Method for removing phytic acid in grains by using superheated steam

Abstract

The invention belongs to the field of grain food processing, and relates to a method for removing phytic acid in cereals by using superheated steam, which specifically comprises the following steps: soaking the cereals at 40 DEG C for 20-30 minutes, and treating the cereals by using the superheated steam at 210 DEG C for 1-2 minutes. Compared with untreated grains, endogenous phytase of the grains is activated to a great extent through soaking treatment, and the highest enzyme activity reaches 373.33 U / kg; the cereal phytic acid removal rate reaches 60% or above under the optimal superheated steam condition; compared with a method of independently using superheated steam, the method has the advantages that the removal rate of the phytic acid in the grains is increased by 10% by soaking and assisting the superheated steam, the novel soaking and superheated steam process parameters are easy to implement in actual application, the energy consumption is low, and the phytic acid content in the grains can be effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of grain food processing, and relates to an improved method for improving the phytic acid removal rate; specifically, it is a method for removing phytic acid from grains by using superheated steam. Background Art

[0002] With the improvement of people's living standards, the demand of consumers for a reasonable dietary pattern and healthy eating behavior is increasing day by day. Compared with "polished rice and white flour", whole grains can better retain dietary fiber, B vitamins, minerals and phytochemicals in grains, and can significantly reduce food waste. The Chinese Dietary Guidelines recommend that grains should be the main component of daily diet, and 50-150 g of whole grains and miscellaneous beans should be consumed every day. However, more than 80% of adult residents in China have serious deficiencies in whole grain intake. The daily intake of whole grains for adult men is 13.9 g, and for women is 14.6 g, far lower than the recommended intake. Consuming a large amount of refined grains is not only unfavorable to public health, but also causes a great deal of food loss and waste. A research report evaluated the consumption situation in 195 countries and found the relationship between the grain intake (bran, biscuits, oats, muesli and other grains) of 502,940 participants and the risk of diabetes onset and progression. Among diabetic patients without cardiovascular disease, consuming more of the above four grains (eating ≥6 bowls of cereal foods per week) was associated with a 13%-32% reduction in the risk of cardiovascular disease and a 9%-28% reduction in the risk of chronic kidney disease.

[0003] However, whole grain foods also contain many anti-nutritional factors that limit the absorption and utilization of nutrients, such as phytic acid, trypsin inhibitors, saponins, tannins, etc. Among them, phytic acid can combine with various nutrients such as minerals to form chelates, hindering their absorption and utilization, and thus having an adverse effect on the health effects of these essential nutrients in the human body. However, humans and other monogastric animals cannot secrete phytase to break down phytic acid, so other processing methods are needed to reduce phytic acid in whole grains and increase the bioavailability of nutrients.

[0004] The phytic acid content in whole grain oats ranges from 0.42% to 1.16%. Although studies have reported that treatments such as soaking, germination, fermentation, microwave, high pressure, and addition of phytase can reduce the phytic acid content in grains to a certain extent, the most effective way to remove phytic acid in the industrial processing of grains is milling. Removing oat bran by milling can effectively reduce phytic acid by 27% - 53%. However, milling also causes almost all of the bran rich in minerals and other nutrients to be lost, which is contrary to the concept of consuming whole grain oat rice. Since phytic acid has strong thermal stability and can only be decomposed at temperatures above 150°C, common thermal processing methods are difficult to effectively remove phytic acid. During the frying process, uneven heating may cause some oats to be burnt on the surface; microwave heating consumes a large amount of energy, so it is mostly used for the bran of grains with extremely high phytic acid content (composed of barley, wheat, and oat bran). When heated at 2450 MHz for 2.5 minutes, the phytic acid content drops from 38.14 mg / g to 17.60 mg / g; high-pressure cooking will cause the starch in oats to gelatinize and change the protein structure, reducing its function. Therefore, when processing whole grain oats with a high phytic acid content, appropriate processing methods and conditions need to be adopted to ensure better removal of phytic acid. There is an urgent need to develop new technologies to reduce the phytic acid content in whole grain oats.

[0005] CN201510394671.5 discloses a wheat bran beverage with the efficacy of preventing constipation, which combines the comprehensive utilization of wheat bran and grain beverages. It uses flowing tap water to wash wheat bran three times to remove phytic acid, and bakes it at 180°C for 2 hours, which is time-consuming and energy-consuming. However, the removal effect of phytic acid is not clear, and the relationship between baking at 180°C and phytic acid in wheat bran is not constructed.

[0006] CN202411011238.4 discloses a method for precisely improving the mineral availability and protein digestibility of plant milk. It uses the enzymatic method to externally add 15U / g of crude phytase to the milk, and enzymatically hydrolyzes it at 55°C for 55 minutes. Subsequently, it is homogenized at 30MPa and sterilized at 90°C for 10 minutes. The effect of externally adding phytase and high-temperature treatment at 90°C on reducing the phytic acid content in plant milk (35% - 70%) is clarified. This method is only applicable to completely broken liquid beverages.

[0007] CN201210434977.5 discloses a method for removing the phytic acid content in broad beans and improving the bioavailability of iron and zinc elements. It uses an accelerated fermentation method, with a material-liquid ratio of broad beans and water of 1:5 (w / v), and ferments naturally at 30°C for 24 hours. After replacing 90% of the water, it continues to ferment for 6 days. It is clarified that accelerated fermentation can reduce the phytic acid content in broad beans by 7.02 mg / g and improve the bioaccessibility of iron and zinc. This method not only takes a long time but also completely changes the physical and chemical properties of the material.

[0008] CN201410193479.5 discloses a method for preparing low phytic acid soy protein isolate with high solubility, which uses an enzymatic method to externally add phytase at 20 U / g of soybean meal, adjusts the pH of enzymatic hydrolysis to 5, the temperature to 20 °C, and the enzymatic hydrolysis time to 30 minutes. It is clarified that externally adding phytase reduces the phytic acid content from 19.87 mg / g to 1.27 mg / g during the extraction of soybeans. This method is only applicable to powdered raw materials and completely changes the physical and chemical properties of the materials.

[0009] Therefore, there is currently a lack of requirements for maximizing the reduction of phytic acid content while retaining the original physical properties of oats, especially by activating endogenous phytase to degrade phytic acid. The law of reducing phytic acid content by superheated steam treatment is not yet clear. Summary of the Invention

[0010] The present invention mainly uses superheated steam and soaking as treatment methods to remove phytic acid from oats. It solves the problem that only relying on physical treatment methods can achieve a removal rate of more than 70% while retaining the original physical properties of oat grains, and provides an industrial processing method for improving the phytic acid removal rate of oats.

[0011] The first aspect of the present invention is to provide a method for removing phytic acid from grains with superheated steam, which is characterized in that the conditions of the superheated steam treatment are 190 - 220 °C for 1 - 2 min; Further, the grains are barley, wheat, rye, brown rice or oats; preferably, the grains are oats; Further, the treatment temperature of the superheated steam is 190 - 210 °C; the treatment time is 60 - 90 sec; Further, the treatment temperature of the superheated steam is 210 °C and the treatment time is 60 sec.

[0012] The second aspect of the present invention is a method for removing phytic acid from grains by using soaking to assist superheated steam treatment, which is characterized in that before the treatment of the method described in the first aspect, the grains are soaked; Further, the grains are barley, wheat, rye, brown rice or oats; preferably, the grains are oats; Further, the soaking treatment method is to wash the grains, remove water and add water according to a material-liquid ratio of 1:4 - 6; the soaking temperature is 35 - 45 °C; the soaking time is 20 - 40 min; Further, the soaking temperature is 38 - 42 °C and the soaking time is 25 - 35 min; Further, the material-liquid ratio in the soaking is 1:5; the soaking temperature is 40 °C and the soaking time is 30 min.

[0013] The second aspect of the present invention is to provide the application of the method described in the first aspect in reducing the phytic acid content in grains.

[0014] Furthermore, the grains are barley, wheat, rye, brown rice or oats; preferably, the grains are oats; Even further, the grains are oats.

[0015] The beneficial effects of the present invention include: 1) By activating the endogenous phytase, the activation conditions of the endogenous phytase in oats are clarified. Oats are treated with an overheated steam device above the phytic acid decomposition temperature, and the key control points of the thermal processing technology for maximizing the removal of phytic acid content in oats are proposed; the results show that the endogenous phytase in oat grains is effectively activated, and the phytic acid removal rate reaches more than 60%; 2) Compared with the previous methods, the present invention combines soaking and overheated steam treatment, and for the first time integrates soaking water treatment and overheated steam heat treatment to achieve a better removal rate of more than 70% without changing the original physical properties (starch gelatinization, protein denaturation) of oat grains.

[0016] In summary, the technology of the present invention only involves the physical treatment of the whole oat grain, which is suitable for the industrialized and continuous production of oat grains. The obtained oat grains not only have a low phytic acid content, but also do not affect their subsequent processing and manufacturing uses. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the phytic acid content (a) and removal rate (b) in oat grains treated with overheated steam and assisted by soaking.

[0018] Figure 2 It is the change in the molecular weight of oat proteins under different heat treatments: including: marker; untreated (1); overheated steam (2); stir-frying (3); microwave (4); high pressure (5). DETAILED DESCRIPTION OF THE INVENTION

[0019] The following further elaborates on the concept and technical effects generated by the present invention in combination with specific embodiments to fully understand the purpose, features and effects of the present invention. The methods are all conventional methods unless otherwise specified. The materials can be obtained from public commercial channels unless otherwise specified. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0020] Example 1: Activation of endogenous phytase in oat grains by water treatment (1)Warm water soaking treatment: After washing and draining the oat rice, mix it with water according to a material-liquid ratio of 1:5, place it in a constant temperature water bath, and set the soaking temperatures at 20, 40, 60, and 80 °C for 40 minutes respectively; soak at 40 °C for 10, 20, 30, and 40 minutes respectively.

[0021] (2)Conditioning treatment: Take 200 g of oat rice and put it into a self-sealing bag. Evenly add deionized water with a sprayer. Control the water addition time at 10, 20, 30, and 60 minutes respectively with a water content of 10%, and control the water addition amount at 10, 20, 30, and 50% respectively. Seal and shake to mix evenly, and then condition for 30 minutes. After treatment, air-dry at room temperature for 24 hours. Weigh 2 g of the sample after pulverization, extract it, and detect its phytic acid content and phytase activity.

[0022] (3)Determination of phytic acid content: Air-dry the oat rice after soaking and conditioning at 40 °C for 12 hours. Weigh 2 g of oat flour after pulverization, and extract and detect the phytic acid content according to the method of GB / T 5009.153-2016.

[0023] (4)Determination of phytase activity: Weigh 0.1 g of pulverized oat flour, and extract and detect the phytase activity according to the method of GB / T 18634-2009 Determination of the Activity of Phytase for Feed: Spectrophotometry.

[0024] The phytic acid content and phytase activity of oat rice after soaking and conditioning are shown in Table 1. During the 40-minute soaking process, as the soaking temperature increases, the phytic acid removal rate and phytase activity show a trend of first increasing and then decreasing. Especially at 40 °C, the phytase activity reaches 353.33 U / kg, and the phytic acid removal rate is 63.98%. Further research found that when soaking for 30 minutes, the highest phytic acid removal rate can reach 68.41%. In contrast, the phytic acid removal rate of the conditioning treatment is only between 7% and 34%, and the phytase activity is between 245 U / kg and 272 U / kg, which is significantly lower than the effect of the soaking treatment. Therefore, the present invention determines that soaking at 40 °C for 20 - 30 minutes is an effective operating condition for improving the phytic acid removal rate and phytase activity of oat rice.

[0025] Table 1 Effects of soaking and conditioning treatments on the phytic acid content and phytase activity of oat rice

[0026] Note: Different letters in the same column indicate significant statistical differences between different condition groups under each treatment method P < 0.05.

[0027] Example 2: Treatment of oat rice with superheated steam Overheated steam treatment: Take 3 kg of oat rice and add it to overheated steam. Set the parameters at 150, 170, 190, and 210 °C for 1 minute respectively; treat it at 210 °C for 1, 1.5, and 2 minutes. Crush the treated oat rice, weigh 2 g of oat flour, extract and detect its phytic acid content.

[0028] The results are as Figure 1 shown in a. As the temperature of overheated steam increases, the phytic acid content in oats shows a downward trend. Especially at 210 °C, the phytic acid content decreases to 1.78 mg / g, and the removal rate reaches 64.19%. However, when the treatment time of overheated steam at 210 °C is extended, the phytic acid removal rate decreases instead.

[0029] Example 3: Effects of overheated steam and frying on phytic acid in oat rice (1) Frying: Place 100 g of oat grains in a frying machine, fry at 210 °C for 1 minute, cool and crush, weigh 2 g, extract and detect its phytic acid content.

[0030] The results are shown in Table 2. After frying oat rice at 210 °C for 1 minute, the phytic acid removal rate reaches 44.27%. At the same temperature, the phytic acid removal rate of oat treated with overheated steam is 19.92% higher than that of frying. This shows that overheated steam treatment in heat treatment methods can more effectively remove phytic acid in oat rice.

[0031] Table 2 Effects of different heat treatments on phytic acid content in oats

[0032] Note: Different letters in the same column indicate significant statistical differences between different condition groups under each treatment method P at <0.05

[0033] Example 4: Effects of different heat treatments on gelatinization characteristics of oats (1) Gelatinization characteristic determination: Weigh 2.47 g of oat rice treated with overheated steam, frying, microwave, and high-pressure boiling respectively, crush and add 24.5 g of deionized water, and place it in an RVA4800 device to determine the gelatinization characteristics of oat starch.

[0034] (2) Under the conditions of achieving the same phytic acid removal rate by each heat treatment method, compare their effects on the gelatinization characteristics of oat rice. Frying at 210 °C for 1 minute, the phytic acid removal rate is 44.27%; overheated steam at 190 °C for 1 minute, the phytic acid removal rate is 43.66%; microwave treatment at a frequency of 2450 MHz for 1 minute, the phytic acid removal rate is 48.64%; high-pressure boiling at 100 kPa (121 °C) for 10 min, the phytic acid removal rate is 41.39%.

[0035] The results are shown in Table 3. Compared with the raw materials, the oats treated with superheated steam showed peak viscosity, retrogradation value and gelatinization temperature closer to those of the raw materials. In contrast, the peak viscosity and retrogradation value of the oat starch after frying and microwave treatment were lower than those of the raw materials, while the breakdown value and gelatinization temperature increased. The gelatinization characteristics of the oat starch treated under high pressure changed significantly, with the peak viscosity, breakdown value, final viscosity, retrogradation value and gelatinization temperature all decreasing significantly. The above results indicate that superheated steam treatment can better maintain the gelatinization characteristics of oat starch without significant changes.

[0036] Table 3 Effects of different treatments on the gelatinization characteristics of oat flour

[0037] Note: Different letters in the same column indicate statistical differences at P <0.05 among different condition groups under each treatment method.

[0038] Example 5: Effects of different heat treatments on oat protein (1) Determination of oat protein molecular weight: Oat proteins from oats treated with superheated steam, frying, microwave and high-pressure boiling were extracted respectively, and then SDS-PAGE was carried out to determine the molecular weight changes.

[0039] The results are as Figure 2 shown. The untreated oat protein showed two bands at 17 - 25KDa and 25 - 48KDa. The protein bands of oats treated with superheated steam and frying were similar to those of the untreated samples, indicating little change in their protein structure; after microwave treatment, the band at 25 - 48KDa showed a darker color; while high-pressure boiling treatment led to complete denaturation of the oat protein, with the band position shifting downwards, indicating a decrease in its molecular weight. The above results indicate that superheated steam treatment can effectively maintain a low degree of denaturation of oat protein, thereby achieving a high phytic acid removal rate while ensuring the stability of basic components.

[0040] Example 6 Removal of phytic acid from oats by soaking-assisted superheated steam Soaking-assisted superheated steam treatment: Take 3 kg of oats and soak them at 40 °C for 30 minutes, then send them into a superheated steam equipment and set the parameters to treat at 210 °C for 1 minute. Crush the treated oats, weigh 2 g of oat flour, extract and detect its phytic acid content.

[0041] Combined with soaking-assisted superheated steam treatment, the removal effect of phytic acid is significantly enhanced, and the highest removal rate can reach 72.23%. This method has a significant phytic acid removal effect and can effectively reduce the phytic acid content in oats. Soaking-assisted superheated steam treatment is superior to the effect of removing phytic acid by superheated steam alone ( Figure 1 b).

[0042] The embodiments described above are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative efforts shall fall within the scope of protection of the present invention.

Claims

1. A method for removing phytic acid from grains using superheated steam, characterized in that, The conditions for the superheated steam treatment are treatment at 190 - 220°C for 1 - 2 minutes.

2. The method according to claim 1, wherein The cereal grains mentioned are barley, wheat, rye, brown rice or oats.

3. The method according to claim 2, wherein The treatment temperature of the superheated steam is 190 - 210°C; the treatment time is 60 - 90 seconds.

4. The method according to claim 3, wherein The treatment temperature of the superheated steam is 210°C and the treatment time is 60 seconds.

5. A method for removing phytic acid from grains by using soaking-assisted superheated steam treatment, characterized in that, Before performing the method described in any one of claims 1 - 4, the cereal grains are subjected to a soaking treatment.

6. The method according to claim 5, wherein The cereal grains mentioned are barley, wheat, rye, brown rice or oats.

7. The method according to claim 6, wherein The soaking treatment method is to wash the cereal grains, remove the water, and then add water according to a solid - liquid ratio of 1:4 - 6; the soaking temperature is 35 - 45°C; the soaking time is 20 - 40 minutes.

8. The method according to claim 7, wherein The soaking temperature is 38 - 42°C and the soaking time is 25 - 35 minutes.

9. The method according to any one of claims 1-8, characterized in that, Among them, the cereal grains are oats.

10. Use of the method described in any one of claims 1 - 9 in reducing the phytic acid content of cereal grains.

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