PROCESS FOR THE PREPARATION OF THERMALLY INHIBITED STARCH AND/OR THERMALLY INHIBITED FLOUR

Abstract

Disclosed is a process for the preparation of thermally inhibited starch and/or thermally inhibited flour having a moisture content lying between 5 and 30 wt. %, having the following steps: a slurrying step, wherein thermally inhibited starch and/or thermally inhibited flour is combined with an aqueous phase to form a slurry; and a drying step, wherein the aqueous phase of the slurry is separated off from the thermally inhibited starch and/or thermally inhibited flour, wherein in the slurrying step the pH of the slurry is brought to a value between 2.0 and 7.5.

Claims

1. A process for the preparation of thermally inhibited starch and/or thermally inhibited flour having a moisture content lying between 5 and 30 wt. %, comprising: a slurrying step, wherein thermally inhibited starch and/or thermally inhibited flour is combined with an aqueous phase to form a slurry, such that the slurry has water as continuous phase and contains between 5 and 60 wt. %, expressed as percentage of dry matter on total weight of the slurry, of particles of thermally inhibited starch and/or thermally inhibited flour; and a drying step, wherein the aqueous phase of the slurry is separated off from the thermally inhibited starch and/or thermally inhibited flour to such an extent that thermally inhibited starch and/or thermally inhibited flour having a moisture content lying between 5 and 30 wt. % is formed, wherein in the slurrying step the pH of the slurry is brought to a value between 2.0 and 7.5.

2. The process according to claim 1, wherein in the slurrying step the slurry is formed such that the slurry has water as continuous phase and contains between 5 and 40 wt. %, expressed as percentage of dry matter on total weight of the slurry, of particles of thermally inhibited starch and/or thermally inhibited flour.

3. The process according to claim 1, wherein the thermally inhibited starch and/or thermally inhibited flour is not pregelatinized and has, when entering the slurrying step, a moisture content of at most 8 wt. % or at most 2 wt. %.

4. The process according to claim 1, wherein the slurrying step is done within three months of preparation of the thermally inhibited starch and/or thermally inhibited flour, or wherein the slurrying step is done immediately following preparation of the thermally inhibited starch and/or thermally inhibited flour.

5. The process according to claim 1, wherein during the slurrying step the temperature of the slurry is, and remains, at least 1 C. below the gel point of the thermally inhibited starch and/or thermally inhibited flour.

6. The process according to claim 1, wherein the drying step is executed such that essentially no gelatinisation takes place.

7. The process according to claim 1, wherein the drying step is executed in a centrifuge or in a filter press, in combination with at least one evaporative dewatering operation.

8. The process according to claim 1, wherein the drying step is executed such that the thermally inhibited starch and/or thermally inhibited flour has a moisture content lying between 10 wt. % and 15 wt. %.

9. The process according to claim 1, wherein in the slurrying step the pH of the aqueous phase, before being combined with the thermally inhibited starch and/or thermally inhibited flour, is or is brought to between 1.0 and 7.5 or between 1 and 7.

10. The process according to claim 9, wherein the pH of the aqueous phase is brought to a value between 2.0 and 6.0 or to a value between 2.5 and 5.0.

11. The process according to claim 1, wherein the pH of the slurry is brought to a value between 2.5 and 7.0 or to a value between 3.0 and 6.7.

12. The process according to claim 11, wherein the pH of the slurry is brought to a value between 3.5 and 6.4 or to a value between 4.0 and 6.0.

13. The process according to claim 1, wherein in the slurrying step the slurry is brought to the desired pH value within one hour of the formation of the slurry or within five minutes of the formation of the slurry.

14. The process according to claim 1, wherein the thermally inhibited starch and/or thermally inhibited flour is derived from rice, maize, wheat, potato, tapioca, or any mixtures thereof.

15. The process according to claim 1, wherein the thermally inhibited starch and/or thermally inhibited flour is chosen from the group consisting of: thermally inhibited rice starch, thermally inhibited waxy rice starch, thermally inhibited rice flour, thermally inhibited waxy rice flour, thermally inhibited maize starch, thermally inhibited waxy maize starch, thermally inhibited maize flour, thermally inhibited waxy maize flour, thermally inhibited wheat starch, thermally inhibited waxy wheat starch, thermally inhibited wheat flour, thermally inhibited waxy wheat flour, thermally inhibited potato starch, thermally inhibited waxy potato starch, thermally inhibited potato flour, thermally inhibited waxy potato flour, thermally inhibited tapioca starch, thermally inhibited waxy tapioca starch, thermally inhibited tapioca flour, thermally inhibited tapioca rice flour, and any mixtures of the aforementioned starches or flours.

16. The process according to claim 15, wherein the thermally inhibited starch and/or thermally inhibited flour is not pregelatinized and is chosen from the group consisting of: thermally inhibited rice starch, thermally inhibited waxy rice starch, thermally inhibited rice flour, thermally inhibited waxy rice flour, and any mixture thereof.

17. The process according to claim 15, wherein any thermally inhibited starch is obtained via a heat treatment at temperatures lying between 100 and 200 C. at an alkaline pH and at a moisture content below 1 wt. %.

18. The process according to claim 2, wherein the thermally inhibited starch and/or thermally inhibited flour is not pregelatinized and has, when entering the slurrying step, a moisture content of at most 8 wt. % or at most 2 wt. %.

19. The process according to claim 2, wherein the slurrying step is done within three months of preparation of the thermally inhibited starch and/or thermally inhibited flour, or wherein the slurrying step is done immediately following preparation of the thermally inhibited starch and/or thermally inhibited flour.

20. The process according to claim 16, wherein the slurrying step is done within three months of preparation of the thermally inhibited starch and/or thermally inhibited flour, or wherein the slurrying step is done immediately following preparation of the thermally inhibited starch and/or thermally inhibited flour.

Description

[0053] The invention will be illustrated with the following Examples and Comparative Experiments, without being limited thereto.

COMPARATIVE EXPERIMENT A

[0054] A sample of a thermally inhibited waxy rice starch was used to form a slurry, using process water as circulating in the starch modification facility as aqueous phase. The process water had a pH of 7.5. The weight ratio between aqueous phase and thermally inhibited waxy rice starch was 70:30. The slurry had a pH of 7.7. The slurry was subsequently de-watered in a centrifuge during 15 minutes at 2,500 g, then dried to a moisture content of 11.3 wt. % to form a slurried-dried starch by means of oven-drying to 40 C.

[0055] Certain properties of the slurried-dried starch were determined by preparing a gel with the slurried-dried starch. The gel was prepared at 94 C. and 300 rpm in a Stephan UMSK 5 cooker equipped with a mixing insert having two rounded blades, using 135 g (dry matter) starch, citric acid and trisodium citrate to acidify and buffer to pH 3.6, and sufficient water to obtain a total weight of 2,500 g, whereby the citric acid and trisodium citrate were combined with the water before the starch was added. After cooling to 25 C., an intensive shearing action on the gel was done by means of a Silverson L4RT mixer using a square hole (2.4 mm) high shear screen mixer head at 5,000 rpm during 1 minute. The selection of rpm is done based a.o. on the nature of the gel; thus, in further examples hereinbelow it may be that another rpm is chosen in order to obtain the most meaningful insight into material behaviour. The rpm as usedalways during one minutewill be reflected in the notation of viscosity parameter by means of a subscript, whereby .sub.3 indicates an rpm of 3,000, .sub.5 indicates an rpm of 5,000, etc.

[0056] The viscosity and tan of a gel, made from the starch concerned, that had first been subjected to an intensive shear action, were determined at a temperature of 20 C. by means of an Anton Paar Rheometer (parallel plate-plate configuration; the plate diameter was 40 mm). As meant herein, the term tan is used in its common meaning of being a loss tangent in the linear viscoelastic region. It gives a ratio between viscous and elastic properties of a system, showing which one is the dominant one. With a tan value of 1, the elastic and viscous properties of the material are equal. The smaller the loss tangent is, the more elastic is the material.

[0057] The viscosity at 0.88 s.sup.1 was determined in a viscosity curve measurement wherein the shear rate varied from 0.1 to 100 s.sup.1.

[0058] The tan was determined from the results of an amplitude sweep measurement having the following characteristics: deformation from 0.01 to 1000%, frequency 1 Hz.

[0059] In the Examples and Comparative Experiments herein, the tan is always determined on a gel that has first been subjected to shear forces as described above, at the rpm as given per Example or Comparative Experiment.

[0060] The results were as follows:

TABLE-US-00001 1,870 mPa .Math. s pH 8.60 tan Above 1 8,600 mPa .Math. s pH 8.60 tan 0.42

COMPARATIVE EXPERIMENT B

[0061] The properties of the thermally inhibited waxy rice starch as such, i.e. the raw material as used in Examples 1-3 without having been subjected to any subsequent process step such as slurrying, were measured. The properties were determined to be:

TABLE-US-00002 4,860 mPa .Math. s tan 0.53

EXAMPLE 1

[0062] A sample of the same thermally inhibited waxy rice starch as was used in Comparative Experiment A was used to form a slurry. An aqueous phase consisting of water which was brought to a pH of 6.8 using sulphuric acid was used. The weight ratio between aqueous phase and thermally inhibited waxy rice starch was 70:30. The slurry had a pH of 7.4. The slurry was subsequently de-watered in a centrifuge during 15 minutes at 2,500 g, then dried to a moisture content of 11.7 wt. % to form a slurried-dried starch by means of oven-drying to 40 C. The properties of the slurried-dried starch were determined to be:

TABLE-US-00003 2,770 mPa .Math. s pH 8.07 tan 0.82 11,600 mPa .Math. s pH 8.07 tan 0.35

EXAMPLE 2

[0063] A sample of the same thermally inhibited waxy rice starch as was used in Comparative Experiment A was used to form a slurry. An aqueous phase consisting of water which was brought to a pH of 5.7 using sulphuric acid was used. The weight ratio between aqueous phase and thermally inhibited waxy rice starch was 70:30. The slurry had a pH of 6.8. The slurry was subsequently de-watered in a centrifuge during 15 minutes at 2,500 g, then dried to a moisture content of 12.6 wt. % to form a slurried-dried starch by means of oven-drying to 40 C. The properties of the slurried-dried starch were determined to be:

TABLE-US-00004 3,320 mPa .Math. s pH 7.51 tan 0.73 13,100 mPa .Math. s pH 7.51 tan 0.32

EXAMPLE 3

[0064] A sample of the same thermally inhibited waxy rice starch as was used in Comparative Experiment A was used to form a slurry. An aqueous phase consisting of water which was brought to a pH of 3.7 using sulphuric acid was used. The weight ratio between aqueous phase and thermally inhibited waxy rice starch was 70:30. The slurry had a pH of 6.6. The slurry was subsequently de-watered in a centrifuge during 15 minutes at 2,500 g, then dried to a moisture content of 12.7 wt. % to form a slurried-dried starch by means of oven-drying to 40 C. The properties of the slurried-dried starch were determined to be:

TABLE-US-00005 4,020 mPa .Math. s pH 7.14 tan 0.66 13,400 mPa .Math. s pH 7.14 tan 0.28

[0065] As is evident from the results of the Comparative Experiments A and B, if slurry-drying not according to the invention is performed then a very significant loss of properties was established. This worsening in properties was evidenced by the much lower viscosity after shearing and by the lower elastic properties as seen in the higher tan in Comparative Experiment A vs. Comparative Experiment B (as is known, the smaller the loss tangent tan is, the more elastic is the material).

[0066] Examples 1-3 show that when slurry-drying according to the invention is executed, the worsening of properties due to slurry-drying is reduced significantly.

COMPARATIVE EXPERIMENT C

[0067] A thermally inhibited waxy maize starch was, three months after its inhibition, used as raw material for a slurrying step. The pH of the aqueous phase was 7.7. The slurry contained 30 wt. % of the thermally inhibited waxy maize starch. The pH of the slurry was 7.6. The slurry was subsequently dried to a moisture content of 12 wt. % by means of filtration under vacuum and further drying in a rapid dryer (TG 200, Retsch) to form a slurried-dried starch. The properties of the slurried-dried starch were determined. The measurements were executed as described in Examples 1-3, with the exception of the rpm in the Silverson mixer. The mixer was set at 9,000 rpm. The results were:

TABLE-US-00006 V.sub.9 8,570 mPa .Math. s tan 0.31

COMPARATIVE EXPERIMENT D

[0068] The properties of the thermally inhibited waxy maize starch that was used in Comparative Experiment C as such, i.e. without having been subjected to remoistening or slurrying, were measured. The properties were determined to be:

TABLE-US-00007 V.sub.9 13,800 mPa .Math. s tan 0.21

EXAMPLE 4

[0069] A sample of the thermally inhibited waxy maize starch as used in Comparative Experiment C was used to form a slurry, however now using a different aqueous phase. The aqueous phase consisted essentially of water, was buffered (citrate buffer) and had a pH of 5.7. The pH of the slurry was 5.8. The slurry was subsequently dried to a moisture content of 12 wt. % by means of filtration under vacuum and further drying in a rapid dryer (TG 200, Retsch) to form a slurried-dried starch. The properties of the slurried-dried starch were determined to be:

TABLE-US-00008 V.sub.9 11,700 mPa .Math. s tan 0.22

[0070] Example 4 shows that when slurry-drying according to the invention is executed, the worsening of properties due to slurry-drying (as evidenced in Comparative Experiment C) compared to the product as such (Comparative Experiment D) is reduced significantly.

COMPARATIVE EXPERIMENT E

[0071] A thermally inhibited waxy wheat starch was, 14 days after its inhibition, used as raw material for a slurrying step. The pH of the aqueous phase was 7.7. The slurry contained 30 wt. % of the thermally inhibited waxy maize starch. The pH of the slurry was 7.6. The slurry was subsequently dried to a moisture content of 12 wt. % by means of filtration under vacuum and further drying in a rapid dryer (TG 200, Retsch) to form a slurried-dried starch. The properties of the slurried-dried starch were determined. The measurements were executed as described in Examples 1-3, with the exception of the rpm in the Silverson mixer. The mixer was set at 7,000 rpm. The results were:

TABLE-US-00009 V.sub.7 5,440 mPa .Math. s tan 0.51

COMPARATIVE EXPERIMENT F

[0072] The properties of the thermally inhibited waxy wheat starch that was used in Comparative Experiment E as such, i.e. without having been subjected to remoistening or slurrying, were measured. The properties were determined to be:

TABLE-US-00010 V.sub.7 10,000 mPa .Math. s tan 0.34

EXAMPLE 5

[0073] A sample of the same thermally inhibited waxy wheat starch as used in Comparative Experiment E was used to form a slurry, however now using a different aqueous phase. The aqueous phase consisted essentially of water, acidified with a citrate buffer to a pH of 5.7. The pH of the slurry was 5.8. The slurry was subsequently dried to a moisture content of 12 wt. % by means of filtration under vacuum and further drying in a rapid dryer (TG 200, Retsch) to form a slurried-dried starch. The properties of the slurried-dried starch were determined to be:

TABLE-US-00011 V.sub.7 10,400 mPa .Math. s tan 0.31

[0074] Also Example 5 confirms that when slurry-drying according to the invention is executed, the worsening of properties due to slurry-drying (as evidenced in Comparative Experiment E) compared to the product as such (Comparative Experiment F) is reduced significantly.

COMPARATIVE EXPERIMENT G

[0075] A thermally inhibited waxy rice starch was used, two months after the thermal inhibition was done, as raw material for a slurrying step. The pH of the aqueous phase was 7.8. The slurry contained 30 wt. % of the thermally inhibited waxy rice starch. The pH of the slurry was 8.0. The slurry was subsequently dried to a moisture content of 12.8 wt. % by means of means of filtration under vacuum and further oven-drying to 50 C. The properties of the slurried-dried starch were determined to be:

TABLE-US-00012 5,550 mPa .Math. s pH 8.9 tan 0.44

Comparative Experiment H

[0076] The properties of the thermally inhibited waxy rice starch that was used in Comparative Experiment G as such, i.e. without having been subjected to remoistening or slurrying, were measured. The properties were determined to be:

TABLE-US-00013 V.sub.5 10,450 mPa .Math. s tan 0.31

EXAMPLE 6

[0077] A sample of the same thermally inhibited waxy rice starch as used in Comparative Experiment G was used to form a slurry, however now using a different aqueous phase. The aqueous phase consisted essentially of water, acidified with a citrate buffer to a pH of 5.7. The pH of the slurry was 5.8 The slurry was subsequently dried to a moisture content of 13 wt. % by means of means of filtration under vacuum and further oven-drying to 50 C. to form a slurried-dried starch. The properties of the slurried-dried starch were determined to be:

TABLE-US-00014 V.sub.5 9,750 mPa .Math. s pH 6.3 tan 0.34

EXAMPLE 7

[0078] A slurry was prepared as in Comparative Experiment G. Five minutes after having been prepared, the pH of the slurry was reduced from 8.0 to 5.9 via the addition of sulphuric acid. After a further resting time of five minutes, during which the slurry was stirred slowly, the slurry was dried in the same way as in Comparative Experiment G. The properties of the slurried-dried starch were determined to be:

TABLE-US-00015 V.sub.5 9,840 mPa .Math. s pH 6.9 tan 0.36

EXAMPLE 8

[0079] Example 6 was repeated, with one difference: instead of adjusting the pH by means of a citrate buffer, the pH of the aqueous phase was adjusted by means of sulphuric acid prior to execution of the slurrying step. The properties of the slurried-dried starch were determined to be:

TABLE-US-00016 V.sub.5 10,100 mPa .Math. s pH 6.3 tan 0.35

COMPARATIVE EXPERIMENT I

[0080] A sample of a rice flour (Remyflo S200, supplier: Beneo-Remy) was brought to a pH of 9.3, then thermally inhibited and subsequently used to form a slurry, using process water as in Comparative Experiment A as aqueous phase. The process water had a pH of 7.8. The weight ratio between aqueous phase and thermally inhibited waxy rice starch was 70:30. The slurry had a pH of 7.6. The slurry was subsequently dried to a moisture content of 8.8 wt. % to form a slurried-dried starch by means of means of filtration under vacuum and further oven-drying to 50 C. The properties of the slurried-dried starch were determined to be:

TABLE-US-00017 21,300 mPa .Math. s pH 8.2 tan 0.46

COMPARATIVE EXPERIMENT J

[0081] The properties of the thermally inhibited rice flour as such, i.e. the raw material as used in Comparative Experiment I without having been subjected to any subsequent process step such as slurrying, were measured. The properties were determined to be:

TABLE-US-00018 28,100 mPa .Math. s pH 7.6 tan 0.40

EXAMPLE 9

[0082] A sample of the same thermally inhibited rice flour as used in Comparative Experiment I was used to form a slurry, however now using a different aqueous phase. The aqueous phase consisted essentially of water, acidified with sulphuric acid to a pH of 2.0. The pH of the slurry was 5.8. The slurry was subsequently dried to a moisture content of 11 wt. % by means of means of filtration under vacuum and further oven-drying to 50 C. to form a slurried-dried starch. The properties of the slurried-dried starch were determined to be:

TABLE-US-00019 V.sub.3 26,900 mPa .Math. s pH 6.2 tan 0.40