A method for determining the appropriate amount of water to be added to rice during steaming using a magnetic field nuclear magnetic resonance instrument

Abstract

The application discloses a method for determining the suitable water amount in steaming rice by using a low-field nuclear magnetic resonance instrument, which sets water-rice ratios with an interval of 0.05, uses the low-field nuclear magnetic resonance instrument to determine the bound water amount in fresh rice and rice after steaming respectively, calculates the bound water loss amount=(the bound water amount in fresh rice)-(the bound water amount in rice placed for 24 hours under the condition of a temperature of 25 DEG C and a humidity of 70%), and determines that the bound water loss amount after being placed for 24 hours under the condition of a temperature of 25 DEG C and a humidity of 70% is less than or equal to 200+ / -30 as a sign for measuring whether the moisture is sufficient or excessive, and the lowest water-rice ratio, which appears earlier and is higher than the water-rice ratio bound water loss amount and keeps the bound water loss amount less than or equal to 200+ / -30, is determined as the suitable water-rice ratio for steaming the rice variety. The application avoids the shortage of determining the water amount in cooking only according to the amylose content in rice, and provides a reference basis for the sensory evaluation of the eating quality of rice.

Description

Technical Field

[0001] This invention belongs to the field of rice quality analysis technology, specifically a method for determining the appropriate amount of water to add when steaming rice using a low-field nuclear magnetic resonance spectrometer. Background Technology

[0002] Moisture, as a crucial component of cooked rice, significantly influences its aroma, appearance, taste, and palatability through its content, distribution, and state. Besides the inherent moisture content of the rice itself, the amount of water added during cooking, and the interaction between water and the rice's components, are paramount. Insufficient water leads to incomplete gelatinization, poor fluffiness, a hard texture, and a tendency to be undercooked; excessive water results in overly wet, mushy rice with reduced stickiness and elasticity, negatively impacting taste. Therefore, for a single rice variety, given its defined composition, the amount of water added during cooking and its interaction with the rice's components are key factors influencing the rice's texture. However, due to limitations in testing technology, research on the amount of water added during cooking, the interaction between water and its components, and the changes and effects of water's state have been limited for a long time.

[0003] Currently, ordinary households mainly rely on personal experience when adding water to cook rice. Professional rice tasting experiments in laboratories primarily use amylose content as the basis for water addition. The agricultural industry standard NY / 593-2021, "Quality of Edible Rice Varieties," issued by the Ministry of Agriculture and Rural Affairs in May 2021, includes a water addition adjustment table for rice preparation in its sensory evaluation section. Based on amylose content, the water addition is divided into five categories: amylose content ≤ 13.0%, water-to-rice ratio = 1.1; 13.0% < amylose content ≤ 17.0%, water-to-rice ratio = 1.2; 17.1% < amylose content ≤ 21.0%, water-to-rice ratio = 1.3; 21.1% < amylose content ≤ 25.0%, water-to-rice ratio = 1.4; amylose content > 25.0%, water-to-rice ratio = 1.5. Furthermore, amylose content is also frequently used as a reference for water addition during cooking in national and local high-quality rice tasting events.

[0004] Because rice varieties with similar or identical amylose content may differ in their amylopectin content and structure, protein composition, and other factors, these differences lead to variations in their ability to bind with water molecules and the interaction between water and rice components, resulting in different water requirements. Therefore, analyzing the state of water binding with rice components after cooking, as well as the changes in the amount of bound water, reflects the state of water in cooked rice after it combines with starch, protein, and other components, providing a more accurate representation of the true water content in cooked rice and a more specific and direct impact on taste.

[0005] Previous studies have found that the water in rice can be roughly divided into three forms: one is bound water, which is tightly bound to macromolecules such as starch and protein in rice by hydrogen bonds and has very weak fluidity; another is water that is retained in the cell and subcellular structure and has relatively weak fluidity, called structural water; and the third is water that can flow freely inside the rice, called free water.

[0006] Existing methods that use amylose content as a reference for the amount of water added during cooking have drawbacks. Different varieties with the same or similar amylose content may have different internal starch structures, protein content, and types, leading to different actual water requirements. In addition, the process of determining amylose content is quite cumbersome. This invention, however, addresses the issue from the perspective of bound water loss, providing a scientific basis and reference for the amount of water added when steaming rice and for sensory evaluation of rice's taste and flavor. Summary of the Invention

[0007] To address the problems existing in the aforementioned background technology, the purpose of this invention is to provide a method for determining the appropriate amount of water to add when steaming rice using a low-field nuclear magnetic resonance spectrometer, specifically achieved through the following technical solution:

[0008] A method for determining the appropriate amount of water to add when steaming rice using a low-field nuclear magnetic resonance spectrometer includes the following steps:

[0009] 1) Weigh 0.5g ± 0.01g of whole rice, accurately record the mass of the whole rice W1, and place the whole rice into a headspace bottle with a mass of W2;

[0010] 2) Wash away the dust on the surface of whole rice in the headspace bottle, set the water-to-rice ratio at intervals of 0.05, and prepare two parallel samples for each water-to-rice ratio to obtain the sample;

[0011] 3) Place the sample in an incubator at 25°C and 70% humidity and let it soak for 30 minutes.

[0012] 4) Place the sample soaked in step 3) in an electric steamer and steam for 30 minutes, then switch to heat preservation for 20 minutes;

[0013] 5) Place the sample after steaming and heat preservation in step 4) into a 25℃ constant temperature oven and let it cool for 30 minutes;

[0014] 6) Immediately place the sample processed in step 5) into a low-frequency nuclear magnetic resonance sample tube and measure the nuclear magnetic resonance curve of fresh rice that has been left to stand at 25°C for 0.5 hours. Two parallel samples are used for each water-to-rice ratio, and each sample is measured twice, that is, each water-to-rice ratio is measured repeatedly four times.

[0015] 7) Place the sample measured in step 6) back into the incubator at 25°C and 70% humidity and let it stand for 24 hours.

[0016] 8) Immediately place the sample from step 7) into a low-frequency nuclear magnetic resonance sample tube and measure it in the same way as in step 6) to obtain the nuclear magnetic resonance curve of rice that has been left to stand at 25°C and 70% humidity for 24 hours (i.e., refluxed for 24 hours).

[0017] 9) Invert the NMR curves obtained in steps 6) and 8), setting the iteration number to 10000. Export the data to an EXCEL table, take the average of 4 measurements, and plot the transverse relaxation time T2 as the x-axis and the instrument response signal value as the y-axis to obtain the moisture spectrum of fresh rice and retrograded rice placed at 25℃ and 70% humidity for 24 hours. Divide the peak areas representing bound water, structural water and free water respectively by the weight W1 of the polished rice sample and perform mass normalization to obtain the water content of bound water, structural water and free water.

[0018] 10) Sort the rice-to-water ratios from low to high, and calculate the amount of bound water lost at different water-to-water ratios. The amount of bound water lost = (the amount of bound water in fresh rice) - (the amount of bound water in rice left at 25℃ and 70% humidity for 24 hours).

[0019] 11) In the order of water-to-rice ratio from low to high, find the water-to-rice ratio corresponding to the earliest occurrence of bound water loss ≤200±30, and when the water-to-rice ratio is greater than this water-to-rice ratio, the bound water loss is ≤200±30. The lowest water-to-rice ratio that meets both of the above conditions is determined as the appropriate amount of water to add when steaming this type of rice.

[0020] Furthermore, in step 1), the headspace bottle model and specifications are Shimadzu 1.5mL, bottle height 32mm, and bottle outer diameter 11.6mm.

[0021] Furthermore, in step 2), the water-to-rice ratio is 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, 1.55, 1.60, 1.65, and 1.70, for a total of 17 types.

[0022] Further, in step 2), rinse the whole rice in the headspace vial with a wash bottle three times. After rinsing, wipe the water off the outer wall and mouth of the headspace vial completely with absorbent paper. Calculate the total mass W3 of the headspace vial, sample, and water after adding water, according to the formula W3 = W1 + W2 + water / rice * W1. Carefully add distilled water to the sample vial using a pipette, avoiding water droplets on the mouth of the vial, until the total mass equals W3.

[0023] Further, before step 3) allows the filter paper with a diameter of 8 mm to stand and soak, place the inner top of the 1.5 mL headspace vial cap and screw the cap with the filter paper onto the headspace vial.

[0024] Furthermore, the brand and model of the low-frequency nuclear magnetic resonance spectrometer is NM120-015V-1, the cavity size is 15mm, and the measurement parameters are: number of sampling points TD=75014, number of repeated scans NS=16, repeated sampling waiting time TW=1500ms, echo time TE=0.15ms, and number of echoes NECH=2000.

[0025] This invention selects different types of rice varieties and refines the water-rice ratio gradient. Using a low-field nuclear magnetic resonance spectrometer, it studies and analyzes the changes in bound water content in fresh rice and rice left at 25°C and 70% humidity for 24 hours under gradient water addition conditions. It innovatively establishes that the amount of bound water loss after 24 hours at room temperature reflects the sufficiency of the rice's moisture content. A bound water loss of ≤200±30 after 24 hours at 25°C and 70% humidity is considered an indication that the rice has sufficient moisture. The lowest water-rice ratio that results in a bound water loss of ≤200±30 earlier and remains ≤200±30 above this water-rice ratio is determined as the suitable water-rice ratio for steaming this rice variety.

[0026] This invention provides a method for determining the appropriate amount of water to add when steaming rice using a low-field nuclear magnetic resonance spectrometer. The method determines the appropriate amount of water to add during steaming by analyzing the loss of bound water in freshly cooked rice and rice left to stand at 25°C and 70% humidity for 24 hours. This avoids the problem of different rice varieties with similar or identical amylose content having different internal starch structures, protein content, and types, leading to potentially different actual water requirements. Furthermore, it avoids the cumbersome steps of measuring amylose content and provides a scientific basis and reference for determining the appropriate amount of water to add when steaming rice and for sensory evaluation of rice's taste quality by focusing on the amount of bound water loss.

[0027] The beneficial effects of this invention are as follows: 1) It establishes that the amount of bound water lost during the storage of rice can be used as a basis for judging whether the water content is sufficient or insufficient; 2) It avoids the current shortcomings of using the amylose content in rice as the basis for adding water, because different varieties with the same or similar amylose content have different internal starch structures, protein content and types, resulting in different actual water requirements; 3) It avoids the cumbersome steps of measuring the amylose content in rice; 4) It reveals the changes in bound water of rice stored at room temperature for 24 hours, providing a reference for the study of the interaction mechanism between water and rice components. Attached Figure Description

[0028] Figure 1 The water loss of rice left at room temperature for 24 hours under different cooking water-to-rice ratios at Zhongjia Early 17;

[0029] Figure 2The change in bound water loss of cooked rice after 24 hours at room temperature with the water-to-rice ratio, and the determination of suitable water-to-rice ratio based on bound water loss ≤200±30. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to specific embodiments in order to better understand the technical solution.

[0031] A method for determining the appropriate amount of water to add when steaming rice using a low-field nuclear magnetic resonance spectrometer includes the following steps: 1) Weigh 0.5g ± 0.01g 1) Take approximately 20 whole grains of polished rice and accurately record the mass W1 of the polished rice. Place the polished rice into a headspace vial. The headspace vial is a Shimadzu 1.5mL type, with a height of 32mm and an outer diameter of 11.6mm. Weigh and record the mass W2 of the headspace vial beforehand. Prepare two parallel samples for each water-rice ratio. 2) Set the water-rice ratio at 0.05 intervals. Set the water / rice (mass ratio) to be 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, 1.55, 1.60, 1.65, and 1.70, for a total of 17 water-rice ratios. 3) Rinse the polished rice in the sample vial with a wash bottle to remove dust from the surface of the polished rice. Rinse 3 times. After thoroughly wiping the water off the outer wall and mouth of the headspace vial with absorbent paper, calculate the total mass W3 of the headspace vial, sample, and water using the formula W3 = W1 + W2 + water / m*W1. Carefully add distilled water to the sample vial using a pipette, avoiding water droplets on the mouth, until the total mass equals W3; 4) Place an 8mm diameter circular filter paper (ordinary medium-speed filter paper) inside the top of the 1.5mL headspace vial cap, tighten the cap with the filter paper onto the headspace vial, and place it in an incubator at 25℃ and 70% humidity (temperature and humidity settings refer to room temperature conditions) for 30 minutes, i.e., the soaking time before steaming is 30 minutes; 5) Place the sample vial obtained in step 4) in an electric steamer and steam for 30 minutes, then switch to heat preservation for 20 minutes. The electric steamer brand and model is Little Bear DZG-C60A1; 6) ... 5) After steaming and keeping warm, the sample vials with headspaces are placed in a 25°C constant temperature chamber and allowed to cool for 30 minutes to avoid high temperature interference with the sample measurement results. This rice is considered fresh rice. 7) The sample vials with headspaces obtained in step 6) are immediately placed into the low-frequency nuclear magnetic resonance sample tube. The low-frequency nuclear magnetic resonance instrument has been preheated and adjusted to the ideal measurement state (the brand and model of the low-frequency nuclear magnetic resonance instrument is NM120-015V-1, the cavity is 15mm, and the measurement parameters are: number of sampling points TD=75014, number of repeated scans NS=16, repeated sampling waiting time TW=1500ms, echo time TE=0.15ms, number of echoes NECH=2000). The nuclear magnetic resonance curve of the rice that has been left to stand at 25°C for 0.5h is obtained. Two parallel samples are used for each water-to-rice ratio, and each sample is measured twice, that is, each water-to-rice ratio is measured four times.8) Place the headspace vial of the sample obtained in step 7) back into the incubator at 25°C and 70% humidity and let it stand for 24 hours; 9) Immediately place the headspace vial of the sample obtained in step 8) into the low-frequency nuclear magnetic resonance sample tube and measure it in the same way as in step 7) to obtain the nuclear magnetic resonance curve of the rice that has been standing at 25°C and 70% humidity for 24 hours, i.e., the rice that has been regenerated for 24 hours; 10) Invert the nuclear magnetic resonance curves obtained in steps 7) and 9), with the inversion set to 10,000 iterations, export the data to an EXCEL table, and plot the transverse relaxation time T2 as the x-axis and the instrument response signal value as the y-axis to obtain the moisture spectrum of fresh rice and regenerated rice that has been placed at 25°C and 70% humidity for 24 hours. Divide the peak areas representing bound water, structured water, and free water by the weight W1 of the refined rice sample, perform mass normalization, and obtain the water content of bound water, structured water, and free water. Take the average value of 4 measurements; 11) Sort the rice-water ratios from low to high, and calculate the loss of bound water under different water-water ratios. Loss of bound water = (Bound water content in fresh rice) - (Bound water content in rice placed at 25℃ and 70% humidity for 24 hours); 12) In the sorting of water-water ratios from low to high, find the water-water ratio corresponding to the earliest occurrence of bound water loss ≤200±30. When the water-water ratio is greater than this water-water ratio, the bound water loss is ≤200±30. The rice with the lowest water ratio that meets both of the above conditions is determined as the appropriate amount of water to add when steaming this type of rice.

[0032] Experimental Example 1

[0033] Thirty rice varieties with amylose (AC) content ranging from 1.8% to 27.3% were selected, milled into polished rice, and the polishing degree was grade one, in accordance with the national standard GB1354-2009.

[0034] Weigh out 0.5g ± 0.01g respectively. Whole rice was used, and 12 different rice-to-rice ratios were set for each variety: 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, and 2.0. Low-frequency nuclear magnetic resonance (NMR) was used to measure the changes in bound water in fresh rice under different rice-to-rice ratios, as well as in rice stored at 25℃ and 70% humidity for 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, and 24 hours. The analysis revealed that as the rice-to-rice ratio increased (i.e., more water was added during cooking), the loss of bound water in all rice varieties decreased during storage at 25℃ and 70% humidity. Different rice varieties showed similar trends in bound water loss under gradient water volume conditions: insufficient water resulted in greater bound water loss during storage; as the amount of water increased, the loss gradually decreased, and when the amount of water was sufficient or excessive, the bound water loss remained ≤200±30. Through comparative analysis of 30 different rice varieties, this method uses a bound water loss of ≤200±30 after 24 hours at 25℃ and 70% humidity as an indicator of whether the water content is sufficient or excessive. The lowest water-rice ratio that first reaches a bound water loss of ≤200±30 and maintains a bound water loss of ≤200±30 is considered to be the suitable water-rice ratio for steaming that rice variety.

[0035] Taking the rice variety Zhongjiazao 17, with an amylose content >25.0%, as an example, this paper illustrates the changes in bound water content of cooked rice over 24 hours at 25℃ and 70% humidity. Figure 1 As shown. When the water-to-rice ratio is 0.9, i.e., the amount of water added during cooking is insufficient, the amount of bound water lost after 24 hours at room temperature is 1388. As the water-to-rice ratio increases, i.e., as the amount of water added during cooking increases, the amount of bound water lost during the room temperature period gradually decreases, at 1088, 1041, 811, 736, 494, and 440 respectively. When the water-to-rice ratio reaches 1.6, the amount of bound water lost drops to 182. As the water-to-rice ratio continues to increase, the change in bound water loss is no longer significant, at 157, 143, and 155 respectively, remaining ≤200±30. When the water-to-rice ratio increases to 2.0, the amount of bound water lost is 177, continuing to remain ≤200±30. Example 1

[0036] 1) Select the high amylose content variety Shaoxian 1905, the medium amylose content variety Zhongjian 2, and the medium-low amylose content variety Ningjing 8. Weigh 0.5g ± 0.01g of whole rice (about 20 grains) from each variety and accurately record the mass W1 of the whole rice. Place the whole rice into a headspace vial. The headspace vial is a Shimadzu 1.5mL vial with a height of 32mm and an outer diameter of 11.6mm. Weigh and record the mass W2 of the headspace vial beforehand. 1) Two parallel samples; 2) Set the water-to-rice ratio at 0.05 intervals, with water / rice (mass ratio) of 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, 1.55, 1.60, 1.65, and 1.70, for a total of 17 water-to-rice ratios; 3) Rinse the whole polished rice in the sample bottle with a wash bottle to remove dust from the surface of the whole polished rice, rinsing 3 times.After thoroughly wiping the water off the outer wall and mouth of the headspace vial with absorbent paper, calculate the total mass W3 of the headspace vial, sample, and water using the formula W3 = W1 + W2 + water / m*W1. Carefully add distilled water to the sample vial using a pipette, avoiding water droplets on the mouth of the vial, until the total mass equals W3. 4) Place an 8mm diameter circular filter paper (ordinary medium-speed filter paper) inside the top of the 1.5mL headspace vial cap. Tightly screw the cap with the filter paper onto the headspace vial and place it in an incubator at 25℃ and 70% humidity (temperature and humidity settings refer to room temperature conditions) for 30 minutes. min, that is, the soaking time of whole rice is 30 min; 5) Place the sample headspace vial obtained in step 4) in an electric steamer and steam for 30 min, then transfer to a heat preservation setting for 20 min. The electric steamer brand and model is Little Bear Electric Steamer DZG-C60A1; 6) Place the sample headspace vial obtained after steaming and heat preservation in step 5) into a 25℃ constant temperature chamber and let it cool for 30 min to avoid high temperature interference with the sample measurement results. This rice is considered as fresh rice; 7) Immediately place the sample headspace vial obtained in step 6) into the low-frequency nuclear magnetic resonance sample tube. The low-frequency nuclear magnetic resonance instrument has been preheated and adjusted to the ideal measurement state ( The brand and model of the low-frequency nuclear magnetic resonance spectrometer was NM120-015V-1, with a cavity size of 15mm. Measurement parameters: number of sampling points TD=75014, number of repeated scans NS=16, repeated sampling wait time TW=1500ms, echo time TE=0.15ms, number of echoes NECH=2000). The NMR curves of freshly cooked rice (cooked at 25℃ for 0.5h) were obtained. Two samples were used per group, and each sample was measured twice, meaning each water-to-rice ratio was measured four times. 8) The headspace vials containing the samples measured in step 7) were returned to a temperature of 25℃ and humidity of 7%. 9) Place the sample vial obtained in step 8) into a low-frequency nuclear magnetic resonance sample tube immediately, and measure it in the same way as in step 7) to obtain the nuclear magnetic resonance curve of the rice that has been placed at 25℃ for 24 hours (i.e., regenerated for 24 hours); 10) Invert the nuclear magnetic resonance curves obtained in steps 7) and 9), with the inversion set to 10000 iterations, and export the data to an EXCEL table. Plot the transverse relaxation time T2 as the x-axis and the instrument response signal value as the y-axis to obtain the moisture spectrum of fresh rice and regenerated rice that has been regenerated for 24 hours under the conditions of 25℃ and 70% humidity. Divide the peak areas representing bound water, structural water, and free water respectively by the weight W1 of the polished rice sample, perform mass normalization, and obtain the water content of bound water, structural water, and free water. Take the average value of 4 measurements; 11) Sort according to the water-to-rice ratio from low to high, and calculate the bound water loss of Shaoxian 1905, Zhongjian 2, and Ningjing 8 varieties under different water-to-rice ratios, such as. Figure 2 As shown, the amount of bound water loss = (the amount of bound water in fresh rice) - (the amount of bound water in rice left to stand for 24 hours at 25℃ and 70% humidity); 12) In the ranking of water-to-rice ratio from low to high, see... Figure 2The Shaoxian 1905 variety first showed a combined water loss of ≤200±30% after 24 hours of rice storage when the water-to-rice ratio was 1.6, with a value of 177, which is greater than the water-to-rice ratio of 1.6. Therefore, the suitable water-to-rice ratio for Shaoxian 1905 is 1.6. The Zhongjian 2 variety first showed a combined water-to-rice ratio of 1.25 when the combined water loss of rice storage was ≤200±30%, which is greater than 1. With a water-to-rice ratio of 25, the combined water loss of the cooked rice after 24 hours is ≤200±30%. Therefore, for Zhongjian No. 2, the appropriate water-to-rice ratio for steaming is 1.25. For Ningjing No. 8, the first water-to-rice ratio with a combined water loss of ≤200±30 after 24 hours is 1.05. Furthermore, with a water-to-rice ratio greater than 1.05, the combined water loss of the cooked rice after 24 hours is ≤200±30%. Therefore, for Ningjing No. 8, the appropriate water-to-rice ratio for steaming is 1.05.

Claims

1. A method for determining an appropriate amount of water to be added to rice during steaming using a low-field nuclear magnetic resonance instrument, characterized by Comprising the following steps: 1) Take 0.5 g ± 0.01 g of whole milled rice, accurately record the mass of the whole milled rice W1, and place the whole milled rice into a headspace bottle with a mass of W2; 2) Wash off the dust on the surface of the whole milled rice in the headspace bottle, set the water-rice ratio at 0.05 numerical interval, set two parallel samples for each water-rice ratio, and prepare the sample; 3) Place the sample into a incubator at a temperature of 25°C and a humidity of 70% for standing and soaking for 30 min; 4) Place the sample soaked in step 3) into an electric steamer for steaming for 30 min, and then transfer to incubation for 20 min; 5) Place the sample steamed and incubated in step 4) into a 25°C constant temperature box for standing and cooling for 30 min; 6) Immediately place the sample treated in step 5) into a low-frequency nuclear magnetic resonance sample tube, and determine the nuclear magnetic resonance curve of the 25°C standing 0.5 h fresh rice, 2 parallel samples for each water-rice ratio, and determine 2 times for each sample, i.e. 4 times for each water-rice ratio; 7) Place the sample determined in step 6) back into a incubator at a temperature of 25°C and a humidity of 70% for standing for 24 h 8) Immediately place the sample in step 7) into a low-frequency nuclear magnetic resonance sample tube, and determine as in step 6), to obtain the nuclear magnetic resonance curve of the 25°C, 70% humidity standing 24 h rice; 9) Invert the nuclear magnetic resonance curves obtained in steps 6) and 8), set the number of iterations for inversion to 10000, export the data to an EXCEL table, take the average of 4 determinations, and plot the transverse relaxation time T2 as the abscissa and the signal value of the instrument response as the ordinate to obtain the moisture spectrum of fresh rice and 24 h retrograded rice under the condition of a temperature of 25°C and a humidity of 70%; divide the peak area of each peak representing bound water, structured water and free water by the mass of the milled rice sample W1 to obtain the water content of bound water, structured water and free water; 10) According to the order of water-rice ratio from low to high, calculate the loss amount of bound water under different water-rice ratios, bound water loss amount = (bound water content in fresh rice) - (bound water content in rice placed at a temperature of 25°C and a humidity of 70% for 24 h); 11) In the order of water-rice ratio from low to high, find the water-rice ratio corresponding to the early appearance of bound water loss amount ≤200±30, and when the water-rice ratio is greater than this value, the bound water loss amount is all ≤200±30, and the lowest water ratio rice that simultaneously satisfies the above two conditions is determined as the appropriate amount of water added when steaming the rice of this variety.

2. The method for determining the appropriate amount of water to be added to rice during steaming using a low-field nuclear magnetic resonance instrument according to claim 1, wherein The headspace bottle in step 1) is Shimadzu 1.5 mL, bottle height 32 mm, bottle outer diameter 11.6 mm.

3. The method for determining the appropriate amount of water to be added to rice during steaming using a low-field nuclear magnetic resonance instrument according to claim 1, wherein the low-field nuclear magnetic resonance instrument is a single-sided low-field nuclear magnetic resonance instrument. In step 2), the water-rice ratio is 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, 1.55, 1.60, 1.65, 1.70, a total of 17 kinds.

4. The method for determining the appropriate amount of water to be added to rice during steaming using a low-field nuclear magnetic resonance instrument according to claim 1, wherein the low-field nuclear magnetic resonance instrument is a single-sided low-field nuclear magnetic resonance instrument. In step 2), rinse the whole milled rice in the headspace bottle with a bottle washer for 3 times. After the rinsing is completed, wipe the water on the outer wall and the bottle mouth of the headspace bottle completely with a water-absorbing paper, then calculate the total mass W3 of the headspace bottle, the sample and the distilled water after the water is added, W3 = W1 + W2 + water / millet * W1, and carefully add the distilled water into the sample bottle with a pipette gun to avoid water drops on the bottle mouth. Add the water to the total mass equal to W3.

5. The method for determining the appropriate amount of water to be added to rice during steaming using a low-field nuclear magnetic resonance instrument according to claim 1, wherein the low-field nuclear magnetic resonance instrument is a single-sided low-field nuclear magnetic resonance instrument. In step 3), before standing and soaking, place a circular filter paper with a diameter of 8 mm on the inner top of the 1.5 mL headspace bottle matched with the bottle cap, and screw the bottle cap with the filter paper on the headspace bottle.

6. The method for determining the appropriate amount of water to be added to rice during steaming using a low-field nuclear magnetic resonance instrument according to claim 1, wherein The brand and model of the low-frequency nuclear magnetic resonance instrument is Nuway NM120-015V-1, the cavity is 15 mm, and the determination parameters are as follows: sampling point number TD = 75014, repeated scanning number NS = 16, repeated sampling waiting time TW = 1500 ms, echo time TE = 0.15 ms, and echo number NECH = 2000.

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