CA1094001A

CA1094001A - Dextrose production with immobilized glucoamylase

Info

Publication number: CA1094001A
Application number: CA292,878A
Authority: CA
Inventors: Ronald E. Hebeda; Harry W. Leach; Dennis J. Holik
Original assignee: Unilever Bestfoods North America
Current assignee: Unilever Bestfoods North America
Priority date: 1976-12-13
Filing date: 1977-12-12
Publication date: 1981-01-20
Also published as: US4132595A; JPS5375342A; JPS6043120B2; AR214105A1; AU509656B2; GB1538823A; NZ185820A; BE861799A; AU3142977A; MY8000059A

Abstract

Case: D-3137 DEXTROSE PRODUCTION WITH IMMOBILIZED
GLUCOAMYLASE

A B S T R A C T
A process for production of dextrose from starch wherein a starch hydrolysate having a high dextrose equivalent produced using soluble glucoamylase is treated solely with an immobilized glucoamylase enzyme to produce a dextrose product.

Description

;10~'~001 This invention relates to the production of dextrose from starch through the use of an immobilized glucoamylase enzyme.
Processes for conversion of starch to dextrose have long been known in the art. Glucoamylase is an enzyme capable of converting starch to dextrose. The use of gluco-amylase for producing dextrose and dectrose-containing syrups is well known in the art. Processes using gluco-amylase generally fall into three categories. These are the acid-liquefaction-enzyme conversion process, the enzyme-liquefaction-enzyme conversion process, and the enzyme-solubilization-enzyme conversion process (the granular starch hydrolysis process as disclosed and claimed in U.S.
Patent Nos. 3,922,1~7; 3,922,198, 3,922,199 and 3,922,200).
In the acid-enzyme process, starch is liquefied and hydrolyzed in an aqueous su~pension containing 20 to 40 percent starch and an acid, such as hydrochloric acid, The su~pension i:~ then heated to a high temperature, i.e., a temperature between about 70C. and about 160C. and at a pH between about 1 and 4.5 to liquefy and partially hydrolyze the starch. The liquefied and partially hydrolyzed starch will generally have a dextrose equivalent (D.E.) value up to about 20 and preferably up to about 15. Typical acid-enzyme processes are disclosed in U.S. Patent Nos.

2,305,168; 2,531,999, 2,893,921, 3,012,944 and 3,042,584.
In the enzyme-enzyme process, starch is liquefied and partially hydrolyzed in an aqueous suspension containing 20 to 40 percent starch and a liquefying enzyme such as bacterial alpha-amylase enzyme at a temperature of from about 85C. to about 105C. The dextrose equivalent value of the liquefied and partially hydrolyzed starch is generally less than about 20 and preferably less than about 15. A

- 2 _ lU~'~OOl process for preparing a low dextrose equivalent partial hydrolysate suitable for converting starch to dextrose and dextrose-containing syrups comprises liquefying starch in water with a bacterial alpha-amylase enzyme preparation to a dextrose equivalent value of from about 2 to about 15, heat treating the slurry containing the liquefied starch to a temperature greater than about 95C., andthereafter converting the liquefied starch with a bacterial alpha-amylase enzyme preparation to a D,E. of up to about 20. This process is disclosed and claimed in U.S. Patent No, 3,853,706.
In the enzyme-liquefaction-enzyme process, dextrose equivalent values of about 97 are regularly obtained.
In the enzyme-solubilization-enzyme process, a slurry of granular starch is digested~~y the action of bacterial alpha-a~ylase (preferably a bacterial alpha-amylase enzyme preparation derived from the microorganism Bacillus licheniformis) under conditions such that some granular starch is present during digestion. The digested starch may be thereafter converted to dextrose or dextrose-containing syrups by other enzymes such as glucoamylase.
The low dextrose equivalent liquefied starchhydrolysates prepared by any one of the three processes mentioned above can then be treated with soluble gluco-amylase enzyme preparations to convert the low dextrose equivalent starch hydrolysate to dextrose or dextrose containing syrups.
Glucoamylase preparations are produced from certain fungi strains such as those of genus Asperqillus, for example, Asperqillus phoenicis, Asper~illus, niqer, Asperqillus awamori, and certain strains from the Rhizopus species and certain Endo~yces species. Glucoamylase effects the hydrolysis of starch proceeding from the non-reducing end o the starch molecule to split off single glucose units at the alpha-1,4 or at the alpha-1,6 branch points. Com-mercial glucoamylase enzyme preparations comprise several enzymes in addition to the predominating glycoamylase, for example, traces of proteinases, cellulases, alpha-amylases, and transglucosidases.
Alpha-amylase enzyme is produced from many types of microorganisms, for example by certain Aspergillus species and Bacillus subtilis. Alpha-amylase is an endo enzyme capable of randomly splitting the starch molecule into smaller chain units and is used in the enzyme-enzyme process as liqufying enzyme. Al~ha-amylase does not selectively split off dextrose units and breaks only the al~ha-1,4 chain link. Debranching enzymes or alpha-1,6-glucosidases have recently been used for their ability to break the alpha-1,6 linkages which cannot be hydrolyzed or broken by the action of alPha-amylase.
Con~iderable interest has been developed in the use of immobilized enzyme technology to continuously produce dextrose from starch. Various procedures have been described for the immobilization of glucoamylase, alpha-amylase, and amylolytic enzyme combinations.
In the art o enzyme immobilization, gluco-amylase immobilization has received considerable attention.
Many methods of glucoamylase immobilization are available, for example, in U.S. Patent Nos. 2,717,852, 3,519,538;

3,619,371, 3,627,638; 3,672,955, 3,715,277; 3,783,101 and 3,g50,222.
Processes using immobilized glucoamylase treat-ment of starch hydrolysates have recently been reported ~rom 10$~4001 Iowa State University. Examples of these processes are the following: Weetall and Suzuki Immobilized Enzyme Technolo~y: Research and Applications, Plenum Press, New York, New York (1975) pp. 269-297; Lee et al Die Starke 27 (1975) No. 11 pp. 384-387; Lee et al Biotechnoloqy and ~ioenaineerinq, Vol. XVII (1976) pp. 253-267, Lee et al Paper 601, 10th ACS Midwest Meeting, Nov. 7, 1974.
In the Iowa State work, glucoamylase was covalently immobilized on Corning* porous silica ceramic carrier.
0 10w dextrose equivalent starch hydrolysates produced by the previously deqcribed processes were continuously passed over the immobilized glucoamylase. The maximum dextrose concentration in the product (based on dissolved solids) varied from 87 to 93 percent depending on the dextrose equivalent and the amount of reverqion products in the feed.
In all examples, yields of dextrose using immobilized gluco-amylase were lower than that obtained using soluble gluco-amyla~e on the same substrate.
High dextrose equivalent hydrolysates produced using alpha= amylase resulted in lower dextrose yields than obtained with low dextrose equivalent hydrolysates. For example, in the Die Starke report, when higher dextrose e~uivalent substrates were substituted for the 24 D.E.
material initially employed, dextrose concentration as percent of total dissolved solids decreased from 90.1%
to 87~/o for 34 D.E. substrate and ~6.6% for 42 D.E, substrate.
~ erman patent application OS 25 38 322 discloses a process for the conversion of starch to dextrose through the use of a combination enzyme system consisting of immobilized glucoamylase and alpha-amylase. The latter * trademark OOl enzyme can be soluble alpha-amylase or immobilized alpha-amylase. It is important to note that, during the immobilization of the glucoamylase preparation, the alpha-amylase inherently present therewith becomes essentially inactive. Thus, in order to provide maximum utilization of the immobilized glucoamylase in the conversion of starch to dextrose, it is taught that additional soluble and/or immobilized alpha-amylase must be made available during the conversion in addition to the glucoamylase.
In accordance with this invention a process is provided for the production of dextrose from starch which comprises the steps of:
a) reacting starch with hydrolytic enzymes or acid to produce a low D,E, starch hydrolysate having a dextrose equivalent from about 2 to about 20;
b) treating the low D.E. starch hydrolysate with a soluble glucoamylase preparation to produce a starch hydrolysate having a dextrose equivalent less than about 85, c) reacting the soluble glucoamylase treated starch hydrolysate with an effective amount of enzyme consisting essentially of glucoamylase in immobilized form, and d) recovering a dextrose product.
In another embodiment, the present invention is also directed to a process for producing dextrose from a low D.E. starch hydrolysate having a dextrose equivalent of about 2 to about 20 which comprises the steps of:

lO~'~l)Ol a) treating a starch hydrolysate with a soluble glucoamylase preparation to produce a starch hydrolysate product having a dextrose equivalent less than about 85, b) reacting the soluble glucoamylase treated starch hydrolysate product with an effective amount of an enzyme consisting essentially of glucoamylase in immobilized form; and c) recovering a dextrose pro~uct.
It has unexpectedly been discovered that through practice of this invention, high dextrose yields can be obtained by continuous treatment of high dextrose equivalent (D.E.) starch hydrolysates utilizing an enzyme process differing from the prior art processes in that the process of this invention consists essentially of an immobilized glucoamylase (devoid of free or immobi~ized active alpha-amylase). In contrast to previous methods, dextrose ~ontents found using an immo~ilized glucoamylase closely parallel those obtained using soluble glucoamylase. Further-more, dextrose content was essentially constant throughout the range of about 3~ D.E. to about 85 D.E. In addition, improved enzyme utilization was obtained as shall be demonstrated more fully hereinafter. The combination of high dextrose yield and improved enzyme utilization in a continuous process using an immo~ilized glucoamylase as the sole enzyme is a commercially significant development for conversion of starch to dextrose.

10~001 The present invention can utilize starch or a low dextrose equi~alent starch hydrolysate of about 2 to about 20 D.E. as starting material. A significant dis-tinction over prior art processes is that the starch or low dextrose equivalent starch hydrolysate must be treated with a soluble glucoamylase preparation to produce a high dext-rose equivalent starch hydrolysate prior to reaction with the immobilized glucoamylase. The high dextrose equivalent hydrolysate has a dextrose equivalent in the range of about 30 to about 85 D.E. and most preferably has a dextrose equivalent in the range of about 45 to about 85 D,E, The low dextrose equivalent starch hydrolysate can be produced as previously described, for example, the acid~ uefaction-enzyme process, the enzyme-liquefaction-enzyme conversion process, or the enzyme-solubilization-enzyme conversion process. If a low dextrose equivalent starch hydrolysate is the starting material, the dextrose equivalent must be increased to the desired high dextrose equivalent level through treatment with a soluble gluco-amylase preparation either alone or in com~ination with other hydrolytic enzymes such aq al~ha-1,6-glucosidases.
According to this invention, the high dextrose e~uivalent starch hydrolysate of le~s than about 85 D.E.
is treated solely with an immobilized glucoamylase pre-paration (i.e. devoid of free or immobilized active alpha-amylase) to produce the dextrose. The immobilized ~luco-amylase preparation is used alone without the addition or combination of other soluble or immobilized alpha-amylase enzymes, and no further steps or enzymatic treatment are required to produce the dextrose level desired in the product.

Dextrose product~ containing about 95 percent dextrose were produced in column operation using immobilized glucoamylase preparations at 25 percent solids and 45C. when the starch hydrolysate feed was greater than 30 D.E, Dilution of the starch hydrolysate feed to 10 percent solids gave an effluent containins about 97 percent dextrose.
Immobilized glucoamylase preparations are well known and can be produced, for example, by any of the methods previously discussed, during which the alpha-amylase portion of the glucoamylase becomes inactivated and can therefore be present as the inactive form of alpha-amylase. It is pre-ferred to use the imm~bilized glucoamylase preparation pro-duced according to U.S. Patent No. 3,783,101 in which the glucoamylase preparation is covalently coupled to silica.
Glucoamylase activity units are determined as follows: The substrate i9 a 10-20 D.E~ alpha-amylase thinned ~lydroly~ate of waxy maize, ~tarch dissolved in water and diluted to 4.0 grams of dry substance per 100 ml. of solution. Exactly 50 ml. of the solution is pipetted into a 100 ml. volumetric flask. To the flask is added 5.0 ml. of 1.0 molar sqdium acetate-acetate acid bu~fer ~pH: 4.3).
The flask is placed in a water bath at 60~C. and after 10 minutes the proper amount of enzyme preparation is added.
At exactly 120 minutes after addition of the enzyme pre-paration the solution is adjusted to a phenolphthalein end-point with 0.5 normal sodium hydroxide. The strength of the sodium hydroxide solution must be adjusted so that the total volume after neutralization is less than 100 ml. The solution i~ then cooled to room temperature, and diluted to volume.
A reducing sugar value, calculated as dextrose, is determined on the diluted sample and on a control with no enzyme pre-paration added. Glucoamylase activity is calculated as follows:

10~'~001 A = S - B
2 x E
where A = glucoamylase activity units per mil (or per gram) of enzyme preparation.
S = reducing sugars in enzyme converted sample, grams per 100 ml.
B = reducing sugars in control, grams per 100 ml.
E = amount of enzyme preparation used, ml. ~or grams).
S should not exceed 1.0 grams per 100 ml.
The term dextrose equivalent or "D.E." value used herein refers to the reducing sugars content of the dis-solved solids in a starch hydrolysate expressed as percent dextro~e a~ measured by the Schoorl method ~Encyclopedia of Industrial Chemical Analysis, Vol. II, pp. 41-42).
Dextrose was determined by the procedure of Scobell, Tai and Hill as reported in Advances in Automated AnalYsis, Technicon International Conqress, Vol. II, p. 70 (1969). In this colorimetric procedure, dextrose is oxidized by glucose oxida~e to gluconic acid and hydrogen peroxide. In the presence of peroxidase, the hydrogen peroxide reacts with potassium ferrocyanide to give the yellow ferricyanide with a colour intensity proportional to the original dextrose concentration.
The following examples demonstrate the conversion of a high D.E. starch hydrolysate to high dextrose contain-in~ products with immobili~ed glucoamylase.
EXAMPLE
A starch hydrolysate having a dextrose equivalent level of 11 D.E. was incubated at 60~C. and pH 4.3 at 30 percent solids by dry weight basis for 16 hours Using a soluble glucoamylase preparation at 14 units per lO0 g. dry weight basis to produce an 84 D.E. hydrolysate product.
Immobilized glucoamylase was prepared by binding glucoamylase to silanized porous silica at pH 7.0 with glut-araldehyde according to the procedure presented in U.S.
Patent ~o. 3,783,101.
After incubation, the 84 D.E. hydrolysate was heated to inactivate any soluble enzymes and adjusted to a feed liquor solids level of 25 percent and fed through a column (inside diameter 30mm, length l90mm) containing a 100 ml. bed of immobilized glucoamylase on porous silica (55 g. dry weight basis or 14 units of glucoamylase per g.
dry weight bases) at a rate of 2.0 bed volumes per hour.
A dextrose level of 95.8 percent dry weight basis was initially obtained. Increasing the flow rate of 5.1 bed volumes per hour and reducing the solids level to 10 percent resulted in a dextrose level of 97.2 percent dry ba~is weight.
EXAMPLE II
A low dextrose equivalent starch hydrolysate of 11 D.E. was treated with soluble glucoamylase at 60C. and pH

4.3 for exactly 16 hours at 25 percent solids by dry weight basis. Glucoamylase dosage and the dextrose equivalent attained are shown below:
Glucoamylase Dosage Dextrose Equivalent Units/100~ Dry Substance Attained 1.4 30 3.1 47 6.4 65 30 13.4 80 ~U~4001 The reaction was stopped by heating at 95C. for 15 minutes. Each substrate was readjusted to 25 percent solids by dry weight basis. Saccharide distribution for each hydrolysate feed is as follows:
Feed Composition % d.b. bY Paper Chromatoqraphy D,E. Dextro~ea) Maltose Isomaltose Maltulose DP-3 DP-4+b) 11 0.8 -------------3.2 ------------ 4.7 91.3 30 26.05.6 0.1 0 7.9 60.4 47 44.0 8.6 0 0.1 6.3 41.0 65 59.9 10.6 0 0.6 0.7 28.2 80 76.63.9 0.5 0.6 0.7 17.7 a)Dextrose by difference (i.e. lOO~o - Sum of percent non-dextrose) b)Degree of Polymerization of "4" and greater as total percent C)$otal Degree Polymerization of "2" components A column containing a 100 ml. bed of glucoamylase preparation immobilized on porous silica was operated at 1 bed volume per hour at 45C. and pH 4.3 using the prepared feeds at 25% solids and also the 11 D.E. starch hydrolysate.
The procedure used for binding glucoamylase was essentially the same as that presented in U.S. Patent ~o. 3,783,101.
Compo~ition of the dextrose containing product ohtained at the various D.E. levels is as follows:

1 )~4001 Product Composition % d.b. bY Paper Chromatoqraphy ) D.E. Dextroseb) Maltose Isomaltose Maltulose DP-3 DP-4 c) 11 93.7 0.8 2.4 0.9 0.3 1.9 94.1 1.0 2.3 0.9 0.3 1.4 47 94.2 0.8 2.6 0.9 0.4 1.1 94.7 0.7 2.6 0.8 0.4 0.8 94.6 0.8 2.8 0.8 0.5 0.5 )Normalized b)Glucose Oxidase Method C)Degree of Polymerization of "4" and greater as total percent EXAMPLE III
Example II was repeated with the exception that the rolumn of immobilized glucoamylase was operated at 1.5 bed volume per hour. Composition of the dextrose contain-ing product obtained at the various D,E. levels is as follows:

_ % d.b. by Paper Chromatogra~h~ ) D.E. Dextroseb) Maltose Isomaltose Multulose DP-3 DP=4 c) 11 92.~ 0.g 1.8 0.9 0.4 3.4 93.2 0.9 1.5 0.7 0.3 3.4 47 93.6 0.9 1.7 0.9 0.3 2.6 ~3.5 0.8 2.2 1.0 0.5 2.0 94.6 0.8 2.2 0.~3 0.4 1.2 a)Normalized b)Glucose Oxidase Method C~Degree of Polymerization of "4" or greater as total percent EXAMPLE IV
Example II was repeated with the exception that the column of immobilized glucoamylase was operated at 0./
bed volume per hour. Composition of the dextrose containing product obtained at various D.E. levels is as follows:

% d.b. bY Paper ChromatoqraPhya) D.E. Dextroseb) Maltose Isomaltose Maltulose DP-3 DP-4+C) lld) 93.2 0.7 4.4 0.8 0.6 0.3 94.4 0.8 3.0 0.8 0.4 0.6 47 94.3 0.7 3.3 0.8 0.4 0.5 94.1 0.9 3.5 0.8 0.4 0.3 93.6 0.7 4.1 0.9 0.5 0.2 a)~ormalized b)Glucose Oxidase Method C)Degree of Polymerization of "4" or Greater as total percent d)This sample (only) run at 0.5 bed volume per hour.
EXAMPLE V
This example shows the effect of flow rate expressed as bed volume per hour (BVH) on the product from the immobilized glucoamylase column using the 80 D.E. hydrolysate prepared as in Example II and further diluted with water to l~/o ~olids (dry weight basis). The column containing a 100 ml. bed of glucoamylase preparation immobilized on porous silica was operated at 45C. and pH 4.~. Composition of the dextrose containing product is as follows:

10~4001 % d.b. bv Paper Chromatoqraphy ) Flow Rate +c) BVH Dextroseb) Maltose Isomaltose Maltulose DP-3 DP-4 2.0 94.9 0.6 2.7 1.2 0.3 0.3 2.4 95.4 0.6 2.3 1.1 0.3 0 3 3.0 95.1 0.6 2.2 1.2 0.3 0.6 4.0 95.7 0.5 1.5 1.0 0,3 1.0 a)Normalized b)Glucose Oxidase Method C)Degree of Polymerization of "4" or Greater as total percent EXAMPLE VI
This example demonstrates the effect of solids dry weight basiY) on the conversion of a high dextrose equivalent starch hydrolysate to a high dextrose product with an immobilized glucoamylase.

OOl An 11 D.E. starch hydrolysate was converted to an 80 D.E. starch hydrolysate as shown in Example II. The 80 D.E.
starch hydrolysate was diluted to different solids levels by dry weight basis and treated with immobilized glucoamylase as shown in Example II. The results of these 80 D.E. starch hydrolysate are as follows:

% d.b. bY PaDer Chromatoara~hva) Flow Solids Rate Dext- Malt- Isomal- Maltu-10yO w/w BVH roseb) ose tose lose DP-3 DP_4+ c) 25 1.0 94.6 0.8 2.8 0.8 0.5 0.5 10 4.0 95.7 0.5 1.5 1.0 0.3 1.0

5 5.5 97.1 0.2 1.1 0.9 0.1 0.6 a) Normalized b) Glucose Oxidase Method c) Degree of Polym~rization of "4" and greater as total percent.
As seen from the above data, dextrose yields using immobilized qlucoamylase according to this invention are essentially constant throughout the entire range of about 30 D,E, to about 85 D.E. In contrast with the prior art, the above data also show h~h dextrose levels produced from high dextrose equivalent starch hydrolysates using solely an immobilized glucoamylase.
Although the foregoing Examples demonstrate a preferred immobilized glucoamylase, it is to be understood that other types of immobilized glucoamylases can be employed, so long as the alpha-amylase portion is in the inactive form and the high D.E.
hydrolysate feed was produced using soluble glucoamylase.
In this specification, the enzyme glucoamylase has the enzyme number 3.2.1.3., the enzyme alpha-amylase has the enzyme number 3.2.1.1.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A process for the production of dextrose from starch characterized by the steps of:
a) treating a low D.E. starch hydrolysate having a dextrose equivalent from about 2 to about 20 with a soluble glucoamylase preparation to produce a starch hydrolysate having a dextrose equivalent from about 30 to about 85;
b) reacting the soluble glucoamylase treated starch hydrolysate with an effective amount of an enzyme consisting essentially of immobilized glucoamylase and:
c) recovering a dextrose product having a dextrose content of at least about 90 percent dry weight basis.

2. A process according to claim 1, wherein the soluble glucoamylase treated starch hydrolysate has a dextrose equi-valent from about 45 to about 85.

3. A process according to claim 1, wherein the immobilized glucoamylase is covalently bound to porous silica.

4. A process according to claim 2 wherein the immobilized glucoamylase is covalently bound to porous silica.

5. A process according to claim 1, 2 or 3, wherein the dextrose product has a dextrose content of at least 93 percent dry weight basis.

6. A process according to claim 1, 2 or 3, wherein the dextrose product has a dextrose content of at least 95 percent dry weight basis.

7. A process according to claim 1, 2 or 3, wherein said soluble glucoamylase treated starch hydrolysate is free of active alpha-amylase enzyme.

8. A process according to claim 1, 2 or 3, wherein said low D.E. starch hydrolysate is produced by reacting starch with a hydrolytic enzyme.

9. A process according to claim 1, 2 or 3, wherein said low D.E. starch hydrolysate is produced by reacting starch with an acid.

10. A process for producing dextrose from a low D.E.
starch hydrolysate having a dextrose equivalence of about 2 to about 20 which comprises the steps of:
a) treating said starch hydrolysate with a soluble glucoamylase preparation to produce a starch hydrolysate product having a dextrose equivalent from about 30 to about 85;
b) reacting the soluble glucoamylase treated starch hydrolysate product with an effective amount of an enzyme consisting of immobilized glucoamylase under conditions to produce a dextrose product having a dextrose content of at least about 93 percent dry weight basis;
and c) recovering said dextrose product.

11. The process of claim 10, wherein the soluble glucoamylase treated starch hydrolysate product has a dextrose equivalent from about 45 to about 85.

12. The process of claim 10, wherein the immobilized glucoamylase is covalently bound to porous silica.

13. The process of claim 10, 11 or 12, wherein the dextrose product has a dextrose content of at least 95 per-cent dry weight basis.

14. A process for the production of dextrose from starch which comprises the steps of:
a) reacting starch with hydrolytic enzymes or acid to produce a low D.E. starch hydrolysate having a dextrose equivalent from about 2 to about 20;
b) treating the low D.E. starch hydrolysate with a soluble glucoamylase preparation to produce a starch hydrolysate having a dextrose equivalent from about 30 to about 85;
c) reacting the soluble glucoamylase-treated starch hydrolysate with an effective amount of an enzyme consisting of immobilized gluco-amylase under conditions to produce a dextrose product having a dextrose content of at least about 93 percent dry weight basis; and d) recovering said dextrose product.

15. The process of claim 14, wherein the soluble glucoamylase treated starch hydrolysate has a dextrose equivalent from about 45 to about 85.

16. The process of claim 14, wherein the immobilized glucoamylase is covalently bound to porous silica.

17. The process of claim 14, wherein the dextrose product has a dextrose content of at least 95 percent dry weight basis.

18. A process for the production of a dextrose product having a dextrose content of at least about 93 percent dry basis weight comprising reacting a starch hydrolysate having a D.E. of about 30 to about 85, said hydrolysate being free of active alpha-amylase enzyme, with an effective amount of an enzyme consisting of immobilized glucoamylase to produce said dextrose product.

19. The process of claim 18, wherein the starch hydrolysate has a dextrose equivalent from about 45 to about 85,

20. The process of claim 18, wherein the immobilized glucoamylase is covalently bound to porous silica.

21. The process of claim 18, 19 or 20, wherein the dextrose product has a dextrose content of at least 95 percent dry weight basis.