FRACTIONATION OF TRIGLYCERIDE OILS

Abstract: Dry fractionation of triglyceride oil using as an additive a crystallisation modifying substance comprising a monoglyceride or diglyceride of fatty acids, optionally esterified with citric acid.

Description: Fractionation of triglyceride oils The present invention is concerned with a process for fractionating triglyceride oils. The fractionation (fractional crystallisation) of triglyceride oils is described by Gunstone, Harwood and Padley in The Lipid Handbook, 1986 edition, pages 213-215. Generally triglyceride oils are mixtures of various triglycerides having different melting points. The composition of triglyceride oils may be modified e.g. by separating from them by crystallisation a fraction having a different melting point or solubility. One fractionation method is the so-called dry fractionation process which comprises cooling the oil until a solid phase crystallises and separating the crystallised phase from the liquid phase. The liquid phase is denoted as olein fraction, while the solid phase is denoted as stearin fraction. The separation of the phases is usually carried out by filtration, optionally applying some kind of pressure. The major problem encountered with phase separation in the dry fractionation process is the inclusion of a lot of liquid olein fraction in the separated stearin fraction. The olein fraction is thereby entrained in the inter- and intracrystal spaces of the crystal mass of the stearin fraction. Therefore the separation of the solid from the liquid fraction is only partial. The solids content of the stearin fraction is denoted as the separation efficiency. For the dry fractionation of palm oil it seldom surpasses 50 wt.% . This is detrimental to the quality of the stearin as well as to the yield of the olein. For the related solvent fractionation process, where the fat to be fractionated is crystallised from e.g. a hexane or acetone solution, separation efficiencies may be up to 95%. Dry fractionation is a process which is cheaper and more environmentally friendly than solvent fractionation. For dry fractionation an increase of separation efficiency is therefore much desired. It is known to interfere with the crystallisation by adding to a crystallising oil a substance which will be generally indicated as crystallisation modifying substance. The presence of small quantities of such a substance in the cooling oil may accelerate, retard or inhibit crystallisation. In certain situations the above substances are more precisely indicated as crystal habit modifiers. Known crystallisation modifiers are e.g. sucrose fatty acid esters, described in US 3,059,010 and fatty acid esters of glucose and derivatives, described in US 3,059,011. These crystallisation modifiers are effective in speeding up the crystallisation rate but are not reported to increase the separation efficiency. They do not even allude to such an effect. Other crystallisation modifiers, e.g. as described in US 3,158,490 when added to kitchen oils have the effect that solid fat crystallisation is prevented or at least retarded. Other types of crystallisation modifiers, particularly referred to as crystal habit modifiers, are widely used as an ingredient for mineral fuel oils in which waxes are prone to crystallize at low temperatures. US 3,536,461 teaches the addition of a crystal habit modifier to fuel oil with the effect that the cloud point (or pour point) temperature is lowered far enough to prevent crystal precipitation. Or, alternatively, the solids are induced to crystallize in a different habit so that the crystals when formed can pass fuel filters without clogging them. Other crystal habit modifiers are actually able to change the habit of the crystallized triglyceride fat crystals in a way such that after crystallization the crystals, the stearin phase, can be more effectively separated from the liquid phase, the olein phase. Publications describing such crystal habit modifiers are e.g. GB 1 015 354 or US 2,610,915 where such effect is accomplished by the addition of small amounts of a polymerisation product of esters of vinyl alcohol or of a substituted vinyl alcohol and in co- pending PCT application WO 95/04122 by the addition of esterified copolymers of maleic anhydride and styrene. US 3,059,008 describes the use of dextrin derivatives for the same purpose. None of them has appeared to be ideal with respect to high separation efficiency and fitness to be used for the preparation of food ingredients. SU 1722377 (DERWENT 93-074294) discloses that fatty acid monoglycerides influence the crystallisation of milk fat. Chemical Abstracts 84, (1976) 42219 deals specifically with monoglycerides of unsaturated fatty acids which accelerate the crystallization of hardened vegetable oils. Fatty acid monoglycerides which have been esterified with citric acid and which are marketed under the name Acidan™ have shown to modify the crystallization rate of triglyceride fat, particularly glycerol tristearin (J. Am. Oil. Chem. Soc. 59, (1982) p. 181-185). STATEMENT OF INVENTION It has been found that in triglyceride fat fractionation monoglycerides or diglycerides of fatty acids are suited to enhance the separation efficiency. Accordingly the invention relates to a process for separating solid fatty material crystallised from a triglyceride oil, which comprises the steps: a. heating the oil until no longer a substantial amount of solid triglyceride is present in the oil, b. cooling and crystallising the triglyceride oil resulting in a solid stearin phase besides a liquid olein phase and c. recovering the stearin phase by separating it from the. olein phase, where before crystallisation starts a crystallisation modifying substance is added to said triglyceride oil or to a solution of said triglyceride oil in an inert solvent, characterized in that the crystallisation modifying substance is a monoglyceride or diglyceride of fatty acids optionally esterified with citric acid. DETAILS OF THE INVENTION The oil to be fractionated is mixed with the crystallisation modifying substance (the additive) before crystallisation starts, preferably before the oil is heated or dissolved in the solvent so that all solid triglyceride fat and preferably also the modifying substance is liquefied. Then the oil or solution is cooled to the chosen crystallisation temperature. A suitable temperature range for e.g. palm oil is 15-35°C. To each temperature belongs a specific composition of the olein and stearin phases. Crystallisation proceeds at the chosen temperature until the crystallised oil stabilises to a constant solid phase content. The crystallisation time increases when more solid phase is desired and the temperature is lowered. Usual times are in the range of 4-16 hours. During crystallisation the oil may remain quiescent or is stirred, e.g. with a gate stirrer. The improvement in separation efficiency may depend on the mode of crystallisation, either stagnant or stirred. Often good results are obtained with " stagnant crystallisation rather than with stirred crystallisation. From the point of view of process economy, however, stirred crystallization is preferred. The stearin and olein phases may be separated by filtration but for an effective separation of the solid from the liquid phase generally a membrane filter press is used, which allows higher pressures. Suitable pressures are 3-50 bar, exerted for about 20-200 minutes. However, already with a low or moderate pressure the stearin phase obtained according to the present invention is easily and with a high efficiency separated from the olein. As a rule it takes about 30-60 minutes to get a proper separation of both phases. The solids content of the crystal slurry before separation and of the stearin phase obtained after separation is measured according to the known pulse NMR method (ref. Fette, Seifen, Anstrichmittel 1978, J3C), nr. 5, pp. 180- 186) . The effect of the invention is believed to be caused by alteration of the crystal structure or crystal habit of the stearin under the influence of the additives. These might interfere in different ways with the growth of the various crystal faces. At microscopic inspection the effect of the presence of the mono- or diglyceride additives is that the crystals and crystal aggregates formed in the oil are conspicuously different from the crystals obtained without those crystallisation modifying substances. These crystals and aggregates can be filtered more effectively in that the stearin fraction retains less of the olein fraction even at low or moderate filtration pressure. The altered crystallisation results therefore in a considerable increase of the separation efficiency. The present process for obtaining stearin with increased solid levels is characterised by the use of crystallisation modifying substances which are mono- or diglycerides of fatty acids. The ester group preferably is situated at either or both of the terminal carbon atoms of the glyceryl moiety. Optionally the remaining hydroxyl group(s) have been esterified with citric acid, preferably 0.5 - 2 mol equivalents, so that a part or all the hydroxyl groups have been esterified. Generally, the best results are obtained when the length of the fatty acid side-chains match the length of the fatty acid chains of the desired stearin phase. Matching chains should have the same or about the same number of carbon atoms. Therefore, when palm oil is fractionated, preferred fatty acids are C 14 , C 16 and C 18 fatty acids. The mono- or diglycerides used in the invention may be derived from a single fatty acid, such as glycerol monopalmitate, mono-oleate or dipalmitate, but usually these are derived from various fatty acids with a distribution which reflects the fatty acid distribution of the edible fat used for the preparation of the mono- or diglyceride. Although the invention is useful for solvent fractionation or detergent fractionation, the process preferably is carried out as a dry fractionation process. The process can be applied on triglyceride oils containing relatively high melting fat, for which fractionation is desired such as palm oil, palm kernel oil, shea oil, coconut oil, cottonseed oil, butter oil, hardened rapeseed oil, hardened soybean oil or fractions of these oils. The process is particularly useful for fractionating palm oil. The palm oil might be crude, but generally a refined quality is used. Palm oil contains fully saturated triglycerides SSS. The palm oil to be fractionated preferably has a SSS content < 8.5 wt.%, more preferably 7-8.5 wt.% and the palmitic acid : oleic acid ratio preferably is less than 1.17, more preferably 1.08-1.16. The crystallisation modifying substance is suitably applied in an amount of 0.005 - 5 wt.%, preferably 0.01-2 wt.% on the total amount of oil. The mono- or diglycerides to be used according to the invention can be prepared using common methods for preparing such well known products. The crystallisation modifying substances of the present invention are generally known and marketed as emulsifiers under various trade names such as Dimodan™. The citric esters are obtained using standard methods e.g. by treating the monoglycerides under proper esterifying conditions with 0.5 - 2 mol equivalents citric acid. The obtained citric ester is neutralised. Such product is marketed as an emulsifier by e.g. GRINDSTED under the trade name Acidan™. A major advantage of the present crystallisation modifying substances is that they have acquired the status of permitted food ingredients and therefore may be used for the fractionation of edible oils. Example l Dry fractionation of palm oil A sample was prepared containing 1000 g of palm oil (neutralised, bleached, deodorised, having a SSS content of 8 wt.% and a palmitic acid : oleic acid ratio of 1.12) and 1 g (0.1%) of Acidan CN™ * . The sample was heated and stirred at 65°C until completely liquefied (no solid phase content) and then slowly cooled. Crystallisation proceeded in a thermostated cabin in a stagnant mode at the chosen temperature of 23°C until a constant solid phase content was reached. The sample was filtered and pressed at 12 bar in a membrane filter press for 30 minutes. After filtration and pressing, the solid phase content of the cake was measured and also the weight of the filtrate (the olein phase) . The stearin yield is the weight of the crystal mass remaining on the filter expressed as a percentage of the feed. Table I shows the measured solid phase content of the slurry, the increase of the solid phase content of the stearin-cake and the olein yield. Acidan CN™ is a neutralised citric acid ester of monoglyceride made from edible, refined, hydrogenated fat as marketed by GRINDSTED, Brabrand, Denmark. Examples 2-6 Dry fractionation of palm oil and palm kernel oil The dry fractionation process of example 1 is repeated with different additives and two oils (palm kernel oil and palm oil) . The palm kernel oil samples have been pressed at 6 bar, the palm oil ones at 12 bar. The ingredients and the results are summarized in Table I. Before filtration samples contained the same amount of solid fat ((12% for palm oil, 25% for palm kernel oil). The results of Table I show that the stearin fractions of the crystallisation modifying substance containing samples 1-6 have retained considerably less olein than the stearin fractions of comparison samples A-D. TABLE I Ex. Additive Add. Fat Slurry Incre Olein wt.% (1) SPC 2) ase % yield wt.% (3) wt.% 1 Acidan™ (8) 0.16 PO 12 80 80 2 Acidan™ (8) 0.16 PK 25 10 50 3 Glycerol 0.1 PO 12 29 70 monopaImitate 4 Glycerol 0.1 PK 25 20 48 monopalmitate 5 Glycerol mono- 0.1 PO 12 29 70 oleate 6 Glycerol 0.1 PO 12 20 68 dipalmitate Comparison examples A No additive - PO 12 0 (9) 60 B No additive - PK 25 0 (10 45 C Admul GLP™ 4) 3.0 PO 12 0 40 D Admul 0.05 PO 12 n.d. n.d. Datem™ (6) E Admul AC™ (7) 0.16 PO 12 n.d. n.d. F Tween 60™ (5) 1.0 PO 12 -3 58 n.d. not determined: separation of stearin and olein phases not possible (1) PK = palm kernel oil PO = palm oil (neutralised, bleached, deodorised, having a SSS content of 8 wt.% and a palmitic acid : oleic acid ratio of 1.12) (2) SPC = solid phase content before stearin/olein separation (3) increase of solid phase content of stearin phase (SE) compared with crystallization without additive (comparison examples A and B) (4) Admul GLP™ = monoacylglyceride esterified with lactic acid (ex Quest) (5) Tween 60™ = a sorbitan ester (ex Quest) (6) Admul Datem™ = monoacylglyceride esterified with diacetyltartaric acid (ex Quest) (7) Admul AC™ = monoacylglyceride esterified with acetic acid (ex Quest) (8) Acidan ™ is a neutralised citric acid ester of a fatty acid monoglyceride made from edible fat (ex GRINDSTED) (9) Separation efficiency of palm oil without additive ?? (10) Separation efficiency of palmkernel oil without additive ?? When the additive is a mono- or diglyceride esterified with another acid than citric acid, as in comparison examples C, D and E, no increase of the solid phase content during dry fractionation is achieved. When using another well known emulsifier as additive as in example F even a negative effect is observed.

Claims: CLAIMS 1. Process for separating solid fatty material from a partially crystallised triglyceride oil, which comprises the steps: a. heating the oil until no longer a substantial amount of solid triglyceride is present in the oil, b. cooling and crystallising the triglyceride oil resulting in a solid stearin phase besides a liquid olein phase and c. recovering the stearin phase by separating it from the olein phase, where before crystallisation starts a crystallisation modifying substance is added to said triglyceride oil or to a solution of said triglyceride oil in an inert solvent, characterized in that the crystallisation modifying substance is a monoglyceride or diglyceride of fatty acids, optionally esterified with citric acid. 2. Process according to claim 1, characterised in that the mono- or diglyceride has been esterified with citric acid using 0.5 - 2 mol equivalents of citric acid per mol mono- or diglyceride. 3. Process according to claim 1 or 2, characterised in that the process is applied as a dry fractionation process. 4. Process according to any one of claims 1-3, characterised in that the triglyceride oil to be fractionated is shea oil, coconut oil, cottonseed oil, butter oil, hardened rapeseed oil, hardened soybean oil or fractions of these oils, but preferably is palm oil or palm kernel oil. 5. Process according to claim 4, characterised in that the palm oil to be fractionated has a SSS content < 8.5 wt.%. 6. Process according to claims 4 or 5, characterised in that the palm oil to be fractionated has a palmitic acid : oleic acid ratio < 1.17. 7. Process according to any one of claims 1-6, characterised in that the crystallisation modifying substance is used in an amount of 0.005-5 wt.%, preferably 0.01-2 wt.% on the total amount of oil.

Inventors: VAN DAM PETRUS HENRICUS J, VAN DEN KOMMER MARCELLE, VISSER ADRIANUS, VAN DAM, PETRUS, HENRICUS, J., VAN DEN KOMMER, MARCELLE, VISSER, ADRIANUS
Applicants: DAM PETRUS HENRICUS J VAN, DEN KOMMER MARCELLE VAN, UNILEVER NV, UNILEVER PLC, VISSER ADRIANUS, UNILEVER N.V., VAN DAM, PETRUS, HENRICUS, J., VAN DEN KOMMER, MARCELLE, VISSER, ADRIANUS
Application year: 1995
Main classification: C11B3
IPC codes: C11B7