阅读说明：本技术 休闲食品丸状物的制造 (Manufacture of snack food pellets ) 是由 詹姆斯·威廉姆斯 马赛尔·欧斯特·因迪尔 卡尔·伊扎特 瑞秋·马林德 于 2018-05-30 设计创作，主要内容包括：一种制造基于淀粉的休闲食品丸状物的方法,其中所述休闲食品丸状物用于制造膨胀休闲食品,所述方法包括步骤：将第一淀粉成分送入烹饪装置中；将机械能和热能输入至所述烹饪装置中,以在所述烹饪装置中烹饪并且糊化所述第一淀粉成分,从而提供经加工的淀粉组分；将包括天然马铃薯淀粉的马铃薯淀粉成分添加至所述经加工的淀粉组分,以提供淀粉混合物；和通过挤压来使所述淀粉混合物成型为丸状物。还揭示了用于制造膨胀休闲食品的基于淀粉的休闲食品丸状物。(A method of making starch-based snack food pellets, wherein the snack food pellets are used to make expanded snack foods, the method comprising the steps of: feeding the first starch component into a cooking device; inputting mechanical and thermal energy into the cooking device to cook and gelatinize the first starch component in the cooking device to provide a processed starch component; adding a potato starch ingredient comprising native potato starch to the processed starch component to provide a starch mixture; and forming the starch mixture into pellets by extrusion. Starch-based snack food pellets for making expanded snack foods are also disclosed.)

1. A method of making starch-based snack food pellets, wherein the snack food pellets are used to make expanded snack foods, the method comprising the steps of:

a. feeding the first starch component into a cooking device;

b. inputting mechanical and thermal energy into the cooking device to cook and gelatinize the first starch component in the cooking device to provide a processed starch component;

c. adding a potato starch ingredient comprising native potato starch to the processed starch component to provide a starch mixture; and

d. the starch mixture is formed into pellets by extrusion.

2. The method of claim 1, wherein the cooking device comprises a mixer.

3. The method according to claim 1 or claim 2, wherein the cooking device is a thermal cooker adapted to input a steam jet into a cooking cavity.

4. A method according to any one of claims 1 to 3, wherein in step b the mechanical energy is provided by mechanical mixing and/or the thermal energy is provided by steam.

5. The method of claim 4, wherein the steam has a temperature of 157 ℃ to 172 ℃ and/or a pressure of 6 bar to 8 bar.

6. The method of any one of claims 1 to 5, wherein, after step b, the processed starch component comprises a cereal starch having a degree of gelatinization of 40% to 80%.

7. The process according to any one of claims 1 to 6, wherein the average molecular weight of the first starch component is reduced during step b.

8. The method of any one of claims 1 to 7, wherein in step a the first starch component comprises or consists of native cereal starch, optionally in combination with one or more of native root starch and native legume starch.

9. The method according to any one of claims 1 to 8, wherein the first starch component comprises 40 to 70 wt% of the starch mixture produced in step c, based on the weight of the starch mixture.

10. Method according to any one of claims 1 to 9, wherein in step c the potato starch component comprises or consists of a first natural potato starch.

11. The method of claim 10, wherein the first natural potato starch comprises 10 to 40 wt% of the starch mixture produced in step c, based on the weight of the starch mixture.

12. The method according to claim 10 or claim 11, wherein in step a, a second native potato starch is input into the cooking device in addition to the first starch component.

13. The method of claim 12, wherein the second native potato starch comprises 10 to 30 wt% of the starch mixture produced in step d, based on the weight of the starch mixture.

14. The method of claim 12 or claim 13, wherein the weight ratio of the first native potato starch and the second native potato starch is from 1:3 to 4: 1.

15. The method of any one of claims 10 to 14, wherein in step c the potato starch component further comprises pregelatinized potato starch.

16. The method of claim 15, wherein the pregelatinized potato starch comprises dehydrated potatoes, optionally in the form of granules and/or flakes.

17. The method of claim 15 or claim 16, wherein the pregelatinized potato starch comprises from 10 to 40 wt% of the starch mixture produced in step c, by weight of the starch mixture.

18. The process according to any one of claims 1 to 17, wherein in step d the starch mixture is mixed and extruded at a temperature in the range of 50 ℃ to 80 ℃ and/or at an absolute pressure of 20 bar to 130 bar.

19. The method of any one of claims 1 to 18, wherein the first starch component comprises a corn component, a wheat component, an oat component, a rice component, or a barley component, or a mixture of any two or more thereof.

20. The method of any one of claims 1 to 19Wherein the bulk density of the pellets is 200kg/m³To 800kg/m³。

21. The method of any of claims 1-20, wherein the moisture content of the pellets is 9 wt% to 13 wt% based on the weight of the pellets.

22. A starch-based snack food pellet produced by the method of any one of claims 1 to 21.

23. A starch-based snack food pellet for the manufacture of expanded snack foods, the pellet comprising a starch matrix formed from a starch mixture, wherein the starch mixture comprises from 40 to 70 wt% gelatinized non-potato starch, from 10 to 40 wt% native potato starch and from 20 to 70 wt% gelatinized potato starch, wherein each wt% is based on the weight of the starch mixture.

24. A starch-based snack food pellet as claimed in claim 23, wherein the moisture content of said pellet is from 9 wt% to 13 wt% based on the weight of said pellet.

25. A starch-based snack food pellet as claimed in claim 23 or claim 24, wherein the non-potato starch comprises or consists of cereal starch, optionally in combination with one or more of root starch and legume starch.

26. The starch-based snack food pellet of claim 25, wherein said cereal starch comprises corn starch, wheat starch, oat starch, rice starch, or barley starch, or a mixture of any two or more thereof.

27. An expanded snack food produced from the starch-based snack food pellet of any one of claims 21 to 26.

28. The expanded snack food of claim 27, which is fried, baked, microwaved, directly extruded, or puffed.

Technical Field

The present invention relates to a method of making starch-based snack food pellets for producing expanded snack foods, a starch-based snack food pellet for producing expanded snack foods, and an expanded snack food produced from the starch-based snack food pellet.

Background

The use of starch-based pellets to produce snack foods, typically in the form of snack food chips, is well known in the art. Pellets were produced by extrusion. In subsequent cooking (e.g., cooking by frying, baking, microwaving, direct extrusion, or popping (popping)), the pellets expand to produce expanded, low-density, porous snack foods.

The pellets contain a high proportion of starch. When subjected to rapid high temperature cooking, it is critical that the starch expand to produce a light and highly porous structure in the expanded snack food that is substantially uniform and substantially avoids the presence of an unexpanded glassy state region.

Many snack food products are produced from pellets having a starch content, which includes a mixture of starches, to provide desired properties in the resulting expanded snack food. For example, many pellets include a significant proportion (up to 100 wt%) of starch in the total starch content. Potato starch can impart unique properties to expanded snack food chips in terms of sensory experience, mouthfeel, crispness (crunchiness), crispness (crispness), degree of expansion, cell size, and cell wall thickness.

When a mixture of starches is used, for example to provide an improved sensory experience, or to provide cheaper pellets using a mixture of potato and non-potato starches or to provide more preferred pellets for the production of an area where no potatoes are native and thus a high proportion of locally sourced ingredients is used, it is possible to combine potato starch with starch from cereals (e.g. wheat, maize, barley, rice etc.) and/or roots (e.g. tapioca or sweet potato) and/or pulses (e.g. peas or beans).

The problem of making pellets from a mixture of potato starch and non-potato starch is: during the manufacture of the pellets, the potato starch is overcooked in order to ensure that the mixture is processed to achieve sufficient processability of the starch so that the starch mixture is sufficiently allowed to expand uniformly during the subsequent expansion process. The effect of such overcooking is that the desired potato characteristics are lost, in whole or in part, in the resulting expanded snack food. In addition, such overcooking can inhibit or prevent the pellets from producing expanded snack foods (e.g., snack food chips) having the desired uniform Light (Light and air) expanded structure desired by consumers.

Disclosure of Invention

The present invention aims to solve the said production problems of the known expanded snack foods produced from pellets having a mixture of potato starch(s) and non-potato starch(s).

Accordingly, the present invention provides a method of making starch-based snack food pellets, wherein the snack food pellets are used to make expanded snack foods, the method comprising the steps of:

a. feeding the first starch component into a cooking device;

b. inputting mechanical and thermal energy into a cooking device to cook and gelatinize a first starch component in the cooking device to provide a processed starch component;

c. adding a potato starch ingredient comprising native potato starch to the processed starch component to provide a starch mixture; and

d. the starch mixture is formed into pellets by extrusion.

Typically, the first starch component comprises or consists of native cereal starch, optionally in combination with one or more of native root (root) (e.g. tapioca or sweet potato) starch and native legume (e.g. pea or bean) starch.

The present invention also provides a starch-based snack food pellet for making expanded snack foods, the pellet comprising a starch matrix formed from a mixture of starches, wherein the mixture comprises from 40 to 70 wt% gelatinized non-potato starch, from 20 to 40 wt% native potato starch and from 20 to 70 wt% gelatinized potato starch, wherein each wt% is by weight of the mixture of starches.

Typically, the non-potato starch comprises or consists of a cereal starch, optionally in combination with one or more of root (e.g. tapioca or sweet potato) starch and native legume (e.g. pea or bean) starch.

The present invention also provides expanded snack foods produced from the starch-based snack food pellets according to the present invention. The expanded snack food may optionally be fried, baked, microwaved, directly extruded, or puffed (popped).

Preferred features of all these aspects of the invention are defined in the dependent claims.

Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a process flow diagram of a method of making starch-based snack food pellets for making expanded snack foods in accordance with an embodiment of the present invention;

FIG. 2 is a schematic side view of an apparatus for performing the process flow of the method of FIG. 1;

FIGS. 3a to 3d are photomicrographs of a cross section through a plurality of pellets having the same starch-based composition, but having different proportions of native potato starch, which were directly processed by the former/extruder and cooking apparatus in the process of FIG. 1;

fig. 4 is a bar graph showing the relationship between enthalpy during starch gelatinization tests for multiple pellet compositions having a starch-based composition, but with different proportions of native potato starch, which were directly processed by the former/extruder and cooking apparatus in the method of fig. 1.

Fig. 5 is a graph showing the relationship between heat flow and temperature during starch gelatinization tests of a plurality of pellet compositions having a starch-based composition, but with different proportions of native potato starch, which were directly processed by the former/extruder and cooking apparatus in the method of fig. 1.

Detailed Description

Referring to fig. 1, there is shown a schematic process flow diagram of a method of making starch-based snack food pellets for use in making expanded snack foods in accordance with a preferred embodiment of the present invention. Fig. 2 schematically shows an apparatus used in the method of fig. 1.

As shown in fig. 1 and 2, in a first step 2 of the method, a first starch component 4 is fed into a cooking device 6. The first starch component comprises or preferably consists of native starch. Preferably, the first starch component comprises or consists of native cereal starch, optionally in combination with one or more of native root starch (e.g. tapioca or sweet potato starch) and native legume starch (e.g. pea or bean starch). Generally, the cooking device 6 is a mixer with input for thermal and mechanical energy, or a thermal cooker suitable for the input of steam jets into the cooking cavity. Both of these devices are well known in the snack food pellet manufacturing art.

In a second step 10, mechanical and thermal energy is introduced into the cooking device 6 in order to cook and gelatinize the first starch component 4 in the cooking device 6. The mechanical energy is provided by mechanical mixing. The heat energy is provided by steam. Preferably, both mechanical mixing and steam are applied to the first starch component 4. In generalIn other words, by using 40s^-1To 100s^-1The shear rate of (a) mixes the cereal starch component 4 to provide mechanical energy. Typically, the steam has a temperature of 157 ℃ to 172 ℃ and/or a pressure of 6 bar to 8 bar. This step 10 provides a processed starch component 12.

Generally, the processed cereal starch component 12 comprises cereal starch in which 40 to 80 wt% of the cereal starch has been gelatinized, as measured by an enzymatic method (e.g., Kansas method, as is known in the art). During step 10, the average molecular weight of the native starch is reduced. After step 10, the native starch in the processed starch component 12 typically has a viscosity of from 100pa.s to 150pa.s and/or a melting point below 150 ℃, e.g. a melting point of from 50 ℃ to 100 ℃, as measured by Differential Scanning Calorimetry (DSC).

Thereafter, in a third step 20, a native potato starch component 22 is added to the processed cereal starch component 12 to provide a starch mixture 24. The potato starch component 22 comprises or, preferably, consists of a first native potato starch 26. The addition can be made within the cooking device 6 or outside the cooking device 6, but the potato starch component 22 is not processed as described for the first starch component 4 within the cooking device 6.

Before the ingredients 12 and 22 begin to extrude/form, preferably during the mixing step 38, the ingredients 12 and 22 are mixed with water in a mixer 36 (e.g., a paddle mixer) to form a starch/water mixture having a moisture content of 30-50 wt% based on the total weight of the starch/water mixture.

Finally, in a fourth step 30, the starch mixture 24 is formed into pellets 32 by extrusion in a former/extruder 34. Typically, the starch mixture 24 is mixed and extruded at a temperature in the range of 50 ℃ to 80 ℃ and/or at a pressure of 20 bar to 130 bar. In general, 3000s in the screw/barrel region of a screw extruder^-1-5000s^-1And in the die of the extruder for 500s^-1-700s^-1The shear rate of (a) and extruding the starch mixture.

After the fourth step 30, the bulk density (bulk density) of the pellets 32 is typically 200kg/m³To 800kg/m³. Preferably, the water content of the pellets is from 9 wt% to 13 wt% based on the weight of the pellets.

With respect to the starch mixture in the pellet 32, the pellet 32 comprises 40 to 70 wt% gelatinized non-potato starch (e.g., cereal starch) derived from the first starch component 4, 10 to 40 wt% native potato starch, and 20 to 70 wt% gelatinized potato starch, per wt% by weight of the starch mixture.

According to the illustrated embodiment of the invention, in the first step 2, a second native potato starch 8 is fed into the cooking device 6 in addition to the further cereal starch component 4. Typically, the second native potato starch 8 comprises 10 to 30 wt% of the starch mixture produced in the fourth step 30, by weight of the starch mixture. When a second native starch 8 is used, the first native potato starch 26 and the second native potato starch 8 are provided from a common source and the first native potato starch 26 and the second native potato starch 8 are distributed between downstream and upstream of addition to the cooking device 6, respectively, and the weight ratio of the first native potato starch 26 to the second native potato starch 8 is from 1:3 to 4: 1.

Furthermore, according to the illustrated embodiment of the invention, in the third step 20, the potato starch composition 22 further comprises a pregelatinized potato starch 28. Pregelatinized potato starch typically comprises dehydrated potatoes (e.g., in the form of potato granules and/or potato flakes), but can also be present in the form of a powder or ground flour. The pregelatinized potato starch 28 can be added to the former/extruder 34 or the mixer 36.

The starch-based snack food pellets 32 produced by the method include a starch matrix formed from a starch mixture. According to an illustrative embodiment of the invention, the starch matrix comprises, wherein each wt% is based on the weight of the starch mixture:

40wt% to 70 wt% gelatinized non-potato starch which is produced from the first starch component 4 and which has been cooked and gelatinized in the cooking device 6;

10 to 40 wt% of native potato starch which is provided by the first native potato starch 26 downstream of the cooking device 6 and which is therefore not gelatinized in the cooking device and which is still substantially crystalline; and

c.20wt% to 70 wt% of gelatinized potato starch produced from the combination of second native potato starch 8 added to cooking device 6 and gelatinized in cooking device 6 and pregelatinized potato starch 28 added to former/extruder 34 downstream of cooking device 6.

When the first native potato starch 26 and the second native potato starch 8 have been added as described above (typically with respect to the starch mixture in the pellet 32) and have been produced in the fourth step 30, the starch mixture comprises 40 to 70 wt% of gelatinized non-potato starch (e.g. cereal starch) derived from the first starch component 4, 10 to 40 wt% of native potato starch derived from the first native potato starch, 10 to 30 wt% of first gelatinized potato starch derived from the second native potato starch and 10 to 40 wt% of second gelatinized potato starch derived from the pre-gelatinized potato starch per wt% by weight of the starch mixture.

The pellets 32 may be used to prepare expanded snack foods by frying, baking, microwaving, and popping. Each of these pellet expansion methods is known per se to those skilled in the art of snack food manufacture.

The present invention is based, at least in part, on the inventors' discovery that: when different starches are processed to form starch-based snack food pellets, the various starches tend to have different natural starting properties prior to processing to form the pellets, different processing parameters used to form the pellets, and different material and structural properties in the resulting pellets, which are reflected in the properties of the resulting expanded snack food.

In particular, native potato starch tends to gelatinize readily when subjected to heat and moisture as compared to native cereal starch, and native potato starch is often used as an initial ingredient in the extrusion of pellets in pre-gelatinized form. When native potato starch is subjected to thermal energy/low shear mechanical extrusion, the molecular weight of the potato starch is substantially retained. Potato starch tends to have a relatively low melting point and therefore when the starch is subjected to elevated cooking temperatures (e.g. in a fryer), the potato starch undergoes a material transformation, especially melting, to provide a starch melt which provides some degree of expansion. Potato starch melt provides a characteristic combination of cellular void (cellular void) size, shape and distribution, and cell wall thickness, which provides typical organoleptic properties to expanded snack foods containing high concentrations of potato starch.

Conversely, some non-potato native starches (e.g., native cereal (or legume or root) starches) tend to gelatinize to a lesser degree than native potato starch when subjected to the same heat and moisture conditions as native potato starch when compared to native potato starch. In particular, native cereal starches tend to require high thermal energy/high shear mechanical extrusion compared to native potato starch in order to provide the corresponding proportion of gelatinized starch. Molecular weight of native cereal starch is typically compromised (e.g., significantly reduced) by high shear mechanical extrusion. During frying, the processed low molecular weight cereal starch melts and exhibits a low viscosity, which provides a high degree of expansion. This results in a very light, swollen texture with large cellular voids and thin cell walls. If there is a relatively high melting point native cereal starch in the pellet, it is likely that the starch will not melt when subjected to elevated cooking temperatures (e.g., in a fryer), which may leave unexpanded starch in the snack food, which is undesirable.

When both native potato starch and native cereal starch are used together as ingredients for producing pellets for subsequent expansion to form snack foods, it is difficult to process the ingredients to provide the resulting typical organoleptic properties, i.e., the characteristic combination of cellular void size, shape and distribution, and cell wall thickness associated with high viscosity potato starch melt, to an expanded snack food containing a high concentration of potato starch. It is difficult to process a mixture of potato starch and cereal starch in a conventional sequence of manufacturing steps, so that a composite starch melt can be provided which, when expanded, provides a controlled and uniform porous microstructure and in particular a uniform target combination of cellular void size, shape and distribution, and cell wall thickness.

These different manifestations of potato starch and non-potato starch have been exploited in the process of the present invention to achieve the desired control over starch processing of the mixture of potato starch and non-potato starch used to form the pellets. The properties of the pellets can be easily controlled and thus the properties of the resulting expanded snack food produced from the pellets can be controlled.

According to a preferred embodiment of the invention, the pellets are produced from a mixture of cereals (or one or more selected from cereals and/or pulses, or a combination of one or more cereals and/or pulses) and potatoes. At least a portion of each starch ingredient class may be processed separately and separately from at least a portion of the other starch ingredient class, then combined into a starch mixture, and then the starch mixture co-extruded. This overcomes the problem of some native starches (e.g. native starches from cereals or legumes) requiring much higher cooking than native potato starch to pre-process their starch components prior to extrusion, and the problem of the potato portion tending to be overcooked if the cereal portion is processed right away, thereby losing desirable potato characteristics in the final expanded snack food product if the starch mixture comprising potato starch and non-potato starch is cooked as a whole.

According to a preferred embodiment of the present invention, the different starch ingredients may be processed separately and separately during cooking and then combined together prior to extrusion and shaping of the product, as opposed to using conventional cooking and extrusion processes to process the entire starch-containing formulation, which may result in under-cooking at least one of the starch components and/or overcooking at least one of the other starch components, with the result having an adverse effect on the quality of the snack food.

The inventors have found that the individual processing of multiple starch ingredients or groups of starch ingredients can provide better control over the properties of the resulting snack food. In a particularly preferred embodiment of the method of the invention, better control of the product quality and performance of the expanded snack food produced from the pellets can be achieved by adding to a standard pellet production line comprising an extruder a mixer with thermal and mechanical energy input and/or a hot cooker adapted to input steam jets to the cooking chamber.

The pellets are produced by a process in which a first starch component (the first starch component comprising or consisting of, for example, cereal starch) is processed in a cooking device to which mechanical and thermal energy is input to cook and gelatinize the cereal starch component in the cooking device to provide a processed cereal starch component. Thereafter, a native potato starch ingredient is added to the processed cereal starch component to provide a starch mixture, which is then formed into pellets by extrusion. Native potato starch is not cooked but formed into pellets by extrusion and the starch remains as starch granules in the extruded pellets and thus has virtually no change in crystallinity and retains a high molecular weight. In the pellet, native potato starch provides localized crystalline regions distributed within the amorphous starch and/or minimally crystalline starch formed from the cooked and gelatinized cereal/potato starch.

Some or all of the total native potato starch is fed directly into the former/extruder and, optionally, a proportion of the total native potato starch may be fed into the cooking apparatus. By controlling the proportion of native potato starch directly fed to the former/extruder, the microstructure of the resulting starch blend in the pellet can be controlled to provide the desired properties in the resulting expanded snack food. For the total native potato starch provided for pellet formation, greater than 0 and up to 100 wt% of the total native potato starch is fed directly into the former/extruder and 0 to less than 100 wt% of the total native potato starch is fed into the cooking apparatus.

Fig. 3 a-3 d are photomicrographs of a cross-section through a plurality of pellets having the same starch-based composition, but with different proportions of native potato starch, which were directly processed by a former/extruder and by a cooking apparatus in the process of fig. 1.

In fig. 3a, 100 wt% native potato starch is processed directly by the former/extruder and 0% native potato starch is processed by the cooking device. The resulting microstructure has a high level of potato crystallinity and minimal cereal starch crystallinity, with a plurality of crystalline potato starch regions 50 distributed within the amorphous cereal/potato starch 52. This microstructure is characteristic of potato starch pellets.

In fig. 3d, 0% native potato starch is processed directly by the former/extruder and 100 wt% native potato starch is processed by the cooking device. The resulting microstructure has minimal crystallinity of potato starch, and some crystallinity of cereal starch, and the resulting structure is a substantially low crystalline and amorphous microstructure 54 of a substantially uniform low crystalline composition. During processing in the cooking device, the potato starch is preferentially dehydrated and gelatinized as compared to the cereal starch, leaving regions 56 of low level of crystallinity of the cereal starch within the generally amorphous cereal/potato starch blend 58.

In fig. 3b, 67 wt% native potato starch is processed directly by the former/extruder and 33 wt% native potato starch is processed by the cooking device. In fig. 3c, 20 wt% native potato starch is processed directly by the former/extruder and 80 wt% native potato starch is processed by the cooking device. These micrographs show that by gradually decreasing the proportion of native potato starch processed directly by the former/extruder and gradually increasing the proportion of native potato starch processed by the cooking apparatus, the crystallinity of the potato starch is decreased, which changes the texture and properties of the pellets during expansion.

Fig. 4 is a bar graph showing the relationship between enthalpy during starch gelatinization tests for a plurality of pellet compositions having a starch-based composition, but with different proportions of native potato starch, which were directly processed by a molder/extruder and by a cooking apparatus in the method of fig. 1. When heating starch in the presence of water, heat is required to effect the conversion of the starch if the starch is gelatinized. In fig. 4, for the bar labeled a, all native cereal starch and native potato starch have been processed by the cooking device, and thus the starch has been gelatinized. When the pellets were tested by heating in the presence of excess water, there was minimal further starch gelatinization and the measured enthalpy was low. In contrast, for the bar labeled D, all native cereal starch and 33 wt% native potato starch were processed by the cooking apparatus and 67 wt% native potato starch was added directly to the input port of the former/extruder and thus most of the native potato starch was crystalline in the pellet. When the pellets were tested by heating in the presence of water, there was significant further starch gelatinization from native potato starch, and the measured enthalpy from the starch conversion was high, and the measured enthalpy from the cereal starch was small. For the bars labeled B and C, 50 wt% or 66 wt% native potato starch was processed by the cooking device and 50 wt% or 33 wt% native potato starch was added directly to the input port of the former/extruder and, in each case, all native cereal starch was processed by the cooking device, respectively. For these figures, about half or a small portion of the native potato starch in the pellet is crystalline. When the pellets were tested by heating in the presence of water, further starch gelatinization from native potato starch was progressively reduced, and the measured enthalpy from the starch conversion was progressively reduced, and the measured enthalpy from the cereal starch was small, compared to bar D.

Fig. 5 is a graph showing the relationship between heat flow and temperature during starch gelatinization tests of multiple pellet compositions having a starch-based composition, but with different proportions of native potato starch, which were directly processed by the former/extruder and cooking apparatus in the method of fig. 1. When heating starch in the presence of water, heat is required to effect the conversion of the starch if it is gelatinised, and the gelatinisation of the starch is indicated by peaks in the heat flow. In fig. 5, for the curve labeled a, all native cereal starch and native potato starch have been processed by the cooking device, and thus the starch has been gelatinized. When the pellets were tested by heating in the presence of water, there was minimal further starch gelatinization and at relatively high temperatures (above 80 ℃) there was a very small peak in the heat flow indicative of cereal starch gelatinization. In contrast, for the curve labeled D, all native cereal starch and 33 wt% native potato starch were processed by the cooking apparatus and 67 wt% native potato starch was added directly to the input port of the former/extruder and thus most of the native potato starch was crystalline in the pellet. When the pellets were tested by heating in the presence of water, there was significant further starch gelatinization from native potato starch, and at relatively low temperatures (below 80 ℃), there was a large peak in the heat flow indicative of potato starch gelatinization, and at relatively high temperatures (above 80 ℃), there was little peak in the heat flow indicative of cereal starch gelatinization, since gelatinization of potato starch occurred in preference to gelatinization of cereal starch. For the curves labeled B and C, 50 wt% or 66 wt% native potato starch was processed by the cooking device and 50 wt% or 33 wt% native potato starch was added directly to the input of the former/extruder and, in each case, all native cereal starch was processed by the cooking device, respectively. For these curves, about half or a small portion of the native potato starch is crystalline in the pellet. When these pellets were tested by heating in the presence of water, the peak indicating potato starch gelatinization gradually decreased in the hot stream at a relatively low temperature (below 80 ℃) and still almost no peak indicating grain starch gelatinization in the hot stream at a relatively high temperature (above 80 ℃) compared to curve D.

When cooking the pellets, the starch component of the starch mixture is heated during the expansion phase. High molecular weight and high crystalline native potato starch melts to form a high viscosity melt, and low molecular weight and amorphous or low crystalline gelatinized cereal/potato starch melts to form a low viscosity melt. The water in the starch evaporates to form steam, which in turn forms cellular voids or pores. A high viscosity melt tends to provide low expansion resulting in a uniform distribution of small cellular voids with thick cell walls, whereas a low viscosity melt tends to provide high expansion resulting in a less uniform distribution of large cellular voids with thin cell walls. The crystalline regions have a high glass transition temperature Tg and tend to reduce the collapse and coalescence of bubbles.

When there is a mixture of high and low crystallinity starches in the pellet, the ratio of crystalline starch and amorphous/low crystallinity starch blend can be varied to vary the resulting expanded microstructure. This can be achieved by gelatinizing the native cereal starch in the cooking device and selecting the proportion of native potato starch added in a different way, wherein the native potato starch is either added as input to the cooking device so as to be gelatinized in the cooking device or is added to the output of the cooking device so as to still be present as crystalline starch in the pellets. Thus, the starch crystallinity in the pellet and the cell structure in the expanded snack food can be altered independently of the conversion of the cereal starch in the cooking device.

Thus, the starch matrix in the pellet of the preferred embodiment of the present invention comprises a relatively crystalline first starch composition consisting essentially of, or consisting only of, native potato starch and a relatively amorphous second starch composition comprising cereal starch and optionally potato starch, the amorphous starch component being more amorphous than the crystalline starch component and the crystalline starch being more crystalline than the amorphous starch component, the amorphous and crystalline starches having been blended together to form the starch matrix. The first starch composition typically comprises 10 wt% to 40 wt% based on the weight of the starch substrate, and the second starch composition typically comprises 10 wt% to 30 wt% based on the weight of the starch substrate.

Various modifications of the invention will be readily apparent to those skilled in the art.