WO2010000935A1

WO2010000935A1 - New dry-milling method for preparing bran

Info

Publication number: WO2010000935A1
Application number: PCT/FI2009/050585
Authority: WO
Inventors: Ilkka Lehtomäki; Olavi Myllymäki
Original assignee: Lehtomaeki Ilkka; Myllymaeki Olavi
Priority date: 2008-06-30
Filing date: 2009-06-29
Publication date: 2010-01-07
Also published as: FI20085673A0; EP2299846A1; EP2299846A4; FI20085673L

Abstract

The present invention relates to a method for preparing a cereal bran product containing beta-glucan. In accordance with the method, after the milling of cereal bran at least part of particles whose size is less than 70 to 100 μm are separated and removed from the process and particles whose size exceeds 300 to 600 μm undergo a new milling and classification, and the fraction passing the sifter in the classification is recovered.

Description

NEW DRY-MILLING METHOD FOR PREPARING BRAN

[0001] Health benefits of cereal grains, such as beta-glucan contained in oats, barley and rye, are well known. Beta-glucan is shown to lower the concentration of harmful LDL cholesterol in blood serum and hence to reduce the risk of contracting cardiovascular diseases. With products containing beta-glucan it is also possible to slow down the absorption of glucose into blood and thus to maintain the blood sugar level steady for a long time. This, in turn, affects the feel of satiety and thereby contributes to weight control. Cereal products containing beta-glucan include oat bran and barley bran, for instance.

[0002] Cereal bran, particularly oat bran, may be prepared for instance by the method described in patent application WO 89/01294 (Myllymaki et a/.), in which the beta-glucan concentration in bran is raised by wet-milling in an organic solvent, or in patent publication US 5,183,677 (Lehtomaki et al.) which employs wet-milling in cold water and FM 13938 (Malkki et al.), in which oat bran is prepared by dry-milling from oat grains. Previous methods for producing cereal bran are also disclosed, for instance, in background descriptions in patents WO 2006/069390 and FM 13938 and in publications by Stevenson et al., 2008, and Paton and Lenz, 1993.

[0003] Typically, a method for preparing cereal bran comprises a plurality of milling and classifying steps. A problem with the methods for preparing bran is that the production capacity of bran is relatively low and other constituents, such as star₍ch, will be found among the bran. Whereas, in the process for preparing bran large amounts of beta-glucan will remain in the flour. ^■

[0004] In a prior art process, which is described in FM 13938, for instance, processing of cereal takes place in dry conditions. This increases static electricity in the process, which makes separation of various constituents more difficult and generates sparking. Milled cereal particles adhere to surfaces, whereby classification of particles by means of sifters is difficult and sifted fractions contain ingredients not belonging thereto.

[0005] Major problems with the processes of prior art dry technology are that /

- the same material is treated several times in the process, which consumes time ancl energy and causes unnecessary costs,

- particle distribution of a bran product is wide, the product is het- erogeneous and the yield is poor, - the flour contains a lot of bran particles.

[0006] The object of the present invention is to solve problems of the prior art.

[0007] The object of the invention is to provide a method which improves the efficiency of bran production by reducing multiple treatments of the same material.

[0008] The object of the present invention is also to provide a method which improves separation of different constituents in the process and thereby improves the specificity of the process.

[0009] The object of the present invention is to provide a bran product having a higher beta-glucan content than in the bran used as starting material.

[0010] The present invention is based on the idea that the smallest particles formed in bran milling are removed after the milling and the coarsest particles are recycled for new milling.

[0011] The method of the invention preferably comprises the following steps of

1. performing milling on cereal bran,

2. classifying the bran for removing the smallest particles,

3. sifting the bran for separating and recycling the coarsest fractions for a new milling.

[0012] As a product there is recovered a beta-glucan-rich bran product.

[0013] More precisely, the method of the invention is mainly characterized by what is set forth in the characterizing part of claim 1.

[0014] The process of the present invention preferably employs cereal bran as raw material.

[0015] According to a preferred embodiment of the present invention the cereal bran is moistened prior to milling.

[0016] Several advantages are achieved with the method of the invention:

[0017] 1. The specificity and flexibility of the process are high compared with previously described dry processes

- Beta-glucan-containing cell walls are efficiently concentrated, because small bran particles rich in beta-glucan are not milled again.

- Large bran particles containing less beta-glucan may be proc- essed effectively, when necessary, in different conditions or with equipment better suited for the purpose.

- Beta-glucan content in the flour will be low.

- The process may use oat bran of various grades, because the process is easier to adjust. For instance, fat content in oat bran may vary considerably.

[0018] 2. The capacity of the process is higher than in previously described dry processes.

- The raw material is bran, from which starch-containing flour has already been removed.

- Only bran, whose processing is necessary, is run in the process.

[0019] 3. The process enables more efficient unit operations, for instance sifting, than earlier dry processes producing beta-glucan bran, because the fine flour fraction is removed immediately from the milled bran by classification.

[0020] 4. Energy consumption of the process is low, because the amount of circulating flows is low.

[0021] 5. Moderate moistening increases significantly the yield of product bran and decreases the beta-glucan content in the flour. Moistening of bran particles is more efficient than that of whole or cut seeds. This is due to the fact that a fibre component absorbs moisture better than other components of the cereal grain and in bran particles the fibre component of the seed is more exposed than in seeds. In pulverization the moistened, flexible bran remains larger than non-moistened bran, which facilitates the separation process. Despite the fibre part flexibility, appropriate milling detaches fine-grade starch flour from the moistened bran particles.

[0022] 6. Moderate moistening reduces heating of bran when milled.

[0023] 7. Moderate moistening reduces static electricity and sparking in the process. Hence unit operations are safer and easier, because a tendency to adhere to surfaces and to other particles is reduced.

[0024] Figure 1 shows the principle of the process for preparing a bran product.

[0025] Figure 2 shows particle size distributions of bran raw material.

[0026] Figure 3 shows particle size distribution of a bran product.

[0027] Figure 4 shows beta-glucan content in particles of different

SUBSTITUTI iEET (Rule 26) sizes as percent by weight of dry substance.

[0028] In connection with milling, the bran becomes a flour, in which up to 80 to 95 % of particles are less than 70 to 100 μm in size. If fine particles are not separated, the flour hampers subsequent unit operations, for instance, sifting.

[0029] The present invention is based on the idea that after bran milling at least part, preferably at least 20%, more preferably at least 30%, more preferably at least 40%, still more preferably at least 50%, even more preferably than that at least 60%, most preferably at least 80% of smallest particles, i.e. typically particles of less than 70 to 100 μm, are separated and removed from the process. In some cases it is preferable to remove only 20 to 40% of the smallest particles.

[0030] In the process, a fraction in which the particle size is larger than 300 to 500 μm, typically larger than 400 to 600 μm, is recycled to new milling. These larger particles contain less beta-glucan than smaller particles (Haapiainen, 2003).

[0031] As a bran product there is recovered a fraction in which the particle size is at least 80 μm and less than 500 to 600 μm, preferably at least 40 μm and less than 300 μm.

[0032] As a starting material (raw material) the method of the present invention may employ cereal bran, such as oat or barley bran, produced by any method. Preferably the bran is oat bran.

[0033] The beta-glucan content in the bran to be used as starting material is at least 8% by weight, preferably at least 12% by weight (at least 11 % by weight of dry substance), typically 11 to 12% by weight (12 to 14% by weight of dry substance). The bran may be prepared by any bran preparing method, for instance, by the method disclosed in patent publication WO 89/01294 in example 1 and in reference publication Paton (1993). The starting material may also be Oatcor oat bran manufactured by Quaker Oats at least since 1999. Oatcor oat bran contains beta-glucan at least 11.5% by weight of dry substance.

[0034] As starting material it is also possible to use cereal bran whose beta-glucan concentration has already been raised by another method, for instance, by the method that is disclosed in patent publication FM 13938. In that case, the bran to be used as the starting material contains beta-glucan about 15 to 18% by weight of dry substance (14 to 17% by weight as such). [0035] The moisture in the bran to be used as starting material is typically 9 to 12% of the weight of the bran.

[0036] Prior to pulverization the oat bran may be moistened with water. Preferably the moisture in oat bran is raised to 13 to 16% by weight of the weight of the oat bran. Moistening may take place in a pre-preparation device. Moistening of bran has an advantage that moistening reduces static electricity in the process, which improves separation of various constituents and sparking may be reduced. The milled cereal particles lose their electrical charge and they do not adhere to surfaces, whereby classification of particles by means of screens becomes easier.

[0037] In order to avoid static electricity it is advantageous to use non-dried air of the process space in all process steps, such as milling step, or in an air classifier.

[0038] It is common that in impact milling, for instance with hammer mills and pin mills, large amounts of air are used for cooling down the mill, for preventing the blocking of the mill and for transferring the material between mill sections. It is common that in pneumatic transfer of oatmeal the air flow is 25 m/s, and consequently a large amount of air is used. In addition, it is common that air classification uses large amounts of air, because particles are separated from one another both by means of the cyclone effect and by means of a classifier wheel. The quantities of air used are, in total, several thousand (even tens of thousands) cubic metres of air per hour. Air intake or inlet into the process space environment takes place directly from outdoor air, possibly filtered. In Finland the average humidity in outdoor air has been over 60% in all seasons (28 June 2008: http://www.fmi.fi/saa/tilastot 7.html).

[0039] At its simplest the "pre-preparation device" is a heated screw conveyor, into which water or vapour is added. The pre-preparation device may also consist of e.g. two adjacent or successive screws so as to provide desired conditions. These conditions may include, for instance, sufficient mixing and providing of stable temperature and humidity.

[0040] The starting material is milled using an appropriate milling method, typically a pulverization method, such as Alpine's Contraplex pin mill (200 m/s) having no sifter, or Alpine's UPZ mill which is mounted having an open milling track without a sifter.

[0041] For milling it is also possible to use Jackering's Ultrarotor (60 to 80 m/s) or Gόrgens' Turborotor grinders. These mills are hammer mills hav- ing a very long milling track but no sifter.

[0042] After milling the bran typically contains 40 to 60% or up to 80% particles of less than 70 to 100 μm in size. This material is separated by classification and removed from the process. Preferably, only 20 to 40% of the smallest particles are removed. Classification is typically carried out by an air classifier, such as Alpine's ATP air classifier.

[0043] After classification, the coarse fraction obtained by classification is sifted. In the sifting it is preferable to use a centrifugal sifter, such as Buehler's vibroschleuder centrifugal sifter (type MKVA).

[0044] Coarse material, typically over 300 to 600 μm or 400 to 500 μm in size, remaining on the sifter will be sifted separately and recycled to new milling. The material that is finer and richer in beta-glucan and that has passed the sifter is recovered.

[0045] In this description a cereal bran product refers to cereal bran which is treated by the method of the invention and whose beta-glucan content has increased thanks to the treatment performed, typically 15 to 25% by weight of dry substance.

[0046] Table 1 shows typical bran yields and beta-glucan contents in flour. The raw material is bran prepared in accordance with the reference publication Paton (1993) and containing beta-glucan 12% by weight of dry substance.

Table 1. Bran yield and beta-glucan content levels in flour. Raw material is bran containing beta-glucan 12% by weight of dry substance.

Examples

Example 1. Beta-glucan-rich oat bran is produced in pilot scale from conventional bran

[0047] The raw material is oat bran that is produced by known technology and contains beta-glucan 12.8% of bran dry substance (11% as such). The particle size distribution in the raw material bran is shown in Figure 2. In PCT application WO 89/01294, example 1 presents bran of this kind containing beta-glucan 11 to 12% by weight (12 to 14% by weight beta-glucan of dry substance). The block diagram of the process is set forth in reference publication Paton (1993).

[0048] Oat bran is milled with Alpine's UPZ 100 multipurpose mill having pin-mill blades. The mill is run at the rate of 15 000 rpm. The mill employs normal non-dried ambient air, the humidity thereof being 48%.

[0049] The milled oat bran is run onto British Reman Minisplit air classifier, which employs the same non-dried ambient air as the milling. In the air classifier, starch-containing flour that detaches in oat bran milling is removed from the process. The particle size of the flour to be separated is adjusted by the amount of air and by the rate of the classifier. In this run the amount of air is 200 m³/h and the rate of the classifier is 4 500 rpm. The particle size of the flour is in 95 per cent less than 90 μm.

[0050] Coarse fraction obtained from the air classifier is sifted with a 500- μm laboratory swinging sifter, because it was stated in the dissertation for the diploma by J. Haapiainen (2003) that large-size bran, over 400 to 600 μm, contains less beta-glucan than a finer bran fraction (Figure 4). Fraction remaining on the sifter will be recycled back to the process. The fraction passing the sifter is an oat bran product that contains beta-glucan 19.2% of dry substance. The particle size distribution of the oat bran product is shown in Figure 3.

Example 2. Beta-glucan-rich oat bran is produced in pilot scale by the process of example 1. Raw material is produced by the method disclosed in patent FM 13938.

[0051] Raw material is OBC N15 oat bran that is prepared by the method of patent publication FM 13938. The particle size distribution of OBC N15 bran is shown in Figure 2. The bran contains beta-glucan 16.4% of dry substance (14.8% as such). OBC N15 bran is otherwise processed in the con- ditions of example 1 , but the rotation rate of Alpine's UPZ 100 multipurpose mill is 18 000 rpm, the rate of air classifier is 4 800 to 5 000 rpm and the coarse fraction from the air classifier is sifted with a 400-μm sifter. The oat bran product passing the sifter contains 22.8% beta-glucan.

Example 3. Beta-glucan-rich oat bran is produced in industrial scale by means of a mill of hammer-mill-type without sifter

[0052] Raw material is the oat bran of example 1 containing 12.8% beta-glucan of dry substance of bran (11 % as such). The particle size distribution is shown in Figure 2.

[0053] The oat bran is milled with Jackering's Ultrarotor UR MIa mill. This mill is a hammer mill having a long grinding track and an integrated blower. Internal circulation of the mill is closed, the peripheral speed of the rotor is 78 m/s and the distance between the rotor and the stator is 3 mm. Milling air is non-dried ambient air and it is used about 3 000 m³/h.

[0054] The milled oat bran is run onto an air classifier that employs the same non-dried ambient air. The amount of air is 3 000 m³/h and the rate of the classifier is 2 000 rpm. From the process is removed the flour, the particle size of which is in 95 per cent less than 90 μm.

[0055] The coarse fraction from the air classifier is sifted with a vi- broschleuder centrifugal sifter having a 500-μm metal mesh sifter. The fraction remaining on the sifter is recycled through the process again. The oat bran product passing the sifter contains beta-glucan 20.2% of dry substance.

Example 4. Beta-glucan-rich oat bran is produced in industrial scale by means of a pin mill without sifter

[0056] Raw material is the oat bran of example 1 containing beta- glucan 12.8% of bran dry substance (11 % as such).

[0057] The oat bran is milled with Alpine's Contraplex 250 CW mill. This mill is a pin mill, in which the pin plates of either side rotate in opposite directions. The peripheral pin rate of the mill is 200 m/s in relation to one another. The mill employs non-dried ambient air in an amount of 2 000 m³/h.

[0058] The milled oat bran is run onto Alpine's ATP 315 air classifier that employs the same non-dried ambient air. The amount of air is 1 600 m³/h and the rate of the classifier is 1 600 rpm. From the process is removed the flour, the particle size of which is in 95 per cent less than 75 μm. [0059] The coarse fraction from the air classifier is sifted with a plansifter having a 400-μm metal mesh sifter. The fraction remaining on the sifter is recycled back to the process. The product oat bran passing the sifter contains beta-glucan 20.5% of dry substance. The bran product yield from raw material bran is 34% and bran moisture is 9.2%.

Example 5. Beta-glucan-rich oat bran is produced in industrial scale by the process of example 4 and raw material bran is moistened

[0060] Raw material bran is moistened in a screw from 11.2% moisture to 15.2% moisture. Water mist is used for moistening. After the moistening screw the bran is allowed to dwell in a container for 25 minutes.

[0061] The process is the same as in example 4.

[0062] The product oat bran contains beta-glucan 19.8% of dry substance. The bran product yield from raw material bran is 39.1 %. Bran moisture is 10.6%.

References

[0063] Haapiainen J., Increasing the solubility of oat bran β-glucan in foodstuffs. Helsinki University of Technology, Laboratory of Biochemistry and Microbiology, 2003.

[0064] Paton D. and Lenz M., Processing: Current Practice and Novel Processes, Oat Bran, edited by Wood P., J. American Association of Cereal Chemists, 1993, 41.

[0065] Stevenson D.G., Eller F.J., Jay-Lin J. and lnglett G., Structure and physicochemical properties of defatted and pin-milled oat bran concentrate fractions separated by air-classification. International Journal of Food Science and Technology 2008, 43, 995-1003.

Claims

1. A method for preparing a cereal bran product, the method comprising performing on cereal grain:

- one or more millings and

- one or more classifications, characterized by using cereal bran as starting material and, after the first milling step, removing by separating from the process at least part of particles whose size is less than 70 to 100 μm and particles whose size is over 300 to 600 μm undergo a new milling and classification and the fraction passing a sifter in the classification is recovered.

2. The method of claim 1, characterized by performing pulverization on the bran.

3. The method of claim 1 or 2, characterized by performing an air classification on the milled bran in order to separate particles of less than 70 to 100 μm in size and coarser particles.

4. The method of any one of claims 1 to 3, characterized by recycling for new milling the particles over 400 to 500 μm in size.

5. The method of any one of claims 1 to 4, characterized in that the bran is oat bran.

6. The method of any one of the preceding claims, characterized in that the bran used as starting material contains at least 8% beta- glucan, typically 12 to 13% by weight beta-glucan of bran dry substance.

7. The method of any one of claims 1 to 6, characterized in that prior to pulverization the oat bran is moistened with water.

8. The method of claim 7, characterized in that moistening is allowed to affect the bran for 20 to 30 minutes.

9. The method of claim 7 or 8, characterized by raising the bran moisture to 13 to 16% of the weight of the bran.

10. The method of any one of the preceding claims, characterized by removing in the classification performed on the bran at least 20%, preferably at least 30%, more preferably 40 to 80% of the particles of less than 70 to 100 μm in size contained in the milled bran.

11. The method of any one of the preceding claims, characterized in that the beta-glucan content of the bran product treated with the method is 15 to 25% by weight of dry substance.

12. The method of any one of the preceding claims, characterized by performing, after re-milling, new classification and sifting.

13. The method of any one of the preceding claims, characterized by performing re-milling one or more times.

14. A cereal bran product prepared by the method of any one of claims 1 to 13.

15. A foodstuff containing a cereal bran product of claim 14.