A method for preparing glutinous rice flour by semi-dry grinding

Abstract

The invention discloses a method for preparing glutinous rice flour by semi-dry grinding. The method comprises the following steps: obtaining glutinous rice grains with cracks on the surface and transverse cracks extending deep into the rice grains after hot steam treatment; increasing the moisture content of the glutinous rice grains, and then crushing and drying. The invention has the following advantages: rapid treatment of glutinous rice with superheated steam can strongly remove part of the moisture in the rice grains and destroy the structure of the glutinous rice grains; at the same time, short-term treatment can reduce the occurrence of browning reaction in the rice grains and maintain the color of glutinous rice flour. Since glutinous rice has a high content of amylopectin, its demand for moisture is much greater than that of polished rice and early indica rice. Therefore, according to different varieties, the content of 35% to 45% is required so that the moisture can be evenly distributed to the entire rice grain. The moisture added in the early stage is relatively high (35% to 45%), and the amount of moisture loss during the crushing process is limited. The step of adding superheated steam drying after crushing solves the problem of sieving clogging the screen and not being able to be stored for a long time.

Description

Technical Field

[0001] The invention relates to a method for preparing glutinous rice flour by semi-dry grinding. Background Art

[0002] Glutinous rice flour is obtained by grinding glutinous rice and used to make glutinous rice products such as glutinous rice balls and Yuanxiao. Water milling has always been the most widely used method in the processing of glutinous rice flour in my country. Water milling generally requires soaking the rice for more than 2 hours and then grinding it with a water mill or other grinding methods. This treatment method allows water to fully enter the rice grains, reduces the input of energy and heat during the grinding process, maintains the integrity of starch particles, and thus obtains high-quality glutinous rice flour with low damaged starch content.

[0003] However, the traditional water-milling method uses a lot of water during soaking. First, a lot of wastewater is generated during the soaking process. Second, the water needs to be removed after crushing and then crushed again after dehydration, which makes the water-milling method energy-intensive and low in production efficiency. In addition, soaking for more than 2 hours is prone to microbial contamination, bringing the risk of high background microbial content in glutinous rice flour.

[0004] Although water-milling has the above-mentioned disadvantages, ordinary dry milling cannot replace it. This is because the direct dry milling of glutinous rice requires too much energy and heat, resulting in the dry milled glutinous rice flour having the disadvantages of high damaged starch content, uneven particle size, poor color, etc., and therefore cannot be processed into glutinous rice products such as glutinous rice balls.

[0005] Chinese patent application (CN 103025176 A) discloses a method for producing polished round-grained rice flour, wherein the rice is treated with air at 40°C to 50°C for 10 to 40 minutes, and then heated by microwave irradiation to produce a large number of fine cracks on the surface of the rice, and then sprayed or showered for 10 to 15 minutes to make the surface of the raw rice adhere to moisture, and the overall moisture of the rice grains is adjusted to 20% to 30%, and then ground by air flow grinding and sieved to obtain rice flour with a weight percentage of more than 75% passing a 200-mesh sieve. According to this manufacturing method, water can be saved and the content of background microorganisms can be reduced.

[0006] However, there are two problems in the preparation of glutinous rice flour by the above manufacturing method. First, the use of the pretreatment method of hot air drying for 10 to 40 minutes plus microwave irradiation will reduce the whiteness of the glutinous rice flour, and finally make the glutinous rice balls yellow, affecting the sensory quality of the product; second, the amount of water sprayed or sprinkled on the hard glutinous rice is insufficient, so that the damaged starch content is still very high and cannot meet the needs of actual production; third, the moisture content of the crushed glutinous rice flour is high without drying treatment, and the screen is easily blocked during screening, and the product is easy to mold and deteriorate during long-distance transportation and storage. Summary of the invention

[0007] The invention aims to provide a method for preparing glutinous rice flour by grinding glutinous rice, which can greatly shorten the pre-treatment time, obtain the high-quality glutinous rice flour with ideal damaged starch content and suitable for long-term storage and transportation.

[0008] The method for preparing glutinous rice flour by semi-dry grinding provided by the present invention comprises the following steps:

[0009] After being treated with hot steam, glutinous rice grains with cracks on the surface and transverse cracks extending into the interior of the rice grains are obtained; the moisture content of the glutinous rice grains is increased, and then the glutinous rice flour is obtained by crushing and drying;

[0010] The moisture content refers to the mass content.

[0011] In the above method, the conditions of the superheated steam treatment are as follows:

[0012] The temperature is 150℃~180℃;

[0013] The time is 30 seconds to 90 seconds;

[0014] For example, treatment at 150°C for 30 seconds or at 180°C for 90 seconds;

[0015] The pre-treatment step of superheated steam treatment can make the moisture of glutinous rice evaporate quickly, generate a large number of cracks on the surface of rice grains, and generate transverse cracks deep into the inside of rice grains, that is, the cracking rate of glutinous rice is significantly increased.

[0016] In the above method, the moisture content of the glutinous rice grains is increased by the following steps, and the steps are performed under stirring:

[0017] The surfaces of the glutinous rice grains are moistened by spraying or showering, and the moisture is allowed to penetrate into the interior of the glutinous rice grains through the cracks and transverse cracks, so that the moisture is evenly distributed inside the glutinous rice grains.

[0018] The stirring time may be 10 to 20 minutes, specifically 10 minutes or 20 minutes, so that the water can fully contact the rice grains and the water can fully penetrate into the inside of the rice grains.

[0019] In the above method, the moisture content of the glutinous rice grains is increased to 35% to 45%, which can be adjusted according to the saturated water absorption rate of different glutinous rice varieties, such as 35% or 45%.

[0020] In the above method, a jet mill is used to carry out the pulverizing step.

[0021] In the above method, the drying is carried out by superheated steam treatment.

[0022] In the above method, the conditions of the superheated steam treatment are as follows:

[0023] The temperature is 150℃~180℃;

[0024] The time is 10 to 20 seconds;

[0025] For example, the temperature may be 150°C for 10 seconds or 180°C for 20 seconds.

[0026] In the above method, after the drying process, the moisture content of the glutinous rice flour is not higher than 15%.

[0027] The glutinous rice flour of which more than 70 weight % passes through a 200-mesh sieve prepared by the above method also belongs to the protection scope of the present invention.

[0028] The present invention has the following advantages:

[0029] (1) Rapid treatment of glutinous rice with superheated steam can effectively remove part of the moisture in the rice grains and destroy the structure of the glutinous rice grains; at the same time, short-term treatment can reduce the occurrence of browning reaction in the rice grains and maintain the color of glutinous rice flour.

[0030] (2) Due to the high content of amylopectin in glutinous rice, its demand for water is much greater than that of japonica rice and early indica rice. Therefore, depending on the variety, the water content must reach 35% to 45% so that the water can be evenly distributed throughout the rice grain.

[0031] (3) The water content added in the early stage is relatively high (35% to 45%), and the water loss during the pulverization process is limited. The step of adding superheated steam drying after pulverization solves the problem of sieve clogging and inability to store for a long time. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a stereomicroscopic photograph of glutinous rice grains after hot steam treatment in Example 1 of the present invention.

[0033] Figure 2 This is the nuclear magnetic resonance imaging of the rice grains after absorbing water in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0035] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0036] Embodiment 1:

[0037] (1) Treating glutinous rice grains with superheated steam

[0038] The moisture content of the ground glutinous rice raw material is about 15%. It is transported from the raw material tank to the superheated steam equipment for treatment, set at 150° C. for 30 seconds, at which time the moisture content of the glutinous rice is reduced to about 13%.

[0039] After the superheated steam treatment in this step, a large number of cracks are generated on the surface of the rice grains and transverse cracks deep into the rice grains, such as Figure 1 The stereomicrograph of rice grains shown (observed and taken with a SMZ800N stereomicroscope) is conducive to subsequent water absorption.

[0040] (2) Adding water to reduce rice hardness

[0041] Use spray to moisten the rice grains quantitatively, add water according to the saturated water absorption rate of different glutinous rice varieties, and make the moisture content of glutinous rice 35%. Tumble and stir in the drum for 10 minutes to make the water evenly penetrate into the rice grains. Figure 2 The MRI image of the rice grains after absorbing water (water molecules appear white, Ascend 500WB Bruker MRI instrument) shows that the water is evenly distributed inside the rice grains.

[0042] (3) Grinding glutinous rice

[0043] The soaked glutinous rice is conveyed to the air flow mill for crushing.

[0044] (4) Drying the glutinous rice flour

[0045] The crushed glutinous rice flour was dried by introducing superheated steam into the discharge port of the air flow mill. The contact time of the glutinous rice flour with the superheated steam at 150° C. was controlled at 10 seconds, so that the mass moisture content of the glutinous rice flour was 11%.

[0046] (5) Screening process: After crushing, the glutinous rice flour was sieved through a 100-mesh sieve (without clogging of the sieve), and the damaged starch content of the glutinous rice flour (measured using a commercially available kit, K-SDAM, Megazyme International Ltd., Wicklow, Ireland) was less than 5%.

[0047] The glutinous rice flour prepared in this embodiment has a passing rate of 70% (by mass) through a 200-mesh sieve.

[0048] The glutinous rice flour prepared in this embodiment is white in color and has no mold or deterioration phenomenon.

[0049] The moisture content of the glutinous rice flour prepared in this embodiment is as low as 11%, and the total colony count, Escherichia coli, yeast and mold contents after superheated steam treatment are significantly reduced, as shown in Table 1.

[0050] Table 1 Analysis of microbial content before and after treatment

[0051]

[0052] Note: Microbiological indicators are measured according to national standards; - means not detected

[0053] Embodiment 2:

[0054] (1) Treating glutinous rice grains with superheated steam

[0055] The moisture content of the milled glutinous rice is about 15%. It is transported from the raw material tank to the superheated steam equipment for treatment. The temperature is set at 180°C for 90 seconds. At this time, the moisture content of the glutinous rice is reduced to about 12%. A large number of cracks appear on the surface of the rice grains, and transverse cracks that penetrate deep into the rice grains appear on the rice grains (microscopic photos of the rice grains and Figure 1 There is no substantial difference), which is conducive to subsequent water absorption.

[0056] (2) Adding water to reduce rice hardness

[0057] The rice grains were quantitatively moistened with water by spraying, and water was added according to the saturated water absorption rate of different glutinous rice varieties to make the moisture content of the glutinous rice 45%. The rice grains were tumbled and stirred in a drum for 20 minutes to allow the water to fully contact the rice grains and to infiltrate the rice grains (MRI of the rice grains after absorbing water and Figure 2 no substantial difference).

[0058] (3) Grinding glutinous rice

[0059] The soaked glutinous rice is conveyed to the air flow mill for crushing.

[0060] (4) Drying the glutinous rice flour

[0061] The crushed glutinous rice flour was dried by introducing superheated steam into the discharge port of the air flow mill. The contact time of the glutinous rice flour with the superheated steam at 180° C. was controlled at 20 seconds, so that the mass moisture content of the glutinous rice flour was 11%.

[0062] (5) Screening process: After crushing, the glutinous rice flour is passed through a 100-mesh sieve (without clogging the sieve) to obtain glutinous rice flour for making glutinous rice balls and Chinese rice dumplings. The damaged starch content of the glutinous rice flour is less than 5%.

[0063] The glutinous rice flour prepared in this embodiment has a passing rate of 70% (by mass) through a 200-mesh sieve.

[0064] The glutinous rice flour prepared in this embodiment is white in color and has no mold or deterioration phenomenon.

[0065] The moisture content of the glutinous rice flour prepared in this embodiment is as low as 11%, and the total colony count, Escherichia coli, yeast and mold contents after superheated steam treatment are significantly reduced, as shown in Table 2.

[0066] Table 2 Analysis of microbial content before and after treatment

[0067]

[0068] Note: Microbiological indicators are measured according to national standards; - means not detected.

Claims

1. A method for preparing glutinous rice flour by semi-dry grinding, comprising the following steps: After being treated with hot steam, glutinous rice grains with cracks on the surface and transverse cracks extending into the interior of the rice grains are obtained; the moisture content of the glutinous rice grains is increased, and then the glutinous rice flour is obtained by crushing and drying; The moisture content mentioned refers to the mass content; The conditions of the superheated steam treatment are as follows: temperature is 150°C to 180°C; time is 30 seconds to 90 seconds; The moisture content of the glutinous rice grains is increased by the following steps, and the process is performed under tumbling and stirring in a drum: the surface of the glutinous rice grains is watered by spraying or showering, and the water is infiltrated into the interior of the glutinous rice grains through the cracks and transverse cracks; the moisture content of the glutinous rice grains is increased to 35% to 45%; the stirring time is 10 minutes to 20 minutes; The pulverizing step is performed using a jet mill; The drying is carried out by superheated steam treatment under the following conditions: temperature of 150° C. to 180° C. and time of 10 seconds to 20 seconds.

2. The method according to claim 1, characterized in that: After the drying process, the moisture content of the glutinous rice flour is not higher than 15%.

3. glutinous rice flour prepared by the method described in claim 1 or 2.

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