Carbohydrate refining process and a supported enzyme for use therein

Description

CER-10

[0001] The present invention relates to a process for improving the filterability of certain aqueous solutions of carbohydrate origin which contain a phospholipid and solid material and which prior to filtration are treated with a phospholipase.

[0002] European patent application 86307549.5, publication number 219269, describes a process for the treatment of an aqueous solution of carbohydrate origin, particularly a wheat starch hydrolysate, which is difficult to filter and/or which produces a cloudy filtrate. The aqueous solution contains a phospholipid and the filtration and quality of the filtrate are improved by treating the solution before filtration with an enzyme composition containing a phospholipase enzyme. The enzyme composition which is used may contain xylanase and beta-glucanase enzymes in which case the ratio of phospholipase enzyme to total xylanase and beta-glucanase enzymes is at least 0.05:1, preferably at least 1:1; more preferably at least 5:1 and particularly at least 10:1.

[0003] EP 219269 describes the preparation of suitable enzyme compositions for use in the treatment of the carbohydrate solutions and exemplifies a process of treatment in which a wheat starch hydrolysate is incubated with the enzyme before being filtered. Although this process is successful and is shown to give an increased filtration rate and clearer filtrate there is an increased cost to the overall process. This is made up of the enzyme cost and the plant operation time which is taken up by the incubation period necessary for the enzyme to produce its effect. The present invention provides a means which enables the enzyme to be used more economically and thereby reduces the cost of the treatment.

[0004] According to the invention therefore a process in which an aqueous solution of carbohydrate origin which contains a phospholipid and difficult-to-filter solid material is treated with a phospholipase enzyme prior to filtration is characterised by the phospholipase enzyme being immobilised on and/or in the particles of a solid support and the particles bearing the enzyme being agi­tated in contact with the aqueous solution.

[0005] The use of immobilised enzymes is, in general, well known and is used in the starch industry in particular to provide continuous processes in which a starch feedstock may be treated with an alpha-amylase, beta-amylase or glucoamylase immobilised on a suitable carrier. Signifi­cantly however these prior art treatments are concerned with homogeneous liquid streams which flow, usually under the effect of gravity, through fixed beds or columns of the particles of the support on which the enzyme is immo­bilised leaving no residue on the support. The aqueous solutions of carbohydrate origin according to the present invention however contain in suspension difficult-to-­filter solid material (usually proteinaceous and fatty material) and, when used in conventional immobilised enzyme columns, this solid material deposits on the enzyme support, suppressing the action of the enzyme and blocking the spaces between the support particles. There is conse­quently a rise in the pressure drop across the bed or column leading eventually to channeling or to complete cessation of flow. We have found however that despite the solid content of the aqueous carbohydrate solution the phospholipase which is immobilised on and/or in a solid support continues to function effectively, provided that the supported enzyme is agitated in content with the solution and that operation in this manner increases the volume of solution treated per unit of enzyme and gives a much shorter treatment time of, for example, up to about 12 mins.

[0006] The support which is used to immobilise the phospho­lipase in the process of the present invention may be an anion exchange resin, a cation exchange resin or a non-ionic macroporous polymer. The latter support is least preferred of the three types because it is our experience that a charged support provides a firmer anchorage for the enzyme which is therefore less likely to be eluted from the support when in use. It is also preferable to use anion exchangers rather than cation exchangers as the enzyme support since the anion exchangers absorb rela­tively more enzyme. The most suitable supports for the enzymes are weak anion exchangers which may be made from polystyrene or from phenol/formaldehyde resins, the latter being preferred.

[0007] The particles bearing the immobilised phospholipase are agitated in contact with the aqueous solution of carbohydrate origin. Agitation may be provided by an agitator such as a stirrer but we have found that an effective way of operating the process is to use the upward flow of the aqueous solution to "fluidise" the particles of the support. In this mode of operation the particles of the support are maintained in a short column or bed with sufficient head space to enable the heavier support particles to fall back into the column or bed, while the lighter fatty and/or proteinaceous solid is carried away in the aqeuous solution. The majority of the support particles preferably have a diameter of 300 to 800 microns, more preferably 400 to 550 microns. The advan­tages of "fluidised" operation are that it may be con­tinuous and not batch, that a given amount of enzyme may be used to treat a large volume o£ solution and that a given volume of solution has a shorter residence time in contact with the phospholipase than in the batch process described in EP 219269 (6 to 12 minutes compared with 10 to 12 hours). The latter advantage, besides increasing plant throughput, is particularly important when the aqueous solution comprises starch maltodextrins which tend to retrograde at the temperature of the phospholipase treatment.

[0008] The process of the present invention may be used in those applications described in EP 219269 and under similar conditions of pH and temperature. Thus, the process is particularly useful in processing various products derived from starch, particularly wheat starch hydrolysates such as maltodextrins and maltose syrups and may be operated at 20 to 110°C, preferably 50 to 100°C more preferably 40° to 70°C and at a pH up to 8 particularly 3.5 to 6.5. The phospholipases which are immobilised on and/or in the support are also preferably those described in EP 219269 eg. it is preferred that the enzyme compositions used to produce the supported phospho­lipase should suitably contain at least 5000 units phospholipase per gram total protein, preferably 15 000 units per gram, more preferably 50 000 units per gram and particularly 100 000 units per gram. The phospholipase is suitably of microbial origin and preferably has L₁, L₂, and/or C activity.

[0009] The invention will now be further described with reference to the following Examples.

Example 1

[0010] An aqueous solution of a commercially available phospholipase, G-ZYME G-999 ("G-ZYME" is a trademark), was gently stirred for five hours with a range of supports in suspension in water at ambient temperature. The amount of enzyme was 3.3 mg per ml. support. The support plus enzyme was then washed with demineralised water to remove soluble protein and enzyme. The amount of protein (enzyme) re­tained by the support was then determined. The results were as follows :-

Resin	Protein immobilised (mg protein per 1 ml support)
Weakly anionic polystyrene	1.1
Non-ionic phenol/formaldehyde	1.9
Weakly anionic polystyrene	1.4
Weakly ionic phenol/formaldehyde	1.4
Weakly ionic polystyrene	1.4
Strongly cationic polystyrene	0.3
Weakly ionic polystyrene	1.3

Example 2

[0011] Two hundred mls of a particulate weakly anionic phenol/formaldehyde resin, DUOLITE A568 (DUOLITE is a trademark), was washed with demineralised water and conditioned to pH 5 with a sodium acetate/acetic acid buffer (0.5M). The bulk of the particle size was 300 - 800 microns.

[0012] An aqueous solution of G-ZYME G-999 was then stirred with the DUOLITE A568 at 3.3 mg enzyme per 1 ml DUOLITE A568 at ambient temperature for five hours. The residual soluble protein and enzyme was next removed from the support by washing with four litres of demineralised water. Protein determination revealed that 1.4 mg protein were immobilised per 1 ml support.

[0013] The supported enzyme was introduced into a glass column so as to give a bed of diameter 5 cm and depth 10 cm. Means were provided to introduce aqueous solution to the base of the column and there was 400 mls free space at the top of the column above the catalyst bed.

[0014] The aqeuous solution fed to the column was an un­clarified wheat starch hydrolysate with a degree of hydrolysis corresponding to 18 DE. The solution had 35% dry substance and a pH of 4.8. Its temperature in the column was 50°C.

[0015] The effectiveness of the treatment provided by the process of the invention was assessed by determining the soluble free fatty acid and soluble lysolecithin content of treated product and its filtration rate in a simulated industrial precoat drum filter (results expressed as litres filtered per square metre of filter area per hour). The effect of the treatment with the phospholipase is to reduce the lysolecithin content of the substrate and to increase the concentration of the free fatty acids which are the product of lysolecithin hydrolysis. Solutions with a low lysolecithin content filter better than those with a higher content.

[0016] The substrate was fed continuously to the base of the column initially at a rate of ten bed-volumes per hour decreasing to five bed-volumes per hour. The support particles in the column were "fluidised" by the upward flow of the substrate which was withdrawn from the top of the column, the support particles being held in the column. The column was operated continuously for several days in this manner without there being any indication that the solids in the liquid feed were blocking the column or interfering in the activity of the supported enzyme. The results were as follows :

Days	Flow Rate (Bed-volumes per hour)	Filtration Rate liters/M²/hour	Soluble Lysolecithin content g/kg dry substance	Soluble fatty acids g/kg dry substance
* 0		144	1.7	3.4
6	10	295	0.5	4.7
7	10	-	0.7	6.2
8	10	164	0.9	5.1
9	7	213	1.4	4.4
10	5	-	0.8	3.8
11	5	-	0.2	8.9
12	5	306	0.3	7.2
13	5	-	0.4	5.1

* Untreated solution.

When the same solution was treated in the process described in EP 219269 the filtration rate was 365 the lysolecithin 0.1 and the soluble fatty acids 4.7.

Claims

1. A process in which an aqueous solution of carbohy­drate origin which contains a phospholipid and difficult-to-filter solid material is treated with a phospholipase enzyme prior to filtration is charac­terised by the phospholipase enzyme being immobilised on and/or in particles of a solid support and the particles bearing the enzyme being agitated in contact with the aqueous solution.

2. A process according to claim 1 characterised in that the solid support is an anion exchanger.

3. A process according to claim 2 characterised in that the anion exchanger is a polystyrene or phenol/for­maldehyde resin.

4. A process according to any one of the preceding claims characterised in that the particles bearing the enzyme are agitated by the upward movement of the aqueous solution through a column or bed of the particles.

5. A process according to any one of the preceding claims characterised in that the majority of the particles of the solid support have a diameter of 300 to 800 microns.

6. A process according to any one of the preceding claims characterised that the residence time of the aqueous solution in the process is up to about 12 mins.

7. A process according to any one of the preceding claims characterised in that the temperature is 40° to 70°C.

8. A process according to any one of the preceding claims characterised in that the pH is in the range 3.5 to 6.5.

9. A process according to any one of the preceding claims characterised in that the aqueous solution is of wheat starch origin.

10. A process according to claim 9 characterised in that the aqueous solution is a solution of a maltodextrin or a maltose syrup.