Patent Publication Number: US-6034130-A

Title: Lipid composition for infant formula and method of preparation

Description:
BACKGROUND OF INVENTION 
     The invention relates to the field of dietetic lipids, in particular for infant formulas. It relates to a lipid composition which is close to that of human milk. 
     Human milk fat is composed essentially of triacylglycerols (TAGs) whose fatty acid structure, composition and distribution are specific. It is characterized in particular by the presence of two long-chain polyunsaturated fatty acids (LC-PUFA), arachidonic acid (AA, C20:4, n-6) and docosahexaenoic acid (DHA, C22:6, n-3) predominantly at the 2-position of the triacylglycerol, by the abundance of saturated (SFA) palmitic acid. (P, C16:0) and by the fact that P is predominantly at the 2-position of the triacylglycerol. 
     Lipid compositions for infant formulas which mimic human milk fat as well as processes for the preparation of such compositions are described in patent EP-B-209327 and in patent applications WO 94/26855 (PCT/EP 94/01306) and WO 94/26854 (PCT/EP 94/01304). These compositions comprise a mixture of TAGs in which more than 50% of the fatty acids at the 2-position of the triacylglycerol are SFAs, predominantly P, and where the fatty acids at the 1,3-positions of the triacylglycerol comprise medium-chain C 8  -C 14  unsaturated fatty acids and saturated fatty acids (MCFA). 
     The process for preparing these compositions, which is described in EP-B-209327, consists in an interesterification, catalysed by a 1,3-regiospecific lipase of a mixture consisting, on the one hand, of a palm oil fraction comprising 80% of tristearin and 20% of 1,3-dipalmitoyl-2-olein and, on the other hand, of a mixture of free fatty acids containing a substantial quantity of unsaturated fatty acids. Under the action of the 1,3-regiospecific lipase, medium-chain unsaturated and/or saturated fatty acid residues are introduced at the 1,3-positions of the 2-palmitoyl-glycerides. The free fatty acids of the crude mixture are then removed by steam distillation. The mixture of synthetic TAGs produced is finally mixed with various vegetable oils. 
     In WO 94/26855, the above mixture of synthetic TAGs, mixed with various vegetable oils in defined portions, is subjected to an interesterification using a 1,3-regiospecific lipase. 
     In WO 94/26854, where appropriate, after removal of the diglycerides by enzymatic treatment, the trisaturated TAGs are partially removed from the above mixture of synthetic TAGs by interesterification using a 1,3-regiospecific lipase in the presence of an oil which is high in mono- or diunsaturated acids. 
     The known processes have disadvantages. 
     Since most of the customary lipases have a low reactivity towards polyunsaturated fatty acids (PUFAs), particularly towards the LC-PUFAs, it is very difficult to incorporate the desired quantities of these fatty acids, in particular of DHA into the TAGs using a 1,3-regiospecific lipase. Thus, to achieve an appreciable degree of incorporation, it is necessary to use a large excess of fatty acid, for example in concentrated form, and a long reaction time. Concentrates of PUFAs are very expensive. The long reaction time can cause significant oxidation of the PUFAs which are particularly sensitive to oxidation when they are in the form of free fatty acids. Such an oxidation reduces the nutritional value of the PUFAs and may produce degradation compounds which are health hazards. 
     Furthermore, the use of 1,3-regiospecific lipase produces trisaturated TAGs in excess and also diglycerides. Subsequent enzymatic treatments are required, in particular to remove the trisaturated TAGs in excess from the crude product, which makes the process complicated and expensive. 
     Finally, the lipid mixture obtained must, in spite of everything, be mixed with other fats in order to correspond to the composition of human milk fat. 
     SUMMARY OF THE INVENTION 
     The aim of the invention is to provide a synthetic TAG composition which is whose composition and structure are close to those of human milk, using a synthesized process for incorporating PUFAs which does not cause significant destructive oxidation of the PUFAs. 
     The invention therefore relates to a synthetic lipid composition in which the content and the distribution of the fatty acids which mimic those of human milk fat, characterized in that: 
     it contains less than 2% by weight of free fatty acids, 
     the fatty acids of the triacylglycerols comprise, by weight: 
     about 35 to 55% of saturated fatty acids, among which 18 to 36% of palmitic acid, 2 to 40% of caprylic and capric acids, at most 10% of lauric acid and at most 10% of myristic acid, 
     about 30 to 45% of monounsaturated fatty acids, 
     about 9 to 22% of polyunsaturated fatty acids, among which less than 2% of long-chain n-6 polyunsaturated fatty acids comprising arachidonic acid and less than 1% of long-chain n-3 polyunsaturated fatty acids comprising docosahexaenoic acid and the n-6:n-3 fatty acid ratio is 5:1 to 15:1, 
     palmitic acid is predominantly at the 2-position of the triacylglycerols and arachidonic and docosahexaenoic acids are distributed between the 1-, 2- and 3-positions of the triacylglycerols. 
     The AA and DHA acids may be predominantly at the 2-position of the triacylglycerols. 
     Since it is more specifically intended for consumption by premature babies, the lipid composition according to the invention is such that the caprylic and capric acids preferably represent about 2 to 10% by weight of the fatty acids of the triacylglycerols. 
     The invention also relates to a process for the preparation of a lipid composition above, characterized by the following successive steps: 
     1) A mixture of lipids containing a palm oil enriched with palmitic acid, a vegetable oil high in the unsaturated linoleic and alpha-linolenic fatty acids, an oil which is the source of arachidonic acid, an oil which is the source of docosahexaenoic acid, in defined proportions, is non-regiospecifically interesterified in order to obtain the required fatty acid composition with a random distribution of the fatty acid residues between the 1-, 2- and 3-positions of the triacylglycerol, 
     2) The mixture of step 1) is interesterified with a mixture of free fatty acids predominantly comprising the medium-chain fatty acids and oleic acid, using a 1,3-regiospecific lipase, and 
     3) The free fatty acids are removed from the product of the reaction of step 2). 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The aim of step 1) is to increase the quantity of P at the 2-position of the TAGs and to incorporate the PUFAs, in particular the LC-PUFAs such as DHA and AA at the 1-, 2- and 3-positions of the TAGs. The starting lipid mixture is enriched with palmitic acid, for example with palm stearin so as to have about 40% of P at the 2-position of the TAGs. The non-regiospecific interesterification can take place by the enzymatic route, catalysed by a non-regiospecific lipase, or, preferably by the chemical route, catalysed by a chemical catalyst. By this reaction, the non-random distribution of the fatty acids existing in the natural lipids between the different positions of the TAGs is converted to a random distribution, that is to say that the fatty acids become rearranged equally at the 3 positions. In this first step, the content of P at the 2-position passes to about 42%, which practically corresponds to the entire P present in human milk. If the one at the 1- and 3-positions is taken into account, an excess of P therefore exists compared with human milk. 
     The PUFA fatty acids, and particularly the LC-PUFAs, undergo the rearrangement reaction in the form of TAGs, which are more stable than mixtures of free fatty acids and with a limited reaction time, at a relatively low temperature and under an inert atmosphere, for example under nitrogen. On the other hand, according to the state of the art, the mixtures of fatty acids intended to serve as lipolysis substrate should first be prepared, which can also cause, in part, their degradation by oxidation. 
     The lipid mixture which results from the reaction has a significantly improved oxidative stability compared with that of a simple physical mixture of lipids of the same PUFA fatty acid composition. This probably results from the PUFA fatty acid distribution between the various positions of the TAGs. 
     The aim of step 2) is to selectively replace the P at the 1- and 3-positions with other fatty acids, in particular with MCFAs and oleic acid (O), but not with the PUFAs. To do this, advantage is taken of kinetic resolution, that is to say of the fact that most of the 1,3-regiospecific lipases, genetically modified or otherwise, for example from Mucor miehei, and Candida cylindracea, and pancreatic lipase, react preferentially for example towards MCFAs, P and O, and in a discriminatory manner towards the LC-PUFAs containing 4, 5 and 6 double bonds, for example DHA and AA. In this manner, the excess P is rapidly exchanged, leaving the PUFAs, in particular DHA practically intact at the 1- and 3-positions. 
     It is observed that after subsequent separation of the free fatty acids, the oxidative stability of the TAGs of the mixture derived from step 2 is maintained or even improved. 
     After the second step of the process according to the invention, it is necessary to remove the free fatty acids in excess as well as those formed during the exchange process which may be subject to oxidation. To do this, it is possible to use any known method such as, for example, conventional neutralization or steam distillation under vacuum. 
     This third step is preferably carried out by performing a controlled neutralization of the free fatty acids and therefore a selective refining, minimizing hydrolysis and saponification. The principle of this selective refining is to carry out the operation in an aqueous-alcoholic phase, with gentle stirring, which leads to partition of the free fatty acids between the lipid phase and the aqueous-alcoholic phase which is immiscible with the lipid phase, while a base, for example a concentrated aqueous NaOH or KOH solution, is gradually added to the aqueous-alcoholic phase, for example by means of a pH-stat regulated at a set point, for example about 9.5. Soaps are formed which are solubilized as they are produced in the aqueous-alcoholic phase, which produces a shift in the equilibrium and a progressive deacidification of the lipid phase. The pH chosen minimizes neutralization of the phenolic derivatives. The reaction temperature chosen is greater than the melting point of the lipids and is less than the boiling point of the aqueous-alcoholic mixture. When all the fatty acids have been extracted, the pH is stabilized, indicating the end of the reaction. After neutralization, the two phases are separated by decantation and the deacidified lipid phase is recovered, from which the ethanol is removed, for example by evaporation under vacuum and the residual soaps are removed, for example by washing with an aqueous-ethanolic solution or by treating with an adsorbent, in particular an amorphous silica gel. 
     The invention also relates to an infant food containing proteins, where appropriate hydrolysed, carbohydrates, lipids and where appropriate vitamins and trace elements, characterized in that it contains, by weight of dry matter, 15 to 35% of lipids of which 50 to 100% consist of the above lipid composition. 
     Such an infant food can be prepared in liquid or powdered form with incorporation of the above lipid composition, by wet mixing of the various constituents, followed by sterilization or pasteurization and aseptic packaging in the case of a liquid product or by drying, for example by spray-drying or by dry mixing in the case of a powder. 
    
    
     EXAMPLES 
     The examples below illustrate the invention. In these, the parts and percentages are by weight, unless otherwise indicated. 
     Example 1 
     1.1) Chemical interesterification 
     A mixture of lipids, the nature and composition of which are indicated in Table 1 below, is used as starting material: 
     
                       TABLE 1                                                     
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Oil/fat Mixture (%)                                                       
                   Origin      Characteristics                            
______________________________________                                    
Fish oil                                                                  
         2         Nippon Suisan                                          
                               high in DHA                                
    Kaisha                                                                
  Oil source  1 Gist-Brocades AA, 37% (oil from a                         
  of AA   unicellular organism)                                           
  Soya bean 10 commercial source of ALA                                   
  oil                                                                     
  Palm stearin  5 Loders Croklaan P, 75%                                  
  Palm oil 82 Morgia source of P                                          
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     The above lipid mixture containing 24 g of fish oil (with 24.6% of DHA and 6.4% of EPA), 12 g of oil which is the source of AA (containing 37% of AA), 60 g of palm stearin (containing 75% of P), 984 g of palm oil and 120 g of soya bean oil (containing LA and ALA) is randomly interesterified in the presence of 0.5% of sodium methoxide as catalyst at 50° C., with continuous stirring, under a nitrogen atmosphere for 4 h. The reaction mixture is then washed with 2 l of hot water in order to remove the soaps, and then it is dried at 50° C. under a 20 mbar vacuum. 
     To avoid oxidation, a small quantity of sodium salt of ethylenediaminetetraacetic acid (EDTA-NA 3 ) may be added thereto. 
     1.2) 1,3-regiospecific enzymatic acidolysis 
     The acidolysis is a rearrangement, catalysed by a 1,3-regiospecific lipase, of a mixture consisting of the product of the preceding step 1 and of a mixture of fatty acids whose composition is indicated in Table 2 below: 
     
                       TABLE 2                                                     
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       Fatty acid                                                         
                %                                                         
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       C8:0     10                                                        
  C10:0 15                                                                
  C12:0 10                                                                
  C14:0 1.6                                                               
  C16:0 3                                                                 
  C16:1 3.2                                                               
  C18:0 1.7                                                               
  C18:1 45                                                                
  C18:2 6.3                                                               
  C18:3 (alpha) 0.3                                                       
  Others 3.9                                                              
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     940 g of the product of the preceding step 1 and 940 g of the mixture of commercial oleic acid and of the C 8-12  :0 acids having the composition indicated in the above Table 2, are subjected to interesterification catalysed by an immobilized 1,3-regiospecific lipase (Lipozyme IM 60®, Novo) in an amount of 10% of lipase relative to the substrates. The water content of the lipase is adjusted by adding 6% water and by allowing it to stand for 10 h before using it. The reaction is then carried out at 40° C. under a nitrogen atmosphere for 5 h. After reacting, the lipase is separated by filtration and a crude mixture containing TAGs and free fatty acids is recovered. 
     1.3) Controlled neutralization in order to remove the free fatty acids 
     1.4 kg of the crude mixture of the preceding step and 3.5 l of 90% ethanol are introduced into a reactor and stirred gently at 40° C. under a nitrogen atmosphere. 670 g of a 25% aqueous KOH solution are continuously added thereto while maintaining the pH of the reaction medium between 8.5 and 9.5 by means of a pH-stat regulated at the set point of 9.5. Soaps are formed which are solubilized as they are formed in the aqueous-alcoholic phase which is immiscible with the lipid phase, producing a shift in the equilibrium for partition of the fatty acids between the lipid phase and the aqueous-alcoholic phase towards the aqueous-alcoholic phase, and as a result a progressive deacidification of the lipid phase. The pH is stabilized, indicating that all the fatty acids have been extracted. The stirring is then stopped; the aqueous-alcoholic phase, which is lighter, separates from the lipid phase and the lipid phase is recovered. 
     The composition of the fatty acids in the product obtained is determined by gas-liquid chromatography of the methyl esters of the acids after methylation of the triglycerides (FAMES). 
     To determine the distribution of the fatty acids between the 2-position and the 1,3-positions of the TAGs, lipolysis is carried out with pancreatic lipase (IUPAC 2.210). 
     The results of the analysis of the principle fatty acids and of their distribution in the mixture obtained are indicated in Table 3 below: 
     
                       TABLE 3                                                     
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                      Fatty acids                                         
                                 Fatty acids                              
    at the at the 1,3-                                                    
   Fatty acids 2-position of positions of                                 
   as % of the the TAGs (%, the TAGs (%,                                  
  Fatty acid (fames) total (fames) analysed) calculated)                  
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C8:0       3.07       0.06       4.56                                     
  C10:0 5.08 0.21 7.48                                                    
  C12:0 4.04 0.39 5.83                                                    
  C14:0 1.2 1.03 1.28                                                     
  C16:0 28.13 40.86 21.88                                                 
  C18:0 3.33 4.62 2.7                                                     
  C18:1 37.83 34.1 39.66                                                  
  C18:2 10.93 12.57 10.12                                                 
  C18:3, n-3 (alpha) 0.56 0.6 0.54                                        
  C20:4, n-6 (AA) 0.26 0.34 0.22                                          
  C20:5, n-3 (EPA) 0.18 0.2 0.17                                          
  C22:6, n-3 (DHA) 0.42 0.35 0.46                                         
  Others 4.97 4.67 5.1                                                    
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     It is observed that the composition of the fatty acids as well as their distribution on the TAGs is very similar to those of human milk. 
     Furthermore, the oxidative stability (OSI) of the product obtained, measured in the accelerated oxidation test with the Omnion (R) apparatus, USA, as period of induction at 80° C. with an air flow rate of 150 ml/min, corresponds to an index of about 160 h, that is to say about 1.5-2 times higher than that of 100 h measured for the starting mixture of lipids. 
     The solids content of the fat, determined by pulsed nucleomagnetic resonance (NMR, IUPAC 2.150 6.2.2.2) is the following: 
     
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Solids content (%) at the temperature (° C.) indicated             
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        N-5  40.3                                                         
  N-10 29.9                                                               
  N-15 19                                                                 
  N-20 10.4                                                               
  N-30 1.2                                                                
  N-35 0                                                                  
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     The preceding result shows that there is no significant quantity, of undesirable trisaturated TAGs. 
     Example 2 
     The procedure is carried out as in Example 1, step 1), except that the composition of the starting lipid mixture is that indicated in Table 4 below: 
     
                       TABLE 4                                                     
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Oil/fat Mixture (%)                                                       
                   Origin      Characteristics                            
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Fish oil                                                                  
        2          Nippon Suisan                                          
                               high in DHA                                
    Kaisha                                                                
  Oil source 1.5 Gist-Brocades AA, 37% (oil from a                        
  of AA   unicellular organism)                                           
  Soya bean 15 commercial source of ALA                                   
  oil                                                                     
  Palm oil 81.5 Morgia source of P                                        
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     The enzymatic interesterification is then carried out as in Example 1, step 2), except that the composition of the mixture of the free fatty acids is as defined in Table 5 below and that the TAGs/mixture of fatty acids ratio is 70:30. 
     
                       TABLE 5                                                     
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       Fatty acid                                                         
                %                                                         
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       C10:0    12                                                        
  C12:0 15                                                                
  C14:0 6.7                                                               
  C16:0 3.2                                                               
  C16:1 3.5                                                               
  C18:0 1.8                                                               
  C18:1 48.6                                                              
  C18:2 6.7                                                               
  C18:3 (alpha) 0.3                                                       
  Others 2.2                                                              
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     The result of the analysis of the principle fatty acids and of their distribution in the mixture obtained are indicated in Table 6 below: 
     
                       TABLE 6                                                     
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               Fatty acids as % of                                        
  Fatty acid (fames) the total (fames)                                    
______________________________________                                    
C10:0          2.89                                                       
  C12:0 4.04                                                              
  C14:0 2.32                                                              
  C16:0 28.84                                                             
  C18:0 4.62                                                              
  C18:1 38.65                                                             
  C18:2 13.23                                                             
  C18:3, n-3 (alpha) 0.94                                                 
  C20:4, n-6 (AA) 0.48                                                    
  C20:5, n-3 (EPA) 0.21                                                   
  C22:6, n-3 (DHA) 0.36                                                   
  Others 3.42                                                             
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     It is observed that the composition of the fatty acids as well as their distribution on the TAGs is very similar to those of human milk fat.