The present invention relates to a new process for preparing enzymatically converted glucose syrups which can be used as countertypes for standard acid converted glucose syrups, i.e. glucose syrups with a DE varying between 30 and 50, and to the new syrups which can be thus obtained.
The standard acid converted glucose syrups are obtained by acidifying a starch slurry to a pH=2,0. This slurry is then pumped into a continuous reactor which operates at elevated temperature and pressure. After the proper time interval, the liquor is returned to atmospheric conditions and neutralised. This liquor is clarified, decolourised with activated carbon and concentrated to the final syrup. The acid process is generally used for syrups in the range of 30-50 DE (Dextrose Equivalent). The acid conversion always yields a product of specific composition because of the random hydrolysis of the starch. Major disadvantages of this process are the high salt content of the syrup, and the special equipment needed to perform the acid conversion reaction.
The acid converted glucose syrups are typically used in hard boiled candy. There they reduce the tendency of sucrose to crystallise, they slow down the tendency to shell-graining and they contribute to the body and "mouthfeel" of the confection on consumption. Glusose syrups are also used in toffees, fudge or fondant where they prevent, slow down or control granulation of sucrose. These acid converted glucose syrups represent a market of more than 400.000 ton dry substance Europe-wide.
The acid converted glucose syrups used today are furhter purified by extended demineralisation,which results in better colour stability and improved organoleptic properties. These additional purification steps, which are needed to produce refined products, require additional equipment and cause additional operating costs. For this reason, alternatives for acid converted glucose syrups have been developed, based on acid-enzyme and enzyme-enzyme converted syrups. These products are already used in a number of food applications. These syrups are characterised by a DE which is the same as the DE of the acid converted syrups, but they differ considerably in sugar spectrum and rheological properties. A comparison between acid converted, acid-enzyme and enzyme-enzyme converted syrups of the same DE is illustrated in table 1:
Other types of syrups, having a sugar spectrum which is closer to that of an acid converted syrup, are commercialised. These syrups are obtained by blending acid or enzymatically converted syrups with high maltose and/or 95DE glucose syrup.
Is is generally admitted that direct enzymatic conversion of starch into an acid converted-type of syrup would have a number of advantages, namely :
The publication "Labo-Pharma-Probl.Tech., Vol 29, no 310, 1981, p.443-447" gives an overview of various processes for converting starch in sugar sirups, and of the sugar distribution (by Degree of Polymerization DP) of those processes, corresponding to the state of the art discussed hereabove.
DE 41 25 969 discloses a process in which a mixture of certain enzymes is used to convert native starch directly into a sirup with high glucose content (DE>80). This type of syrup is very different from the so called acid converted glycose syrups for which the present invention aims at providing a countertype product.
DE 30 12 143 discloses a continuous process for the conversion of starch into a glucos syrup by means of a mixture alpha-amylase and amyloglycosydase, also yielding sugar syrups with a DE value above 80.
Applicants have now found unexpectedly that such glucose syrups having a sugar spectrum and rheological behaviour comparable to that of an acid converted syrup can be obtained.
It is therefore one object of the present invention to provide as new product, starch based, enzymatically converted glucose syrups of specific properties.
The glucose syrups according to the invention, which are obtainable by the process according to the invention, consist of a starch based, enzymatically converted glucose syrups, having a DE value (Dextrose Equivalent) between 30 and 50 and a sugar spectrum in which
Applicants have also developped well determined conditions of a double enzymatic process allowing the preparation of such new glucose syrups.
It is therefore also an object of the present invention to provide a new process for preparing glucose syrup by treating starch with enzymes.
The process according to the invention comprises treating a liquified starch substrate by means of an enzyme mixture in a single enzymatic conversion step, whereas said enzyme mixture comprises together a bacterial alpha amylase, a maltogenic amylase and a glucoamylase.
The starting substrate for the process according to the invention is a liquified starch, as may for instance be obtained by liquifaction of native starch with a thermostable alpha amylase to a DE of 10-12, deactivation of the thermostable alpha amylase, and cooling of the liquified starch to a temperature of about 60°C.
Although other starting liquified starch substrates may be contemplated in the process according to the invention, the specifically liquified starch mentionned by way of example is most preferred.
The enzymes used in the enzyme mixture according to the invention are widely available on the market.
The preferred glucoamylase, exo-1,4-aplha-D-glucosidase, can in particular be obtained from a selected strain of Aspergillus niger by submerged fermentation.
The recommended reaction conditions for this enzyme are pH=4,5 and T=60°C. The enzyme activity of the glucoamylase (AGU) is defined as the amount of enzyme which hydrolyses 1 micro-mol maltose per minute under standard conditions (T=25°C;pH=4,3;reaction time 30 minutes).
The bacterial alpha amylase is preferably an endo-amylase which hydrolyses 1,4-alpha-glucosidic bonds in gelatinised starch. The alpha amylase can be produced by fermentation of a selected strain of Bacillus subtilis.
Recommended operating conditions for this enzyme are pH=6-6,5 and T=70-90°C. The enzyme activity of the alpha amylase (KNU) is defined as the amount of enzyme which breaks down 5,26g starch per hour at Novo's standard method for determination of alpha amylase under standard conditions (substrate=soluble starch; Ca-content in solvent=0,0043M;T=37°C;pH=5,6).
The preferred maltogenic amylase (EC3.2.1.133) hydrolyses 1,4-alpha-glucosidic linkages in starch, partially hydrolysed starch and low-molecular weight oligosaccharides, including maltotriose. Maltose units are removed in a stepwise manner from the non-reducing chain ends. The enzyme, which can come from Bacillus stearothermophilus, can be expressed in and produced by a genetically modified strain of Bacillus subtilis. For industrial applications the recommended operating conditions are 60°C and pH 5,0-5,5. The enzyme activity of this maltogenase is defined as the amount of enzyme which hydrolyses 1 micromole of maltotriose under standard conditions, (substrate concentration 10mg/ml;T=37°C;pH=5,0;incubation time=30 min.)
The single enzymatic conversion step - i.e. a saccharification step - applied to the starting substrate in accordance with the invention is preferably performed at a temperature in the range from 55 to 65° C for a period of 10 to 48 hours, at a pH between 4,9 and 5,1; most preferably at a temperature in the range from 60 to 62° C for a period of 18 to 24 hours, at a pH between 4,9 and 5,1.
Of course shorter or longer reaction times are not excluded, but this could result in too high enzyme costs or too high investments in storage or reaction vessel capacity.
During the enzymatic conversion step the dry substance content of reaction mixture is preferably between 30 and 40% , more preferably between 32 and 37% , and most preferably between 33 and 35%.
The process according to the invention is particularly suitable for preparing the new glucose syrups according to the invention as defined above.
The enzyme concentrations and the enzyme ratios during the enzymatic conversion step according to the invention entirely depend on the process conditions applied and on the specific properties of the glucose one wishes to obtain. These concentrations will readily be determined by the skilled art worker on the basis of the data provided by the supplier of the commercial enzymes used in the process and/or by using mathematical calculations on the basis of empirical models, as is already known in the art ("Development and field confirmation of a mathematival model for amyloglucosidase/pullulanase saccharification" by T.R. Swanson et al. - Starch/Staerke (1986), 38 (11), 382-387). An empirical model can be construed based on information obtained from a design set-up of experiments of saccharification tests. By selecting an appropriate model, equations are obtained by which the amount (%w/w) of the different DP fractions in function of the concentrations of the different enzymes and the time can be calculated. The empirical equations are then used to calculate those combinations of enzyme concentrations and reaction time which fit at best the sugar spectrum of the acid converted glucose syrup which has to be countertyped.
The invention will be further illustrated and explained by way of the following examples describing a number of specific embodiments of the invention. It should be observed that the specific features of these examples are only described as preferred embodiments of what is intended within the above general disclosure of the invention and should by no means be interpretted as limiting the scope of the invention as such and as set forth in the claims.
Native starch was suspended in water at a concentration of 33-35% d.s. and at a slightly acidic pH (3,5-4,0). This slurry was then gelatinised at 160°C. After cooling to 95°C, pH was adjusted to 5,7-5,9 and thermostable alpha amylase was added (0,5-0,6ml comm./kg d.s.). This slurry was then further liquified during 2-3 hours at 90-95°C until a DE of 10-12 was reached. Then the alpha amylase was inactivated by adjusting the pH to 4 while heating the liquefied starch for an additional 5 minutes at 95°C.
This substrate was then cooled to 60°C and pH was adjusted to 5,0. To this liquified starch a mixture of enzymes was added composed of a glucoamylase, a maltogenic amylase and a bacterial alpha amylase. The following enzyme quantities were used :
Native starch was suspended in water at a concentration of 33-35% d.s. and at a slightly acidic pH (3,5-4,0). This slurry was then gelatinised at 160°C. After cooling to 95°C, pH was adjusted to 5,7-5,9 and thermostable alpha amylase was added (0,5-0,6ml comm/kg d.s.). This slurry was then further liquified during 2-3 hours at 90-95°C until a DE of 10-12 is reached. Then the alpha amylase was inactivated by adjusting the pH to 4 while heating the liquified starch for an additional 5 minutes at 95°C. This substrate was then cooled to 60°C and pH is adjusted to 5,0. To this liquefied starch a mixture of enzymes was added composed of a glucoamylase, a maltogenic amylase and a bacterial alpha amylase. The following enzyme quantities were added :