A PROCESS FOR REDUCING GLYCIDOL AND GLYCIDYL ESTERS IN MONOGLYCERIDES AND/OR DIGLYCERIDES

Abstract

 The present invention relates to a process for reducing the level of glycidol and/or glycidyl esters in a preparation of monoglycerides and/or diglycerides prepared by transesterification between glycerol and triglycerides or direct esterification between glycerol and fatty acids. The process comprises least a first holding step in which reaction products from said transesterification or direct esterification are maintained at a temperature in the range of 140-210°C for a period of time (the holding time) in the range of 10-90 minutes, or at a temperature in the range of 70-130°C for a period of time (the holding time) in the range of 1-14 days, in a separate temperature-controlled unit.

Description

FIELD OF INVENTION

[0001] The present invention relates to a process for reducing the level of glycidol and glycidyl esters in preparations of monoglycerides and/or diglycerides.

BACKGROUND OF THE INVENTION

[0002] Glycidol and glycidyl esters are formed during high temperature processing of materials containing tri-, di- or monoglycerides or glycerol. Glycidol is classified as a genotoxic carcinogen (IARC 2000 and COMMISSION REGULATION (EU) 2018/290 of 26 February 2018) and consequently it is desirable to provide a method of reducing the level of glycidol and glycidyl esters in products containing these compounds.

[0003] Several solutions to reducing or eliminating the contamination of edible oils and fats with glycidol and glycidyl esters have been proposed in the art.

[0004] WO 2011/069028 discloses several methods of removing glycidyl esters from an oil, including contacting the oil with an absorbent and subsequently steam refining the oil; contacting the oil with an enzyme and subsequently steam refining the oil; deodorizing the oil at a temperature not exceeding 240°C; contacting the oil with an acid solution; rebleaching the oil, etc.

[0005] US 2014/0357882 discloses a process of reducing the content of glycidyl esters in vegetable oils using an acid-activated bleaching earth as an absorbent and deodorizing the oil at less than 200°C for at least 30 minutes.

[0006] WO 2012/031176 discloses a process for reducing glycidol from oils using a carboxylate anion and cation counterion to react with glycidol.

[0007] WO 2016/189328 discloses a process for removing glycidol and glycidyl esters from glyceride oils by treatment with a basic ionic liquid.

[0008] WO 2014/012759 discloses a process for reducing the amount of MCPD and glycidol in triglyceride oils by bleaching the oil with a base while passing steam through the oil at reduced pressure.

[0009] EP 2471897 discloses a process for reducing MCPD and glycidyl esters from oils, for instance by treating deodorized oils with silica gel and/or alkaline activated carbon or by mixing the oil with an organic acid aqueous solution and dehydrating at 50-180°C under reduced pressure.

[0010] Shimizu, M. et. al.; J. Am. Oil Soc. (2013), 90,1449-1454 discloses Temperature Dependency When Generating Glycidyl and 3-MCPD Esters from Diolein'.

[0011] Matthäus, B. et. al.; Eur. J. Lipid Sci. Technol. (2016), 118 (3), 418-424 discloses 'Degradation of glycidyl esters in RDB palm oil as a function of storage conditions.

[0012] Monoglycerides and/or diglycerides are widely used as emulsifiers in the food industry. They are typically prepared by transesterification between glycerol and triglycerides or by direct esterification between glycerol and fatty acids. The esterification or transesterification are carried out at elevated temperatures such as temperatures above 230°C, in the presence of a catalyst, such as a base, for example a carboxylate ion. The product from the esterification or transesterification reaction is a blend of mono-, di- and tri-glycerides and glycerol. Glycerol is removed by processes such as centrifugation or stripping at a lower temperature such as for example 180°C. Monoglycerides may be separated or concentrated from diglycerides and triglycerides by distillation, such as by vacuum short path distillation, such as at temperatures above 210°C.

[0013] The functional groups of the monoglyceride and diglyceride molecules foster glycidol and glycidyl ester formation by several potential reaction mechanisms illustrated below (wherein R represents an alkyl group), particularly when submitted to temperatures above 220°C. Consequently, the glycidyl ester formation is especially high during the transesterification and direct esterification process; and furthermore, substantial glycidyl ester formation is expected during the high temperature distillation process to obtain concentrated monoglycerides.

[0014] One possible pathway for glycidyl ester formation is during the 1,2-rearrangement that constantly takes place within the monoglyceride molecule. The fatty acid can change position by acyl migration between the C₁ and C₂-atoms. During the transition state water is eliminated from the intermediate as shown in reaction scheme I, thereby forming an epoxide ring at the neighbouring C-atoms.

[0015] A second possible pathway for glycidyl ester formation is during the elimination of a fatty acid from a diglyceride as shown in reaction scheme II. The elimination results in a transition state similar to that of the pathway shown in scheme I, from which the epoxide ring can form.

[0016] A third possible pathway for glycidyl ester formation is via formation of glycidol from glycerol as shown in reaction scheme III. The formed glycidol reacts with a triglyceride or free fatty acid in the same way as glycerol does. The catalyst is the same as in the direct esterification or transesterification process, i.e. a carboxylate ion or base.

[0017] The epoxide ring in glycidol and glycidyl esters is highly reactive and under certain reaction conditions it may react with any molecule containing a hydroxyl group (e.g. a hydroxyl group in water, glycerol, monoglyceride) resulting in the opening of the epoxide ring and converting the glycidyl ester as shown in reaction schemes IV below.

[0018] It would be desirable to provide cost-effective and efficient procedure for reducing the level of glycidol and glycidyl esters formed when producing monoglycerides and/or diglycerides. Furthermore, it would be desirable to provide a procedure which would result in only an insignificant decrease of the content of monoglycerides and/ or diglycerides.

SUMMARY OF THE INVENTION

[0019] It has been found that keeping preparations of monoglycerides and/or diglycerides at temperatures below 210°C may reduce the level of glycidol and/or glycidyl esters. The reduction rate of glycidol and glycidyl esters depend on the temperature applied. Mono- and diglycerides degrade on prolonged heat exposure and the optimal treatment time and temperature for reducing the level of glycidol and glycidyl esters is a balance between an efficient reduction of glycidol and glycidyl esters and an acceptable level of degradation of monoglycerides.

[0020] Thus, it has been found that the level of glycidol and/or glycidyl esters are reduced when reaction products from transesterification between glycerol and triglycerides or direct esterification between glycerol and fatty acids are maintained at a temperature in the range of 140-210°C for a period of time (the holding time) in the range of 10-90 minutes, or at a temperature in the range of 70-130°C for a period of time (the holding time) in the range of 1-14 days.

[0021] Accordingly, the present invention relates to a process for reducing the level of glycidol and/or glycidyl esters in a preparation of monoglycerides and/or diglycerides prepared by transesterification between glycerol and triglycerides or direct esterification between glycerol and fatty acids, the process comprising at least one holding step in which reaction products from transesterification between glycerol and triglycerides or direct esterification between glycerol and fatty acids are maintained at temperatures in the range of 140-210°C for a period of time (the holding time) in the range of 10-90 minutes or at a temperature in the range of 70-130°C for a period of time (the holding time) in the range of 1-14 days in separate temperature controlled units.

DETAILED DESCRIPTION OF THE INVENTION

[0022] It has been found important to maintain the temperature of the holding step(s) at a level that provides maximum reduction of the level of glycidol and glycidyl esters and at the same time leads to the least degradation of the monoglycerides.

[0023] In an embodiment of the invention the process comprises a first holding step wherein mono- and/or diglycerides prepared by transesterification between glycerol and triglycerides or by direct esterification between glycerol and fatty acids are maintained at a certain temperature and for a certain period of time (holding time) in a temperature-controlled unit.

[0024] In a preferred embodiment of the present process, the temperature of the first holding step is in the range of 170-200°C, such as 175-200°C, such as 180-195°C, such as 184-194°C, or such as 185-190°C.

[0025] The holding time for the first holding step is preferably in the range of 10-90 minutes, such as 20-80 minutes, such as 20-60 minutes, such as 25-50 minutes, such as 25-40 minutes, such as about 30 minutes.

[0026] In an embodiment of the invention the temperature of the first holding step is in the range of 140-200°C, such as 140-190°C, such as 140-180°C, such as 150-175°C, such as 150-170°C, such as 155-175°C, such as 160-170°C, such as about 160°C or such as about 170°C and the holding time is in the range of 10-90 minutes, such as in the range of 20-70 minutes, such as 25-80 minutes, such as 30-65 minutes, such as 30-60 minutes, such as 30-40 minutes, such as about 35 minutes or such as about 30 minutes.

[0027] In an embodiment of the invention, the temperature of the first holding step is in the range of 140-180°C, and wherein the holding time in the first holding step is in the range of 25-80 minutes.

[0028] In an embodiment the first holding step is performed prior to a distillation step wherein monoglycerides are distilled or concentrated from diglycerides and triglycerides from the transesterification or direct esterification step.

[0029] In an embodiment the first holding step is performed prior to a glycerol removal step and prior to a distillation step wherein monoglycerides are distilled or concentrated from diglycerides and triglycerides from the transesterification or direct esterification step.

[0030] In an embodiment of the invention the process comprises a glycerol removal step and a distillation step.

[0031] In an embodiment of the invention glycerol is removed by processes such as stripping or centrifugation prior to a distillation step.

[0032] In an embodiment of the invention a distillation step is performed as a vacuum short path distillation, such as at temperatures above 210°C. During the distillation step monoglycerides are separated or concentrated from diglycerides and/or triglycerides from the direct esterification or transesterification step.

[0033] In an embodiment of the invention the process comprises a second holding step wherein the concentrated monoglycerides after glycerol removal and distillation are maintained at a certain temperature and for a certain period of time (the holding time) in a temperature-controlled unit.

[0034] In an embodiment of the invention the temperature of the second holding step is in the range of 140-200°C, such as 140-190°C, such as 140-180°C, such as 150-175°C, such as 150-170°C, such as 155-175°C, such as 160-170°C, such as about 160°C or such as about 170°C and the holding time is in the range of 10-90 minutes, such as in the range of 20-70 minutes, such as 25-80 minutes, such as 30-65 minutes, such as 30-60 minutes, such as 30-40 minutes, such as about 35 minutes or such as about 30 minutes.

[0035] In yet an embodiment of the invention the temperature of the second holding step is in the range of 70-130°C, such as in the range of 75-125°C, such as 80-100°C, such as 80-120°C, such as 85-110°C, such as 85- 95°C, such as about 90°C and the holding time is in the range of 1-14 days, such as 1-6 days, such as 2-6 days, such as 2-5 days, such as 2-4 days, such as about 3 days.

[0036] In yet another embodiment of the invention, the present process comprises a third holding step wherein the monoglycerides and/or diglycerides are maintained at a temperature in the range of 70-130°C for a period of time (the holding time) in the range of 1-14 days. The temperature of the third holding step is suitably in the range of 70-130°C, such as in the range of 75-125°C, such as 80-100°C, such as 80-120°C, such as 85-110°C, such as 85-95°C, such as about 90°C. The holding time for the third holding step is in the range of 1-10 days, such as 1-6 days, such as 2-6 days, such as 2-5 days, such as 2-4 days, such as about 3 days.

[0037] In an embodiment of the invention the second and/or third holding step is carried out after a glycerol removal step and a distillation step in which monoglycerides are concentrated from diglycerides and triglycerides from the transesterification or direct esterification step.

[0038] In an embodiment the third holding step is carried out with the liquid monoglyceride product being treated in a separate unit.

[0039] In an embodiment of the invention, the second and/or third holding step is carried out on a liquid mono- and diglyceride product, wherein the mono- and diglyceride product has been subjected to a glycerol removal step, such as a stripping or centrifugation step, and wherein the second and/or third holding step is carried out in a separate temperature controlled unit at a temperature in the range of 70-130°C for a period of time in the range of 1-14 days, such as at a temperature in the range of 75-125°C, such as 80-100°C, such as 80-120°C, such as 85-110°C, such as 85- 95°C, such as about 90°C and a holding time in the range of 1-6 days, such as 2-6 days, such as 2-5 days, such as 2-4 days, such as about 3 days.

[0040] In another preferred embodiment of the present process for reducing the level of glycidol and/or glycidol esters in a preparation of mono- and diglycerides, the temperature of the first holding step is in the range of 70-130°C, such as in the range of 75-125°C, such as 80-100°C, such as 80-120°C, such as 85-110°C, such as 85- 95°C, such as about 90°C and the holding time is in the range of 1-14 days, such as 1-6 days, such as 2-6 days, such as 2-5 days, such as 2-4 days, such as about 3 days, or wherein the temperature of the first holding step is in the range of 80-100°C and wherein the mono- and/or diglycerides are kept for a period of time (the holding time) in the range of 2-6 days, wherein the first holding step is performed in a temperature-controlled unit such as for example a batch tank reactor or a heating cabinet. In a preferred embodiment glycerol is removed from the preparation of mono- and diglycerides by processes such as stripping or centrifugation prior to the first holding step.

[0041] In one embodiment of the present process, the temperature-controlled unit suitable for use in the holding step(s) may be a plug flow reactor, packed column, tray column or stirred tank reactor (continuous, semi-batch or batch) or similar equipment which may provide a specified residence time at a specified temperature to the material. The temperature may suitably be controlled by a heat transfer jacket on the temperature-controlled unit, an internal heating coil inside the temperature-controlled unit, heat exchangers in the feed-flow pipe or a combination of the different heating sources.

[0042] In an embodiment of the invention the temperature-controlled unit used in a holding step carried out prior to the distillation step is a plug flow reactor, packed column, tray column or continuous or batch stirred tank reactor.

[0043] In an embodiment of the invention the temperature-controlled unit used in the second or third holding step is a tray column or a plug flow reactor.

[0044] In an embodiment of the invention the temperature-controlled unit used in the second or third holding step is a batch tank reactor.

[0045] The starting material for preparing the monoglycerides and/or diglycerides may be a vegetable or animal oil, fat or fatty acids. Fats and oils are mixtures of acyl glycerides with triglycerides as the predominant species although they may also contain mono- and diglycerides as well as free fatty acids. The fat or oil for transesterification may suitably be selected from edible oils and fats such as palm oil, sunflower oil, corn oil, soybean oil, safflower oil, peanut oil, rapeseed oil, grape kernel oil, cottonseed oil, coconut oil, rice bran oil, olive oil, lard, tallow or castor oil. The fats and oils maybe refined, fully hydrogenated, partially hydrogenated or selectively hydrogenated and/or blended. Fatty acids are produced by hydrolysing acyl glycerides from edible fats or oils. The fatty acids for direct esterification may suitably be selected from edible oils and fats such as palm oil, sunflower oil, corn oil, soybean oil, safflower oil, peanut oil, rapeseed oil, grape kernel oil, cottonseed oil, coconut oil, rice bran oil, olive oil, lard, tallow or castor oil; and the oils maybe refined, fully hydrogenated, partially hydrogenated or selectively hydrogenated before hydrolysing to retrieve the free fatty acids. The fatty acids maybe also be refined, fully hydrogenated, partially hydrogenated or selectively hydrogenated, and they may be blended or separated into the pure fatty acid types.

[0046] The monoglycerides and diglycerides in the preparation are of the general formula 1:

wherein one or two of R₁, R₂ and R₃ is an acyl group and the remaining one or two of R₁, R₂ and R₃ are hydrogen. The acyl groups have saturated or unsaturated, aliphatic chains with chain lengths of C₇-C₂₃. It is understood that the monoglycerides and/or diglycerides present in the preparation may comprise a mixture of monoglycerides and/or diglycerides with a variety of acyl chains.

[0047] During the course of the present invention it has furthermore surprisingly found that the level of glycidol and/or glycidyl esters in solidified monoglycerides which have been prepared by transesterification between glycerol and triglycerides, wherein said triglycerides comprise 90-100% saturated aliphatic fatty acid esters and 0-10% unsaturated aliphatic fatty acid esters or by direct esterification between glycerol and fatty acids, said fatty acids comprising 90-100% saturated aliphatic fatty acids and 0-10% unsaturated aliphatic fatty acids, is further reduced upon storage of said solidified monoglycerides; such as storage at temperatures between 10-40°C for a period of time between 1-30 days.

[0048] Accordingly, in an embodiment the invention relates to a process for reducing the level of glycidol and/or glycidyl esters in a in a preparation of solidified monoglycerides which have been prepared by transesterification between glycerol and triglycerides, wherein said triglycerides comprise 90-100% saturated aliphatic fatty acid esters and 0-10% unsaturated aliphatic fatty acid esters or by direct esterification between glycerol and fatty acids, said fatty acids comprising 90-100% saturated aliphatic fatty acids and 0-10% unsaturated aliphatic fatty acids, the process comprising at least a first holding step in which reaction products from transesterification between glycerol and triglycerides or direct esterification between glycerol and fatty acids are maintained at temperatures in the range of 140-210°C for a period of time (holding time) in the range of 10-90 minutes in a temperature controlled unit, a glycerol removal step and a distillation step, a solidification step followed by storage of the solidified monoglycerides at temperatures between 10-40°C for a period of time between 1-30 days.

[0049] The monoglycerides which have been prepared by transesterification between glycerol and triglycerides, wherein said triglycerides comprise 90-100% saturated aliphatic fatty acid esters and 0-10% unsaturated aliphatic fatty acid esters or by direct esterification between glycerol and fatty acids, said fatty acids comprising 90-100% saturated aliphatic fatty acids and 0-10% unsaturated aliphatic fatty acids, are of the general formula (I); wherein one of R₁, R₂ and R₃ is an acyl group and the remaining two of R₁, R₂ and R₃ are hydrogen. The acyl groups comprise 90%-100% saturated aliphatic chains having chain lengths of C₇-C₂₃ and 0-10% unsaturated aliphatic chains having chain lengths of C₇-C₂₃. It is understood that the monoglycerides present in the preparation may comprise a mixture of monoglycerides with a variety of acyl chains.

[0050] Monoglycerides prepared by transesterification between glycerol and triglycerides, wherein said triglycerides comprise 90-100% saturated aliphatic fatty acid esters and 0-10% unsaturated aliphatic fatty acid esters or by direct esterification between glycerol and fatty acids, said fatty acids comprising 90-100% saturated aliphatic fatty acids and 0-10% unsaturated aliphatic fatty acids, may be solidified in powder form by a spray process, pellet or flake form by solidification on a cold surface or block form by natural convection or cooling process, e.g. in a cooling tunnel. Storage temperature for reducing the glycidol and glycidyl ester content in said solidified monoglycerides is suitably in the range of 5-30°C, such as in the range of 10-25°C, such as about 25°C. The storage time is in the range of 1-30 days, such as 2-20 days, such as 3-10 days, such as 5-8 days.

[0051] The level of glycidol and glycidyl esters in the mono- and diglyceride preparations was determined by a method based on DGF (Deutsche Gesellschaft für Fettwissenschaft) standard method C-III 18 (09). In this method, acyl groups are cleaved off leaving glycerol, glycidol and monochloropropanediol (MCPD) that are subjected to GC-MS analysis. According to the method, an excess of NaCl is added, causing the glycidol to react with the chlorine atom thereby being converted to MCPD which is therefore the compound measured in the GC-MS analysis. It has been found, however, that the quantity of MCPD and MCPD esters in the samples is very low and that for all practical purposes it could be ignored.

[0052] The present invention is described in further detail in the following examples which are not in any way intended to limit the scope of the invention as claimed.

EXAMPLES

Example 1

[0053] 1 kg of a reaction mixture comprising mono- and di-glycerides prepared by transesterifications of glycerol and various triglycerides with an alkaline catalyst at 240°C was neutralised with acid and was afterwards kept in a 2-litre stirred glass flask at a holding temperature of 180°C, for a holding time of 30 minutes. The combined glycidol and glycidyl ester content was measured in the product before and after the holding step and the percentage-wise reduction of glycidol and glycidyl ester (GE) content was calculated. Results are disclosed in Table 1.

Table 1

No.	Triglyceride	Average temperatu re (°C)	Holding time (minutes)	Glycidol and GE reduction during holding step (%)
1	Hydrogenated palm oil	180	30	93
2	Hydrogenated palm oil	180	30	78
3	Cotton seed oil	180	30	94
4	Soybean oil	180	30	92
5	Hydrogenated tallow fat	180	30	93

Example 2

[0054] Reaction mixtures comprising mono- and di-glycerides prepared by transesterifications with glycerol and various triglycerides at 240°C was treated in a plug flow reactor (5,000-10,000 kg/h) at holding temperatures between 184-190°C (average temperature through the column), with holding times between 27-36 minutes. The combined glycidol and glycidyl ester content was measured in the product before and after the holding step and the percentage-wise reduction of glycidol and glycidyl ester (GE) content was calculated. Results are disclosed in Table 2.

Table 2

No.	Triglyceride	Average temperature (°C)	Holding time (minutes)	Glycidol and GE reduction during holding step (%)
1	Palm oil	190	30	80
2	Palm oil	184	29	78
3	Palm oil	189	30	74
4	Hydrogenated palm oil	190	27	74
5	Hydrogenated palm oil	190	34	80
6	Hydrogenated palm oil	190	30	78
7	Hydrogenated palm oil	190	30	79
8	Selectively hydrogenated soy oil	190	30	75
9	Selectively hydrogenated rapeseed oil	189	36	78
10	Selectively hydrogenated rapeseed oil	189	30	77
11	Selectively hydrogenated rapeseed oil	190	30	74
12	Sunflower oil	190	30	81
13	Sunflower oil	190	30	78
14	Partially hydrogenated oil	189	28	74
15	Partially hydrogenated oil	189	28	73

Example 3

[0055] Reaction mixtures comprising mono- and di-glycerides prepared by transesterifications between glycerol and various triglycerides, were treated in plug flow reactor at 190°C for 30 minutes (a first holding step) resulting in 78 - 80% reduction of the glycidol and glycidyl ester (GE) during the first holding step. Glycerol was removed by stripping and the reaction mixture was distilled in a short path distillation column to furnish concentrated monoglycerides. The distilled monoglycerides were treated in a tray column (a second holding step; 1,000-4,000 kg/h) with holding temperatures of 144-168°C, and with holding times of 29-60 minutes. The combined glycidol and glycidyl ester content was measured in the product before and after the treatment in the tray columns (the second holding step) and the percentage-wise reduction of glycidol and glycidyl ester (GE) content was calculated. Results are disclosed in Table 3.

Table 3

No.	Triglyceride basis	Average temperature, second holding step (°C)	Holding time, second holding step (min)	Glycidol and GE reduction during second holding step (%)
1	Hydrogenated palm oil	144	60	53
2	Hydrogenated palm oil	152	60	62
3	Hydrogenated palm oil	159	60	68
4	Hydrogenated palm oil	165	30	65
5	Hydrogenated palm oil	168	30	61
8	Sunflower oil	165	30	62
9	Sunflower oil	166	29	68
10	Sunflower oil	167	30	55

Example 4

[0056] Saturated monoglycerides were prepared by transesterification between glycerol and triglycerides. The reaction mixtures were treated with a first holding step (190°C, 30 minutes), glycerol was removed by stripping and the monoglycerides were concentrated to a purity of more than 95% by short path distillation. Subsequently, the distilled monoglycerides were treated with a second holding step (180°C, 30 minutes). 0.5 kg of the material was kept in closed containers in a heating cabinet at 90°C for 3 days. The combined glycidol and glycidyl ester content was measured in the product before and after storage in the heating cabinet and the percentage-wise reduction of glycidol and glycidyl ester (GE) content was calculated. Results are disclosed in Table 4.

Table 4

No.	Triglyceride	Glycidol and GE reduction during three days at 90°C (%)
1	Hydrogenated palm oil	78.8
2	Hydrogenated palm oil	81.4
3	Hydrogenated palm oil	79.3

Example 5

[0057] Mono- and diglycerides, having a monoglyceride content between 42-47%, were prepared in full scale by transesterification with various triglycerides at 240°C. Glycerol was removed by stripping in a stripping column. 0.5 kg of the product was kept in closed containers in a heating cabinet at 90°C for 3 days (a first holding step). The combined glycidol and glycidyl ester content was measured in the product before and after storage in heating cabinet and the percentage-wise reduction of glycidol and glycidyl ester (GE) content was calculated. Results are disclosed in Table 5.

Table 5

No.	Triglyceride	Glycidol and GE reduction after three days (%)
1	Hydrogenated palm oil	67.9
2	Hydrogenated palm oil	73.3
3	Hydrogenated palm oil	72.2
4	Hydrogenated rapeseed oil	67.8
5	Rape seed oil	57.0

Example 6

[0058] A distilled monoglyceride with a purity of more than 95% was prepared from triglycerides of hydrogenated palm oil, said triglycerides having a content of saturated fatty acid esters of 97 -100% and a content of unsaturated fatty acid esters of 0-3%. The product was treated with a first holding step (180°C, 30 min) after the transesterification reaction and a second holding step (160°C, 30 min) after the distillation step. The distilled monoglycerides were solidified by spraying with an average outlet temperature of 21.5°C. The freshly sprayed powders were sampled and analysed for glycidol and glycidyl ester (GE) content before packaging. For each batch, the powder was packed in 25 kg cartons and placed in 3 layers on a pallet, 9 cartons in each layer. The pallet was stored at 20°C. After 7 days, the monoglyceride the top layer of the central carton of was sampled and analysed for glycidol and glycidyl ester (GE) content and the percentage-wise reduction in glycidol and glycidyl ester (GE) content was calculated. The glycidol and glycidyl ester (GE) content was reduced by 88% upon seven days of storage at 20°C.

Claims

1. A process for reducing the level of glycidol and/or glycidyl esters in a preparation of mono- and/or diglycerides prepared by transesterification between glycerol and triglycerides or by direct esterification between glycerol and fatty acids, the process comprising at least a first holding step in which reaction products from said transesterification or direct esterification are maintained at a temperature in the range of 140-210°C for a period of time (the holding time) in the range of 10-90 minutes, or at a temperature in the range of 70-130°C for a period of time (the holding time) in the range of 1-14 days, in a separate temperature-controlled unit.

2. The process of claim 1, wherein the temperature of the first holding step in the range of 170-200°C.

3. The process of any one of claims 1-2, wherein the holding time in the first holding step is in the range of 20-45 minutes.

4. The process of any one of claims 1-3 furthermore comprising a glycerol removal step and a distillation step.

5. The process according to claim 4 comprising an additional holding step wherein monoglycerides are kept at a temperature in the range of 140-200°C for a period of time in the range of 10-90 minutes, and wherein said additional holding step is carried out after the glycerol removal step and the distillation step.

6. The process of claim 5, wherein the temperature of the additional holding step is in the range of 140-180°C.

7. The process of any one of claims 5-6, wherein the holding time in the additional holding step is in the range of 25-80 minutes.

8. The process of claim 1, wherein the temperature of the first holding step is in the range of 140-180°C, and wherein the holding time in the first holding step is in the range of 25-80 minutes

9. The process of any one of claims 2-8 comprising an additional holding step wherein the mono- and/or diglycerides are kept at a temperature in the range of 70-130°C for a period of time in the range of 1-14 days.

10. The process of claim 9, wherein the temperature of the additional holding step is in the range of 80-100°C.

11. The process of claims 9-10 wherein the mono- and/or diglycerides are kept for a period of time in the range of 2-6 days.

12. The process of claim 1, wherein the temperature of the first holding step is in the range of 80-100°C, wherein the mono- and/or diglycerides are kept for a period of time (the holding time) in the range of 2-6 days.

13. The process of any one of claims 1-12, wherein the temperature-controlled unit used in a holding step is a plug flow reactor, packed column, tray column, continuous stirred tank reactor, or batch stirred tank reactor.

14. The process according to any one of claims 4-7, wherein distilled monoglycerides have been prepared by transesterification between glycerol and triglycerides, wherein said triglycerides comprise 90-100% saturated aliphatic fatty acid esters and 0-10% unsaturated aliphatic fatty acid esters or by direct esterification between glycerol and fatty acids, wherein said fatty acids comprise 90-100% saturated aliphatic fatty acids and 0-10% unsaturated aliphatic fatty acids, the process furthermore comprising solidification of the distilled monoglycerides and storage at of the solidified monoglycerides at 10-40°C for 1-30 days.

15. The process of any one of claims 1-14, wherein the monoglycerides and/or diglycerides are of the general formula 1

wherein one of R₁, R₂ and R₃ represents an acyl group and two of R₁, R₂ and R₃ represent hydrogen, or wherein two of R₁, R₂ and R₃ represent an acyl group and one of R₁, R₂ or R₃ represents hydrogen, and wherein said acyl groups comprise saturated and/or unsaturated aliphatic C₇-C₂₃ chains.