JP7521771B2 - Fine rice flour, its manufacturing method and its uses - Google Patents

Description

The present invention relates to fine rice flour, its manufacturing method, and its uses.

Increasing demand for rice flour as an alternative ingredient to wheat flour has become an issue, and with regard to rice flour bread, a lot of knowledge has been found, such as rice flour with a small particle size and damaged starch content being well suited for bread making, and the demand for rice for rice flour has been on the rise since 2003. However, as growth has been sluggish, remaining at around 20,000 tonnes recently, it is important to develop high-added-value applications other than rice flour bread and increase demand for rice flour overall.

Rice flour for frying has been commercialized as a coating material made by puffing and grinding raw rice (see, for example, Patent Document 1), as well as fine-grained rice flour and premixes with reduced starch damage. However, the former technology requires a puffing process for the raw rice before grinding, while the latter technology requires water absorption and drying processes before and after grinding, which creates a problem of complicated manufacturing processes.

Regarding fine rice flour, for example, Non-Patent Document 1 publishes findings on the damaged starch content and dough properties of fine rice flour produced using a jet stream mill, but does not mention the effects on batter viscosity or the texture of fried foods.

JP 2012-39896 A

Seiko Naganuma, Bulletin of the Faculty of Education and Culture, Akita University, Natural Sciences, Vol. 58, pp. 29-35, 2003

The objective of the present invention is to provide a new use for fine rice flour and to provide a technology for controlling the viscosity of batters for fried foods and the texture of fried foods.

The inventors therefore investigated milling methods and processing suitability of rice flour suitable for frying, and found that fine rice flour that has been pulverized to an average particle size of less than 40 μm and has a damaged starch content of 15% by mass or more is effective in improving the viscosity of batter for fried foods and the texture of fried foods. Based on this knowledge, the inventors have completed the present invention.

The present invention relates to fine rice flour characterized by an average particle size of less than 40 μm and a damaged starch content of 15% by mass or more, granules made of said fine rice flour, mixed flour containing them, and fried foods or rice flour processed foods containing them.

The present invention also relates to a method for producing fine rice flour, fried food, or rice flour processed food, which includes a step of grinding raw rice that is not gelatinized and has a moisture content of 20% by mass or less, and is characterized by preparing fine rice flour having an average particle size of less than 40 μm and a damaged starch content of 15% by mass or more.

The present invention further relates to a method for controlling the viscosity of batter or dough for fried foods using the fine rice flour, granules or mixed flour according to the present invention, and a method for controlling the texture of fried foods or rice flour processed foods.

The present invention provides a new use for fine rice flour and a technology for controlling the viscosity of batters for fried foods and the texture of fried foods. Specifically, batters and doughs for fried foods made with fine rice flour having a specific particle size and specific damaged starch content can be widely controlled in viscosity at lower concentrations than with conventional coarse rice flour, which is expected to improve workability in the frying process and reduce the amount used. In terms of texture, it becomes possible to produce fried foods with a crispier, lighter texture than with conventional rice flour.

1 is a graph showing the relationship between damaged starch content and average particle size in rice flours prepared by dry milling in Example 1 and Comparative Examples 1 and 2. The vertical axis shows damaged starch content (unit: mass%), and the horizontal axis shows average particle size (unit: μm). 1 is a graph showing the relationship between the concentration of batter liquid and the viscosity after 1 minute of stirring using rice flour of Example 1 and Comparative Examples 1, 2, and 3. In the figure, ▲ indicates Example 1, ◆ indicates Comparative Example 1, and ■ indicates Comparative Example 2. The vertical axis indicates viscosity (unit: cP), and the horizontal axis indicates rice flour concentration (unit: mass%). 1 is a graph comparing the viscosity of various batter liquids after stirring for 5 minutes. In the graph, from the left, Examples 2, 3, 4, 5, and 6, Comparative Examples 5 and 6, and commercially available weak flour are shown for each concentration, and the vertical axis indicates viscosity (unit: cP). 4 is a graph showing the relationship between the mixing ratio of fine rice flour in the mixed flour and the viscosity of the batter liquid after stirring for 5 minutes. Fig. 4(a) shows the results for the mixed flour of Example 7, and Fig. 4(b) shows the results for the mixed flour of Example 8. In each figure, the horizontal axis shows the mixing ratio of fine rice flour (mass%), and the vertical axis shows the viscosity (unit: Pa s). 5 is a graph comparing the compressive stress values of fried dumplings made using rice flour in Examples 9 and 10 and Comparative Examples 7 to 10. In Fig. 5, from the left, Example 9, Comparative Examples 7 and 8, Example 10, Comparative Examples 9 and 10, and commercially available weak flour are shown, and the vertical axis indicates the compressive stress value (unit: kPa). 6 is a graph comparing the adhesion of batters using rice flour of Examples 9 and 10 and Comparative Examples 7 to 10 to ingredients. Fig. 6(a) shows the results for a batter with a rice flour concentration of 30% by mass, and Fig. 6(b) shows the results for a batter with a rice flour concentration of 20% by mass. In each figure, from the left, Example 9, Comparative Examples 7 and 8, Example 10, Comparative Examples 9 and 10, and commercially available weak flour are shown, and the vertical axis shows the weight difference (unit: g) of the ingredients before and after adhesion.

Hereinafter, an embodiment of the fine rice flour of the present invention will be described in detail.
The fine rice flour of the present embodiment is characterized by an average particle size of less than 40 μm and a damaged starch content of 15 mass% or more.

The fine rice flour of this embodiment has an average particle size of less than 40 μm, preferably 2 μm to less than 40 μm, more preferably 2 to 35 μm, and even more preferably 2 to 30 μm. If the average particle size is larger than the above range, it is not preferable because when it is used in a batter, the viscosity does not increase, especially at low concentrations. The average particle size can be measured in a dry state using a particle size distribution measuring device that uses the laser diffraction/scattering method (for example, the product name "LS13320" manufactured by Beckman Coulter, Inc.).

The damaged starch content of the fine rice flour of this embodiment is 15% by mass or more, preferably 15 to 90% by mass, more preferably 17 to 80% by mass, and even more preferably 20 to 70% by mass. If the damaged starch content is lower than the above range, the rice flour will have poor dispersibility when suspended in water, and the rice flour will be more likely to settle, and the viscosity will not increase easily when used in a batter, which is not preferable. The damaged starch content can be measured using a commercially available damaged starch measurement kit (for example, the product name "K-SDAM", manufactured by Megazyme Co., Ltd.).

As a raw material for fine rice flour, any raw rice that has not been gelatinized (gelatinized) can be used, regardless of whether it is non-gelatinized (gelatinized) rice, non-glutinous rice, germinated rice, or variety, but non-glutinous rice is particularly suitable. In addition, it can be used regardless of the polishing ratio, and any of the following rice types may be used: brown rice, white rice (polishing ratio 92% or less), partially polished rice such as 70% polished rice, 50% polished rice, and 30% polished rice (polishing ratio between 92% and 100%).

The above-mentioned raw material may be rice with a general moisture content of 12 to 16% by mass, which may be used as is, or may be rice that has been pretreated by washing, absorbing water, drying, heat sterilization, etc. If pretreatment such as washing or absorbing water is performed, the moisture content of the raw material must be adjusted to 20% by mass or less before grinding. This is because if the moisture content exceeds 20% by mass, the damaged starch content of the rice flour cannot be sufficiently increased. There are no particular limitations on the means of moisture adjustment, and any conventional method may be used.

Next, an embodiment of the granules of the present invention will be described.
The above fine rice flour may be used as it is in the manufacture of fried foods and the like, or may be granulated and used as granules. By forming it into granules, it becomes easier to handle as it is less likely to form lumps. There are no particular limitations on the granulation method, and granulation can be performed by known methods such as fluidized bed granulation and extrusion granulation. In addition to the fine rice flour, general materials can be blended into the granules depending on the granule manufacturing method and application. For example, granulation promoters (binders) such as starch and polysaccharides can be mentioned.

Further, an embodiment of the mixed powder of the present invention will be described.
The fine rice flour of the present embodiment may be used alone or as a mixed flour containing other grain flour components. As the "other grain flour components", general materials can be used according to the purpose of the mixed flour. For example, in the case of a mixed flour for batter liquid of fried foods, examples of the ingredients include rice flour that is outside the above-mentioned range of average particle size and damaged starch content, wheat flour (strong flour, weak flour, medium flour, whole wheat flour, etc.), corn flour, soy flour, barley flour, leavening agent, starch such as potato starch, dextrin, vegetable protein, dietary fiber, oils and fats, salt, sugar, processed starch, emulsifier, egg powder, thickening polysaccharide, seasonings, spices, flavorings, vitamins, minerals, etc., and one or more of these can be optionally contained.

In particular, by mixing fine rice flour with rice flour that falls outside the above average particle size range, the viscosity of the batter can be increased, making it possible to adjust the viscosity and texture over a wide range using only rice flour. In addition, in the cooking process for deep-fried foods, it is possible to improve workability by making it easier for the batter to adhere to the ingredients, and it is expected that the texture after deep-frying will be improved, such as making the food crispy and soft. The content ratio of ingredients other than fine rice flour can be 1 to 90% by mass, with the entire mixed flour being 100% by mass.

Further, an embodiment of the food product of the present invention will be described.
The above-mentioned fine rice flour, granules and mixed flour (hereinafter sometimes referred to as "fine rice flour, etc.") can be used to produce foods containing rice flour or other cereal flours, such as fried foods and rice flour processed foods. Fried foods include, for example, tempura, kakiage, fritters, nuggets, fried chicken, croquettes, etc. Rice flour processed foods include, for example, Japanese sweets, Western sweets, fried sweets, etc., but are not limited to these. These foods produced using fine rice flour, etc., have an unprecedented crispy and light texture in the case of fried foods, and an unprecedented extremely smooth texture in the case of rice flour processed foods. In addition, the viscosity of the batter liquid can be increased at a lower concentration than when using general commercially available coarse grain rice flour or other cereal flours, so the amount of raw materials used can be reduced.

Further, an embodiment of the viscosity control method of the present invention will be described.
The above-mentioned fine rice flour etc. can be used to control the viscosity of batter liquid or dough for fried foods. That is, when preparing batter liquid for fried foods or dough for rice flour processed foods by adding water to the above-mentioned fine rice flour etc., the viscosity of the batter liquid or dough can be widely controlled by making the concentration of the fine rice flour 20% by mass or more. That is, when the rice flour concentration is 20% by mass or more, the rate of increase in the viscosity of the batter liquid or dough with an increase in concentration is higher for fine rice flour than for coarse rice flour.

For this reason, by mixing coarse grain rice flour with fine grain rice flour, a highly viscous batter can be easily prepared using only the rice flour even at a low concentration, which is expected to result in improved workability during the frying process, such as better adhesion of the rice flour batter to ingredients (batter made with coarse grain rice flour tends to have rice flour settle and has low viscosity, so adhesion is poor and workability is poor). Also, when it comes to dough for rice flour processed foods, by mixing fine grain rice flour, it is possible to create a dough with a higher viscosity at a lower concentration than with coarse grain rice flour.

Further, an embodiment of the food texture control method of the present invention will be described.
The above-mentioned fine rice flour, etc. can be used to control the texture of fried foods or rice flour processed foods. That is, when preparing fried foods or rice flour processed foods using the above-mentioned fine rice flour, etc., the texture of the fried foods or rice flour processed foods can be widely controlled by changing the mixing ratio of coarse grain rice flour and fine rice flour. As a specific example, it has been found that fried foods produced using fine rice flour, etc. have a penetration hardness reduced to 1/3 or less compared to fried foods using commercially available rice flour, and have a light and crispy texture, and it is expected that rice flour processed foods will also have a similar smooth texture. The higher the concentration of fine rice flour, the lighter and softer the texture of fried foods will be, and the smoother the texture of rice flour processed foods will be.

Next, an embodiment of a method for producing fine rice flour will be described.
The manufacturing method of this embodiment is characterized by including a step of grinding raw rice that has not been gelatinized (gelatinized) and has a moisture content of 20% by mass or less, and preparing fine rice flour with an average particle size of less than 40 μm and a damaged starch content of 15% by mass or more. Here, the raw material "ungelatinized raw rice" and the pretreatment before grinding are as described above.

[Crushing process]
In this embodiment, the pulverization may be performed by any method, such as dry or wet, as long as fine rice flour having the above-mentioned average particle size and damaged starch content is obtained, but dry pulverization is preferred. Dry pulverization is a method of pulverizing raw rice having a moisture content of about 12 to 16% by mass as is. There are no particular limitations on the means used for dry pulverization as long as it is capable of pulverizing the rice into fine particles, and examples of such means include airflow pulverizers (jet mills, etc.) and mechanical impact pulverizers (hammer mills, etc.). On the other hand, wet pulverization is a method of immersing rice in water, etc., to absorb water, and then pulverizing the rice. There are no particular limitations on the means used for wet pulverization as long as it is capable of pulverizing the rice into fine particles, and examples of such means include airflow pulverizers (jet mills, etc.).

The grinding conditions may be any conditions that ultimately produce fine rice flour with an average particle size of less than 40 μm and a damaged starch content of 15% by mass or more. In dry grinding, grinding to an average particle size within the above range will produce fine rice flour with a damaged starch content generally within the above range. On the other hand, in the case of wet grinding, in order to increase the damaged starch content, it is necessary to allow the raw rice to absorb water and then adjust the moisture content to 20% by mass or less before grinding. Note that classification (sieving) may be performed after grinding, and rice flour with large particle sizes may be repeatedly ground or removed to reduce the average particle size and satisfy the above conditions.

The fine rice flour produced as described above may be used as is for the production of fried foods, etc., or may be used as granules produced by known methods as described above. Also, as described above, it may be used as a mixed flour containing other grain flour ingredients.

Furthermore, an embodiment of a method for producing fried foods or rice flour processed foods will be described.
As described above, the above-mentioned fine rice flour, etc. can be used in the production of foods containing rice flour or other cereal flours, such as fried foods and rice flour processed foods. These foods can be produced by known methods, except that all or part of the rice flour or other cereal flour is replaced with the fine rice flour, etc. As described above, batter liquids and doughs prepared using the fine rice flour, etc. have a significantly increased viscosity even at low concentrations, so that the amount of raw material used can be reduced compared to the case of using conventional rice flour or other cereal flours.

For example, in a method for producing fried foods, water is first added to the fine rice flour or the like and the mixture is stirred to prepare a batter. The resulting batter is then applied to any food material and fried in oil to obtain fried foods. There are no limitations on the concentration of fine rice flour in the batter, but if conventional rice flour or other grain flour is not used, a concentration of 20% by mass or more can be used to obtain a batter with the desired viscosity. In addition, if conventional rice flour or other grain flour is mixed with the fine rice flour, it is preferable that the concentration of fine rice flour in the entire batter be 5% by mass or more.

Batters containing fine rice flour have the advantage of being more dispersible than those using conventional rice flour. For example, when coarse rice flour is used in batters, the rice flour tends to settle, but fine rice flour, especially rice flour pulverized in a jet mill with an average particle size of around 10 μm and a damaged starch content of 15% by mass or more, has good dispersibility and is less likely to settle. In addition, because it has high water absorption, the viscosity of the batter increases easily even at low concentrations, and it is believed that the high viscosity can be maintained for a longer period of time than with coarse rice flour.

In addition, in a method for producing rice flour processed foods (e.g., fried snacks), first, the fine rice flour or the like is mixed with water and kneaded to prepare a dough. Next, the dough is shaped and boiled, steamed, or the like, and then fried in oil to produce fried snacks. The concentration of fine rice flour in the dough is not limited, but if conventional rice flour or other grain flour is not used, a dough with a higher viscosity than conventional rice flour can be produced with, for example, 20% by mass or more. In addition, if a flour is mixed with conventional rice flour or other grain flour, it is preferable that the concentration of fine rice flour in the entire dough be 5% by mass or more.

The following examples are provided to specifically explain the embodiments of the present invention, but the present invention is not limited to these examples.

[Example 1 and Comparative Examples 1 to 4]
The polished rice used was Koshihikari brown rice polished to a polishing ratio of about 91% (water content about 14% by mass). The polished rice was dry-pulverized as it was using a hammer mill (Yoshida Seisakusho Co., Ltd., 1018-S-3), a type of mechanical impact crusher, to an average particle size of about 120 μm and 170 μm, respectively, to prepare the rice flours of [Comparative Example 1] and [Comparative Example 2]. The polished rice was dry-pulverized using a jet mill (Nippon Pneumatic Mfg. Co., Ltd., IDS-2), a type of airflow crusher, to prepare the rice flour of [Example 1]. Commercially available rice flour (joshinko) and wheat flour (weak flour) were used as [Comparative Example 3] and [Comparative Example 4], respectively.

The average particle size, moisture content, and damaged starch content of these powders were measured and compared. The average particle size was measured in dry conditions using a particle size distribution analyzer (product name "LS13320", manufactured by Beckman Coulter) that uses the laser diffraction/scattering method. The moisture content was measured using the normal pressure heat drying method (135°C, 1 hour). The damaged starch content was measured using a damaged starch measurement kit (K-SDAM, manufactured by Megazyme).

The results are shown in Table 1 and Figure 1. Figure 1 is a graph showing the relationship between the damaged starch content and average particle size in the rice flours of Example 1 and Comparative Examples 1 and 2, which were prepared by dry milling. The vertical axis shows the damaged starch content (unit: mass%), and the horizontal axis shows the average particle size (unit: μm).

The damaged starch content of the three types of dry-milled rice flour increased with a decrease in average particle size. Furthermore, the rice flour of [Example 1] milled using a jet mill was the finest (average particle size: 12 μm) and had the highest damaged starch content (23.8% by mass). It was confirmed that with dry milling, if the rice flour is milled so that its average particle size is approximately 150 μm or less, the damaged starch content can be increased to 10% by mass or more. It is estimated that the damaged starch content can be increased to 10% by mass or more even if the average particle size is adjusted to 150 μm or less by classification (sieving) after dry milling.

Figure 1 shows that there is a high negative correlation ( ^R2 = 0.999) between the average particle size of dry-milled rice flour and the damaged starch content, suggesting that in order to obtain rice flour with a damaged starch content of 20% or more by mass, the average particle size should be adjusted to approximately 50 μm or less, and that in order to obtain rice flour with a damaged starch content of 15% or more by mass, the average particle size should be adjusted to approximately 100 μm or less.

Next, batters for fried foods were prepared at the concentrations shown in Table 2 using the above powders, and the viscosities were compared. The above powders were added to 25 g of water to give a dry weight ratio of 10 to 30% by mass, and the viscosity of the batters was measured using a Rapid Visco Analyzer (Newport Scientific, model: RVA-4) while stirring at 25°C for 30 minutes (stirring at 960 rpm for 10 seconds, followed by stirring at 160 rpm until the end of the measurement).

The results are shown in Table 2 and Figure 2. Figure 2 is a graph showing the relationship between the rice flour concentration of batter liquid using the rice flours of Example 1 and Comparative Examples 1, 2, and 3 and the viscosity after 1 minute of stirring. In Figure 2, ▲ indicates Example 1, ◆ indicates Comparative Example 1, ■ indicates Comparative Example 2, and × indicates Comparative Example 3. The vertical axis indicates viscosity (unit: cP), and the horizontal axis indicates rice flour concentration (unit: mass%).

The three types of dry-milled rice flour did not show much change in viscosity with increasing concentration up to a concentration of 20% by mass, and the difference in viscosity with commercially available rice flour and wheat flour was small. However, at concentrations above 20% by mass, the smaller the average particle size of the rice flour, the greater the increase in viscosity with increasing concentration, and rice flour with high starch damage tended to have a tendency to have an increased viscosity. Among them, the fine rice flour produced by the jet mill in [Example 1] had the smallest average particle size (12 μm), the highest damaged starch content (23.8% by mass), and the largest viscosity increase rate with concentration. On the other hand, the joshinko in [Comparative Example 3] had an average particle size of 40 μm or more and a damaged starch content of less than 15% by mass, which is thought to be why the viscosity of the batter did not increase much.

The wheat flour (weak flour) batter in [Comparative Example 4] may be adjusted to a concentration of more than 30% (Kawaraya Chiyoko, "Wheat Flour Cooking", Life Hygiene, 29(2), 111-115:1985), and wheat flour batter liquids of 35%, 40% and 45% concentrations (all by mass) were prepared and their viscosities were measured in the same manner as above. As a result, the viscosities after one minute of stirring were approximately 289 cP, 717 cP and 1791 cP, respectively, and it was found that the jet milled flour in [Example 1] could impart the same degree of viscosity at a lower concentration (approximately 24-30% by mass).

These results show that if fine rice flour with an average particle size of less than 40 μm and a damaged starch content of 15% by mass or more is used, the viscosity can be adjusted over a wide range by changing the rice flour concentration in the batter. Furthermore, variable control of batter viscosity using this fine rice flour is expected to improve workability, such as making it easier for batter to adhere to ingredients during the frying process, and reduce the amount of raw rice flour used (Figure 2).

Furthermore, fried balls were made using the various batter liquids prepared above, and their physical properties were compared. The batter liquids with a concentration of 30% by mass from Example 1 and Comparative Examples 1, 2, and 3 were placed in an RVA aluminum cup with holes in the bottom (diameter: approximately 3.8 mm, height: approximately 6.8 cm. At least 20 holes of 2 mm in diameter were made in the bottom), dropped into salad oil heated to approximately 180°C, and fried for approximately 2 minutes to make fried balls, and their penetration hardness was measured. The penetration hardness was measured by determining the maximum hardness when a plunger with a diameter of 2 mm penetrated 50% of the thickness of the fried ball. The average value (± standard deviation) of measurements of 15 fried balls is shown in Table 3.

The three types of milled rice flours showed a tendency for the penetration hardness to decrease as the average particle size decreased, and the higher the damaged starch content, the lower the hardness. Among them, the fine rice flour milled using the jet mill in [Example 1] had the lowest hardness. A low penetration hardness indicates that the fried food has a crispy, light, and soft texture. On the other hand, the joshinko in [Comparative Example 3] had an average particle size of 40 μm or more and a damaged starch content of less than 15% by mass, which is thought to be why the penetration hardness of the fried dumplings was high.

From the above, it was confirmed that fine rice flour with an average particle size of less than 40 μm and a damaged starch content of 15% by mass or more is effective in reducing the hardness of fried foods and imparting a light, crispy texture. In addition, it was suggested that by changing the blend ratio of coarse rice flour to create a mixed flour, it may be possible to widely control the texture of fried foods using rice flour alone.

[Examples 2 to 6 and Comparative Examples 5 and 6]
The white rice used was Koshihikari brown rice polished to a polishing ratio of about 91%. In order to verify the effect of differences in raw material moisture on grindability in a jet mill (Japan Pneumatic Mfg. Co., Ltd., IDS-2), five types of white rice with significantly different initial moisture contents were produced by drying and hydration treatment, and the fine rice flours of [Example 2] to [Example 6] were prepared.

Specifically, in [Example 2] and [Example 3], polished rice was dried until its moisture content was 8.3% and 11.5% (both by mass), respectively, and then directly ground using a jet mill. In [Example 4], polished rice (moisture content 13.5% by mass) was directly ground using a jet mill. In [Example 5] and [Example 6], polished rice was added with water to adjust its moisture content to 15.6% and 18.2% (both by mass), respectively, and then directly ground using a jet mill. In addition, polished rice was dry ground using a small hammer mill (IKA, MF10.2) to prepare rice flour in [Comparative Example 5]. In addition, commercially available rice flour (joshinko) was used as [Comparative Example 6].

The moisture content, average particle size, damaged starch content and loose bulk density of these powders were measured and compared. The moisture content, average particle size and damaged starch content were measured using the methods described above. Loose bulk density refers to the packing density when a powder sample is allowed to fall naturally into a cup of a certain volume, and is a useful evaluation index when designing hoppers and packaging filling in the manufacturing process. Loose bulk density was measured using a powder property measuring instrument (MT-1001, manufactured by Seishin Enterprise Co., Ltd.).

The results are shown in Table 4. It was confirmed that the jet milled flours of [Examples 2 to 6] had little effect on the average particle size and damaged starch content even when the initial moisture content of the raw materials fluctuated between 8 and 19% by mass due to drying or water absorption, and could stably produce fine rice flour with an average particle size of around 10 μm and a damaged starch content of 27 to 30% by mass. It was found that these jet milled flours had extremely small particle size and bulk density compared to the hammer milled flour of [Comparative Example 5] (average particle size 420.7 μm) and the commercially available joshinko flour of [Comparative Example 6] (average particle size 111.8 μm).

Next, 20% and 30% batters were prepared using the above powders and commercially available soft flour, and the viscosities were compared. 25 g of water (taking into account the moisture content of the powder) was added to each powder to achieve the above concentrations on a dry basis, and the viscosity of the batter was measured using a Rapid Visco Analyzer (Newport Scientific, model: RVA-4) while stirring at 25°C for 30 minutes (stirring at 960 rpm for 10 seconds, then at 160 rpm until the end of the measurement). The viscosity was finally compared 5 minutes after the start of the measurement.

The results are shown in Figure 3. Figure 3 is a graph comparing the viscosity of various batter liquids after 5 minutes of stirring. In Figure 3, from the left, each concentration is shown for Examples 2, 3, 4, 5, 6, Comparative Examples 5 and 6, and commercially available weak flour, and the vertical axis shows viscosity (unit: cP).

At a concentration of 20% by mass, there is little difference in viscosity between the samples, but at a concentration of 30% by mass, the jet-milled rice flours of [Examples 2] to [Examples 6] showed viscosities more than 2.5 times higher (all 1,000 cP or higher) than the hammer-milled flour of [Comparative Example 5] and the commercially available joshinko and soft flours of [Comparative Example 6], even when the initial moisture content of the raw materials varied from 8 to 19% by mass. This confirmed that the viscosity increase of fine rice flour at concentrations of 20 to 30% by mass was significant even when the initial moisture content of the raw materials was different, and that the batter viscosity can be controlled more widely than with coarse grain rice flour. However, since there are slight differences in viscosity due to differences in initial moisture between fine rice flours, care must be taken to standardize the moisture content of the raw materials when milling in order to produce a stable high-viscosity fine rice flour (Figure 3).

[Examples 7 and 8]
The polished rice used was Koshihikari brown rice polished to a polishing ratio of about 91% (moisture content about 13.7% by mass). The polished rice was dry-ground as is using a hammer mill (Yoshida Seisakusho Co., Ltd., 1018-S-3) to prepare coarsely ground rice flour with average particle sizes of 125 μm and 50 μm, respectively. The polished rice was also dry-ground using a jet mill (Nippon Pneumatic Mfg. Co., Ltd., IDS-2) to prepare fine rice flour with an average particle size of 10 μm.

The average particle size and damaged starch content of these rice flours were measured using the methods described above. As a result, the damaged starch content of rice flours with average particle sizes of 125 μm, 50 μm, and 10 μm was 13.4%, 24.0%, and 26.5%, respectively.

Next, the above-mentioned two types of coarsely ground rice flour (average particle size 125 μm and 50 μm) were blended with the above-mentioned fine rice flour (average particle size 10 μm) to obtain mixed flours of [Example 7] and [Example 8]. Then, using these mixed flours, 30% by mass of batter liquid was prepared, and the relationship between the mixing ratio of fine rice flour to mixed flour and the viscosity of the batter liquid was examined. 25 g of water (taking into account the moisture contained in the powder) was added to each powder to make it 30% by mass on a dry basis, and the viscosity of the batter liquid was measured using a Rapid Visco Analyzer (Newport Scientific, model: RVA-4) while stirring at 25°C for 30 minutes (stirring at 960 rpm for 10 seconds and then stirring at 160 rpm until the end of the measurement). Finally, the viscosity 5 minutes after the start of the measurement was compared.

The results are shown in Figure 4 (Figures 4(a) and 4(b)). Figure 4(a) is a graph showing the change in viscosity of batter liquid depending on the mixing ratio of fine rice flour to coarsely ground rice flour (average particle size 125 μm) in [Example 7]. Figure 4(b) is a graph showing the change in viscosity of batter liquid depending on the mixing ratio of fine rice flour to coarsely ground rice flour (average particle size 50 μm) in [Example 8]. In Figure 4, the horizontal axis shows the mixing ratio of fine rice flour (mass%), and the vertical axis shows viscosity (unit: Pa·s). For reference, the measured viscosity (0.4 Pa·s) for a batter liquid of the same concentration using only weak flour is also shown in the figure.

In the case of the mixed flour of [Example 7] blended with coarsely ground rice flour (average particle size 125 μm), it was found that mixing 50% fine rice flour gave it the same viscosity as weak flour batter. In the case of the mixed flour of [Example 8] blended with coarsely ground rice flour (average particle size 50 μm), it was found that mixing 50% fine rice flour gave it about four times the viscosity of weak flour batter. In addition, it was shown that by mixing fine rice flour with coarse grain size rice flour, it is possible to adjust the viscosity of a batter of a fixed concentration (30 mass%) widely and seamlessly (0.2 to 3 Pa·s). Furthermore, it was shown that within the viscosity range of 1 to 3 Pa·s, any batter viscosity can be reproduced by changing the mixing ratio of fine rice flour, even if the grain size of the coarsely ground rice flour to be blended is different.

The particle size of the coarsely ground rice flour blended affects the texture (roughness, hardness, etc.) of the final product, such as fried foods and rice flour processed foods. Therefore, these results suggest that by adjusting the particle size of the coarsely ground rice flour in the mixed flour and the mixing ratio of fine rice flour, it may be possible to variably control the texture of the final product without changing the viscosity of the batter or dough (i.e., while keeping the handling characteristics in the product's primary processing step unchanged).

[Examples 9 and 10 and Comparative Examples 7 to 10]
As the Koshihikari white rice, Koshihikari brown rice polished to a polishing ratio of about 91% (moisture content about 13.7% by mass) was used. As the high amylose white rice, high amylose brown rice polished to a polishing ratio of about 91% (moisture content about 13.3% by mass) was used. Various types of white rice were dry-ground as they were using a hammer mill (Yoshida Seisakusho Co., Ltd., 1018-S-3) to prepare rice flours with average particle sizes of 125 μm and 50 μm, respectively, in [Comparative Examples 7 to 10]. Furthermore, various types of white rice were dry-ground using a jet mill (Nippon Pneumatic Mfg. Co., Ltd., IDS-2) to prepare fine rice flours with an average particle size of 10 μm, in [Examples 9 and 10].

The average particle size and damaged starch content of these rice flours were measured using the methods described above. The results of the damaged starch content are shown in Table 5.

The various rice flours prepared above were used to make fried dumplings and their physical properties were compared. First, water was added to the rice flours of Examples 9-10 and Comparative Examples 7-10, and batter liquid with a rice flour concentration of 30% by mass was prepared by mixing and stirring. The obtained batter liquid was placed in an RVA aluminum cup with holes in the bottom (diameter: approximately 3.8 mm, height: approximately 6.8 cm. More than 20 holes with a diameter of 2 mm were made in the bottom), dropped into salad oil heated to approximately 180°C, and fried for approximately 3 minutes to make fried dumplings.

The compressive stress value of the fried dumplings made in this way was measured using a tensipressor (manufactured by Takemoto Denki). The compressive stress value was measured by determining the maximum stress value when the fried dumplings were compressed to 50% of their thickness using a plunger with a diameter of 25 mm. As a control, fried dumplings were also made using commercially available wheat flour (weak flour) under the same conditions as above, and the compressive stress value was measured.

The results are shown in Figure 5. Figure 5 is a graph showing the compressive stress values of fried dumplings made from rice flour of various particle sizes and varieties. From the left in Figure 5, Example 9, Comparative Examples 7 and 8, Example 10, Comparative Examples 9 and 10, and commercially available weak flour are shown, and the vertical axis shows the compressive stress value (unit: kPa). The compressive stress value is the average value (± standard deviation) measured for 10 fried dumplings.

The compressive stress value is generally used as an index of food hardness, and a low compressive stress value indicates that fried foods have a light and soft texture. Figure 5 shows that, regardless of variety, the coarser the grain size, the higher the stress value and the harder the texture tends to be. With rice flour with an average grain size of 125 μm, both varieties had values similar to those of weak flour, and no significant differences were observed between varieties. On the other hand, with fine rice flour, the stress value for both varieties was reduced to about one-third that of weak flour, indicating an extremely light and soft texture.

These results suggest that, regardless of the variety, by using fine rice flour in batters and doughs, it is possible to produce fried foods with a light and soft texture and rice flour processed foods with a smooth texture. In addition, it was suggested that by using a flour mix containing fine rice flour and adjusting its ratio, it is possible to widely and finely adjust the texture of fried foods and rice flour processed foods.

Furthermore, the adhesiveness of the batters prepared using the various rice flours as described above to the ingredients was compared. First, water was added to the rice flours of Examples 9-10 and Comparative Examples 7-10, and the batters with rice flour concentrations of 20% and 30% by mass were prepared by mixing and stirring. Next, sweet potatoes formed into 1 cm cubes were prepared as ingredients, and the above batter was applied to them to examine the adhesiveness of the batter. The adhesiveness was measured by determining the change in weight (g) of the ingredients before and after application. As a control, batters were also prepared using commercially available wheat flour (weak flour) under the same conditions as above, and the adhesiveness to the ingredients was measured.

The results are shown in Figure 6 (Figures 6(a) and 6(b)). Figure 6 is a graph comparing the adhesion of batters made from rice flours of various particle sizes and varieties to ingredients. Figure 6(a) shows the results for a batter with a rice flour concentration of 30% by mass, and Figure 6(b) shows the results for a batter with a rice flour concentration of 20% by mass. In each figure, from the left, Example 9, Comparative Examples 7 and 8, Example 10, Comparative Examples 9 and 10, and commercially available weak flour are shown, and the vertical axis shows the weight difference (unit: g) of the ingredients before and after adhesion. The weight difference is the average (± standard deviation) of three measurements.

Figure 6 shows that the smaller the grain size of rice flour, the easier the batter liquid adheres to the ingredients, regardless of the variety. It was found that the difference in adhesion between varieties (difference due to amylose content) is small compared to the physical properties (compressive stress value) in Figure 5. At a rice flour concentration of 20% by mass (Figure 6(b)), the difference in adhesion due to differences in grain size is small, but at a rice flour concentration of 30% by mass (Figure 6(a)), which is a typical concentration for batter liquid containing only weak flour, the adhesion weight of fine rice flour increased by more than four times compared to rice flour with an average grain size of 125 μm for both varieties. In addition, at a rice flour concentration of 30% by mass (Figure 6(a)), the adhesion of the fine rice flour of [Examples 9-10] was significantly higher than that of commercially available weak flour. It is thought that the adhesion improved because the viscosity of the batter liquid of fine rice flour increases significantly between 20 and 30% by mass of rice flour, as shown in Figures 2 and 3.

As described above, because fine rice flour batter has a high adhesiveness to ingredients, it was suggested that by using a mixed flour containing fine rice flour and adjusting its ratio, it is possible to variably control the adhesiveness of the batter to ingredients.

Claims (6)

A batter for fried foods, which contains fine rice flour having an average particle size of less than 40 μm and a damaged starch content of 15% by mass or more, or granules made of said fine rice flour, and does not contain wheat flour. The batter for fried foods according to claim 1, characterized in that the concentration of the fine rice flour in the batter for fried foods is 20% by mass or more. A method for producing batter for fried foods, comprising the steps of: preparing fine rice flour having an average particle size of less than 40 μm and a damaged starch content of 15% by mass or more by a method including a step of grinding raw rice that is not gelatinized and has a moisture content of 20% by mass or less; using said fine rice flour or granules made of said fine rice flour; and not using wheat flour. A method for producing fried foods, comprising using the batter liquid for fried foods according to claim 1 or 2. A method for controlling the viscosity of batter for fried foods or dough for rice flour processed foods, characterized by using fine rice flour with an average particle size of less than 40 μm and a damaged starch content of 15% by mass or more, or granules made of said fine rice flour, and by not using wheat flour. The method for controlling viscosity of batter for fried foods or dough for rice flour processed foods according to claim 5, characterized in that the concentration of the fine rice flour in the batter for fried foods or dough for rice flour processed foods is 20 mass% or more, and the rice flour processed food is a fried snack.