and glycidyl fatty acid ester formation during the refining process.
Without being bound by any particular theory, of the possible reactions or interactions of the quaternary ammonium salt in the oil, anion exchange with free chloride ions is considered to be a means by which the free chloride content of the oil may be reduced. Meanwhile, the basicity of quaternary ammonium salt may also reduce the proton activity of the oil such that glycidyl fatty acid ester formation is also reduced. For example, the quaternary ammonium salt used in accordance with the present invention has also been found to neutralise FFA present in the oil and form salts comprising the quaternary ammonium cation of the salt used in contact step (i) and the carboxylate anion of FFA. It is also possible that the salt product of this acid-base reaction between the quaternary ammonium salt and FFA in the oil may also complex chloride anions and/or chlorine-containing compounds and contribute to their removal from the oil upon separating the quaternary ammonium fatty acid salt from the treated oil.
Thus, in some embodiments, the salt comprising the quaternary ammonium cation separated in step (ii) of the process may comprise a chloride anion. In embodiments where the glyceride oil which is contacted in step (i) comprises FFA, the salt comprising the quaternary ammonium salt which is separated in step (ii) may comprise an anion of a fatty acid.
Preferably, the process of the invention is used to prevent or reduce the formation of fatty acid esters of chloropropanol in glyceride oil. Most preferably, the process of the invention is used to prevent or reduce the formation of a fatty acid ester of 3-MCPD in glyceride oil.
In accordance with the process of the present invention, at least one further refining step is conducted after treatment of the glyceride oil with the liquid comprising the quaternary ammonium salt. The skilled person is aware of the different refining steps typically used in edible oil processing, including for example refining steps discussed in: “Practical Guide to Vegetable Oil Processing”, 2008, Monoj K. Gupta, AOCS Press, as well as in the Edible Oil Processing section of the “AOCS Lipid Library” website lipidlibrary.aocs.org.
The at least one further refining step (iii) may, for instance, be selected from: degumming, bleaching, winterization, depigmentation and deodorisation. Since the heat exposure typically associated with the deodorisation step is known to be responsible for a large increase in the formation of fatty acid esters of chloropropanol and glycidol, the quaternary ammonium salt treatment preferably precedes deodorisation. Thus, in preferred embodiments, the at least one further refining step according to the process of the present invention comprises deodorisation.
In some embodiments, the at least one further refining step (iii) comprises the steps of degumming, bleaching and deodorization. Alternatively, in other embodiments, the at least one further refining step (iii) comprises a deodorisation step and the process does not comprise a step of degumming and/or bleaching. Therefore, in exemplary embodiments, the at least one further refining step comprises the steps of degumming and deodorization, but no bleaching. In other exemplary embodiments, the at least one further refining step comprises the steps of bleaching and deodorization, but no degumming step.
An additional advantage of the treatment with quaternary ammonium salt in accordance with the present invention is that the basic quaternary ammonium salt has also been found to at least partially remove pigments and odiferous compounds which are typically removed in a high temperature (for example, 240° C. to 270° C.) deodorization step during conventional refining processes. Treatment of glyceride oil with the quaternary ammonium salt means that lower temperatures and/or shorter time periods can be used for the deodorization step as part of the overall refining process. This has the advantage of reducing the energy requirements of the refining process.
Degumming typically involves contacting the oil with aqueous phosphoric acid and/or aqueous citric acid to remove both hydratable and non-hydratable phosphatides (NHP). Typically, citric acid or phosphoric acid is added as a 50 wt % aqueous solution. Suitably, the aqueous acid is used in an amount of about 0.02% to about 0.30% of acid by weight of oil, preferably 0.05% to about 0.10% of acid by weight of oil. Suitably, the degumming step is carried out at a temperature of from about 50 to 110° C., preferably 80° C. to 100° C., for example 90° C. The degumming step may suitably last from 5 minutes to 60 minutes, preferably 15 to 45 minutes, more preferably, 20 to 40 minutes, for example 30 minutes. After settling of the mucilage following the acid treatment, the aqueous phase is separated before the degummed oil is typically dried. Drying of the degummed oil suitably takes place at a temperature of from 80 to 110° C. for a suitable time period, for example 20 to 40 minutes, at reduced pressure, for instance, at 2 to 3 kPa (20 to 30 mbar).
As the skilled person is aware, for glyceride oils with low phosphatide content (for example, less than 20 ppm by weight of phosphorus) a dry degumming process may be used in which the phosphoric acid or citric acid is added without significant dilution with water (for example, an 85% acid solution). NHP are converted into phosphatidic acid and a calcium or magnesium bi-phosphate salt which can be removed from the oil in a subsequent bleaching step. For oils rich in phosphatides, particularly NHP, dry degumming is known to be less well suited since excessive amounts of bleaching earth are required.
Bleaching is incorporated into an edible oil refining process to reduce colour bodies, including chlorophyll, residual soap and gums, trace metals and oxidation products. Bleaching typically involves contacting the oil with an amount of bleaching clay or earth, for example from 0.5 to 5 wt. % clay based on the mass of the oil. Bleaching clays or earths are typically composed of one or more of three types of clay minerals: calcium montmorillonite, attapulgite, and sepiolite. Any suitable bleaching clay or earth may be used in accordance with the present invention, including neutral and acid activated clays (e.g. bentonite). The oil is suitably contacted with bleaching clay for 15 to 45 minutes, preferably 20 to 40 minutes before the earth is separated, typically be filtration. The oil is typically contacted with bleaching clay or earth at a temperature of from 80° C. to 125° C., preferably at a temperature of from 90° C. to 110° C. Following an initial period of contact (“wet bleaching”) conducted under atmospheric pressure, a second stage of the bleaching process is conducted under reduced pressure (“dry bleaching”), for example at 2 to 3 kPa (20 to 30 mbar).
Conventional glyceride oil refining processes typically include a FFA neutralisation step with a strong base, for example sodium hydroxide or potassium hydroxide (corresponding to a so called “chemical refining” process). Alternatively, deacidification can be achieved by adjusting the deodorisation parameters accordingly to ensure that volatile FFA is removed in that step (a so called “physical refining” process). A disadvantage of a FFA neutralisation step (“chemical refining”) is that it is accompanied by unwanted saponification of oil, lowering triglyceride content, whilst soap formation from FFA can lead to substantial neutral oil losses as a result of emulsification. The quaternary ammonium salt treatment forming part of the refining process of the present invention is effective at neutralising FFA in the oil and may entirely replace a conventional neutralisation step used in a chemical refining process. Advantageously, treatment with the quaternary ammonium salt has the benefit that it leads to less or no saponification, in particular when a bicarbonate salt is used, and leads to less or no emulsification of neutral oil. Thus, in preferred embodiments of the present invention, the refining process does not include a neutralisation step with an inorganic base (e.g. sodium hydroxide).
As the skilled person is aware, deodorization corresponds to a stripping process in which an amount of stripping agent is passed through an oil, typically by means of direct injection, at reduced pressure for a period of time so as to vaporize and drive off volatile components, such as FFA, aldehydes, ketones, alcohols, hydrocarbons, tocopherols, sterols, and phytosterols. The stripping agent is preferably steam, although other agents such as nitrogen may be used. The amount of stripping agent suitably used is from about 0.5% to about 3% by weight of oil. Stripping may be carried out in a distillation apparatus for recovering volatile compounds removed with the stripping agent.
The temperature range of deodorization for the refining process according to the present invention is suitably from 160° C. to 270° C. Where reference is made herein to the temperature of the deodorization step, this refers to the temperature of the oil. The pressure range of deodorization is suitably from 0.1 to 0.4 kPa (1 to 4 mbar), preferably 0.2-0.3 kPa (2 to 3 mbar). Suitable time periods for deodorization are typically from 30 to 180 minutes, for example 60 to 120 minutes, or 60 to 90 minutes.
The skilled person is able to determine a suitable length of deodorization by analysing the appearance and composition of the glyceride oil, for instance by determining the p-anisidine value (AnV) of the oil. The p-anisidine value of an oil is a measure of its oxidative state and, more specifically, provides information regarding the level of secondary oxidation products contained in an oil, which are primarily aldehydes such as 2-alkenals and 2,4-dienals. The p-anisidine value (AnV) therefore also gives an indication of the level of oxidation products which are intended to be removed by means of the deodorization step. For instance, satisfactory deodorization may be achieved where, for example, the AnV is less than 10, preferably less than 5, as determined by AOCS Official Method Cd 18-90.
In addition or alternatively, the amount of aldehyde and ketone components of the oil can be determined, which are typically associated with a crude oil's odour, to determine whether sufficient deodorization has taken place. Typical volatile odiferous aldehyde and ketone components of crude or rancid palm oil include: acetaldehyde, benzaldehyde, n-propanal, n-butanal, n-pentanal, n-hexanal, n-octanal, n-nonanal, 2-butenal, 3-methylbutanal, 2-methylbutanal, 2-pentenal, 2-hexenal, 2E,4E-decadienal, 2E,4Z-decadienal, 2-butanone, 2-pentanone, 4-methyl-2-pentanone, 2-heptanone, 2-nonanone. Preferably, each of these components is individually present in a deodorized oil in an amount less than 3 mg/kg of oil, more preferably less than 1 mg/kg of oil, most preferably less than 0.5 mg/kg of oil.
The amount of aldehydes and ketones may be readily determined by chromatographic methods, for instance GC-TOFMS or GCxGC-TOFMS. Alternatively, derivatization of aldehydes and ketones may be used to improve chromatographic analysis. For example, it is known that aldehydes and ketones may be derivatized with 2,4-dinitrophenylhydrazine (DNPH) under acidic conditions. This reagent does not react with carboxylic acids or esters and therefore the analysis is not affected by the presence of such components in a glyceride oil sample. Following derivatization, HPLC-UV analysis can quantify the total amount of aldehydes and ketones which are present in a sample.
Conventional deodorisation temperatures are typically in excess of 220° C., for example 240° C. to 270° C., and deodorisation is typically operated for 60 to 90 minutes. Where lower than conventional temperatures are used for deodorisation as allowed by the process of the present invention, for example 160° C. to 200° C., the time periods for deodorization may be lengthened to ensure sufficient deodorization, yet still involve less energy consumption than a conventional deodorization operated at higher temperature, for example 240° C. to 270° C., for a shorter period.
In preferred embodiments, the same or lower than conventional deodorization time periods are used in combination with the lower than conventional deodorization temperature, yet achieve the same extent of deodorization as a result of the preceding quaternary ammonium salt treatment. In other preferred embodiments, where conventional temperatures are used for the deodorization step included in the refining process of the invention, for example 240° C. to 270° C., the time period for the deodorization may be reduced compared to that which is conventionally used and still achieve a comparable level of deodorization as a result of the preceding quaternary ammonium salt treatment.
The quaternary ammonium salt treatment therefore also has the advantage that it may reduce energy consumption during a subsequent deodorization step. In addition, by reducing either the temperature or time period of exposure to heat during the deodorization step, side reactions that can lead to undesirable organoleptic properties of the oil or formation of unwanted, potentially harmful by-products may also advantageously be reduced.
Where the at least one further refining step according to the process of the present invention comprises deodorisation, the temperature of the deodorization is preferably from 160° C. to 270° C. and more preferably from 160° C. to 240° C. In particularly preferred embodiments, the temperature of the deodorization is from 160° C. to 200° C., more preferably 170° C. to 190° C. Preferably, the time periods over which deodorisation is conducted at these temperatures is from 30 to 150 minutes, more preferably 45 to 120 minutes, most preferably 60 to 90 minutes.
The quaternary ammonium salt treatment according to the process of the present invention may suitably be applied to crude glyceride oil which has not undergone any previous refining steps following oil extraction. Alternatively, the process of the present invention may be applied to glyceride oil which has undergone at least one additional refining step prior to treatment with quaternary ammonium salt. Preferably, the at least one additional refining step is selected from bleaching and/or degumming.
As discussed above, degumming typically involves the addition of citric acid and/or phosphoric acid to remove phospholipids in the oil. It is possible that this step can increase the proton activity of the oil so as to increase the formation of glycidyl fatty acid esters on exposure to heat. It is also known that bleaching clay or earth which has been acid activated can be a source of contaminants such as chloride anions, for instance where hydrochloric acid has been used for acid activation. Such acid activated bleaching earth or clay can also increase the proton activity and potentially increase formation of glycidyl fatty acid ester formation on subsequent exposure to heat.
As such, in some embodiments, it is preferred that degumming precedes the quaternary ammonium salt treatment since this provides for the proton activity of the oil to be reduced by the quaternary ammonium salt after exposure of the glyceride oil to acid. In some embodiments, it is preferred that bleaching, particularly where a material comprising a source of chloride anions is used, precedes the quaternary ammonium salt treatment since this provides the opportunity for such contaminants to be removed by the quaternary ammonium salt treatment.
Advantageously, it has been found that the quaternary ammonium salt treatment forming part of the process of the present invention is also capable of at least partially degumming the oil and removing pigments which means that the extent of degumming and bleaching steps can be scaled back, for example, in terms of treatment time or materials. As mentioned above, the quaternary ammonium salt treatment forming part of the process of the present invention obviates a separate FFA neutralisation step used in a chemical refining process. Meanwhile, the quaternary ammonium salt treatment forming part of the process of the present invention may also be capable of reducing energy consumption in a deodorization step.
The basic quaternary ammonium salt treatment used in accordance with the present invention is intended to obviate the use of ion exchange resins and ultrafiltration membranes and the like for removing contaminants which can contribute significantly to the materials costs associated with glyceride oil refining. Thus, in preferred embodiments, the refining processes described herein do not comprise treatment of the glyceride oil with ion exchange resins or ultrafiltration membranes.
In some embodiments, the quaternary ammonium salt used in contact step (i) may be regenerated from the salt comprising the quaternary ammonium cation separated in step (ii) (where these salts are different) by means of a regeneration process in order to recycle the quaternary ammonium salt to the refining process of the invention, if desired. For instance, a regeneration process may comprise anion or cation exchange steps to obtain a quaternary ammonium salt comprising the desired basic anion as described hereinbefore.
In an embodiment, the regeneration process for regenerating choline bicarbonate from a choline fatty acid salt comprises the steps of:
(a) contacting the choline fatty acid salt with carbonic acid; and
(b) separating choline bicarbonate from FFA formed in step (a).
Preferably, step (a) is performed by contacting an aqueous solution comprising the choline fatty acid salt with CO2 (e.g. by bubbling CO2 through the aqueous solution).
The present invention also provides a use of contacting a glyceride oil with a basic quaternary ammonium salt as described hereinbefore for preventing or reducing formation of fatty acid esters of chloropropanol and/or glycidol in glyceride oil upon heating the oil. The contacting is preferably carried out before the oil is heated to temperatures in excess of 100° C., such as heating to a temperature of from 100° C. to 250° C., where substantial formation of fatty acid esters of chloropropanol and/or glycidol in glyceride oil would normally be expected.
The basic quaternary ammonium salt may be used in the form of a liquid comprising the basic quaternary ammonium salt as described hereinbefore. Preferably, the basic quaternary ammonium salt is used to prevent or reduce the formation of fatty acid esters of chloropropanol in the glyceride oil. Most preferably, the quaternary ammonium salt is used to prevent or reduce the formation of a fatty acid ester of 3-MCPD in the glyceride oil. Preferred embodiments of other aspects of the invention relating to the nature of the anion and cation of the quaternary ammonium salt, as well as the nature of the glyceride oil, equally apply to this aspect of the invention. For instance, it is most preferred that the glyceride oil is palm oil and that the quaternary ammonium salt is choline bicarbonate.
This use of a basic quaternary ammonium salt treatment provides treated oils that are better suitable for use in frying foods, preventing the formation fatty acid esters of chloropropanol and/or glycidol when the oil is used for frying food.
An analytical method for determining the concentration of MCPD in glyceride oil is described in R. Weißhaar, “Determination of total 3-chloropropane-1,2-diol (3-MCPD) in edible oils by cleavage of MCPD esters with sodium methoxide”, Eur. J. Lipid Sci. Technol. (2008) 110, 183-186. The amended German Society for Fat Science (DGF) Standard Method C-III 18(10) (German Standard Methods 2010) also provides a suitable procedure for determining the level of MCPD, or fatty acid esters thereof, as well as an indirect method for determining the presence of glycidol, or fatty acid esters thereof. Direct procedures for determining the content of chloropropanol and glycidol and their fatty acid esters involves use of Liquid Chromatography-Time of Flight Mass Spectrometry (LC-TOFMS), as reported in J Am Oil Chem Soc. January 2011; 88: 1-14.
Embodiments of the invention described hereinbefore may be combined with any other compatible embodiments to form further embodiments of the invention.
The present invention will now be illustrated by way of the following examples.
General Method for Determination of Acid Value (mg KOH/g of Oil) and FFA (wt. %) Content of Palm Oil.
To a beaker containing 60 ml of isopropanol was added 0.5 ml of phenolphthalein. This mixture was heated until boiling and 0.02 M potassium hydroxide in isopropanol was added until a faint pink colour persisted for approximately 10 s.
To a glass vial was added 0.200 g of the palm oil sample which was subsequently dissolved in 50 ml of the above hot isopropanol solution. The resulting solution was titrated whilst stirring with 0.02 M potassium hydroxide solution using a 25 ml burette graduated in 0.1 ml to the end point of the phenolphthalein indicator i.e until the pink colour persisted for at least 30 s.
The Acid Value (mg KOH/g of oil) was subsequently calculated using the formula:
56.1×N×V/m
where:
56.1 is the molecular weight (g/mol) of potassium hydroxide;
V is the volume (ml) of potassium hydroxide solution used;
N is the normality (mol/l) of the potassium hydroxide solution; and
m is the mass (g) of the palm oil sample.
Once the Acid Value has been determined, the FFA content may be derived. The FFA content for the purposes of the present disclosure is defined as a mass percentage while assuming the FFA to be an equal mixture of palmitic acid (molecular weight 256 g/mol) and oleic acid (molecular weight 282 g/mol), giving an average molecular weight of 269 g/mol. Oil with a FFA content of 1 wt. % contains 0.01 g of oleic/palmitic acid per 1 g of oil, which amount of oleic/palmitic acid corresponds to 3.171×10−5 mol. The amount of KOH required to neutralise this amount of oleic/palmitic acid (i.e. the Acid Value—AV) is calculated to be 2.086 mg of KOH/g of oil (3.171×10−5×56.1). Calculation of FFA content (wt. %) therefore has the following formula:
Wt. % FFA=Acid Value×0.479
A sample of 1 kg of crude palm oil (CPO) having a measured FFA content of 3.8 wt. % was heated to 50° C. in a thermostatically controlled water bath. The homogenized CPO was then added to a 2 l stirred tank reactor in which the reactor temperature was maintained at 50° C. by means of circulating heated oil. A stoichiometric amount of choline bicarbonate (80 wt. % in water supplied by Sigma-Aldrich UK) relative to the FFA content of the CPO was then introduced to the reaction vessel at a rate of 1-2 ml per minute. The mixture was stirred at 500 min−1 using a mechanical overhead stirrer for 1 h. Thereafter, the mixture was centrifuged at 4000 min−1 for 3 minutes to separate a phase comprising quaternary ammonium fatty acid salts and a treated CPO phase.
The separated oil phase was titrated and found to contain 0.29 wt. % FFA. Additional quality parameters were determined for the CPO and for the treated CPO, including diglyceride content, monoglyceride content, 3-MCPD fatty acid ester (3-MCPD-FA-Ester) content and glycidyl fatty acid ester (GE-FA-Ester) content. Results are provided in Table 2 below alongside the measuring methods used.
A sample of the same CPO as used in Example 1 having a measured FFA content of 3.78 wt. % was refined by a conventional physical refining process involving degumming, bleaching and deodorization using industry standard conditions set out in Table 1 below. Quality parameters for the refined oil were determined, including phosphorus value. Results are provided in Table 2 below alongside the measuring methods used.
Where reference is made herein to the use of the refining stages according to Table 1 as part of an oil refining treatment, experiments were performed using laboratory scale equipment (for example, a three-necked flask with stirring device, temperature measurement and vacuum connection). With regard to the deodorization according to Table 1, as well as the two-stage deodorization reported in examples below, this step was carried out with equipment including Deso-pistons allowing for water addition for steam stripping, a vacuum generator, a condenser, a thermometer and a heating mantle.
A sample of the quaternary ammonium salt treated palm oil from Example 1 was subjected to degumming, bleaching and deodorisation using the conditions set out in Table 1 above. Quality parameters for the refined oil were determined, including phosphorus value. Results are provided in Table 2 below alongside the measuring methods used.
Example 3 was repeated without the bleaching and degumming steps. Quality parameters for the quaternary ammonium salt treated and deodorized oil were determined, including phosphorus value. Results are provided in Table 2 below alongside the measuring methods used.
The results in Table 2 illustrate the advantages of the quaternary ammonium salt treatment as part of the refining process of the present invention. The results for Example 1 (quaternary ammonium salt treated oil) in comparison with CPO demonstrate that the quaternary ammonium salt treatment removes a significant amount of FFA whilst having minimal impact on mono- and di-glyceride content of the oil. The results for Examples 3 and 4 also demonstrate that, when the quaternary ammonium salt treatment is followed by deodorization, substantially all of the FFA in the oil is removed.
A comparison of the results of Examples 2, 3 and 4 also illustrates the benefit of the quaternary ammonium salt treatment in preventing or reducing the formation of chloropropanol fatty acid esters and glycidyl fatty acid esters in palm oil as a result of subsequent physical refinement. In Example 2, corresponding to a conventional physical refinement of CPO involving degumming, bleaching and deodorization, formation of 3-MCPD fatty acid ester is significant—increasing from 0.2 mg/kg in CPO to 2.8 mg/kg in the refined oil. Formation of glycidyl fatty acid ester is also substantial for this conventional refining process—increasing from 0.1 mg/kg in CPO to 23.9 mg/kg in the refined oil.
In contrast, when the quaternary ammonium salt treatment is integrated into the conventional physical refinement (Example 3), formation of 3-MCPD fatty acid ester and glycidyl fatty acid ester is significantly reduced—increasing from 0.2 mg/kg in CPO to only 0.5 mg/kg in the refined oil—despite a conventional high deodorization temperature (260° C.) being used. In Example 4, the quaternary ammonium salt treatment is employed and followed with deodorization, without intervening degumming and bleaching steps. A similar reduction in the formation of 3-MCPD fatty acid ester and glycidyl fatty acid ester in the refined oil is also observed for this example.
In Example 3 the quaternary ammonium salt treatment was followed by conventional degumming, bleaching and deodorization steps. In comparison, the conventional process of Example 2 differs by the absence of the quaternary ammonium salt treatment. Surprisingly, the phosphorus level observed for the oil of Example 3 is significantly lower than that of Example 2 (0.5 mg/kg compared to 1.1 mg/kg). This demonstrates that the quaternary ammonium salt treatment contributes to degumming of the oil. In Example 4, the quaternary ammonium salt treatment is followed only by deodorization, without any intervening degumming or bleaching steps. Although the quaternary ammonium salt treatment alone is not as effective as a conventional degumming step when a comparison is made between the phosphorus values of the oils of Examples 2 and 4 (1.1 mg/kg and 2.6 mg/kg respectively), the quaternary ammonium salt treatment alone is nevertheless capable of producing a satisfactory level of degumming. A desirable level of degumming in the case of refined palm oil corresponds to a reduction in phosphorus value to 5 ppm or below. Therefore, a value of 2.6 mg/kg (2.6 ppm) is well within a typical specification. This demonstrates that the quaternary ammonium salt treatment is capable of replacing a degumming step.
A sample of CPO having a measured FFA content of 3.97 wt. % was refined by a conventional physical refining process involving degumming, bleaching and deodorisation using the conditions set out in Table 1 above. Quality parameters were determined before and after refining of the oil. Results are provided in Table 3 below alongside the measuring methods used. Sensoric tests of the refined oil were also undertaken at KIN GmbH Lebensmittel Institute with a panel of four examiners judging color, taste, appearance and smell according to method BVL L 00.90-6 (published in the online database managed by Beuth-Verlag: “Official Collection of Testing Methods according to § 64 LFGB, § 35 of the Draft Tobacco Regulation and pursuant to § 28b of the Genetic Engineering Act”). Examiners judge each parameter on a scale of from 1 to 5 (1/2=Not for consumption, 3=Sufficient, 4=Good, 5=Excellent) and mean and median values of the judgement are presented as final results for each parameter. Typically, for an oil sample to be considered commercially acceptable, values for each parameter are required to be either 4 or 5. Results are provided in Table 4 below.
A sample of 4 kg of the same CPO as used in Example 5 was heated to 50° C. in a thermostatically controlled water bath before being added to a stirred tank reactor in which the reactor temperature was maintained at 50° C. by means of circulating heated oil. A stoichiometric amount of choline bicarbonate (80 wt. % in water supplied by Sigma-Aldrich UK) relative to the FFA content of the CPO was then introduced to the reaction vessel at a rate of 1-2 ml per minute. The mixture was stirred at 500 min−1 using a mechanical overhead stirrer for 1 h. Thereafter, the mixture was centrifuged at 4000 min−1 for 3 minutes to separate a phase comprising quaternary ammonium-FFA salts and a phase of treated palm oil. The separated oil phase was titrated and found to contain 0.05 wt. % FFA.
The treated palm oil was then subjected to a two stage deodorization, the first stage at a temperature of 240° C. for 10 minutes and the second at a temperature of 180° C. for 120 minutes (lower than a conventional deodorization temperature) and both stages operating at 0.2 to 0.3 kPa (2 to 3 mbar). No degumming or bleaching steps were undertaken. Quality parameters were determined for the treated palm oil before and after deodorization. Results are provided in Table 3 below alongside the measuring methods used. Sensoric tests of the quaternary ammonium salt treated and deodorized oil were also undertaken at KIN GmbH Lebensmittel Institute as described for Example 5. Results are provided in Table 4 below.
The two stage deodorization of example 6 was repeated, but the second deodorization stage was carried out with a temperature of 200° C. instead of 180° C.
A sample of the quaternary ammonium salt treated palm oil from Example 6 was subjected to degumming and bleaching steps as set out in Table 1 above followed by the two stage deodorization of example 6.
Example 8 was repeated, but the second deodorization stage was carried out with a temperature of 200° C. instead of 180° C.
1= Quaternary ammonium salt treated oil prior to deodorization;
2= Quaternary ammonium salt treated oil after deodorization.
The results in Tables 3 and 4 further illustrate the advantages of the quaternary ammonium salt treatment as part of the refining process of the present invention. As with the results provided in Table 2, Table 3 shows that the quaternary ammonium salt treatment is capable of substantially reducing the formation of chloropropanol fatty acid esters and glycidyl fatty acid esters in palm oil during a subsequent physical refinement. This can clearly be seen from a comparison of the chloropropanol fatty acid ester and glycidyl fatty acid ester contents of the oils of Examples 6 to 9 with the oil of Example 5, corresponding to the conventional physical refinement.
Table 3 also demonstrates that degumming and/or bleaching steps can also have a significant effect on the formation of glycidyl fatty acid esters following deodorization. For instance, when degumming and bleaching steps are included as part of the refining process (Examples 8 and 9), the content of glycidyl fatty acid esters is close to an order of magnitude higher than for refining processes where these steps are not included (Examples 6 and 7). This may be a result of changes in the proton activity of the oil following these process steps. Thus, where these steps can be at least partially or even fully replaced by the quaternary ammonium salt treatment, then the reduction in glycidyl fatty acid ester formation will be even further enhanced. Alternatively, bleaching and/or degumming steps may be implemented prior to treatment with the quaternary ammonium salt, such that the negative impact these steps have toward formation of glycidyl fatty acid ester may be eliminated prior to high temperature treatment in the subsequent deodorization.
The results in Table 4 indicate that when the quaternary ammonium salt treatment is integrated into a physical refining process, including degumming and bleaching, yet with a lower temperature deodorization stage (Examples 8 and 9) then results range from sufficient to excellent. The first higher temperature stage of the two-stage deodorization is intended to perform the majority of oil depigmentation. Lowering the deodorization temperature to 200° C. in the second stage (Example 9) results in a lower score in the refined oil's smell compared with the conventional physical refinement including a single stage high temperature deodorization (Example 5). However, superior sensoric results were surprisingly obtained when the temperature of the second stage of the two-stage deodorization was lowered still further to 180° C. following quaternary ammonium salt treatment, degumming and bleaching (Example 8). The quaternary ammonium salt treatment forming part of the process of the invention thus offers the possibility of lowering deodorization temperatures to reduce the energy expenditure of the refining process whilst still providing a product with adequate olfactory qualities.
Where the quaternary ammonium salt treatment also effectively replaces degumming and bleaching steps, sensoric qualities of the oil may not be satisfactory unless a conventional prolonged high temperature deodorization step is incorporated, as suggested by the results for Examples 6 and 7 in Table 4. However, it can again be seen that the sensoric results for Example 6 with the lower deodorization temperature of 180° C. were in fact better (and sufficient for consumption) when compared to Example 7 where a higher deodorization temperature of 200° C. was used. This suggests that other factors may be affecting the balance of odiferous compounds, for example aldehydes and ketones, at the lower deodorization temperatures.
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