Modified polydextrose and process therefor

Abstract: An improved, water-soluble polydextrose containing less than 0.01 mol % of bound citric acid, a process for preparing an improved, water-soluble polydextrose containing 0.3 mol % or less of bound citric acid, and foods containing same.

Description: This invention relates to a process for preparing improved polydextrose characterized by its content of 0.3 mol percent or less of citric acid bound in the form of ester groups. The improved, water-soluble polydextrose of this invention is prepared by reducing the bound citric acid content of unimproved, water-soluble polydextrose, by passing the unimproved, water-soluble polydextrose through one of more specified resins. Bound citric acid is also referred to herein as citric acid bound in the form of ester groups. These citrate esters are primarily dibasic, and so generally retain a measure of acidity. While the process of the invention coincidentally reduces free citric acid to less than 0.1 mol %, free citric acid can be added back where acidity is desired. As used herein, the expression "water-soluble polydextrose" (also known as polyglucose or poly-D-glucose) specifically refers to the water-soluble polydextrose prepared by melting and heating dextrose (also known as glucose or D-glucose), preferably with about 5-15% by weight of sorbitol present, in the presence of a catalytic amount (about 0.5 to 3.0 mol %) of citric acid. Water-soluble polydextrose is an item of commerce which, as an approved food additive, is defined in the Food and Drug Section of the Code of Federal Regulations (21 C.F.R. 172.841). In its unimproved form, it is also described by Rennhard, U.S. Patent, 3,766,165, which claims, inter alia , a "[w]ater soluble highly branched poly[dextrose] wherein the linkage of 1 → 6 predominates, having number average molecular weight between about 1,500 and 18,000 and containing from about 0.5 to 5 mole percent of [citric] acid ester groups ...", i.e., water-soluble polydextrose charactrized by its content of from about 0.5 to 5 mol % of bound citric acid; and by Rennhard, U.S. Patent 3,876,794, which claims various foods containing same. According to Rennhard, water-soluble polydextrose is preferably prepared using 0.5-5 mol percent of citric acid as catalyst. However, since Rennhard's use of about 6 mol percent of citric acid produced more than two thirds undesired insoluble polydextrose, we prefer use of citric acid at a level in the range of about 0.5 to 3 mol percent, approximating the 1% by weight noted in the C.F.R., cited above. Rennhard also specified optional use of about 5-20% (preferably 8-12%) by weight of sorbitol in the polymerization. The narrower range approximates the 10% by weight of sorbitol also noted in the C.F.R., cited above, However, as variously noted in the art [Torres in U.S. Patent 4,622,233; Goff et al., J. Food Science, vol. 49, pp. 306-307; Lim et al., J. Food Science, vol. 54, pp. 625-628 (1989)] Rennhard's polydextrose possesses a slight bitter taste which limits the breadth of its use in foods. Torres believed that the bitter taste of Rennhard's polydextrose was due to the presence of anhydroglucose. While that compound has not been ruled out as one of the factors in the bitter taste, we have now surprisingly found that bound citric acid (i.e., the 0.5 to 5% mol % of citric acid ester groups in Rennhard's polydextrose) is the most important factor in causing said bitter taste. Rennhard generally suggested the use of ion exchange as a method of reducing the acidity of his polydextrose; e.g., at column 6, lines 48-50 of U.S. 3,766,165. Three types of basic ion exchange resins are available for this purpose, viz : Types I and II strong base anion resins, and weak base anion resins. Type I resins, which contain quaternized amine functional groups, are the most strongly basic and have the greatest affinity for weak acids such as carboxylic acids. However, not all operating conditions for use of Type I resins are effective in preparing the improved polydextrose of this invention. Use of a Type I strongly basic exchange resin outside of the conditions disclosed by this invention leads to polydextrose with inferior taste. Rennhard also suggested dialysis as a method of reducing the acidity of polydextrose. However, this method is well known to selectively remove low molecular weight compounds which diffuse through a membrane where higher molecular weight solutes do not. We now know that the citrate ester compounds (bound citric acid) which are primarily responsible for the bitterness in unimproved polydextrose span a wide range of molecular weights comparable to the molecular weight range of polydextrose itself. Thus, dialysis would be unsuitable for the removal of such compounds. EP 380248, published August 1, 1990, discloses improved, water-soluble polydextrose containing 0.01 to 0.3 mol percent of bound citric acid, a process for producing the polydextrose and foods containing the polydextrose. EP 458748, published November 27, 1991, discloses a polydextrose composition that is substantially free of bitter tasting and color causing compounds which is useful as a bulking agent in low calorie foods, and a process for producing the polydextrose. The present invention provides a process capable of producing an improved form of the water-soluble polydextrose defined above having reduced levels of citric acid bound in the form of ester groups. The present process coincidentally reduces the level of unbound or so-called free citric acid to less than 0.1 mol percent or even to less than 0.01 mol percent. However, this is not a critical feature of the present invention, and there will be circumstances where it will be desirable to add back the citric acid, for its acidity and/or for its lemony taste. The product of the present invention may be used in foodstuffs, particularly those further comprising one or more sweetening agents selected from the group consisting of alitame, aspartame, acesulfame and saccharin, most particularly to those further comprising alitame or aspartame; and dry low calorie sweetener compositions comprising at least 50% by weight of said improved polydextrose and one or more sweetening agents selected from the group consisting of alitame, aspartame, acesulfame and saccharin, particularly one with alitame. According to the invention, there is provided a process for preparing an improved water-soluble highly-branched polydextrose containing 0.3 mol percent (0.36 weight percent) or less of citric acid bound in the form of ester groups from unimproved highly-branched polydextrose which has been prepared by a process which comprises melting dextrose at a temperature below its decomposition point in the presence of 0.5 to 3.0 mol percent (0.59 to 3.56 weight in percent) of citric acid, said process comprising passing an aqueous solution containing 10-70% by weight of unimproved polydextrose through one or more resins selected from the group consisting of: (a) an adsorbent resin having amine functionality wherein the solution is passed at a temperature of 10 to 80°C; (b) a weakly basic ion exchange resin wherein the solution is passed at a flow rate of 0.05 to 8 bed volumes per hour and a temperature of 10 to 70°C; and (c) a mixed bed resin comprising a weakly basic ion exchange resin or a Type I strongly basic ion exchange resin or a Type II strongly basic ion exchange resin and a cation exchange resin wherein the solution is passed at a flow rate of 0.05 to 8 bed volumes per hour and a temperature of 10 to 70°C when said mixed bed resin comprises a weakly basic ion exchange resin, wherein the solution is passed at a flow rate of 0.1 to 12 bed volumes per hour and a temperature of 10 to 50°C when said mixed be resin comprises a Type I strongly basic ion exchange resin and wherein the solution is passed at a flow rate of 0.05 to 8 bed volumes per hour and a temperature of 10°C to the upper limit of temperature for use of the Type II strongly basic ion exchange resin when said mixture bed resin comprises a Type II strongly basic ion exchange resin; provided that, when an adsorbent resin or weakly basic ion exchange resin is used, said resin is used in combination with a Type I strongly basic ion exchange resin wherein the solution is passed at a flow rate of 0.1 to 12 bed volumes per hour and a temperature of 10 to 50°C; or a Type II strongly basic ion exchange resin wherein the solution is passed at a flow rate of 0.05 to 8 bed volumes per hour and a temperature of 10°C to the upper limit of temperature for use of the resin; or a mixed bed resin as defined in (c) above. As an optional step, the aqueous solution of polydextrose can be passed through a cation exchange resin after passage through any of the resins described above. In general, unimproved water-soluble polydextrose is prepared by melting dextrose containing about 0.5 to 3 mol percent of citric acid at a temperature below its decomposition point, maintaining said molten mixture at a temperature of 140 to 295°C and at reduced pressure in the substantial absence of water until substantial polymerization occurs and simultaneously removing water formed during said polymerization. Preferably, from about 5 to 15% of sorbitol by weight is incorporated into the mixture prior to melting and polymerization; even more preferred is to incorporate sorbitol in the range of about 8 to 12% by weight. The reduced pressure is preferably less than 40kPa(300 mm) of mercury. The preferred level of citric acid in the polymerization is in the range of about 0.7 to 1.3 mol percent, nominally about 1% by weight per the C.F.R. cited above. A preferred ion exchange resin is weakly basic ion exchange resin, particularly one containing tertiary dimethylamine functionality. The most preferred ion exchange resin of this type is Amberlite IRA-93 (Trade Mark) manufactured by Rohm and Haas. Another preferred ion exchange resin for use in combination with a weakly basic ion exchange resin is a Type I strongly basic ion exchange resin with quaternary trimethylamine functionality. The most preferred ion exchange resin of this type is Amberlite IRA 900 (Trade Mark) manufactured by Rohm and Haas. Yet another preferred ion exchange resin for use in combination with a weakly basic ion exchange resin is a Type II strongly basic ion exchange resin with quaternary dimethylethanolamine functionality. The most preferred ion exchange resin of this type is Dowex 22 (Trade Mark) manufactured by Dow. A preferred cation exchange resin for use in the mixed bed resins described hereinabove is a macroreticular resin containing sulfonic acid functionality on a styrene-divinylbenzene matrix. Preferred cation exchange resins of this type are Amberlite 200 (Trade Mark) manufactured by Rohm and Haas and Dowex 88 (Trade Mark) manufactured by Dow. Preferred ion exchange resins for use in the mixed bed resins described hereinabove are the preferred and most preferred weakly basic ion exchange resins, Type I strongly basic ion exchange resins and Type II strongly basic ion exchange resins also described hereinabove. The most preferred mixed bed resin comprises a mixture of about 2:1 v/v of one of the most preferred ion exchange resins hereinabove described and either Amberlite 200 or Dowex 88. When an adsorption resin is used, the preferred resin is one which contains amine functionality on a styrene-divinylbenzene matrix, for example Dow's XU-40285.00 (Trade Mark). When a weakly basic ion exchange resin is used, it is preferable to pass the resulting solution through a Type II strongly basic ion exchange resin or a mixed bed resin described above. Preferred resins for such dual passage are those described immediately above. Further, after passage through any of such resins, the resulting solution can be passed through a cation exchange resin. Preferred cation exchange resins are given above. The preferred Type II resins hereinabove described have, as an upper temperature limit, 40°C. When a mixed bed resin containing a basic ion exchange resin is used in the practice of this invention, an aqueous solution containing about 10-70% by weight of the unimproved polydextrose is passed through the mixed resin at a flow rate and temperature which is preferable for the basic ion exchange resin used in said mixed bed resin. Preferred flow rate and temperature ranges for the basic ion exchange resins are described above. However, when using such mixed bed resins, a lower flow rate within the ranges given above is preferred. When employing a cation exchange resin following passage of the solution through any of said resins, it is preferable to pass such a solution containing about 10-70% by weight of the polydextrose at a flow rate of about 1-20 bed volumes per hour and a temperature of about 10-80°C through said cation exchange resin. When a combination of such resins are used in sequence, it is preferable to employ the preferred conditions specified above for each such resin in turn. As those skilled in the art are aware, the effectiveness of the particular resin or resins employed in the practice of this invention will vary depending upon the capacity of the resin or resins employed. Therefore, to optimize yield of desired improved polydextrose, adjustment of the ratio of unimproved polydextrose to resin, as well as the flow rate and temperature, will be necessary and all such adjustments are within the skill of those who practice in the art enabled by this disclosure. For example, it may be necessary to employ a higher flow rate within the flow rate ranges described above when practicing the process at a higher temperature within the temperature ranges described above. However, it is to be noted that any adjustment to the conditions for use of Type I strongly basic ion exchange resins must be made carefully since the conditions under which use of such resins will yield the improved polydextrose of this invention are stringent and are believed to be within the preferable ranges described hereinabove. In the preferred method of isolating the present improved polydextrose in solid form, water is removed using film evaporation. As used here and elsewhere herein, "bound citric acid" refers to citric acid which is released when polydextrose is subjected to base catalyzed hydrolysis conditions. The "mol % of citric acid" used as catalyst in the polymerization is calculated from the weight % of citric acid as follows: In its preferred variation, the dilute polydextrose solutions which are collected at the beginning and end of the run are held apart from the more concentrated solution collected during normal operations. The dilute solutions are then used in the makeup of the next batch of concentrated solutions for resin treatment. In the unimproved polydextrose product directly formed by heating and melting dextrose in the presence of citric acid, the total wt % of bound and unbound citric acid will be increased in the polymerization by the fact that water is lost in this process. However, the total mol % of bound and unbound citric acid will stay the same since there is no net loss of glucose, sorbitol or citric acid residues. Thus, the mol % of unbound and bound citric acid in unimproved polydextrose is readily calculated from the proportions by weight of each of free and bound citric acid to total citric acid, factored by the mol % of citric acid originally introduced into the polymerization. However, when the polydextrose is modified and improved according to the present process, undetermined amounts of bound and unbound citric acid, as well as glucose and sorbitol residues are removed, such that as a practical matter, the mol % of either bound or unbound citric acid is best calculated by simply multiplying the weight % by 162/192, the ratio of the molecular weights of a glucose unit (glucose - H 2 O) and of citric acid. For the sake of conformity and ease of comparison with Rennhard's U.S. Patents cited above, such mol % values for free and bound citric acid are used in the present claims. The present invention is readily carried out. Dextrose and optionally a specified amount of sorbitol are polymerized in the presence of the specified amount of citric acid according to methods earlier disclosed by Rennhard in U.S. Patents cited above, preferably by a continuous process such as that exemplified below. The resulting unimproved water-soluble polydextrose product, which corresponds to that of Rennhard, is then solubilized in water, preferably at high concentration, e.g., in the range of about 50-70% w/w, and at somewhat elevated temperature (e.g. about 30-70°C). Preferably at the same elevated temperature and, if desired, at somewhat elevated pressure (e.g., up to about 5 mpa (5 atmospheres), the resultant solution is passed through one or more of a column of weakly basic ion exchange resin, of Type II strongly basic ion exchange resin, of an adsorbent resin or of a mixed bed resin comprising a basic ion exchange resin and a cation exchange resin, provided that when a column of an adsorbent resin or a weakly basic ion exchange resin is used, at least one column of another of said resin types is used in combination therewith. Further, following passage through any of said resins or combinations thereof, the solution can be passed through a cation exchange resin. In any case, the present improved polydextrose, now containing less than 0.1 mol % of free citric acid and 0.3 mol % or less of bound citric acid, is collected from the column as an aqueous solution, which in many applications can be used directly without further isolation. Alternatively, the improved polydextrose is recovered from the solution by conventional means, e.g., by removing the water under vacuum and/or the addition of a non-solvent such as alcohol. A preferred method is to recover the polydextrose as a melt in a thin film evaporator and to solidify the melt by cooling. Free and bound citric acid are determined by HPLC. To detrmine total citric acid (free and that bound as ester), an alkaline solution of polydextrose is heated to hydrolyze citric acid esters, and the hydrolyzate is analyzed for citric acid. In method A, described below, free citric acid is also detrmined by direct analysis of an unhydrolyzed solution of polydextrose. Bound citric acid is then calculated as total citric acid less free citric acid. Method B, also described below, is more sensitive than Method A but determines total citric acid only. Free citric acid can not be independently determined because citric acid esters are partially hydrolyzed under the conditions of HPLC analysis employed in Method B. This is unimportant for analysis of highly purified polydextrose, however, since levels of free citric acid are extremely low. HPLC Method A To determine free citric acid, 0.050 ml of a 100 mg/ml solution of polydextrose is injected at the top of a BioRad Cation H guard column (cat. no. 125-0129) which is in series with a BioRad Aminex HPX-87H (Trade Mark) analytical column (cat.no. 02833). The mobile phase is 0.036 N H 2 SO 4 , the flow rate is 0.6 ml/minute, and the temperature is ambient. Citric acid is detected by its ultraviolet absorption at 210 nm, and is measured against a standard citric acid solution (0.8 mg/ml) chromatographed in like manner. The citric acid chromatographic peak, which appears at a retention time of about 8 minutes, is sometimes superimposed on the trailing edge of an unidentified larger peak. When necessary, it is resolved from this peak by tangential skimming, a well-known method which is described, for example, on page 13 of chapter 6 of the Spectra-Physics SP4270 Operator's Manual, copyright 1982. Total citric acid is determined by adding 2.0 ml of 2.5 N NaOH to 5 ml of a 100 mg/ml solution of polydextrose, heating the resulting basic solution at 70°C for 2 hours, cooling and acidifying the hydrolysate with 2.0 ml of 2.88 N H 2 SO 4 , diluting to 10 ml with mobile phase, and analyzing for citric acid by HPLC by the same method. Bound citric acid is calculated as total citric acid less free citric acid. HPLC Method B The HPLC system includes an injector with a 10-microliter sample loop, and Ionpac AS5A (Trade Mark) 5-micron separator column (Dionex cat. no. 037131), and a conductivity detector equipped with a chemical suppression system (Dionex cat. no. 038019 or equivalent). The mobile phase is carbonate-free 0.048 M NaOH, at a flow rate of 1.0 ml/minute. Total citric acid is determined by diluting a 250 mg sample of polydextrose, or equivalent quantity of solution, to 25 ml with mobile phase, heating for 60 minutes at 70°C, cooling and analyzing the resulting solution by HPLC against a standard citric acid solution (0.02 mg/ml). The citric acid chromatographic peak, which appears at a retention time of about 5 minutes, is measured as described in Method A, above. Average molecular weight (M n ) values were determined by using methods earlier described by Rennhard in the patents cited above. See also Isbell, J. Res. Natl. Bur. Stds. 24 , 241 (1940). The present improved polydextrose is incorporated into foods according to methods previously disclosed by Rennhard and Torres in the three U.S. patents cited above, and as further exemplified below. The improved taste of food products prepared with present modified polydextrose is reflected in the so-called hedonic test, a common method of measuring food acceptance. The test employs a taste panel, generally 15-20 in number. It is a straight acceptance test, and does not necessarily require an experienced panel. Panelists are given coded samples to rate for acceptance by checking a point on the so-called Hedonic scale as shown in Table I. At the same time, the panelists are given a space to provide optional comments. In a special form of the hedonic test, generally used in the present studies, pairs of coded food samples, one containing conventional, unimproved polydextrose and one containing present modified, improved polydextrose are compared side by side, without the panel knowing which sample contained the improved polydextrose. The hedonic score is calculated as the numerical average of the individual scores assigned by the individual panel members. Hedonic Scale for Evaluating Foods Scale 9 Like Extremely 8 Like Very Much 7 Like Moderately 6 Like Slightly 5 Neither Like Nor Dislike 4 Dislike Slightly 3 Dislike Moderately 2 Dislike Very Much 1 Dislike Extremely For evaluation of bulk lots of polydextrose, two different methods were used. In one such method, hereinafter referred to as Test Method I, unflavored hard candy prepared from the polydextrose to be tested was evaluated by a taste panel as described above. Hard candy for evaluation was made by heating a mixture of polydextrose 50% in water (49.98 wt %) with Lycasin 50% in water (49.9 wt %) to 157-160°C in an oil bath at 180°C, cooling to 140°C and adding citric acid (0.08 wt %) and alitame 10% triturate in mannitol (0.23 wt %) with thorough stirring. The mass was transferred to a lightly oiled marble slab, cooled to 80°C, and stamped into hard candy. The hedonic value which was determined for the resulting hard candies was the hedonic value assigned to the bulk polydextrose. Another test method, hereinafter referred to as Test Method II, involves the evaluation, by a trained food technologist, of an aqueous solution containing about 50% polydextrose. Usually, for Test Method II, the polydextrose solution and a sample thereof was redissolved in water for evaluation. As a control, unimproved polydextrose was evaluated in aqueous solution at the same concentration. As with Test Method I, the Hedonic scale as shown in Table I was used. The present invention is illustrated by the following examples. However, it should be understood that the invention is not limited to the specific details of these examples. EXAMPLE 1 Unimproved Polydextrose Dextrose monohydrate, sorbitol and citric acid were continuously and intimately mixed in the following proportions by weight: dextrose monohydrate/sorbitol 89.8:10.2 to 90.3:9.7, with citric acid at a level of 0.9 to 1.0% of the total weight. This blend was continuously fed to a reactor operating at an average temperature of 137°C and at a pressure in the range of 28.3 to 31.7kPa (4.1 to 4.6 psia). The feed rate was adjusted to achieve at least 96% polymerization as determined by analysis of residual glucose by the method described on page 59 of the Second Supplement to the Third Edition of the Food Chemicals Codex, (National Academy Press, copyright 1986). The following data were obtained from three representative batches of the polydextrose product: by HPLC Method A, free citric acid 0.35, 0.47 and 0.37 wt %; and citric acid bound as ester 0.65, 0.54 and 0.60 wt %, respectively. Under these conditions, the 0.9 to 1.0 wt % of citric acid used as catalyst is calculated to be 0.92 to 1.02 mol %, 0.97 mol % on average. The total of free and bound citric acid in the polydextrose product will likewise be 0.97 mol %. From the ratios of free and bound citric acid determined analytically , one calculates for the above three representative batches of polydextrose: free citric acid 0.34 , 0.45 and 0.37 mol %; bound citric acid 0.63, 0.52 and 0.60 mol %, respectively ( vide supra ). The hedonic scores for the same three batches, determined according to Test Method I, were 3.7, 4.8, and 5.1, respectively. EXAMPLE 1 Improved Polydextrose By Treatment With A Weakly Basic Amine Resin Followed By A Quaternary Dimethylethanolamine Resin A bulk lot of polydextrose, prepared as described in Example 1, was dissolved in water to make 1472 grams of a 60 % w/w solution. This solution was passed through a freshly-prepared column of 150 cubic centimeters of Rohm and Haas Amberlite IRA 93 anion exchange resin at about 48-50°C and a flow rate of about 1.4 bed volumes per hour. IRA 93® is a macroreticular resin containing tertiary amine functionality on a styrene-divinylbenzene matrix. Water initially displaced from the column was discarded. Over a period of 5.75 hours, 1402 grams of improved polydextrose solution was collected. The effluent was diluted with water to make 57 % w/w solution. A 1082-gram portion of this solution was passed through a freshly-prepared column of 100 cubic centimeters of Dowex 22 anion exchange resin at about 34-36°C and a flow rate of about 1.4 bed volumes per hours. Dowex 22 (Trade Mark) is a macroreticular resin containing quaternary dimethylethanolamine functionality on a styrene-divinylbenzene matrix. Water initially displaced from the column was discarded. Over a period of about 6 hours, 983.5 grams of improved polydextrose solution was collected. By HPLC analysis of the solution using HPLC Method B, the improved polydextrose contained 0.002 wt % total citric acid. The hedonic score, determined for the solution by Test Method II, was 7.0. A control solution containing the same concentration of the unimproved starting material had a hedonic score of 4.0. EXAMPLE 2 Improved Polydextrose By Treatment With A Weakly Basic Amine Resin Followed By A Mixed Bed Resin A bulk lot of polydextrose, prepared as described in Example 1, was dissolved in water to make 432 kg (950.0 pounds) of a 55 % w/w solution. This solution was passed through two freshly-prepared columns of 11.5 litres (0.7 cubic feet) each of Rohm and Haas Amberlite IRA 93 (Trade Mark) anion exchange resin at about 25-28°C and a flow rate of about 1.6 bed volumes per bed volume per hour. IRA 93 (Trade Mark) is a macroreticular resin containing tertiary amine funtionality on a styrene-divinylbenzene matrix. Water initially displaced from the column was recycled for later make-ups. Over a period of about 11 hours, 405 kg (890.0 pounds) of improved polydextrose solution was collected. The resin was regenerated with a 4% sodium hydroxide solution at 35-38°C, at a level of 2.7 kg(6.0 pounds) of dry sodium hydroxide per cubic foot of resin, then rinsed by the manufacturer's recommended procedure. Additional polydextrose was then processed through the column. The partially improved polydextrose was recovered by evaporating the water in a thin film evaporator and solidifying the melt in trays. A portion of the resulting solid was dissolved in water to make 214 kg (470.0 pounds) of 55 % w/w solution. This solution was passed at about 37-38°C and a flow rate of about 0.6 bed volumes per hour through a freshly-prepared column of 6.4 litres (0.39 cubic feet) of Dowex 22 anion exchange resin intimately mixed with 3.3 litres (0.20 cubic feet) of Amberlite 200 cation exchange resin. Dowex 22 (Trade Mark) is a macroreticular resin containing quaternary dimethylethanolamine functionality on a styrene-divinylbenzene matrix, whereas Amberlite 200 is a macroreticular resin containing sulfonic acid functionality on a styrene-divinylbenzene matrix. Water initially displaced from the column was discarded. Over a period of about 17 hours, 193 kg (425.0 pounds) of improved polydextrose solution was collected. The column was regenerated by first separating the resins, then passing a 4% sodium hydroxide solution at 35-38°C through the column from the top at a level of 6.8 kg (15.0 pounds) of dry sodium hydroxide per cubic foot of anion exchange resin, followed by a water rinse by the manufacturer's recommended procedure. This leaves the anion exchange resin in the hydroxide form and the cation exchange resin in the sodium form. Finally, the cation exchange resin was regenerated by passing acid through a distributor located at the top of the cation exchange resin, followed by a water rinse by the manufacturer's recommended procedure. The regenerant was 5% sulfuric acid at a level of 6.8 kg (15.0 pounds) of concentrated sulfuric acid per cubic foot of cation exchange resin. Improved polydextrose was recovered by evaporating the water in a thin film exaporator and solidifying the melt on a cooling belt. By HPLC analysis using HPLC Method B, the improved polydextrose contained 0.002 wt % total citric acid. The hedonic score, determined for a 50% aqueous solution by Test Method II, was 6.5. A control solution containing the same concentration of the unimproved starting material had a hedonic score of 4.0. EXAMPLE 3 Improved Polydextrose By Treatment With A Weakly Basic Amine Resin Followed By A Mixed Bed Resin A bulk lot of polydextrose, prepared as described in Example 1, was dissolved in water to make 1555 kg (3420 pounds) of a 55 wt % solution. This solution was passed through a freshly-prepared column of 147 litres (9.0 cubic feet) of Rohm and Haas Amberlite IRA 93 (Trade Mark) anion exchange resin at about 28-30°C and a flow rate of about 1.1 bed volumes per hour. IRA 93 (Trade Mark) is a macroreticular resin containing tertiary amine functionality on a styrene-divinylbenzene matrix. Water initially displaced from the column was recycled for later make-ups. Over a period of 3-4 hours, 1166 kg (2565 pounds) of improved polydextrose solution was collected. To make recovery nearly quantitive, residual polydextrose was flushed from the column with about two bed volumes of water. The resulting dilute solution was used in make-up of the next batch of 55 wt % solution. The resin was regenerated with a 4% potassium hydroxide solution at 35-38°C, at a level of 2.95 kg (6.5 pounds) of dry potassium hydroxide per cubic foot of resin, then rinsed by the manufacturer's recommended procedure. Additional polydextrose was then processed through the column. The partially improved polydextrose was recovered by evaporating the water in a thin film evaporator and solidifying the melt on a cooling belt. A portion of the resulting solid was dissolved in water to make 409 kg (900.0 pounds) of 55 % w/w solution. This solution was passed at about 37-38°C and a flow rate of about 0.8 bed volumes per hour through a freshly-prepared column of 6.4 litres (0.39 cubic feet) of Dowex 22 (Trade Mark) anion exchange resin intimately mixed with 0.20 cubic feet of Amberlite 200 cation exchange resin. Dowex 22 (Trade Mark) is a macroreticular resin containing quaternary dimethylethanolamine functionality on styrene-divinylbenzene matrix, whereas Amberlite 200 is a macroreticular resin containing sulfonic acid functionality on a styrene-divinylbenzene matrix. Water initially displaced from the column was discarded. Over a period of about 25.5 hours, 370 kg (815.0 pounds) of improved polydextrose solution was collected. The column was regenerated by first separating the resins, then passing a 4% sodium hydroxide solution at 35-38% through the column from the top at a level of 6.8 kg (15.0 pounds) of dry sodium hydroxide per cubic foot of anion exchange resin, followed by a water rinse by the manufacturer's recommended procedure. This leaves the anion exchange resin in the hydroxide form and the cation exchange in the sodium form. Finally, the cation exchange resin was regenerated by passing acid through a distributor located at the top of the cation exchange resin, followed by a water rinse by the manufacturer's recommended procedure. The regenerant was 5% sulfuric acid at a level of 6.8 kg (15.0 pounds) of concentrated sulfuric acid per cubic foot of cation exchange resin. Improved polydextrose was recovered by evaporating the water in a thin film evaporator and solidifying the melt on a cooling belt. By HPLC analysis using HPLC Method B, the improved polydextrose contained 0.007 wt % total citric acid. The hedonic score, determined for a 50% aqueous solution by Test Method II, was 6.5. A control solution containing the same concentration of unimproved polydextrose had a hedonic score of 4.0. EXAMPLE 4 Improved Polydextrose By Treatment With A Mixed Bed Resin At Low Flow Rate A bulk lot of polydextrose, prepared as described in Example 1, was dissolved in water to make 9.1 kg (20.0 pounds) of a 55 % w/w solution. This solution was passed at about 30-40°C and a flow rate of about 0.05 bed volumes per hour through a freshly-prepared column of 1.6 litres (0.098 cubic feet) of Dowex (Trade Mark) anion exchange resin intimately mixed with 0.81 litres (0.049 cubic feet) of Amberlite 200 cation exchange resin. Dowex 22 is a macroreticular resin containing quaternary dimethylethanolamine functionality on a styrene-divinylbenzene matrix, whereas Amberlite 200 is a macroreticular resin containing sulfonic acid functionality on a styrene-divinylbenzene matrix. Water initially displaced from the column was discarded. Over a period of about 19.5 hours, 4.1 kg (9.1 pounds) of improved polydextrose solution was collected. By HPLC analysis of the solution using HPLC Method B, the improved polydextrose contained less than 0.002 wt % total citric acid. The hedonic score, determined for the solution by Test Method II, was 7.5. A control solution containing the same concentration of unimproved polydextrose had a hedonic score of 4.0. EXAMPLE 5 Improved Polydextrose By Treatment With A Mixed Bed Resin At Intermediate Flow Rate A bulk lot of polydextrose, prepared as described in Example 1, was dissolved in water to make 1150 grams of a 55 % w/w solution. This solution was passed at about 35-37°C and a flow rate of about 0.8 bed volumes per hour through a freshly-prepared column of 100 cubic centimeters of Dowex 22 (Trade Mark) anion exchange resin intimately mixed with 50 cubic centimeters of Amberlite 200 cation exchange resin. Dowex 22 (Trade Mark) is a macroreticular resin containing quaternary dimethylethanolamine functionality on a styrene-divinylbenzene matrix, whereas Amberlite 200 is a macroreticular resin containing sulfonic acid functionality on a styrene-divinylbenzene matrix. Water initially displaced from the column was discarded. Over a period of about 8 hours, 1121 grams of improved polydextrose solution was collected. By HPLC analysis of the solution using HPLC Method B, the improved polydextrose contained 0.020 wt % total citric acid. The hedonic score, determined for the solution by Test Method II, was 6.5. A control solution containing the same concentration of the unimproved starting material had a hedonic score of 4.0. EXAMPLE 6 Improved Polydextrose By Treatment With A Mixed Bed Resin At Intermediate Flow Rate A bulk lot a polydextrose, prepared as described in Example 1, was dissolved in water to make 1753 grams of a 40 wt % solution. This solution was passed at about 25°C and a flow rate of about 1.5 bed volumes per hour through a freshly-prepared column of 100 cubic centimeters of Dowex 22® anion exchange resin intimately mixed with 50 cubic centimeters of Amberlite 200 cation exchange resin. Dowex 22® is a macroreticular resin containing quaternary dimethylethanolamine functionality on a styrene-divinylbenzene matrix, whereas Amberlite 200 is a macroreticular resin containing sulfonic acid functionality on a styrene-divinylbenzene matrix. Water initially displaced from the column was discarded. Over a period of about 6.5 hours, 1624 grams of improved polydextrose solution was collected. By HPLC analysis of the solution using HPLC Method B, the purified polydextrose contained 0.043 wt % total citric acid. The hedonic score, determined for the solution by Test Method II, was 6.5. A control solution containing the same concentration of the unimproved starting material had a hedonic score of 4.0.

Claims: A process for preparing an improved water-soluble highly-branched polydextrose containing 0.3 mol percent (0.36 weight percent) or less of citric acid bound in the form of ester groups from unimproved highly-branched polydextrose which has been prepared by a process which comprises melting dextrose at a temperature below its decomposition point in the presence of 0.5 to 3.0 mol percent (0.59 to 3.56 weight percent) of citric acid, said process comprising passing an aqueous solution containing 10-70% by weight of unimproved polydextrose through one or more resins selected from the group consisting of: (a) an adsorbent resin having amine functionality wherein the solution is passed at a temperature of 10 to 80°C; (b) a weakly basic ion exchange resin wherein the solution is passed at a flow rate of 0.05 to 8 bed volumes per hour and a temperature of 10 to 70°C; and (c) a mixed bed resin comprising a weakly basic ion exchange resin or a Type I strongly basic ion exchange resin or a Type II strongly basic ion exchange resin and a cation exchange resin wherein the solution is passed at a flow rate of 0.05 to 8 bed volumes per hour and a temperature of 10 to 70°C when said mixed bed resin comprises a weakly basic ion exchange resin, wherein the solution is passed at a flow rate of 0.1 to 12 bed volumes per hour and a temperature of 10 to 50°C when said mixed bed resin comprises a Type I strongly basic ion exchange resin and wherein the solution is passed at a flow rate of 0.05 to 8 bed volumes per hour and a temperature of 10°C to the upper limit of temperature for use of the Type II strongly basic ion exchange resin when said mixture bed resin comprises a Type II strongly basic ion exchange resin; provided that, when an adsorbent resin or weakly basic ion exchange resin is used, said resin is used in combination with a Type I strongly basic ion exchange resin wherein the solution is passed at a flow rate of 0.1 to 12 bed volumes per hour and a temperature of 10 to 50°C; or a Type II strongly basic ion exchange resin wherein the solution is passed at a flow rate of 0.05 to 8 bed volumes per hour and a temperature of 10°C to the upper limit of temperature for use of the resin; or a mixed bed resin as defined in (c) above. A process according to claim 1 wherein both the unimproved and improved polydextrose contain 5-15% by weight of sorbitol residues. A process according to claim 1 or 2 wherein the resin is a mixed bed resin comprising a basic ion exchange resin and a cation exchange resin. A process according to claim 1 or 2 which comprises the further step of passing the aqueous solution through a cation exchange resin. A process according to claim 1 in which said aqueous solution is passed through said weakly basic ion exchange resin and then through a strongly basic ion exchange resin or mixture thereof with a cation exchange resin.

Inventors: GUZEK DONALD BRIAN, HAUSMAN RUSSELL JOSEPH, SHAH BHARAT KIRITKUMAR, GUZEK, DONALD BRIAN, HAUSMAN, RUSSELL JOSEPH, SHAH, BHARAT KIRITKUMAR
Applicants: CULTOR OY, CULTOR LTD.
Application year: 1991
Main classification: C08B37
IPC codes: A21D2, A23L1, A23G3, C08B37