A METHOD FOR POLISHING A RICE AND POLISHED RICE BY IT

TECHNICAL FIELD

The present invention is related to a method of polishing brown rice at low speed and under constant pressure, such that the rice polished by using the method retains embryo buds rich in nutrients and has the same whiteness as general white rice, and rice polished by using the method, and more particularly, to a method of polishing brown rice at low speed and under constant pressure under predetermined polishing conditions to polish the brown rice, such that rice polished by using the method has improved delicacy and stickiness for better taste when cooked as compared to conventional brown rice or conventional rice having embryo buds and is more nutritious than white rice, and rice polished by using the method.

BACKGROUND ART

The structure of a grain of brown rice includes: rice bran layers, such as a seed vessel, a testa, and an aleurone layer; an embryo bud occupying a small part of the core of a rice grain; and an albumen layer occupying most of the remaining part of the rice grain. Most of the albumen layer is filled with starch particles. The albumen layer is the part of a rice grain which is eaten individually as white rice.

In comparison to white rice, brown rice is more preservable, is less likely to be damaged by harmful insects or microorganisms, and loses little nutrition during processing. Thus, brown rice is richer in fat, protein, gamma oryzanol, vitamin A, vitamin Bi, and vitamin B ₂ in comparison to white rice. Furthermore, there is little reduction in quantity of brown rice after processing.

Accordingly, brown rice is far superior in many aspects than white rice. However, brown rice has a rough texture, the taste of brown rice is inferior to that of white rice when cooked, and nutrients of brown rice are hard to be digested and absorbed sufficiently. Furthermore, brown rice is harder to cook in comparison to white rice. Thus, brown rice is not widely used.

Furthermore, the nutrients of a rice grain are concentrated in an embryo bud. An embryo bud contains phytic acid, which counteracts poisonous effects of heavy metals, six times as much in comparison to white rice, and is rich in protein, fat, and carbohydrate. Furthermore, fibers, vitamins such as vitamin A, vitamin B ₁ , B ₂ , and B ₆ , pantothenic acid, linolenic acid, etc., and minerals are well balanced in an embryo bud.

In addition, an embryo bud even contains chelators which have a controlling effect on carcinogenic substances.

Furthermore, an embryo bud contains ingredients such as tocotrienol, which is a substance with stronger antioxidative effects than tocopherol, and oryzanol preventing strokes and dementia by revitalizing brain cells. Fibers richly contained in an embryo bud increase absorption of water, so that constipation can be prevented. The fibers also slow down production of insulin, and thus brown rice is good for preventing diabetes.

In conventional rice polishing methods, the only requirement was polishing brown rice and producing white rice. Therefore, embryo buds of rice mostly fall off during the polishing. Recently, as more and more attention is put on health, various studies on methods of polishing rice without damaging the nutrients contained in rice are being made. Particularly, an embryo bud of a rice grain contains many ingredients advantageous to the human body, such as vitamin B-i, vitamin E, natural tocopherol, gamma oryzanol, etc., and thus devices for polishing brown rice without damaging embryo buds to produce rice having embryo buds for consumption are being researched and developed.

Generally, 95 percent of brown rice has embryo buds. However, only 3 percent of white rice still has embryo buds, this is because most embryo buds fall off during rice polishing. Generally, grinding type rice polishing devices can preserve more embryo buds as compared to friction type rice polishing devices, due to low and evenly distributed pressure in the polishing chamber.

More particularly, embryo buds of rice fall off easily by momentary shock and friction in the polishing chamber due to pivoting spin of the polishing chamber. Therefore, falloff of embryo buds is affected by internal pressure due to the pace of injecting rice into the polishing chamber (the quantity of rice injected into the polishing chamber in any one period of time), shocks due to pace of pivoting spin of the cleaning chamber, particle size of a grindstone, a gap between the axis of spin and a screen, the shape of the screen, the vacuum pressure inside the polishing chamber, resistance at a polished rice outlet, and so on.

Conventional rice having embryo buds is under-polished rice, which has been polished by a special rice polishing device (device for polishing rice having embryo buds) to preserve embryo buds. To preserve embryo buds, the special rice polishing device polishes brown rice less than white rice; approximately whiteness 34 percent as much polishing. Conventional "under-polished" rice having embryo buds has between 3 percent and 4 percent more of an aleurone layer remaining, which is an outer layer of brown rice, as compared to white rice due to under-polishing. Thus, when cooked, the taste of the rice is not good and the color of cooked rice become yellowish.

Furthermore, since aluerone which is rich in fat largely remains, there are risks of acidification and decay during storage.

Conventional technologies for preserving the nutrients and embryo buds of rice are described below. Korean Utility No. 20-0384236 discloses a device for polishing and cleaning rice specifically to produce polished rice having embryo buds, the device including a circular punched metal gauze.

Korean Patent No. 10-0599555 discloses a modification of a punched metal gauze in a conventional rice polishing device and a rice polishing device including a loader having a groove for preventing friction at its center, such that decay of polished rice is prevented and the quality of polished rice is improved.

Korean Patent No. 10-0407834 discloses a rice polishing device capable of polishing rice and protecting embryo buds during the polishing. The rice polishing device includes a rotating grindstone installed on a spinning disk and a fixed grindstone installed to directly face the rotating grindstone.

Korean Patent No. 10-0356531 discloses a rice polishing device. In the rice polishing device, a punched metal gauze has rectangular punched holes each of which has a sloped bottom, rising from inside the punched metal gauze towards the outside when viewed from a driving axis, where the direction in which the sloped bottom rises is opposite to the direction in which rice flows.

Korean Patent No. 10-0636421 discloses a method and an apparatus for polishing rice capable of polishing and cleaning rice without removing embryo buds so that damage inflicted to rice can be reduced.

Although there is much conventional research in progress, such as looking into germed brown rice and devices for polishing rice while retaining embryo buds, and research for preserving nutrition of rice, all types of rice produced by the research have rougher textures than white rice, have yellowish color when cooked, and are difficult to cook, and thus they do not attract consumers.

Furthermore, the conventional technologies for preserving embryo buds are only involved with research and development of mechanical devices, and do not suggest how to set specific rice polishing conditions. Thus, the technologies fail to provide easy-to-cook rice, which has excellent taste, texture, and color and is without loss of nutrition, to consumers.

BRIED DESCRIPTION OF THE DRAWINGS FIG. 1 is a flowchart showing polishing operations of rice according to exemplary

embodiments of the present invention;

FIGS. 2A and 2B are explanation diagrams showing principles of rice polishing at low speed and under constant pressure; and

FIGS. 3A, 3B, and 3C are sectional views of brown rice, rice polished according to the present invention, and general white rice, respectively, obtained by photographing sections of each of the rice grains using a scanning electron microscope (SEM).

DETAILED DESCRIPTION OF THE INVENTION

TECHNICAL PROBLEM The present invention provides a method of polishing rice at low speed and under constant pressure to produce rice having embryo buds which is easy to cook like general white rice, has good taste when cooked and has the same whiteness as general white rice while preserving embryo buds which contain excellent nutritional value.

The present invention also provides rice having embryo buds produced by using the method.

TECHNICAL SOLUTION

According to an aspect of the present invention, there is provided a method of polishing rice at low speed and under constant pressure, the method including: (a) gradually decreasing the revolving speed of a rice polishing chamber;

(b) reducing the quantity of rice injected into the rice polishing chamber in correspondence to the decrease of the revolving speed of the rice polishing chamber; and

(c) repeating (a) and (b). Furthermore, the rice polishing chamber polishes rice by revolving from 8 to 10 times while the revolving speed of a center axis of the rice polishing chamber is decreased from 700 rpm to 300 rpm.

Furthermore, the rate of rice injection into the rice polishing chamber is decreased from 60 kilograms per minute to 30 kilograms per minute in correspondence to the decrease of the revolving speed of the rice polishing chamber.

Furthermore, the resistance at a polished rice outlet, which is the opening of a polished rice outlet, is fixed to be constant.

Rice polished according to the present invention has 60% or more of embryo buds remaining and 38% or higher whiteness like general white rice.

ADVANTAGEOUS EFFECTS

The present invention is a method of polishing brown rice at low speed and under constant pressure to produce rice which retains as many embryo buds as possible while

having the same whiteness as that of general white rice. Rice polished by the method of the present invention has more than 60% of embryo buds remaining, has more than 38% whiteness as general white rice does, shows quality and taste of cooked rice that are the same as or superior than those of general white rice, and contains nutritional ingredients, that are beneficial to the human body, in larger amounts than contained in general white rice. Furthermore, the rice polished using the method of the present invention can easily be cooked in an average household.

BEST MODE A method of polishing rice at low speed and under constant pressure, the method according to the present invention includes: (a) gradually decreasing the revolving speed of a rice polishing chamber; (b) reducing the quantity of rice injected into the rice polishing chamber in correspondence to the decrease of the revolving speed of the rice polishing chamber; and (c) repeating (a) and (b).

MODE OF THE INVENTION

The present invention has been developed through research carried out to develop polished rice having nutrient-abundant embryo buds, the same whiteness as general white rice, and as good a taste as white rice when cooked. Through the present invention, it is been confirmed that, rice having more than 60 percent of embryo buds remaining therein and being polished to a whiteness of more than 38 percent (like the whiteness of white rice) can be obtained through use of a method according to the present invention in which conditions affecting the polishing, such as wind pressure, a gap between a grinding roll and a punched metal gauze, particle size of the punched metal gauze and a grindstone, revolving pace of central axis of revolution, factors affecting friction, such as electrical resistance of a rice polishing device and rate of rice injection are appropriately set. Accordingly, aleurones are removed, so that rice polished by using the method of present invention is resistant against decay and is easy to cook. Furthermore, as a subaleurone layer and embryo buds are preserved in the rice, the rice has improved delicacy and stickiness and is more nutritious than white rice. A method of polishing rice at low speed and under constant pressure according to an embodiment of the present invention produces rice which is more than 38 percent polished like general white rice while more than 60 percent of embryo buds remain.

Referring to FIG. 1 , the method of polishing rice begins with filtering out impurities from brown rice (operation S11 ).

In the filtering out operation S11 , rice grains containing more than 16 percent of moisture easily lose their embryo buds during polishing and easily decay after polishing.

Thus, only brown rice grains which contain between 14 percent and 15 percent of moisture are selected.

Next, selected brown rice grains are injected into a rice polishing device (operation S12). Although the rice is injected in a quantity of between 360 kilograms and 400 kilograms in the present invention, the present invention is not limited thereto, and thus the quantity of injected rice may vary according to device specification and capacity of a rice polishing device.

Next, polishing operations are performed (operations S13 and S14). The polishing operations are operations for polishing brown rice to the same whiteness as general white rice while preserving more embryo buds.

Since a general rice polishing device polishes large quantity of rice at high speed, embryo buds easily fall off. Therefore, it is important to set polishing conditions appropriately.

A general rice polishing device for polishing rice having embryo buds can be used in the method according to the present invention. The general rice polishing device includes a grinding roll attached to its center axis to rotate and a punched metal gauze housing the grinding roll and forming space for polishing.

In the operations S13 and S14, wind pressure is under 0.5 kPa. A gap between a grinding roll and a punched metal gauze is fixed between 0.9 centimetres and 1.0 centimetres. The revolving speed of the center axis of the rice polishing device is set to gradually decrease; between 700 rpm (revolutions per minute) and 600 rpm in first and second revolutions, between 600 rpm and 540 rpm in third and fourth revolutions, between 540 rpm and 450 rpm in fifth and sixth revolutions, 450 rpm and 390 rpm in seventh and eighth revolutions, and 390 rpm and 300 rpm in ninth and tenth revolutions. As the revolving speed of the center axis decreases, the rate of rice injection is decreased from 60 kilograms per minute to 30 kilograms per minute, and the resistance of the polished rice outlet is appropriately lowered (i.e. from 39 ohm to 30 ohm) before continuing to polish rice.

Accordingly, rice is polished while the pressure inside the rice polishing device becomes even as the revolving speed of the center axis, rate of injecting rice, and resistance at the rice outlet are coordinated.

Accordingly, the rice polishing device polishes rice under constant pressure by balancing the rate of rice injected and the rate of polished rice output while gradually slowing down the speed of revolving. At this time, the current of the rice polishing device in each of rice polishing steps is constant around 2OA. Thus, since rice is polished under constant pressure, polished rice has the same whiteness as general white rice and maintains most of embryo buds.

Furthermore, as rice is polished in the rice polishing chamber which gradually revolves ten times, loss of subaleurone layer, in which ingredients regarding taste of rice when cooked are concentrated, is less than a general rice polishing device polishing a large quantity of rice in shorter time. Thus, rice polished using the method of the present invention has more delicate taste and higher stickiness as compared to conventional white rice.

Among the rice polishing conditions, the concept of polishing rice regarding the revolving speed of the rice polishing chamber and the quantity of injecting rice is illustrated in FIG. 2. When the revolving pace of the center axis of the rice polishing chamber is high (FIG. 2B), rice grains having elliptical shapes are arranged such that longer axis of the rice grain is laid out horizontally due to the force of the revolution and centrifugal force. Thus, embryo buds of rice are damaged by the grindstone and the punched metal gauze. However, in the case of slow revolution (FIG. 2A), the rice grains are arranged such that the longer axis of the rice grain is parallel to the center axis. Thus, less damage is inflicted on the embryo buds.

Furthermore, conventionally if the quantity of rice injected increases, pressure inside the rice polishing chamber increases. Thus, friction between each rice grain rises and more force is concentrated on rice grains contacting the grindstone and the punched metal gauze. As a result, embryo buds of the rice are easily damaged. In the present invention, the revolving pace of the center axis and the quantity of injecting rice are optimized to reduce damage inflicted on the embryo buds.

Furthermore, the subaleurone layer, which improves the taste of rice when cooked, is the outermost layer of white rice and is the layer containing most ingredients such as oligosaccharide in a rice grain. Thus, if the aleurone layer is damaged while rice is polished by general rice polishing device, starches in the rice leak out while the rice is being cooked. As a result, stickiness and sweetness of the rice when cooked decrease.

FIG. 3A is a sectional view of general brown rice, FIB. 3B is a sectional view of rice polished using the method of the present invention, and FIG. 3C is a sectional view of general white rice. FIGS. 3A through 3C are obtained by photographing sections of each of the rice grains using a scanning electron microscope (SEM).

Rice polished by slowly revolving a rice polishing chamber ten times according to the method of the present invention has more of a subaleurone layer remaining as compared to rice polished by general rice polishing method. Thus, the taste and the stickiness of the rice polished using the method of the present invention are excellent when cooked.

In the polishing method above, if rice is polished under a condition that the wind pressure is 0.5 kpa or more, pressure at a rice bran inlet, into which rice bran is sucked,

increases. Thus, rice is sucked into a punched metal gauze, and embryo buds of the rice may be easily damaged. In contrast, if the wind pressure is too low, rice bran produced by polishing rice cannot pass through the punched metal gauze. Thus, the punched metal gauze may jam, and polishing efficiency may decrease. As a result, rice cannot be polished well.

If a gap between a grinding roll and a punched metal gauze is too large, the quantity of rice passing through a rice polishing chamber increases and the rice may be subjected to the force of the revolution more easily. Thus, embryo buds of the rice may be easily damaged. In contrast, if the gap between the grinding roll and the punched metal gauze is too small, the quantity of rice passing through the rice polishing chamber decreases and the rice may receive more frictional force. Thus, embryo buds of the rice may be easily damaged, and overall yield may decrease.

Therefore, brown rice polished using the method of the present invention has embryo buds with minimum damage and the same whiteness as general white rice. Furthermore, damage to a aleurone layer can be prevented. Therefore, rice being superior in nutrition and taste when cooked by including a large number of nutritionally excellent embryo buds, can be produced using the method of the present invention.

Rice completely polished using the method of the present invention goes through a dry rice cleaning operation (operation S15) before selection. More particularly, in the rice cleaning operation, rice bran remaining on the surface of polished rice is removed to improve the appearance thereof and to prevent decay of the polished rice due to the rice bran when stored. To minimize loss of embryo buds, rice cleaning conditions according to the present invention are set to 1 kpa wind pressure and 55 kilograms of rice injected per minute. After the rice cleaning operation, the cleaned rice sequentially goes through a color selecting operation (operation S16), a broken rice selecting operation (operation S17), and a packaging operation (operation S18) before shipment. The operations S16 through S18 are operations well known in the prior art.

Rice, produced by using the polishing method described above, contains more nutrition than general white rice, exhibits more stickiness than general rice with embryo buds and can be easily cooked in an average household using the same cooking method as that for general white rice.

Furthermore, rice polished using the method of the present invention can not only be cooked to form cooked rice, but can also be used as a source of processed food such as gruel, health food, asepsis rice, etc.

Furthermore, it is possible to retain more embryo buds by polishing rice less than detailed above or to produce rice which doesn't have to be washed before cooking, if required.

Hereinafter, the present invention will be described more fully with reference to embodiments below. The embodiments are only exemplary, and thus the present invention is not limited thereto.

[Embodiment 1]

First, to confirm nutritional superiority of an embryo bud of rice, embryo buds are removed from brown rice. Then, the brown rice having the embryo buds removed is polished to white rice polished 38% or more by using a small grinding type rice polishing device, and white rice, and rice bran are separately obtained. The weight ratios of the separated embryo bud, rice bran, and albumen (white rice) with respect to a grain of brown rice were 2.74%, 6.05%, and 91.21 %, respectively. Nutritional analysis of each of the separated portions and a grain of brown rice is shown in Table 1 of Experimental Example 1.

[Embodiment 2]

After optimizing a wind pressure to not damage embryo buds and optimizing a gap between a grinding roll and a punched metal gauze between 0.9 centimeter and 1.0 centimeter, a rice polishing chamber is revolved once at a speed of from 700 rpm to 600 rpm, is revolved once at a speed of from 600 rpm to 540 rpm, and then revolved at gradually slower speeds of from 560 rpm to 300 rpm. By revolving the rice polishing chamber ten times without changing the electrical resistance of the rice polishing device and the quantity of rice after the second revolution, whiteness and embryo bud remaining amounts are analyzed.

A negative relationship, in which less embryo buds remain as the whiteness increases during the rice polishing, is confirmed. Since there were no changes in the resistance and in the quantity of rice injected by the revolving speed, more embryo buds fell out with no increase in the whiteness.

[Embodiment 3]

After optimizing a wind pressure to not damage embryo buds and optimizing a gap between a grinding roll and a punched metal gauze between 0.9 centimeter and 1.0 centimeter, a rice polishing chamber was revolved at gradually slower speeds of from 700 rpm to 300 rpm. By revolving the rice polishing chamber ten times while optimizing the electrical resistance of the rice polishing device and the quantity of rice injected, whiteness and embryo bud remaining amounts are analyzed.

A negative relationship, in which less embryo buds remain as the whiteness increases during the rice polishing, is confirmed. When rice is polished with high initial revolving speed and then the revolving speed is gradually slowed down thereafter, the whiteness gradually increases. Thus, after the final revolution, the whiteness of the polished rice was 38% or more, and 68% or more embryo buds remained.

[Experimental Example 1]

Nutritional evaluation and quality of the brown rice when cooked, the embryo buds, the rice bran, and the white rice (albumen), obtained in the embodiments above, are compared to those of general white rice, and the results are shown in Tables 1 through 4.

Nutritional Evaluation 1

First, to confirm nutritional excellence of an embryo bud, the applicant of the present invention requested the Korean Food Industry Association to perform analysis of nutritional ingredients in the source brown rice, the embryo buds, the rice bran, and the white rice (albumen), obtained in the Embodiment 1. Results of the analysis are shown in Table 1.

[Table 1]

(The analysis above is based on source rice with 15% moisture. The analysis regarding GABA is performed by the applicant.)

As shown in Table 1 , major portions of vitamins, gamma oryzanol, minerals, and gamma-aminobutyric (GABA), which are major nutrients of rice, are concentrated in an embryo bud, and thus it is clear that rice having embryo buds is nutritionally superior than general white rice. Thus, the purpose of the present invention is to polish brown rice to produce rice which retains embryo buds and has the same whiteness as that of general white rice.

Nutritional Evaluation 2

To evaluate nutritional ingredients and composition of the nutrients of the rice having embryo buds obtained in Embodiment 3 and general white rice, the applicant has requested that analysis of products obtained in Embodiment 3 be carried out by Korea Health Supplement Association. Results of the analysis is shown in Table 2.

(Nutritional values of "general white rice" are quoted from 'Recommended Dietary Allowance for Koreans (7 ^th Revision)'.)

As shown in Table 2, the rice having embryo buds according to the Embodiment 3 of the present invention contains more nutrients beneficial to the human body, such as Vitamin A, Vitamins B1 and B2, Vitamin E, and gamma oryzanol, than general white rice does.

Quality Evaluation 1 Consumer research regarding the rice having embryo buds obtained in

Embodiment 3 is performed to examine the quality of rice polished under polishing conditions according to the present invention. Results of the research are shown in Table 3. This quality evaluation employed a 5-point Likert type scale, and rice used to compare with the rice having embryo buds of the present invention was lchon King Rice, which is a general domestic white rice popular to customers in Korea.

Quality Evaluation 2

Consumer acceptance research regarding the rice having embryo buds obtained in Embodiment 3 is performed to examine the quality of rice polished under polishing conditions according to the present invention. Results of the research are shown in Table 4. This quality evaluation employed a 5-point Likert type scale, and rice used to compare with the rice having embryo buds of the present invention was Gyeonggi rice, lchon rice, and organic rice.

[Table 4]