GB2049698A - Process for Preparing Non- Crystallizing Starch Syrups Containing Both Dextrose and Maltose - Google Patents

Abstract

Syrups containing substantial amounts of dextrose and maltose (e.g., syrups containing 35%-40% dextrose, about 35% maltose, the balance being higher saccharides), are continuously prepared by passing a starch hydrolyzate containing maltose in an amount greater than that desired in the final product through a column of immobilized glucoamylase to bring the dextrose content to the desired level. Problems invariably encountered in stopping completely the saccharification reaction at precisely the desired end-point are thus overcome.

Description

SPECIFICATION Process for Preparing Non-crystallizing Starch Syrups Containing Both Dextrose and Maltose Background of the Invention This invention relates to an improved process for preparing, particularly on an industrial scale, non-crystallizing syrups containing substantial amounts of both dextrose and maltose.

Starch hydrolyzate syrups, which will not spontaneously crystallize (or "haze") at concentrations of up to 80% or higher, and which contain up to about 40% to 44% dextrose and at least about 20% maltose, have been for many years popular products for the food and beverage industries. Syrups of this type, and processes for making them, are described in a number of patents, including the following U.S. patents: 2,891,869 to Langlois; 2,822,303 to Campbell et al; 3,067,066 to Ehrenthal et al; 3,137,639 to Hurst et al; 3,630,844 to Hurst et al; and 3,644,126 to Bodnar et al.

Although the patent literature describes numerous processes for the manufacture of such products, the most practical and economic industrial process comprises treating a starch hydrolyzate which contains a substantial amount of maltose (more than the amount of maltose desired in the final product) with glucoamylase enzyme, in order to saccharify a portion of the maltose and the higher saccharides to dextrose, and terminating the action of the glucoamylase when the desired dextrose level has been reached.

Methods of making suitable starting materials, i.e., hydrolyzates of starch containing a substantial amount of maltose, are well-known in the art and are simple to perform on an industrial scale. One such well-known method comprises first liquifying starch with acid or enzyme such as alpha-amylase and then saccharifying with a maltogenic enzyme such as beta-amylase. Within recent years methods for preparing starch hydrolyzates containing 70% or more maltose have been reported, which methods generally involve saccharifying liquified starch with both a maltogenic enzyme and a starchdebranching enzyme such as pullulanase. U.S. Patent No. 3,565,765 to Heady et al describes such a process.

As mentioned, preparation of a suitable high-maltose starting material presents no problems to the industrial manufacturer of maltose-dextrose syrups. Problems are encountered in the glucoamylase saccharification step or, more precisely, in stopping the saccharification at exactly the right desired end point. Industrial processes employ, as it well-known, very large quantities of reactants in large reaction vessels. Termination of an enzymatic reaction is customarily accomplished either by increasing the temperature or by chemical addition; neither technique will "instantly" terminate an enzymatic reaction taking place in an industrial-size reaction tank. Other disadvantages to the customary techniques are that heating requires a large expenditure of energy, while chemical addition introduces undesirable materials into the product which must be subsequently removed by refining.

The problem of precise control of the glucoamylase reaction, with attendant precise control of the final product composition, is extremely acute in the manufacture of dextrose-maltose syrups, for the following reasons. If the dextrose content of such syrups is much over 40% (in certain types of syrups a dextrose content of up to 44% can be tolerated, but generally 40% is the upper limit) the syrups, at commercial concentrations of about 80% dry substance, will spontaneously crystallize, or haze, upon standing. Furthermore, these syrups are sold under precise specifications as to maltose and dextrose contents and, naturally, customers expect the products to meet these specifications.In commercial practice the manufacturer conducts the glucoamylase reaction until the approximate end point is reached, terminates the reaction by heat or chemical addition, and then analyses the finished product.

Except in those exceedingly rare cases when the finished product meets the specifications, he then blends the product with one or more other starch hydrolyzates to product his final syrup.

In accordance with my invention, all of the problems of control of the glycoamylase reaction and final product composition are eliminated by employing the glucoamylase in immobilized form, and conducting the saccharification reaction by continuously passing the high-maltose hydrolyzate substrate through a mass of the immobilized glucoamylase.

It is known to immobilize glucoamylase enzyme, and various techniques for such immobilization have been widely reported in the literature, for example: British Patent 1,444,539 to Novo Industrie A/S; Lee, D. D., Y. Y. Lee and G. T. Tsao "Continuous Production of Glucose from Dextrin by Glucoamylase Immobilized on Porous Silica" Die Stake 27, No. (1975) pp 384-387; Solomon, B.

and Y. Levin "Adsorption of Amyloglucosidase on Inorganic Carriers" Biotech. and Bioeng. XVII (1975) pp 1323-1333; Lee, Douglas D., Yoon Y. Lee, Peter J. Reilly, Edgar V. Collins, Jr. and George T. Tsao "Pilot Plant Production of Glucose with Glycoamylases Immobilized to Porous Silica" Biotech. and Bioeng. XVIII (1976) pp 253-267; U.S. Patents 4,011,137 and 4,102,745 both to Thompson et al; and Belgian Patents 861,799 and 870,096, both to CPC International Inc.

However, in all of the prior art publications relative to immobilized glucoamylase of which I am aware, the immobilized enzyme has been employed to saccharify a liquified or partially hydrolyzed starch substrate to obtain dextrose in the highest possible amounts. I am unaware of any process being reported involving the saccharification of a maltose-containing substrate with immobilized glucoamylase to produce and recover dextrose-maltose syrups.

Brief Description of the Invention My invention comprises the process of preparing non-crystallizing syrups containing substantial amount of dextrose and maltose comprising subjecting a maltose-containing starch hydrolyzate to the saccharifying action of glucoamylase, characterized in that the glucoamylase is in immbolized form and the saccharifaction reaction is performed by continuously passing the maltose-containing substrate through a mass of immobilized glucoamylase.

As will be seen from the examples, the process of my invention permits the manufacturere of dextrose-maltose syrups to prepare such syrups, having any desired predetermined compositions, simply by appropriate adjustment of the saccharifying conditions, e.g., amount and activity of the glucoamylase and the rate at which the substrate is passed through the mass of immobilized enzyme.

The means by which the glucoamylase is immobilized, and the agent employed for the immobilization, are immaterial to the practice of my invention, the only criteria being, obviously, that the immobilized glucoamylase have sufficient activity to result in the desired saccharifaction. For reasons of economy and simplicity I prefer to immobilize the glucoamylase by adsorption onto a suitable porous carrier material, rather than to employ more costly methods such as chemical coupling or entrapment. During the development work of the invention a number of porous materials were screened for their efficacity as carriers for glucoamylase, by offering to the carrier material (in a column) a large amount of a liquid glucoamylase preparation (12 gms. enzyme preparation to 50 ml.

carrier, or about 40 AU/ml. carrier), and determining the amount retained, or bound, by the carrier. To evaluate the bound activity retention of the carriers a malto-dextrin of 1 8 D.E., 30% dry substance, was passed through the column at rates to produce an 80 D.E. hydrolyzate.

Table 1 sets forth the data obtained during the screening. It should be noted that these data are mereiy presented as a general guide to the practitioner in selecting a suitable carrier material, and do not illustrate the practice of the invention.

As will be seen from the data presented in Table 1, a number of the carriers tested showed good binding capacity for glucoamylase as well as good retention of enzyme activity.

Table 1: Evaluation of Carriers for Glucoamylase Binding and Retention BV/H to reach 80 D.E.

Carrier Binding % 3 hrs. 24 hrs. 45 hrs.

(1) Corning Alumina 20.85 5.1 4.8 4.0 (2J Akzo j-Alumina .004-1.5 E 20.48 5.2 5.2 4.5 (2) Akzo Alumina .008-1.5 E 21.97 < .1 - (2) Akzo Alumina pellets 10.1 < .1 - (3) Aluminium oxide &num;36 10.5 < .1 - (3) Aluminium oxide &num;46 5.2 < .1 (3) Silicium carbide &num;36 3.5 < .1 - (3) Silicium carbide &num;46 17.5 < .1 Ground Bricks 9.4 < .1 (4) Duolite S-761 86.7 8.2 5.6 4.1 (4) Duolite S-762 88.9 6.5 5.8 5.2 (4) Duolite ES-562 73.2 6.1 5.9 5.3 (4) Duolite ES-861 F 56.9 3.2 < .1 (4) Duolite A-7 fines 73.2 6.4 6.3 6.3 (2) Imac SYN 106 94.1 5.6 5.2 4.1 (2) Imac SYN C 218 P .2 - - - (1) From Corning Glass Works, Corning, N.Y., and described in U.S.Patents 3,850,751; 3,868,304 and 3,992,329 (2) From Akzo N.V., Arnhem, The Netherlands (3) From Carborundum Overseas Co., London (4) From Diamond Shamrock Corp., Cleveland, Ohio Detailed Description of the Invention The starting material can be any maltose-containing starch hydrolyzate having a sufficiently high content of maltose to provide, after the glucoamylase saccharifaction, the desired level of maltose in the final product. A solution of pure (100%) maltose could be employed, in which case the final product will consist solely of dextrose and maltose, and such products could be quite vaiuable to the pharmaceutical industry, which would justify the cost of employing pure maitose as a starting material.

For most purposes, e.g., to prepare syrups for use by the food and beverage industries, starch hydrolyzates containing at least about 35% maltose, some dextrose, and the balance higher saccharides (having degrees of polymerization of 3 and higher) are perfectly suitable starting materials.

During the glucoamylase saccharification which is preferably conducted in a column filled with the immobilized enzyme, the pH should be within the range of 3.5 to 6.0 (preferably 4.2) and the temperature should be from 50 OC., to 65 OC., (preferably about 6O0C.). The substrate concentration is immaterial to the practice of the invention, but for reasons of economy and to minimize problems of fermentation it should be as high as possible. Concentrations of 50% dry substance or higher are particularly suitable. The rate or rates at which the substrate is passed through the column of immobilized enzyme (expressed as bed volumes per hour, or BV/H) will depend, of course, upon the composition of the substrate, the conditions of the saccharification reaction, and the end product desired.The skilled operator will readily be able to select the optimum rate for his particular process.

In the examples to follow, which illustrate the practice of the invention, jacketed columns having inner diameters of 2.6 cm. were employed, and were filled with carrier material to a height of 9.4 cm.

All runs were conducted at 600 C., maintained by means of hot water circulation through the column jackets. In each case the column was first half-filled with 700C., demineralized water, the carrier was introduced, and was washed and "degassed" by circulating 700 C. demineralized water through the column, entering at the bottom, for 30 minutes. The pH was then adjusted to 3.5 4.5 by washing with dilute acetic acid (circulation of 8 BV of 0.1 M acetic acid, entering at the top, at a rate of 4 BV/H), and the carrier was then washed with 250C. water to a pH of about 4.0.

The enzyme, which was dispersed in a 0.1 M sodium acetate solution, was introduced at the top of the column and circulated, at 250C., for 20 hours at a rate of 4 BV/H. The column was then washed with .1 M sodium acetate and the effluent collected and analysed for enzyme, in order to determine the percent of offered enzyme bound onto the carrier. Substrate was then sent onto the column, at 25"C., until the outlet concentration was the same as the concentration of substrate being introduced. The column was then ready for operation.

The activity of the glucoamylase, expressed in activity units (AU), is the number of grams of reducing sugars produced by 1 gram of enzyme in 1 hour at 600C., and pH 4.3, during an incubation period of a total of 2 hours during using, as the substrate, a starch hydrolyzate having a D.E. in the range of 10 to 20.

Example I In this example the maltose-containing starting material was a commercially available syrup, sold by CPC International under the trade-mark Mor-Sweet, having the following composition: DE 42 Dextrose 13% Maltose 38 -0% Maltotriose 1214% Higher Saccharides 3336% The glucoamylase enzyme employed was a transglucosidase-free enzyme preparation derived from Aspergillus Niger, having an activity of 1 65 AU per gm. of enzyme. The carrier material employed was Duolite ES-562, a porous, phenol-formaldehyde, weakly basic anion exchange resin.

The desired final product was one having a dextrose content of about 38, a maltose content of about 34%, the balance being higher saccharides. The enzyme was offered to the column in an amount of 25 mg. enzyme, or 4.1 Au, per ml of carrier; 100% binding was achieved at this level.

The pH was 4.2. The maltose-containing hydrolyzate, at a solids concentration of 30%, was sent through the column at an initial rate of 8.0 bed volumes per hour, the flow rate being gradually decreased to 6.6 bed volumes per hour after 400 hours of operation. The final product consistently had the following composition: DE 60 Dextrose 3739% Maltose 3335% Maltotriose 45% Higher Saccharides 2226% The trial was repeated except that the enzyme was offered to the carrier in an amount of 50 mg/ml of carrier (8.25 AU/ml carrier), which again resulted in 100% binding, and the substrate was passed through the column at an initial rate of 12.0 bed volumes per hour, gradually decreasing to 10.6 bed volumes per hour after 400 hours.Products of identical composition to the previous run were consistently obtained.

Example II The starting material and desired final product were identical to those of Example I. The glucoamyiase employed was a commercially available product from Miles Kali Chemie known as Optidex L150, having an activity of 110 AU/mg. The substrate concentration was 50% d.s. The carrier was Duoiite ES-562.

Two runs were made, designated as A and B, employing different amounts of enzyme and correspondingly different flow rates. The pH was 4.2.

Table 2 sets forth the conditions of the two runs. The term "1 st half life, days" means the number of days elapsed from the start of the run to the point at which the flow rate had been reduced to onehalf the initial rate. The term "2nd half life, days" indicates the remaining time elapsed to the point at which the flow rate had been reduced to one-quarter of the initial rate. The runs were stopped when the flow rates reached 0.5 bed volume per hour.The products obtained had consistently the same composition as the products obtained in Example Table 2 A B Enzyme offered mg./ml. carrier 20 60 AU/ml. carrier 2.2 6.6 Enzyme binding 100% 100% Initial BV/H 3.9 10.6 1 st half life, days 38.5 43.7 2nd half life, days 20.0 27.1 Total life, days 68.7 83.3 (O.5 BV/H) Total bed volumes 3,547 11,600 Enzyme Consumption gm./kg. d.s. 0.0091 0.00842 AU/kg. d.s. 0.0010 0.00093 Example lil In this example Duolite ES-562 was used as the carrier, the glucoamylase was Optidex L1 50, and the desired end product was one having about 48% dextrose and a higher content of maltose than in the previous examples (greater than 50% maltose).

The starting material (substrate) used, which was at a concentration of 50% d.s., was a high maltose hydrolyzate prepared by saccharifying liquefied starch with pullulanase and beta-amylase and having the following composition: DE 53.2 Dextrose 1.5% Maltose 77.4% Maltotriose 15.4% Higher Saccharides 5.7% Table 3 sets forth the conditions of the saccharification, which was conducted at a pH of 4.2.

Table 3 Enzyme offered mg./ml. carrier 60 AU/ml. carrier 6.6 Enzyme binding 100% Initial BV/H 7.0 1 st half life, days 30.0 2nd half life, days 18.0 Total life, days 56.0 (e0.5 BV/H) Total bed volumes 4,875 Enzyme Consumption gm./kg. d.s. 0.01251 AU/kg. d.s. 0.00137 The final product consistently had the following composition: DE +72 Dextrose 3739% Maltose 5657% Maltotriose 2.53.5% Higher Saccharides 24% Example IV In this example the carrier used was Duolite ES-762, a porous non-ionic plenolic resin. The enzyme was Optidex L-1 50. The desired end product was a syrup containing 30% dextrose and about 40% maltose.The substrate selected was a starch hydrolyzate having the following composition: Dextrose 4% Maltose 50% Maitotriose 15% Higher Saccharides 31% The substrate concentration was 50% d.s., the temperature during the reaction was maintained at 60 C., and the pH was 4.2. Table 4 sets forth the reaction conditions.

Table 4 Enzyme offered mg./ml. carrier 40 AU/ml. carrier 4.4 Enzyme binding 100% Initial BV/H 6.2 1 st half life, days 25.0 2nd half life, days 12.5 Total life, days 45.8 (It0.5 BV/H) Total bed volumes 3,685 Enzyme Consumption gm./kg. d.s. 0.0088 AU/kg. d.s. 0.00096 The final product consistently had the following composition: Dextrose 30% Maltose 40% Maltotriose 3.5% Higher Saccharides 26.5% It will be noted that in this and the other examples the temperature throughout the saccharification was kept constant (6000.) while the flow rate was reduced to compensate for loss of enzyme activity. One could also, of course, maintain the flow rate constant for a longer period of time while raising the temperature as the enzyme activity decreases. The examples are presented merely to illustrate the various methods of practicising the invention, and to guide the skilled practitioner in selecting suitable conditions for his particular operation.

Claims (7)

Claims

1. The process of preparing non-crystallizing syrups containing substantial amounts of dextrose and maltose comprising subjecting a maltose-containing starch hydrolyzate to the saccharifying action of glucoamylase, characterized in that the glucoamylase is in immobilized form and the saccharification reaction is performed by continuously passing the maltose-containing substrate through a mass of the immobilized glucoamylase.

2. The process of Claim 1 characterized in that the glucoamylase is immobilized by means of adsorption onto a porous carrier material.

3. The process of Claims 1 or 2 characterized in that the substrate contains at least 35% maltose.

4. The process of any of the preceding claims wherein the pH of the saccharification is within the range of 3.5 and 6.0.

5. The process of any of the preceding claims wherein the pH of the saccharification reaction is within the range of 4.0 and 4.2.

6. The process of any of the preceding claims wherein the temperature of the saccharification reaction is within the range of 500C. and 650C.

7. The process of any of the preceding claims wherein the substrate has a solids concentration of 50% or higher. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~