Polyol polyester synthesis

Abstract: Polyol polyesters are purified by a process comprising bleaching with a specific silica gel and/or treating with oxygen followed by heat treatment and removal of volatile products by steam deodorization. Any steam deodorization is accomplished at reduced temperatures or in admixture with triglycerides to minimize thermal degradation of the polyol polyesters.

Description: This invention relates to improved purification of higher polyol fatty acid polyesters, especially sucrose polyesters, prepared via transesterification, and more specifically to removal of undesirable materials like color materials from said fatty acid polyesters. BACKGROUND OF THE INVENTION Processes for preparing polyol fatty acid polyesters, including solvent-free transesterification reactions, have been described in U.S. Pat. No. 3,963,699, Rizzi et al., issued June 15, 1976; U.S. Pat. No. 4,517,360, Volpenhein, issued May 14, 1985; and U.S. Pat. No. 4,518,772, Volpenhein, issued May 21, 1985; all of said patents being incorporated herein by reference. In order to. have a better commercial process it is desirable to have available a number of improvements, e.g., purification procedures that can better remove undesirable compounds like color materials from the polyol fatty acid polyesters. Each of said improvements individually can improve the finished product and the combination of the improvements can provide a truly superior product. SUMMARY OF THE INVENTION The present invention relates to improved, commercial, processes for removing minor amounts of undesirable materials such as color materials; materials that affect odor or flavor; or precursors of such materials, from higher polyol fatty acid polyesters which comprise a process step of: (1) heat treating the said polyesters, first in the presence of oxygen up to about saturation levels and then while excluding oxygen, for a sufficient time to first create peroxygen groups when the oxygen is present and then to reduce the content of said peroxygen groups when the oxygen is excluded and, either subsequently or contemporaneously, removing the resulting undesirable volatile materials by, e.g., steam stripping, preferably either at a temperature below about 450F (230°C) or after first mixing with at least about 25% of a triglyceride to minimize thermal degradation; and combination of steps (1) with (2). (2) treating the said polyesters with silica gel having: (a) average particle size of from about 10 to about 30 microns; (b) average pore diameter of from about 50 to about 70 Angstrom Units; (c) surface area of from about 720 to about 800 square meters per gram; (d) pore volume of from about 0.9 to about 1.9 cc/g; (e) pH, measured at a level of about 5% in water, of from about 5 to about 8; and (f) total volatiles of less than about 20%; The color of the finished product should be lighter than about 1.5, preferably lighter than about 1.2, more preferably lighter than about 0.8 Lovibond Red, and the flavor and odor should be bland. Stability upon exposure to air is increased by up to about a factor of 3, especially when the said silica gel is used to remove undesirable minor components. The purified polyol fatty acid polyester is sufficiently stable that mixtures with at least about 25% of triglyceride containing natural antioxidants are surprisingly stable as compared to mixtures with such triglycerides comprising unpurified polyol fatty acid polyesters. DETAILED DESCRIPTION OF THE INVENTION The Polyol Polyesters As used herein, the term "polyol" is intended to include any aliphatic or aromatic compound containing at least four free hydroxyl groups. In practicing the process disclosed herein, the selection of a suitable polyol is simply a matter of choice. For example, suitable polyols can be selected from the following classes: saturated and unsaturated straight and branched chain linear aliphatics; saturated and unsaturated cyclic aliphatics, including heterocyclic aliphatics; or mononuclear or polynuclear aromatics, including heterocyclic aromatics. Carbohydrates and nontoxic glycols are preferred polyols. Monosaccharides suitable for use herein include, for example, mannose, galactose, arabinose, xylose, ribose, apiose, rhamnose, psicose, fructose, sorbose, tagitose, ribulose, xylulose, and erythrulose. Oligosaccharides suitable for use herein include, for example, maltose, kojibiose, nigerose, cellobiose, lactose, melibiose, gentiobiose, turanose, rutinose, trehalose, sucrose and raffinose. Polysaccharides suitable for use herein include, for example, amylose, glycogen, cellulose, chitin, inulin, agarose, zylans, mannan and galactans. Although sugar alcohols are not carbohydrates in a strict sense, the naturally occurring sugar alcohols are so closely related to the carbohydrates that they are also preferred for use herein. The sugar alcohols most widely distributed in nature and suitable for use herein are sorbitol, mannitol and galactitol. It is desirable that the aldehyde groups be changed to alcohol groups or reacted with alcohol groups to form ether linkages. E.g., the polyol can be an alkyl glycoside or polyglycoside, especially glucosides and polyglucosides. Particularly preferred classes of materials suitable for use herein include the monosaccharides, the disaccharides and sugar alcohols. Preferred carbohydrates and sugar alcohols include xylitol, sorbitol and sucrose. The most preferred is sucrose. As used herein, the term "fatty acid esters" is intended to include the C₁-C₄ (preferably methyl), 2-methoxy ethyl and benzyl esters of fatty acids containing about eight or more carbon atoms, and mixtures of such esters. Suitable reactant esters can be prepared by the reaction of diazoalkanes and fatty acids, or derived by alcoholysis from the fatty acids naturally occurring in fats and oils. Suitable fatty acid esters can be derived from either synthetic or natural, saturated or unsaturated fatty acids and include positional and geometrical isomers. Suitable preferred saturated fatty acids include, for example, caprylic, capric, lauric, myristic, palmitic, stearic, behenic, isomyristic, isomargaric, and anteisoarachadic. Suitable preferred unsaturated fatty acids include, for example, myristoleic, palmitoleic, ricinoleic, linoleic, oleic, elaidic, linolenic, eleasteric, arachidic, arachidonic, erucic, and erythrogenic acids. Mixtures of fatty acids derived from soybean, palm, safflower, rapeseed, canola, peanut, sunflower, cottonseed and/or corn oils are especially preferred for use herein. For example, rapeseed provides a good source for C₂₂ fatty acid. C₁₆-C₁₈ fatty acid can be provided by tallow, soybean oil, or cottonseed oil. Shorter chain fatty acids can be provided by coconut, palm kernel, or babassu oils. Corn oil, lard, olive oil, palm oil, peanut oil, safflower seed oil, sesame seed oil, and sunflower seed oil, are examples of other natural oils which can serve as the source of the fatty acid component. It is very important for the preparation of improved polyol polyesters that these fatty acid esters be highly purified to remove color/odor materials, oxidation products, and their precursors. Such materials include those that have a color, odor or taste that is objectionable, or which develop an objectionable color, odor, or taste upon heat treatment and/or oxidation. In addition, highly polar materials which coat the catalyst surface should be removed. Preferably, the carbonyl value should be less than about 200 ppm, preferably less than about 100 ppm, more preferably less than about 50 ppm. The percent transmittance at 375 nm with a heptane standard should be greater than zero, preferably greater than 60, most preferably greater than 80. For typical ester sources without added colored materials, these values define operable reactants. I.e., the carbonyl content is generally indicative of the total level of polar materials present. The low level of color/odor materials and/or oxidation products in the reactants helps provide improved color polyol polyester products that can be further improved by a combination of the process improvements set forth herein. Alkali metal soaps are typically used in the processes for preparing polyol polyesters of the types described herein. As used herein, the term "alkali metal fatty acid soap" is intended to include the alkali metal salts of saturated and unsaturated fatty acids having from about 8 to about 18 carbon atoms. Accordingly, suitable alkali metal fatty acid soaps include, for example, the lithium, sodium, potassium, rubidium, and cesium salts of the fatty acids described hereinbefore, especially saturated fatty acids such as capric, lauric, myristic, palmitic, and stearic acids, as well as mixtures thereof. Palmitic and stearic are preferred. Mixtures of fatty acids derived from soybean oil, palm, peanuts, canola, cottonseed, sunflower oil, safflower oil, and/or corn oil are preferred for use herein. Accordingly, preferred alkali metal fatty acid soaps include, for example, the potassium soap made from soybean oil fatty acids. The essentially fully hydrogenated materials, e.g., I.V. of less than about 8, preferably less than about 2 are especially preferred. In a preferred process of preparing polyesters of sucrose especially utilizing the methyl esters of soybean oil fatty acids, it is highly desirably to have present an alkali metal, e.g., potassium or sodium, salt of saturated fatty acids containing from about 16 to about 22 carbon atoms. Intimate mixture of the very finely divided ingredients is important to achieving a good reaction. The basic catalysts generally suitable for use in preparing the polyol polyesters described herein are those selected from the group consisting of alkali metals, such as sodium, lithium and potassium: alloys of two or more alkali metals, such as sodium-lithium and sodium-potassium alloys; alkali metal hydrides, such as sodium, lithium and potassium hydride; and alkali metal alkoxides, such as potassium t-butoxide and sodium methoxide. In one desirable embodiment of the present invention, the basic catalyst used in the reaction is potassium carbonate, sodium carbonate, barium carbonate, or mixtures of these compounds. It has been found that when these specific compounds are used as the catalyst, increased yields of light colored higher polyol polyesters are obtained when compared to essentially identical reactions carried out using more conventional catalysts, such as sodium hydride, potassium hydride, soap, or sodium methoxide. These preferred catalysts can also be used in admixture with the more conventional basic catalysts, described above. Potassium carbonate is a highly desirable catalyst for use herein. The use of these catalysts is further disclosed and claimed in U.S. Pat. No. 4,517,360, Volpenhein, issued May 14, 1985, entitled "Synthesis of Higher Polyol Fatty Acid Polyesters using Carbonate Catalysts," incorporated herein by reference. More reactive catalysts such as potassium or sodium methoxide should be protected until their addition into the reaction mixture. Preferably the catalyst should be suspended in, or more preferably encapsulated by, a material that will either be present in the reaction mixture or be readily separated from the reaction mixture. Suitable encapsulating agents include said alkyl esters of, e.g., C₁₆-C₂₂ fatty acids. Addition of these more alkaline, reactive catalysts in the later stages after the polyol has an average degree of esterification of more than 60%, preferably more than 85%, can provide improved reaction kinetics and result in a greater degree of esterification of the polyol yet does not create the level of color/odor materials that would be created if such catalysts are present from the start of the reaction. The Reaction In general, by way of example, an initial heterogeneous reaction mixture comprises from 10% to 30%, preferably from 14% to 18%, by weight of polyol; from about 60% to 90%, preferably from 70% to 80%, by weight of the fatty acid esters; from 0.1% to 20%, preferably from 0.2% to 10%, by weight of the emulsifier, e.g., alkali metal fatty acid soap; and from 0.1% to 3%, preferably from 0.1% to 1%, by weight of basic catalyst component. In general it is desirable, and even preferred, to effect the reaction in at least two steps. In any later step, additional fatty acid esters and, optionally, more reactive catalyst are added. In any second, or later step, fatty acid esters are added to raise the overall ratio of fatty acyl groups to the polyol above the theoretical, fully esterified level, e.g., by at least 25%, or even by at least 50%. The catalyst in the initial step can be potassium carbonate as described hereinbefore or alkali metal hydroxide at a low level and, in any later step, the catalyst can be either the same as the initial catalyst or can also be potassium or sodium methoxide. The reaction mixture is heated to a temperature within the range from 240°F (115°C) to 300°F (150°C), desirably from 250°F (120°C) to 280°F (140°C), under a pressure of from 0.1 mm to 760 mm Hg, and preferably from 0.3 mm to 100 mm Hg. It is highly preferred that the reaction mixture, or mixtures, be stirred as vigorously as possible and maintained in as intimate a mixture as is possible. Finished Product Clean-up After the reaction has reached the desired state of completion, the catalyst, the excess fatty esters, and the emulsifier, e.g., soap must be destroyed and/or removed if they cannot be used in the eventual consumption of the polyol fatty acid polyesters. The normal materials that are in triglycerides derived from natural sources (naturally occuring triglycerides) are not present in the poly fatty acid polyesters, since the processing, the reaction, etc. destroy and/or remove such materials. E.g., such normal materials, like phospholipide and tocophenols, are removed in the process for preparing the esters that are reacted with the polyol to form the polyol fatty acid polyesters. The soap and catalyst can be removed to a large extent by a water separation step. Water is added, preferably at a ratio of from 0.5:1 to 10:1 relative to the amount of soap being removed. Separation of the soap and catalyst is facilitated by passing the water and reaction-mix through a centrifuge. A useful known process that can be used, in addition to the improvements described hereinafter, for removing undesirable materials comprises a high temperature vacuum steam distillation process, and involves deaerating the polyol polyester to a level of less than 0.10% by volume of dissolved oxygen and heating the deaerated oil to a temperature between 390°F (200°C) and 480°F (250°C) and then stripping with a stripping medium in the amount of 0.2% to 20% by weight of the oil at an absolute pressure of less than 15 mm Hg for a time of between 5 seconds and 15 minutes. This vacuum stripping at very high temperatures for short residence times minimizes the content of undesirable materials. It is desirable to either maintain the temperature below 450°F (230°C), preferably less than 350°F (about 180°C), in a batch deodorizer, or admix the polyol polyester with a fatty acid triglyceride to protect the polyol polyester from excessive thermal degradration. The Improvements After the initial treatments, as described hereinbefore, the undesirable materials can reform due to degradation of the oil/-fatty acid ester. In addition, some undesirable color materials remain after the high temperature vacuum steam distillation process. The very low levels of color/odor/flavor materials, precursors, and/or oxidation products most preferred for use herein can be achieved by a clean-up procedure comprising a heat treating process step (1) which involves introducing oxygen up to about saturation level, as a separate step and/or by the silica gel, and then raising the temperature to at least about 200°F (about 90°C), preferably at least about 380°F (about 190°C), but less than about 425°F (about 220°C), preferably less than about 400°F (about 205°C), to produce peroxygen groups and hold the product at the elevated temperature for a period of time sufficient to reduce the peroxygen content and/or reduce the content of colored materials present, e.g., from about 1 to about 150 minutes, preferably from about 1 to about 20 minutes, and most preferably from about 5 to about 10 minutes. (The level of oxygen in the polyol polyester is believed to be from about 0.001 to about 0.16 volumes of oxygen per volume of polyol polyester assuming similar values to those reported for triglycerides.) This can be accomplished separately, or in combination with a steam deodorization step, as described hereinbefore. The time should not be so long as to start again increasing the color. The volatile materials created by heating first with oxygen and then in the absence of oxygen are alkanes, alcohols, esters, aldehydes, ketones, fatty acids, aromatics, and/or lactoses having molecular weights of less than about 300. In the preferred processes set forth herein, the amount of said volatile materials that needs to be removed is quite low, typically less than about 200 ppm, and, for the best processes, less than about 100 ppm. Despite the low level of such volatile materials, removal is important to the stability of the polyol fatty acid polyesters. The removal of the volatile materials resulting from the oxygen/heat treatment are preferably removed by steam deodorization. However, it is also possible to remove the volatile materials by any of the other known removal techniques including: (a) solvent extraction; (b) straight distillation under reduced pressure; (c) extraction with other gases to reduce the partial vapor pressure; (d) absorption on materials like silica gels, alumina, charcoal, molecular sieves, porous polymers, etc.; and (e) combinations of techniques. Steam deodorization, however, can provide the heat and is a relatively safe, inexpensive procedure that is commonly applied to fatty materials. Prior to the heat treating process step (1), the said polyesters can be treated by (2) a step involving treatment with silica gel having the following properties: (a) a particle size of ranging from 10 to 30, preferably from 20 to 25 microns; (b) average pore diameter of from 50 to 70 microns; (c) surface area of from 720 to 800, preferably from 770 to 800 m²/gm; (d) pore volume of from 0.9 to 1.9, preferably from 1.2 to 1.4 cm³/gm; (e) a pH of from 5 to 8, preferably from 5 to 7.3 measured at a level of 5% in water; and (f) total volatiles of less than 20%, preferably from 6.5% to 10.5%, and more preferably from 8% to 10.5%. Such silica gels are extremely effective as compared to other known materials. Said silica gel is added to the product at levels of from 0.25% to 5%, preferably from 1% to 2%. Any steam deodorization steps prior to the silica gel bleaching step 2 ○ and/or after the heat treatment step 1 ○ can be accomplished in the presence of a conventional triglyceride in ratios of higher polyol polyester to triglyceride of from 1:10 to 10:1, preferably from 1:5 to 5:1, more preferably from 1:3 to 3:1. This "codeodorization" minimizes thermal degradation of said polyester. The operating conditions for codeodorization are from 300°F (about 150°C) to 600°F (about 315°C), preferably from 350-525°F (about 175-275°C); 0.1-20 mm Hg (preferably 1-10 mm Hg) vacuum; and steam to product ratio of 0.001-0.30 (preferably 0.005-0.10). As compared to deodorization of the polyol polyester by itself, codeodorization permits the use of higher temperatures, e.g., from 300°F (150°C) to 600°F (315°C), preferably from 350°F (175°C) to 525°F (275°C), and/or longer times without excessive degradation and can be desirable if equipment limitations are present. The triglyceride is usefully any common triglyceride, e.g., those derived from cottonseed, peanut, safflower, sunflower, coconut, rapeseed, canola, palm, palm kernel, and/or soybean oils. Combinations of one or more of these steps reduce the quantity of undesired materials to a very low level. When the initial reactants have been properly cleaned up and the preceding clean-up steps have been applied properly, the color of the polyol polyester is less than 1.5, preferably less than 1.2 Lovibond Red, more preferably less than 0.8 Lovibond Red, and the flavor grade of the polyol polyester is at least 7, preferably at least 8 panel score units (psu) as measured by a panel of experts using a grade system in which 10 is bland and 1 is severely oxidized. Such a finished polyol polyester has improved oxidative, flavor, and thermal stability during its subsequent uses. When combined with a typical triglyceride, containing natural antioxidants, in ratios of polyol polyester to triglyceride of from 1:10 to 10:1, preferably at ratios of from 1:3 to 3:1, more preferably at ratios of from 1:3 to 1:1, the stability is further surprisingly enhanced. Apparently, the reactive materials are reduced to a level where the natural antioxidants can provide improved long term stability. A useful composition comprises a naturally occurring triglyceride and from about 10% to about 75% of said finished polyol polyester. Especially preferred polyol polyesters are those of sucrose which have been esterified to a level of more than about 65%, preferably from 70% to 90% octaester for "solid" shortenings. Such sucrose polyesters have superior thermal stability, especially when they contain only the low levels of color/odor materials and/or other oxidation products. All percentages, parts and ratios herein are by weight unless otherwise specified. EXAMPLE I Methyl esters of a fully hydrogenated (Iodine Value about 1) soy oil (90.7 kg), 20 kg of potassium hydroxide pellets, and 136 kg of methanol are mixed in a stainless steel batch reactor. This mixture is then heated to 145°F (63°C) with agitation for 1 to 3 hours at atmospheric pressure. During this time, a portion of the methyl esters are saponified to form soap. An additional 591.9 kg of methyl esters of a partially hydrogenated soy oil with an I.V. of 85, is then added to the soap mixture. The methyl esters are prepared by distillation under vacuum without fractionation. Granular sucrose (136.1 kg) is added to the soap/ester mixture to give an about 5:1 molar ratio of ester to sucrose. Granular potassium carbonate is then added to the mixture (∼0.5% of the reaction mix) to catalyze the transesterification. This mixture is agitated and slowly heated at atmospheric pressure until the temperature reaches 225°F (107°C). This is to remove the methanol. A vacuum is then pulled and the mixture agitated for up to about 4 hours to form the mono-, di-, and triesters. Small quantities of tetra- and pentaesters are also formed during this stage. Additional methyl ester (about 945.7 kg) is added to bring and maintain the molar ratio of the esters to sucrose to 12:1. Additional potassium carbonate is then added to the mixture (∼0.5% of the initial reaction mix). When the reaction conditions stabilize at about 275°F (135°C), a nitrogen sparge is used to improve agitation and promote methanol stripping. This second reaction stage lasts approximately 4 to 16 hours. The reaction mixture is then cooled under nitrogen to between 149°F (65°C) and 185°F (85°C). The crude reaction mixture is agitated with between 0.25% and 6% water. The hydrated crude reaction mixture is passed through a centrifuge to separate a heavy and a light phase. The heavy phase which contains the soaps, excess sugars, and potassium carbonate is discarded. The light phase which contains methyl esters and the sucrose polyester (SPE) is then dried to remove moisture at from about 160°F (71°C) to about 200°F (93°C) under 70 mm Hg or less vacuum for 30 to 60 minutes. Filtrol TM 105, an absorbing clay, (0.5-3%) is added and the mix is agitated at 167°F (75°C) to 200°F (93°C). The slurry is separated by filtration or other means until there is less than 0.1% fines. The liquid is then passed through a 1 micron filter. The refined and bleached reaction mix is then passed through a stainless steel wiped-film evaporator or other suitable equipment to distill off the bulk of the methyl esters. The distillation takes place at 392°F (200°C) to 455°F (235°C) under approximately 3 mm Hg of vacuum. The SPE is then deodorized by passing downward through a stainless steel packed column deodorizer or other suitable device at from 392°F (200°C) to 482°F (250°C) under a vacuum of 5 mm Hg or less. The lower than normal processing temperatures herein minimize formation of undesirable materials. Steam is introduced to the bottom of the column and passes counter-currently to the sucrose polyester. Feed rates and temperature are adjusted until the methyl ester content of the SPE is below 1000 ppm. The mixture is then cooled to between 130°F (54.5°C) and 185°F (85°C) and passed through an 1 micron filter. SPE from the preceeding reaction is bleached in 3 separate batches using between 0.5% and 5.0 wt% silica gel at 125-350°F (52-177°C) for from 0.5 to 4.0 hours. The silica gel used in this example has a particle size of 19 microns, an average pore diameter of 54 Angstroms, surface area of 770 m²/gm, pore volume of 1.0 cc/gm, a pH measured at 8 measured in water at a concentration of 5%, and total volatiles of 8.9%. Even better performance is achieved using a silica gel with a particle size that ranges from 20 to 25 microns, a surface area of from 770 to 800 m²/gm, pore volume of from 1.2 to 1.4 cc/gm, and pH of from 5 to about 7.3 measured in water at 5% concentration. Silica gel is added directly to the SPE in lined carbon steel drums with a nitrogen blanket and agitated. The slurry is separated by filtration until no fines are observed and then cooled. Color of the SPE is reduced from 1.5 Lovibond Red and 6.5 Lovibond Yellow to 0.9 Lovibond Red and about 3.4 Lovibond Yellow. The bleached and filtered SPE is then mixed with triglyceride in the presence of air in drums in a ratio of 50:50 and deodorized in 5 separate batches. In each deodorizer batch, a total of 154.2 kg of the mixture is transferred into the pot, nitrogen sparge is introduced and agitation started. Steam is generated by introduction of distilled water into the pot when temperature reaches 250°F (about 120°C) during heatup. Deodorization is conducted at a temperature of 400°F (about 205°C) for from 2 hours to 4 hours at 3 mm Hg of vacuum. The mixture is then cooled and stored in clean drums. Color of the mixture is reduced from 0.9 Lovibond Red and 4.6 Lovibond Yellow to 0.6 Lovibond Red and 3 Lovibond Yellow during deodorization. Color reduction observed during deodorization is a function of heat treatment first forming peroxides from oxygen absorbed during silica gel addition and mixing with triglyceride followed by decomposition of the organic peroxides and color compounds with heat. Formation of organic peroxides in the SPE improves color by oxidizing the undesirable color bodies in a manner analogous to chemical bleaching by inorganic peroxides. The organic peroxides break down to more volatile materials that can then be more readily removed, e.g., by steam deodorization. Air trapped within the silica gel, in both pores and between particles, provides oxygen to form the peroxides (believed to be via the free radical oxidation mechanism). Mixing SPE and triglyceride in air also provides contact with oxygen. An additional method of providing oxygen, to increase peroxide levels to obtain greater bleaching upon decomposition, is to bubble air into the SPE or mixture under controlled conditions. It is generally accepted that air should always be excluded from triglyceride processing to avoid oxidation which leads to undesirable flavors and colors. Controlled polyol polyester, e.g., SPE oxidation can be used in the process to provide color improvements as long as peroxides are subsequently decomposed to generate mostly volatile oxidation products which are then removed. These oxidation products which cause undesirable flavors are removed by steam deodorization. Increased oxidative stability in the presence of air is a substantial quality benefit because it equates with increased flavor stability. Good fresh flavor and flavor stability are key consumer expectations which strongly influence consumer satisfaction for an edible product. Poor oxidative stability results in generation of off flavors and odors during routine exposure to air encountered with product use and storage. Oxidative stability of the SPE and the triglyceride/SPE mixture is also dramatically increased when prepared as described in Example 1. There are believed to be three primary contributing steps, each individually increasing stability, and together providing the most stable combination. The three steps are: (1) silica gel bleaching; (2) oxygen and/or heat treatments either prior to continuous deodorization, or during batch deodorization (optionally codeodorizing with triglycerides); and (3) blending with triglyceride which contains natural antioxidants. The silica gel which effectively reduces color, also removes undesirable materials resulting in increased oxidative stability of the polyol polyester. It is believed that heat treatment first forms peroxygen compounds from air absorbed during bleaching with the silica gel or by mixing with air and/or mixing with triglyceride in the presence of air, and then decomposes those peroxygen compounds into volatile oxidation products, such as hexanal, while excluding air, which oxidation products are subsequently removed by, e.g., steam deodorization. With the improved stability that results from the two preceding processes, blending with triglyceride containing natural antioxidants at a level of at least 25%, preferably at least 50%, triglyceride results in substantial oxidation stability improvement because there is now a sufficient level of natural antioxidants present in the triglyceride to also protect the polyol-polyester/triglyceride mixture. Oxidative stability is measured using a modified Active Oxygen Method (AOM) which measures an increase in peroxide value (AOCS Method Cd 8-53) over time while sparging air through the sample at about 208°F (98°C). The AOM is a standard method used in the fats and oils industry to measure oxidative stability of triglyceride. (AOCS Method Cd 12-57) This method has been modified for ease of application in the time frame of 0-5 hr. where oxidation impact on flavor is especially important. The method used to measure stability is described as follows: Charge 300 gm of sample into the glass flask, and begin purging the sample with nitrogen. Heat to 208F (98°C) using a heating mantle connected to a thermo watch to control temperature. Switch from nitrogen to air at 8.57 cc/min./ml of sample and collect a baseline sample for time zero reference and analyze for ppm peroxide. Collect samples every 20 to 40 min. and analyze for ppm peroxide. The first table is included to show the effect of silica gel bleaching on stability of SPE. Effect of Silica Gel Bleaching on SPE Stability Peroxide Value (ppm) Time (Min.) Unbleached SPE Bleached SPE 0 11.8 5.5 20 22.8 10.0 40 36.1 13.2 60 40.3 14.6 90 47.2 19.0 120 43.9 23.2 As can be seen from Table 1, peroxide value is substantially greater in the sample of SPE which was not treated with silica gel. At 120 min. the untreated sample contains 89% more peroxide than the treated sample. Heat treatment was accomplished in the batch deodorizer at the high temperature and long residence time during deodorization of the mixture of SPE and triglyceride. Without the triglyceride being present, a temperature of from 275°F (135°C) to 350°F (175°C) is used. In the deodorizer any absorbed oxygen forms peroxides which are then decomposed into volatile oxidation products that are subsequently removed by steam deodorization. This heat treatment step prevents high levels of peroxides from passing through deodorization and into storage and finished product application where they eventually decompose and impart off-flavors into the product. In a continuous dedorization process where residence time is comparatively short, a separate heat treatment step is used just prior to deodorization to increase formation and/or breakdown of the peroxides. The second table illustrates the unexpected stability benefit gained from blending with triglyceride and using the natural antioxidants present in the triglyceride to provide the most stable mixture. SPE contains little or no natural antioxidants because of their removal in multiple processing steps in making methyl esters from triglyceride and the production of SPE. Effect of Blending SPE with Triglyceride on Stability Peroxide Value (ppm) Time (Min.) Triglyceride Bleached, Heat Treated and Deodorized SPE Mixture 0 6.7 5.5 5.9 20 7.3 10.0 5.6 40 8.2 13.2 6.0 60 9.6 14.6 7.9 90 10.5 19.0 7.4 120 11.7 23.2 12.4 SPE bleached with silica gel and heat treated is clearly less stable than either the triglyceride or the SPE/triglyceride blend. Careful inspection of the data will reveal that blend stability is very near that of the triglyceride itself, not merely a blend of their respective stabilities. The peroxide value for a blend of a triglyceride and SPE is often actually higher than the arithmetic average of the individual components. With the exception of the last data point at 120 min., the blend is actually more stable than the triglyceride although this may not be significant because of normal variability in the modified AOM and peroxide value methods. When the SPE is sufficiently treated to improve stability prior to blending, the level of natural antioxidants in the triglyceride is able to protect the entire mixture. Without thorough treatment to improve SPE stability prior to blending, the level of natural antioxidants in the triglyceride afford little benefit toward protecting the SPE from oxidation. Since this particular modified AOM stability method accelerates the effects of exposure to air by providing intimate contact at a temperature relatively high compared to normal storage and handling conditions prior to use in finished product applications, these stability benefits are greatly magnified during normal storage and handling procedures which are at much less severe conditions. Benefits are also realized by separate deodorization of SPE and triglyceride followed by immediate blending under nitrogen to avoid contact with air and subsequent generation of peroxides. Blending SPE with undeodorized oil, which contains greater levels of natural antioxidants than deodorized oil, provides even greater stability benefits during extended storage prior to deodorization. This is especially advantageous in manufacturing facilities where extended storage and large scale handling of SPE without some incidental air contact are not possible. EXAMPLE 2 This example demonstrates the stabilizing effects of post bleaching and heat treatment on SPE followed by continuous deodorization without triglyceride present. The SPE is prepared using about 54 parts of hardened (I.V. ∼1) and about 46 parts of partially hardened soybean methyl esters (I.V. ∼85) in a manner similar to that in Example 1 prior to the addition of silica gel. About 1200 gm of SPE at 140°F (60°C) is added to a glass 2 liter reaction flask which has been flushed with nitrogen to remove air. A vacuum of approximately 5 mm Hg is provided to deaerate the SPE while heating to 200°F (93°C). When bleaching temperature is reached the vacuum is broken with nitrogen and 36 gm of silica gel is added and agitation is started. The SPE is sparged with nitrogen for about 0.5 min. and vacuum is reapplied for 10 min. to deaerate the silica gel. The vacuum is broken with nitrogen and agitation is continued for aproximately 1 hour. The SPE is filtered with a Buchner funnel using Whatman 40 filter paper. The silica gel used in this example has a particle size of 20 microns, an average pore diameter of 65 Angstroms, surface area of 770 m²/gm, pore volume of 1.4 cc/gm, a pH measured at a concentration of 5% in water, and total volatiles of 10.3%. Use of other types of silica gel will not result in the same degree of color improvement. A total of 10 other different types of silica gel were tested with SPE and none reduce color levels to the same extent. The types of silica gel evaluated have pore volumes between 0.34-1.9 cc/gm, surface area between about 320-800 sq. m/gm, total volatiles between 5.7-20 wt%, pH between 3-8, an average pore diameter between 20 and 200 Angstroms, and average particle size between 10-30 microns. The silica gels that were evaluated with the SPE of Example 1 had the following characteristics. Average Pore Diameter % Color Reduction (Angstroms) (Lovibond Red) 20.4 36 65.0 63 68.4 63 122 45 202 27 As can be seen from the above, Pore Diameters that are larger than 70 Angstroms and smaller than about 50 Angstroms do not provide the optimum color removal that, in combination with the other process steps, provides superior polyol fatty acid polyester. Only silica gel with a combination of the hereinbefore stated requisite properties is able to achieve a greater than an 80% color reduction on SPE made by the described reaction process. The silica gel of choice is also best suited to remove undesirable color materials generated in the reaction by thermal degradation caused by excessive reaction temperature. The most preferred silica gel is the only type capable of removing 44% of color generated by thermal degradation in a single treatment. This makes it the overall best choice for consistently producing best possible color material by removing the greatest amount of undesirable color materials. A portion of the bleached and filtered SPE is then heat treated by elevating the temperature to 414°F (212°C) for a period of 18 min. while excluding the presence of air. Table 3 illustrates the of effects of silica gel treatment and heat treatment on SPE using the modified AOM method. The unbleached, bleached, and bleached and heat treated samples are all deodorized as a final step. Data is reported as the time it takes to reach a specified peroxide value. Initial peroxide values of unbleached, bleached, and bleached and heat treated SPE are 55, 35, and 20 ppm, respectively. Both bleached, and bleached and heat treated, were continuously deodorized in a small glass laboratory steam deodorizer after treatment. Effect of Silica Gel Bleaching and Heat Treatment on Oxidative Stability Time Required to Reach Specified Peroxide Value (Min.) Specified PV (ppm) Unbleached Bleached Bleached and Heat Treated 100 22 70 115 200 40 92 140 400 58 120 162 600 80 146 177 In order to reach a peroxide value of 100 ppm, only 22 min. is required for an unbleached SPE, while bleached and heat treated SPE requires 115 min. This example shows that with silica gel bleaching and bleaching with heat treatment, oxidative stability of the SPE is substantially improved over untreated SPE. The bleached and heat treated SPE is over 4 times as oxidatively stable up to a 100 ppm peroxide value. Deodorization is required after bleaching and heat treatment to achieve good flavor by removing oxidation products which are generated. EXAMPLE 3 Sucrose polyester is prepared in the same manner as Example 1 prior to silica gel treatment with the exception that 78 parts hardened soybean methyl ester with an I.V. of 1, and 22 parts partially hardened soybean methyl esters with an I.V. of about 85 are used as the methyl esters for the reaction. In this example the SPE is heat treated and codeodorized in about a 40:60 blend SPE/triglyceride without prior silica gel treatment of the SPE. SPE is first mixed with triglyceride in clean drums without excluding air which provides contact with oxygen. The mixture is then deodorized/heat treated in four separate batches consisting of about 161 kg per batch. This codeodorization is conducted in the same manner as codeodorization described in Example 1 at 400°F (204°C) for a period of from 2 hours to 4 hours. After deodorization the mixture is then cooled and stored in clean drums. A mixture is then made of the SPE/triglyceride blend produced in Example 1 with the SPE/triglyceride blend produced in Example 3 in a ratio of 60:40. Blending of these two mixtures is accomplished by melting material stored in drums and pumping into a stainless steel tank with agitation. Additional typical minor ingredients used to prepare shortening are added to this 60:40 mixture. The resulting final mixture produces a solid shortening with substantially improved color and oxidative stability. EXAMPLE 4 In a continuous process, heat treatment is used after silica gel bleaching and immediately prior to steam deodorization. The primary purpose is to improve oxidative stability by terminating the free radical oxidation mechanism, react any remaining dissolved oxygen into peroxygen compositions, and then decompose these peroxygen compounds into volatile oxidation products which can be removed by steam deodorization. Since residence time in a continuous deodorizer is much less than in a batch deodorizer, a separate heat treatment step is required prior to continuous deodorization to assure reaction of all absorbed oxygen into peroxygen compounds and then maximum decomposition of these peroxygen compounds. Long residence times encountered in a batch deodorizer allow deodorization and heat treatment to occur simultaneously in the same unit operation. Another beneficial purpose of heat treatment is to improve color of, e.g., SPE, by taking advantage of the unexpected color decrease which occurs as the material is oxidized. It is generally accepted that air should always be excluded from triglyceride processing to avoid oxidation which leads to undesirable flavors and colors. Controlled SPE oxidation can be used in the process to provide color improvement as long as the resulting peroxygen compounds are subsequently decomposed to generate mostly volatile oxidation products which are removed by steam deodorization. An example of heat treatment on unbleached SPE, of the type disclosed in Example 1, at 375°F (190°C) is included in Table 4. The SPE is first saturated with air by vigorous mixing in a glass vessel. Heat is applied for the first 50 minutes without excluding air to provide sufficient oxygen to form peroxygen groups. After 50 minutes air is excluded and the peroxygen compounds are decomposed by heat. 30 minutes is required to reach 375°F (190°C). The starting time is arbitrarily chosen at 205°F (97°C), after heating is begun, since formation of peroxygen compounds begins to increase significantly at that temperature. Heat Treatment Effects on Peroxide Value and Lovibond Color Lovibond Color Time (min.) Peroxide Value (ppm) Red Yellow Original material <1.0 0.9 3.4 0 5.7 0.7 3.7 5 6.1 0.9 4.0 10 11.4 0.8 3.8 15 24.6 0.7 3.4 20 53.4 0.7 3.3 30 79.3 0.6 2.9 40 143.1 0.5 2.4 50 379.1 0.4 2.2 --------Begin Air Exclusion at about 50 minutes-------- 110 37.6 0.4 2.2 Peroxide value is seen to increase while both Lovibond Red and Yellow color decrease during the oxidation phase of heat treatment. Once air is excluded after 50 minutes, peroxide value decreases sharply as peroxygen groups are decomposed into mostly volatile oxidation products while color remains consistently low. Prior art teaches that darkening occurs during oxidation of triglycerides so lightening of SPE is suprising. A sample of triglyceride is heated in a similar fashion in the presence of oxygen and color is observed to increase from 0.4/3.9 to 10/>70 Lovibond Yellow over 180 minutes. This unexpected benefit can be used commercially in both a batch and continuous manner to further improve polyol polyester, e.g., SPE color. In a batch manner the process comprises sparging the polyol polyester with up to about saturation level of air, and heating to the preferred temperature and time while maintaining a nitrogen atmosphere in the storage tank. In a continuous manner the process comprises sparging air into the polyol polyester and passing through a tubular reactor containing inline mixers. Air amount is controlled in such a way as to reach about saturation level, or to keep peroxide value to at, or below, 500 ppm to obtain maximum color reduction without excessive oxidation. Conditions for heat treatment are 1-150 minutes at 200-425°F (93-220°C), with 1-20 minutes at 380-415°F (190-215°C) being preferred, and 380-400°F (150-200°C) for 5-10 minutes being most preferred. These conditions will provide the optimum between maximum peroxide and color reduction without substantial color reformation from thermal degradation. EXAMPLE 5 Deodorization with steam is used in initial manufacture of SPE, and again after exposure to oxygen and extended storage has degraded flavor, to improve flavor by removing oxidation byproducts. However, darkening will occur by thermal degradation if temperatures normally used in triglyceride processing are applied. Adding triglyceride to the SPE and then deodorizing the mixture, termed "codeodorization", allows this to be successfully accomplished at higher temperatures with lower steam usage than with SPE alone. Impact of deodorization temperatures on flavor and color of SPE and SPE/triglyceride mixtures is investigated using a small one-pound batch deodorizer in the laboratory. Temperature effects are shown between 300°F (150°C) and 450°F (230°C) for 2-3 hours at a pressure of 3 mm Hg. Distilled water is injected into the deodorizer beginning at 250°F (120°C) to produce steam. The SPE is prepared in a manner similar to that of Example 2, using hardened and partially hardened soybean methyl esters, prior to the addition of silica gel. The blend ratio used in the SPE/triglyceride mixture is 1:2. The SPE has undergone steam deodorization to remove residual methyl esters in its manufacture: the triglyceride has been refined and bleached without deodorization. Table 5 presents the results of steam deodorization on color of SPE and the 1:2 SPE/triglyceride blend at various times and temperatures. The red color of the SPE without triglyceride increases with increasing temperature. At 450°F (230°C) there is a dramatic increase in red color even at a residence time of only about two hours. Yellow color also increases with temperature, but not as rapidly. In the blend, red color initially decreases with time and then increases at 450°F (230°C). After two hours at 450°F (230°C), the red color of the SPE has increased about six times compared with that of the blend, and yellow color has increased about one and a half times. If the SPE deodorized at 450°F (230°C) for about two hours with a final red color of 21.5 is mixed in an approximately 1:2 ratio with a typical deodorized triglyceride having a color of 0.5, the final blend color is 6.8 Red. A final blend color of about 3.1 indicates that the color effect is not just dilution of SPE color with triglyceride, but that addition of triglyceride prevents thermal degradation of the SPE and corresponding color increase. Measurement of percent polymer at 450°F (230°C) for two hours shows an increase from <0.1% to 0.8% with the SPE, and no increase from <0.1% in the blend. This provides further evidence that the triglyceride protects SPE from thermal degradation. Flavor of all samples after deodorization increased to acceptable levels of greater than or equal to about 7.0 with the exception of the blend at about 300°F (150°C) for three hours. This is because at the low temperature not all of the components from the undeodorized triglyceride were removed. In continuous deodorization it is believed that higher temperatures could be achieved for both SPE and the SPE/triglyceride blend because of the shorter residence times involved with continuous deodorization operation. However, the blending of triglycerides would still enable operation of the continuous deodorizer at higher temperatures than with SPE alone. Higher temperature deodorizer operation enables lower steam usage to remove the same levels of volatiles, and allows deodorization of SPE to be accomplished more readily on existing oil deodorizers without significant modification to accommodate lower temperatures.

Claims: A process for removing undesirable materials from higher polyol fatty acid polyesters which comprises a process step consisting of heat treating the said polyesters at a temperature from (200°F) 90°C to (425°F) 220°C, preferably from (380°F) 190°C to (425°F) 220°C, first in the presence of oxygen and then while excluding oxygen, for a sufficient time to first create peroxygen groups and then reduce the content of said peroxygen groups followed by the step of removing the resulting undesirable more volatile materials. The process of claim 1 comprising said process step wherein the oxygen is introduced at a level up to about saturation level, and wherein the time is from 1 minute to 150 minutes, preferably from 1 minute to 20 minutes, to reduce the peroxygen content. The process of claims 1 and 2 wherein the heat treatment is accomplished in combination with a steam deodorization step. The process of claims 1 through 3 wherein the heat treatment is followed by a steam deodorization step. The process of claim 1 further comprising the step of treating the said polyesters prior to the heat treating of said polyesters with silica gel having : (a) particles ranging in size from 10 to 30 microns, preferably from 20 to 25 microns; (b) an average pore diameter of from 50 to 70 Angstroms; (c) surface area of from 720 to 800, preferably from 770 to 800 square meters per gram; (d) pore volume of from 0.9 to 1.9, preferably from 1.2 to 1.4 cc/gm; (e) pH of from 5 to 8, preferably from 5 to 7.3, when measured at a concentration of 5% in water; and (f) total volatiles of less than 20%, preferably from 6.5% to 10.5%, more preferably from 8% to 10.5%. The process of claims 1 through 5 wherein said polyester is at least 70% sucrose octaester. The process of claim 3 wherein the steam deodorization step is accomplished in the presence of conventional triglyceride. The process according to claim 7 of steam deodorizing a polyol fatty acid polyester, mixed with a triglyceride in a ratio of from 10:1 to 1:10. The process of claims 7 and 8 wherein said polyester is sucrose polyester containing at least 70% octaester, the temperature of the steam deodorizing step being from (300°F) 150°C to (600°F) 315°C, preferably from (350°F) 175°C to (525°F) 275°C, and the ratio of polyester to triglyceride is from 1:3 to 3:1.

Inventors: ADAMS KEITH DAVID, HOUSTON ROBERT, MCCABE GREGORY MICHAEL, SARAMA ROBERT JOSEPH, SEIDEN PAUL, VANDIEST SCOTT ALAN, ADAMS, KEITH DAVID, HOUSTON, ROBERT, MCCABE, GREGORY MICHAEL, SARAMA, ROBERT JOSEPH, SEIDEN, PAUL,, VANDIEST, SCOTT ALAN
Applicants: PROCTER & GAMBLE, THE PROCTER & GAMBLE COMPANY
Application year: 1990
Main classification: C07H13
IPC codes: C07C69, C07C67, C07H13, C07B63