Starch gel and preparation method thereof

Abstract

The invention relates to the field of food processing, and discloses starch gel and a preparation method thereof. The method comprises the following steps: mixing starch and water-soluble hemicellulose to obtain a mixed solution, and carrying out heat treatment on the mixed solution; wherein the mass ratio of the starch to the water-soluble hemicellulose is (8-15): 1; wherein in the starch, the mass of amylose accounts for more than 60wt% of the total mass of the starch. After the food containing the starch gel provided by the invention is eaten, the starch digestibility is obviously lower, the blood sugar rising degree is lower, and the starch gel provided by the invention is healthier and more suitable for being applied to food production.

Description

Technical Field

[0001] The invention relates to the field of food processing, and in particular to a starch gel and a preparation method thereof. Background Art

[0002] Starch is an indispensable part of people's daily diet. In 2020, my country's apparent demand for starch was 36.061 million tons, an increase of 41.2% compared with 2016 (25.532 million tons). However, starch can be quickly digested after entering the human gastrointestinal tract, resulting in a rapid increase in blood sugar levels after meals. Long-term large fluctuations in blood sugar levels increase the prevalence of metabolic diseases such as type 2 diabetes.

[0003] At present, there are also some starch products with digestion resistance, which are used in food production and can play a role in digestion resistance to a certain extent. However, after eating foods containing such starch products, the starch digestibility and blood sugar level are still high, so the digestion resistance of such starch products on the market still has a lot of room for improvement. Summary of the invention

[0004] The purpose of the present invention is to overcome the above-mentioned problems existing in the prior art and to provide a starch gel and a preparation method thereof. Compared with foods not containing resistant starch products or foods containing resistant starch available on the market, after eating foods containing the starch gel provided by the present invention, the starch digestibility is significantly lower. The starch gel provided by the present invention is healthier and more suitable for application in food production.

[0005] In order to achieve the above object, the present invention provides a method for preparing starch gel, which comprises: mixing starch and water-soluble hemicellulose to obtain a mixed solution, and heat treating the mixed solution;

[0006] The mass ratio of starch to water-soluble hemicellulose is (8-15):1;

[0007] Among them, in starch, the mass of amylose accounts for more than 60wt% of the total mass of starch.

[0008] The second aspect of the present invention provides starch gel prepared by the method described in the first aspect.

[0009] The starch gel prepared by the method provided by the present invention is applied in food production to significantly reduce the starch digestibility. Compared with foods that do not contain resistant starch products or foods that contain resistant starch available on the market, after eating foods containing the starch gel provided by the present invention, the starch digestibility is significantly lower and the degree of blood sugar increase is lower. The starch gel provided by the present invention is healthier and more suitable for application in food production. DETAILED DESCRIPTION

[0010] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0011] In a first aspect, the present invention provides a method for preparing starch gel, the method comprising: mixing starch and water-soluble hemicellulose to obtain a mixed solution, and heat-treating the mixed solution;

[0012] The mass ratio of starch to water-soluble hemicellulose is (8-15):1;

[0013] Among them, in starch, the mass of amylose accounts for more than 60wt% of the total mass of starch.

[0014] The inventors of the present invention have found in their research that when the water-soluble hemicellulose and the starch as above are treated in the above manner, the starch gel obtained can be used in food processing to obtain food with a significantly lower starch digestibility after consumption, thereby better controlling the degree of increase in blood sugar. The starch gel provided by the present invention is healthier and more suitable for use in food production.

[0015] The mass percentage of amylose in starch was determined using the K-AMYL kit method from Megazyme.

[0016] In addition, it is understood that the starch and the water-soluble hemicellulose are mixed in the presence of a dispersant, which is generally water. The starch, water and the water-soluble hemicellulose can be mixed and then allowed to stand at room temperature for 8-15 minutes to stabilize the mixture before subsequent heat treatment.

[0017] According to the present invention, preferably, the mass ratio of starch to water-soluble hemicellulose is (10-12): 1. The inventors of the present invention further found in the study that when the above range is met, the digestion resistance of the prepared starch gel can be further guaranteed, and at the same time, the color of the starch gel can be fully guaranteed to be light amber, and when used for processing products, a better appearance can be obtained.

[0018] According to the present invention, preferably, in starch, the mass of amylose is 65-75wt% of the total mass of starch (for example, it can be 65wt%, 66wt%, 67wt%, 68wt%, 69wt%, 70wt%, 71wt%, 72wt%, 73wt%, 74wt%, 75wt% and the range formed by any two of the above values ​​and the values ​​within the range).

[0019] According to the present invention, preferably, the weight average molecular weight of starch is (1×10 6 )-(8×10 7 )g / mol (for example, it can be 1×10 6 g / mol, 4×10 6 g / mol, 8.5×10 6 g / mol, 1×10 7 g / mol, 3×10 7 g / mol, 5×10 7 g / mol, 8×10 7 g / mol and the range formed by any two of the above values ​​and the values ​​within the range).

[0020] According to the present invention, preferably, in the mixed solution, the mass content of starch is 7.2-9.2wt% (for example, it can be 7.2wt%, 7.5wt%, 7.8wt%, 8wt%, 8.2wt%, 8.5wt%, 8.8wt%, 9wt%, 9.2wt% and the range formed by any two of the above values ​​and the value within the range). In this way, the digestion resistance of the prepared starch gel can be further guaranteed.

[0021] According to the present invention, preferably, the weight average molecular weight of the water-soluble hemicellulose is (3.5-8.5)×105Da, and the molecular weight distribution index (i.e., Mw / Mn, the ratio of the weight average molecular weight to the number average molecular weight) is 1-130 (for example, it can be 1, 2, 10, 20, 40, 60, 80, 100, 120, 130 and the range formed by any two of the above values ​​and the value within the range). The use of the water-soluble hemicellulose as described above can further ensure that a starch gel with a lower starch digestibility is obtained.

[0022] Hemicellulose is a type of heteropolysaccharide. Different raw material sources lead to differences in the composition of hemicellulose. Its monosaccharide composition can include D-xylose, L-arabinopyranose, D-glucose, D-galactose, D-mannose and a small amount of uronic acid. According to the different monosaccharide compositions, hemicellulose generally includes galactans (mainly arabinogalactose), xyloglucans (with glucan as the main chain, connected by β-1,4 glycosidic bonds, and a large number of xylose side chains connected to the 6th position of the glycosidic bond), mannans (mainly mannose chain molecules connected by β-1,4 glycosidic bonds), and xylans (with xylan as the main chain, connected by β-1,4 glycosidic bonds, which can be extracted from a variety of plants, such as grass plants). Water-soluble hemicellulose is also a polymer composed of different types of monosaccharides (such as xylose, arabinose and galactose, etc.). The monosaccharides obtained by hydrolyzing the water-soluble hemicellulose have a composition and content that are not particularly limited and are related to the composition of the water-soluble hemicellulose itself.

[0023] According to the present invention, preferably, the heat treatment method comprises: heating the mixed solution to a constant temperature, then maintaining the constant temperature, and then cooling to room temperature; wherein the constant temperature is 80-150°C (for example, it can be 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C and the range formed by any two of the above values ​​and the value within the range), more preferably 90-145°C (for example, it can be 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 145°C and the range formed by any two of the above values ​​and the value within the range). The inventors of the present invention have found in their research that after the mixed solution has undergone the process as described above, the starch gel obtained can have better resistance to digestion.

[0024] It is understandable that in general households or restaurants, the cooking temperature is 80-100° C., and in the production of food industry, such as the production of pre-prepared dishes, the products are generally sterilized at 140-150° C. The inventors of the present invention have found that by using the method of the present invention, when the constant temperature is 80-150° C., a starch gel with good digestion resistance can be obtained, so the method provided by the present invention is applicable to daily life or the food industry.

[0025] According to the present invention, preferably, the heating method includes: heating the mixed solution to 45-55 (for example, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55 and the range and value within the range formed by any two of the above values) ° C / min at a heating rate of 20-25 (for example, it can be 20, 21, 22, 23, 24, 25 and the range formed by any two of the above values ​​and the value within the range) ° C; then heating the mixed solution to a constant temperature for the second time at a heating rate of 4-7 (for example, it can be 4, 5, 6, 7) ° C / min. It can be understood that before the heat treatment, the mixed solution material is at room temperature. The inventors of the present invention further found that when the temperature is raised using the process as described above, the prepared starch gel has better resistance to digestion.

[0026] According to a particularly preferred embodiment of the present invention, the second heating rate is 5-6°C / min.

[0027] According to the present invention, preferably, the constant temperature time is 3-8 min, more preferably 4-6 min (for example, it can be 4 min, 4.5 min, 5 min, 5.5 min, 6 min, and the range formed by any two of the above values ​​and the value within the range).

[0028] According to the present invention, preferably, the cooling method includes: first cooling the mixed solution to 45-55 (for example, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55 and the range formed by any two of the above values ​​and the value within the range) ° C at a cooling rate of 4-7 (for example, 4, 5, 6, 7) ° C / min, keeping warm for 1-3 minutes, and then naturally cooling the mixed solution to room temperature. Among them, the natural cooling rate can generally be 8-15 ° C / min, and the natural cooling can generally be completed in 1.5-3 hours.

[0029] According to the present invention, preferably, the first cooling rate is 5-6°C / min.

[0030] The inventors of the present invention have found that the specific heating, constant temperature and cooling process as described above can further ensure that the prepared starch gel has good digestion resistance. In order to make the temperature or material conditions in the mixed solution more uniform, the heat treatment can be carried out under stirring, and the stirring speed of the first 10s of the heating process can be 900-980rpm, and the stirring speed of the remaining heating process, constant temperature process and the first cooling process can be 140-180rpm, and no stirring is required during the natural cooling process.

[0031] According to a particularly preferred embodiment of the present invention, the method for preparing the water-soluble hemicellulose comprises:

[0032] (1) subjecting a material liquid containing corn bran to a first enzymatic hydrolysis in the presence of α-amylase; subjecting the material after the first enzymatic hydrolysis to a second enzymatic hydrolysis in the presence of alkaline protease, and performing a first solid-liquid separation after inactivating the enzyme;

[0033] (2) mixing the solid phase obtained in step (1) (i.e., the corn bran treated in step (1)) with an alkali to obtain an alkali-containing mixed liquid, and performing an alkali treatment; performing a second solid-liquid separation on the alkali-treated material, and taking a supernatant;

[0034] (3) The supernatant is mixed with an organic reagent to obtain a precipitate.

[0035] Among them, the obtained precipitate is water-soluble hemicellulose. The water-soluble hemicellulose prepared by the above method can further ensure that a starch gel with a lower starch digestibility is obtained, and can also meet the above requirements of weight average molecular weight and molecular weight distribution index. In addition, the hemicellulose obtained by using gramineous plants as raw materials is xylan (mainly 4-O-methyl glucuronic acid arabinoxylan, and xylan is the main chain, connected by β-1,4 glycosidic bonds). After the water-soluble hemicellulose prepared in this way is hydrolyzed, monosaccharides such as xylose, arabinose, galactose and glucose can be obtained, and the amount of xylose can account for 45-60wt% of the total monosaccharide amount, and the amount of arabinose can account for 30-40wt% of the total monosaccharide amount. Galactose and glucose can also be contained, and the amount of the two is not particularly limited, such as the amount of galactose can account for 5-12wt% of the total monosaccharide amount, and the amount of glucose can account for 2-7wt% of the total monosaccharide amount.

[0036] According to the present invention, preferably, in the corn bran-containing liquid, the average particle size of corn bran is 0.01-0.5 mm, more preferably 0.1-0.3 mm (for example, it can be 0.1 mm, 0.15 mm, 0.18 mm, 0.2 mm, 0.23 mm, 0.25 mm, 0.28 mm, 0.3 mm, and the range formed by any two of the above values ​​and the value within the range).

[0037] According to the present invention, preferably, in step (1), the weight content of corn bran in the corn bran-containing liquid is 5-10 (for example, it can be 5, 6, 6.25, 6.5, 6.8, 7, 7.5, 7.8, 8, 8.2, 8.5, 9, 10 and the range formed by any two of the above values ​​and the values ​​within the range) weight %.

[0038] It can be understood that the feed liquid containing corn bran is a material obtained by mixing corn bran and water. The corn bran can be washed, decolorized (sodium hypochlorite solution can be mixed with corn bran for decolorization, and the amount of sodium hypochlorite used can be 30-50g relative to 100g of corn bran; then centrifuged, and the solid phase is taken for subsequent operations), dried, and crushed to the above degree, and then mixed with water to obtain a feed liquid with the above corn bran content.

[0039] According to the present invention, preferably, in step (1), relative to 100g of corn bran, the amount of α-amylase used is 45000-70000U, and the amount of alkaline protease used is 200000-450000U.

[0040] According to the present invention, more preferably, relative to 100g of corn bran, the dosage of α-amylase is 48000-68000U (for example, it can be 48000U, 49000U, 50000U, 51000U, 52000U, 54000U, 58000U, 60000U, 62000U, 64000U, 68000U and the range formed by any two of the above values ​​and the value within the range), the dosage of alkaline protease is 48000-68000U (for example, it can be 48000U, 49000U, 50000U, 51000U, 52000U, 54000U, 58000U, 60000U, 62000U, 64000U, 68000U and the range formed by any two of the above values ​​and the value within the range), The dosage is 220000-420000U (for example, it can be 220000U, 240000U, 250000U, 260000U, 270000U, 280000U, 300000U, 320000U, 350000U, 375000U, 380000U, 385000U, 400000U, 420000U and the range formed by any two of the above values ​​and the value within the range).

[0041] The enzyme activity of α-amylase is defined as the amount of enzyme that releases 1 mg of reducing sugar from a 2 wt% soluble starch solution per hour at a temperature of 60°C and a pH of 5.6, which is defined as 1 enzyme activity unit (U).

[0042] The enzyme activity of alkaline protease is defined as the amount of enzyme that produces 1 mg of tyrosine within 1 min at a temperature of 40°C and a pH of 11, which is defined as 1 enzyme activity unit (U).

[0043] According to the present invention, preferably, in step (1), the conditions of the first enzymolysis include: a temperature of 50-60°C (for example, 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C, 60°C and a range formed by any two of the above values ​​and a value within the range), a time of 1.5-2.5h, and a pH of 6-6.6 (for example, 6, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6 and a range formed by any two of the above values ​​and a value within the range). The obtained corn bran-containing liquid can be adjusted to the above pH range, and then α-amylase is added.

[0044] According to the present invention, preferably, in step (1), the conditions of the second enzymolysis include: a temperature of 50-60°C (for example, it can be 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C, 60°C and the range formed by any two of the above values ​​and the values ​​within the range), a time of 1.5-2.5h, and a pH of 8.8-9.3 (for example, it can be 8.8, 8.9, 9, 9.1, 9.2, 9.3 and the range formed by any two of the above values ​​and the values ​​within the range). The material after the first enzymolysis can be adjusted to the above pH range, and then alkaline protease is added.

[0045] The method of inactivating the enzyme may be: after the second enzymolysis, placing the material in a boiling water bath to inactivate the enzyme for 5-10 minutes.

[0046] The first solid-liquid separation can be centrifugation, and the centrifugal speed can be 3000-5000rpm (for example, it can be 3000rpm, 3200rpm, 3500rpm, 3800rpm, 4000rpm, 4200rpm, 4500rpm, 4800rpm, 5000pm and the range formed by any two of the above values ​​and the values ​​within the range), and the time can be 4-6min (for example, it can be 4min, 5min, 6min and the range formed by any two of the above values ​​and the values ​​within the range).

[0047] According to the present invention, preferably, in step (2), in the alkali-containing mixed solution, the mass concentration of the alkali is 2-7wt%, more preferably 2.5-6.5 (for example, it can be 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5 and the range formed by any two of the above values ​​and the value within the range) wt%. The alkali can be selected from inorganic bases, such as KOH and / or NaOH, and can be used in the form of its aqueous solution.

[0048] According to the present invention, preferably, in step (2), the conditions for the alkali treatment include: a temperature of 75-85°C (for example, it can be 75°C, 76°C, 77°C, 78°C, 79°C, 80°C, 81°C, 82°C, 83°C, 84°C, 85°C and a range formed by any two of the above values ​​and values ​​within the range), and a time of 1.5-2.5h.

[0049] Wherein, the specific mode of the second solid-liquid separation is not particularly limited, for example, it can be filtration or centrifugation. The centrifugal conditions may include a rotation speed of 3000-5000rpm (for example, it can be 3000rpm, 3200rpm, 3500rpm, 3800rpm, 4000rpm, 4200rpm, 4500rpm, 4800rpm, 5000rpm and the range formed by any two of the above values ​​and the value within the range), and a time of 4-6min (for example, it can be 4min, 5min, 6min and the range formed by any two of the above values ​​and the value within the range).

[0050] According to the present invention, preferably, before mixing the supernatant and the organic reagent, the method further comprises: adjusting the pH of the supernatant to 6-7, and concentrating and dialyzing the supernatant in sequence. The pH of the supernatant can be adjusted using glacial acetic acid or sodium hydroxide.

[0051] Preferably, the specific method of concentration is: rotary evaporation concentration at 40-65°C (for example, it can be 40°C, 42°C, 45°C, 48°C, 50°C, 52°C, 55°C, 58°C, 60°C, 62°C, 65°C and the range formed by any two of the above values ​​and the values ​​within the range) and a stirring speed of 50-100rpm.

[0052] Preferably, the specific method of the dialysis is: the concentrated supernatant is dialyzed for 6-12 hours at room temperature using a dialysis bag with a molecular weight cutoff of 500-3000Da (for example, 500Da, 800Da, 1000Da, 1500Da, 2000Da, 2500Da, 3000Da, and a range formed by any two of the above values ​​and a value within the range). In this way, impurities such as sodium ions and acetate ions in the supernatant can be fully removed. The portion that does not pass through the dialysis bag is taken for subsequent mixing with the organic reagent.

[0053] According to the present invention, preferably, the organic reagent is selected from at least one of ethanol and acetone. The ethanol can be used in the form of anhydrous ethanol or an ethanol-water solution with an ethanol concentration of 70-95wt% (e.g., 75wt%, 95wt%), more preferably anhydrous ethanol. When ethanol is selected, both the extraction effect and the cost can be taken into account.

[0054] According to the present invention, preferably, in step (3), the volume ratio of the supernatant to the organic reagent is 1:(2-4).

[0055] According to the present invention, preferably, in step (3), after the supernatant and the organic reagent are mixed, the method further comprises: subjecting the material to a third solid-liquid separation. The third solid-liquid separation may be carried out by centrifugation, the speed may be 3000-5000 rpm, and the time may be 4-6 min.

[0056] The obtained precipitate can also be dried, and the drying method can be freeze-drying. The specific operating conditions may include: vacuum condition of 0Pa<vacuum degree<20Pa, and the freeze-drying time can be 18-36h (for example, it can be 18h, 20h, 24h, 28h, 30h, 32h, 36h).

[0057] In the second aspect, the present invention provides a starch gel prepared by the method as described above. After texture property analysis, it was found that compared with the corn starch gel that has not been processed with resistance, the starch gel prepared by the present invention has stronger elasticity, smaller hardness and better taste. Among them, the hardness of the starch gel prepared by the present invention can be 1.0-30N, the adhesion can be 0.50-4.74mJ, the elasticity can be 1-10mm, the chewiness can be 2-10mJ, and the peak viscosity can be 10-2000cP. The above-mentioned texture property analysis is carried out under the following conditions: the test probe is a cylindrical probe P / 5 with a diameter of 2cm, the probe test rate is 30mm / s, the deformation is 50%, and the trigger force is 1N. Compared with the corn starch gel that has not been processed with resistance, the starch digestibility can be reduced by 5-20% compared with the native starch digestibility.

[0058] The method of use of the starch gel prepared by the present invention is not particularly limited, and similar methods of use can be used with existing resistant starch products. Generally, in the preparation of food, a part of conventional starch (such as wheat starch, corn starch, etc., can be replaced by equal quality) is replaced to exert the ability to inhibit starch digestion. The starch gel prepared by the method provided by the present invention has significantly improved texture characteristics (such as elasticity, adhesion, elasticity, chewiness, peak viscosity), and significantly reduced digestive characteristics. In addition, the starch gel obtained can also be obtained by other post-processing, such as freeze-drying (such as freeze-drying 18-36h under the vacuum condition of 0Pa<vacuum<20Pa), and dry powder can be obtained. When used, dry powder can be blended with water in proportion to form food, supplement dietary fiber, and provide energy. The starch gel provided by the present invention, compared to conventional starch, or existing starch gel products on the market, has a lower starch digestibility after use, and has more advantages.

[0059] The present invention will be described in detail below through preparation examples and examples.

[0060] In the following preparation examples, α-amylase was purchased from Roan, product number 9000-90-92;

[0061] Alkaline protease was purchased from Roan, catalog number 9068-59-1;

[0062] For the product prepared in the preparation example, the monosaccharide composition and content of the sample were analyzed by PMP pre-column derivatization HPLC method (Huang Xiaolan, He Xufeng, Yang Qin, et al. Determination of monosaccharide composition of Radix Glehniae polysaccharides by PMP pre-column derivatization HPLC method [J]. Food and Fermentation Industries, 2020, 46(07): 250-256. DOI: 10.13995 / j.cnki.11-1802 / ts.022499.) and confirmed to be water-soluble hemicellulose.

[0063] The weight average molecular weight and number average molecular weight were determined using a GPC-20A gel permeation chromatograph, and narrow distribution PEO or Pullulan polysaccharide standards were used as standard curves. Chromatographic column: TSKgel GMPWXL aqueous gel chromatographic column; mobile phase: 0.1NNaNO3+0.06% NaN3 aqueous solution; flow rate: 0.6mL / min; test column temperature: 35°C; detector: RID-20A differential refractive index detector.

[0064] In the following preparation examples, the decolorization method is to use a sodium hypochlorite solution for decolorization, wherein the amount of sodium hypochlorite used is 40 g relative to 100 g of bran. After decolorization, centrifugation is performed, and the solid phase is taken for subsequent operations.

[0065] Preparation Example 1

[0066] The corn bran is washed, decolorized, dried, and then crushed to an average particle size of 0.18 mm, and then mixed with water to obtain a feed liquid with a weight content of corn bran of 6.25% by weight.

[0067] The pH of the feed liquid was adjusted to 6.2, and α-amylase was added to the feed liquid so that the amount of α-amylase used was 60000 U relative to 100 g of corn bran. The reaction was carried out at 55° C. for 2 h to obtain a material after the first enzymolysis.

[0068] The pH of the material after the first enzymolysis was adjusted to 9, and alkaline protease was added to the material solution so that the amount of alkaline protease used was 385000 U relative to 100 g of corn bran. The reaction was carried out at 55° C. for 2 h to obtain the material after the second enzymolysis.

[0069] The material after the second enzymatic hydrolysis was then placed in a boiling water bath to inactivate the enzyme for 8 minutes, and then centrifuged at 5000 rpm for 4 minutes to obtain a solid phase, which was the corn bran treated in step (1).

[0070] (2) Mixing the corn bran treated in step (1) with a NaOH solution to obtain an alkaline mixed solution having a NaOH mass concentration of 5 wt%, and reacting the mixture at 80° C. for 2 h.

[0071] The alkali-treated material was centrifuged at 4000 rpm for 5 min, and the supernatant was collected.

[0072] The pH of the supernatant was adjusted to 6.3 with glacial acetic acid, and then concentrated by rotary evaporation at 50° C. and 90 rpm. The concentrated supernatant was then placed in a dialysis bag with a molecular weight cutoff of 1000 Da and dialyzed at room temperature for 8 hours.

[0073] (3) The liquid that did not pass through the dialysis bag was mixed with anhydrous ethanol in a volume ratio of 1:3, and centrifuged at 4000 rpm for 5 min to obtain a precipitate.

[0074] The precipitate was freeze-dried under a vacuum of 8 Pa for 24 h. The weight average molecular weight of the prepared water-soluble hemicellulose was 7.7×10 5 Da, Mw / Mn is 2. After hydrolysis by PMP pre-column derivatization HPLC method, xylose accounts for 50.62wt% of the total monosaccharides, arabinose accounts for 36.5wt% of the total monosaccharides, galactose accounts for 7.4wt% of the total monosaccharides, and glucose accounts for 3.1wt% of the total monosaccharides.

[0075] Preparation Example 2

[0076] The corn bran is washed, decolorized, dried, and then crushed to an average particle size of 0.25 mm, and then mixed with water to obtain a feed liquid with a weight content of corn bran of 8 weight%.

[0077] The pH of the feed liquid was adjusted to 6.5, and α-amylase was added to the feed liquid so that the amount of α-amylase used was 50000 U relative to 100 g of corn bran. The reaction was carried out at 60° C. for 2.5 h to obtain a material after the first enzymolysis.

[0078] The pH of the material after the first enzymolysis was adjusted to 9.3, and alkaline protease was added to the material solution so that the amount of alkaline protease used was 250000 U relative to 100 g of corn bran. The reaction was carried out at 60° C. for 2.5 hours to obtain the material after the second enzymolysis.

[0079] The material after the second enzymatic hydrolysis was then placed in a boiling water bath to inactivate the enzyme for 10 min, and then heated at 4000

[0080] Centrifuge at rpm for 5 min and take the solid phase, which is the corn bran treated in step (1).

[0081] (2) Mixing the corn bran treated in step (1) with a NaOH solution to obtain an alkaline mixed solution having a NaOH mass concentration of 2.5 wt%, and reacting the mixture at 76° C. for 2.5 h.

[0082] The alkali-treated material was centrifuged at 4000 rpm for 5 min, and the supernatant was collected.

[0083] The pH of the supernatant was adjusted to 6.6 with glacial acetic acid, and then concentrated by rotary evaporation at 45°C and 80 rpm. The concentrated supernatant was then placed in a dialysis bag with a molecular weight cutoff of 2000 Da and dialyzed at room temperature for 10 hours.

[0084] (3) The liquid that did not pass through the dialysis bag was mixed with anhydrous ethanol in a volume ratio of 1:4, and centrifuged at 4000 rpm for 5 min to obtain a precipitate.

[0085] The precipitate was freeze-dried under a vacuum of 15 Pa for 24 h. The weight average molecular weight of the prepared water-soluble hemicellulose was 6.7×10 5 Da, Mw / Mn is 120. After hydrolysis by PMP pre-column derivatization HPLC method, xylose accounts for 49.40wt% of the total monosaccharides, arabinose accounts for 35.6wt% of the total monosaccharides, galactose accounts for 7.2wt% of the total monosaccharides, and glucose accounts for 2.7wt% of the total monosaccharides.

[0086] The following examples were carried out in an RVA (Rapid Visco Analyzer).

[0087] Example 1

[0088] Take the weight average molecular weight (8.5×10 6 g / mol) of starch (the mass of amylose accounts for 70wt% of the total mass of starch), water, and the water-soluble hemicellulose obtained in Preparation Example 1 are mixed, the mass ratio of starch to water-soluble hemicellulose is 11:1, and the mass content of starch in the obtained mixed solution is 8wt%. The mixed solution is allowed to stand at room temperature for 10 minutes.

[0089] The mixed solution was first heated to 50°C at a heating rate of 23°C / min, and then the mixed solution was second heated to 95°C at a heating rate of 5.3°C / min, and kept at this temperature for 5 minutes. The mixed solution was then first cooled to 50°C at a cooling rate of 5.3°C / min, and kept at this temperature for 1 minute.

[0090] In the above process, the stirring speed is 960 rpm for the first 10 seconds of the heating process, and the stirring speed is 160 rpm for the remaining heating process, the constant temperature process at 95°C and the first cooling process. Then the mixed solution is naturally cooled to room temperature within 2 hours (without stirring), and starch gel is obtained.

[0091] Example 2

[0092] Take the weight average molecular weight (3.99×10 6 g / mol) of starch (the mass of amylose accounts for 75wt% of the total mass of starch), water, and the water-soluble hemicellulose obtained in Preparation Example 1 were mixed, the mass ratio of starch to water-soluble hemicellulose was 11.5:1, and the mass content of starch in the obtained mixed solution was 8.5wt%. The mixed solution was allowed to stand at room temperature for 12 minutes.

[0093] The mixed solution was first heated to 53°C at a heating rate of 25°C / min; then the mixed solution was second heated to 140°C at a heating rate of 5.6°C / min, and the temperature was kept constant for 5.3 minutes. Then the temperature of the mixed solution was first cooled to 53°C at a cooling rate of 5.6°C / min, and kept warm for 2 minutes. In the above process, the stirring speed of the first 10s of the heating process was 920rpm, and the stirring speed of the remaining heating process, the constant temperature process of 140°C and the first cooling process was 150rpm, and then the mixed solution was naturally cooled to room temperature (without stirring) within 2 hours. Starch gel was obtained.

[0094] Example 3

[0095] Take the weight average molecular weight (1.0×10 7 g / mol) of starch (the mass of amylose accounts for 68wt% of the total mass of starch), water, and the water-soluble hemicellulose obtained in Preparation Example 1 were mixed, the mass ratio of starch to water-soluble hemicellulose was 10.2:1, and the mass content of starch in the obtained mixed solution was 8.7wt%. The mixed solution was allowed to stand at room temperature for 8 minutes.

[0096] The mixed solution was first heated to 48°C at a heating rate of 22°C / min; then the mixed solution was heated to 100°C for the second time at a heating rate of 5.8°C / min, and the temperature was kept constant for 4.8 minutes. Then the temperature of the mixed solution was first cooled to 48°C at a cooling rate of 5.8°C / min, and kept warm for 3 minutes. In the above process, the stirring speed was 940rpm for the first 10s of the heating process, and the stirring speed was 170rpm for the remaining heating process, the constant temperature process of 100°C and the first cooling process. Then the mixed solution was naturally cooled to room temperature (without stirring) within 2 hours. Starch gel was obtained.

[0097] Example 4

[0098] The method of Example 1 was followed, except that the water-soluble hemicellulose obtained in Preparation Example 1 was replaced by the water-soluble hemicellulose obtained in Preparation Example 2.

[0099] Example 5

[0100] The method of Example 1 was followed, except that the mass ratio of starch to water-soluble hemicellulose was 15:1, and the total mass amount of starch and water-soluble hemicellulose was consistent with that in Example 1.

[0101] Example 6

[0102] The method of Example 1 was followed, except that the mass content of starch in the mixed solution was 10 wt %. The mass ratio of starch to water-soluble hemicellulose was the same as that in Example 1.

[0103] Example 7

[0104] The method of Example 1 was followed, except that in the mixed solution, the water-soluble hemicellulose was purchased from Shaanxi Baicao Xintian Power Factory, the model was 95 type sugar powder, and its weight average molecular weight was 1.0×10 3 Da, Mw / Mn is 1.51.

[0105] Example 8

[0106] The method of Example 1 is followed, except that the second heating rate is 3° C. / min. The first cooling rate is 3° C. / min.

[0107] Example 9

[0108] The method of Example 1 was followed, except that after the temperature was raised to 95° C., the temperature was maintained constant for 7 minutes.

[0109] Example 10

[0110] The method of Example 1 was followed, except that the mixed solution was heated directly from room temperature to 95° C. at a heating rate of 23° C. / min.

[0111] Embodiment 11

[0112] The method of Example 1 was followed, except that after the constant temperature at 95° C. was completed, the mixed solution was directly cooled naturally to room temperature.

[0113] Comparative Example 1

[0114] The method of Example 1 was followed, except that the mass ratio of starch to water-soluble hemicellulose was 20:1.

[0115] Comparative Example 2

[0116] The method of Example 1 was followed, except that the mass of the amylose in the starch accounted for 30 wt % of the total mass of the starch.

[0117] Test Example 1

[0118] The starch gel provided by the present invention is used to replace a portion of conventional starch when preparing starch food, thereby exerting the ability to inhibit starch digestion. The following experiment illustrates the inhibition of starch digestion by the starch gel provided by the present invention when used.

[0119] Rapidly digestible starch: refers to the starch that is digested and absorbed in the small intestine within 20 minutes. Rapidly digestible starch % refers to the percentage of this part of starch in the total amount of starch, reflecting the starch digestibility within 0-20 minutes.

[0120] Slowly digestible starch: refers to the starch that is digested and absorbed in the small intestine within 20-120 minutes. Slowly digestible starch % refers to the percentage of this part of starch in the total amount of starch, reflecting the starch digestibility within 20-120 minutes.

[0121] Resistant starch: starch that cannot be digested and absorbed within 120 minutes. This part will not be digested and absorbed in the small intestine, but can reach the colon and be fermented by colonic microorganisms, and then play an effective physiological role. Resistant starch % refers to the percentage of this part of starch in the total amount of starch.

[0122] The gel prepared in each example and comparative example was taken and the starch content therein was measured using a total starch assay kit (AA / AMG) from Megazyme, Ireland, USA, which is the total starch content.

[0123] Take 50 mg dry weight of conventional wheat starch, starch gel prepared in each embodiment and comparative example (in an amount such that the dry weight of starch is also 50 mg) and carry out the following experiments respectively:

[0124] Starch gel (or regular wheat starch) was dispersed in 2 mL of distilled water, and 8 mL of enzyme solution (containing 0.33 mg of pancreatin and 16.67 μL of amyloglucosidase) was added to sodium acetate buffer (0.2 M, pH 6.0) at 37°C. Stirring was performed at 37°C and 300 rpm, and 0.1 mL was taken and mixed with 0.9 mL of anhydrous ethanol at 0, 20, and 120 min to stop the enzymatic reaction.

[0125] For the above liquids after stopping the enzymatic reaction, the digested starch content was obtained by using the total starch assay kit (AA / AMG) and the glucose content assay kit (GOPOD Format) of Megazyme, Ireland, USA. The ratio of the digested starch content measured at each time to the total starch content is the rapidly digestible starch % and the slowly digestible starch %. The resistant starch % is deducted from the slowly digestible starch % from 100%.

[0126] The results are shown in Table 1.

[0127] Table 1

[0128]

[0129]

[0130] It can be understood that the higher the percentage of resistant starch in the total amount of starch, the lower the starch digestibility when it is used in food, and the better the digestion resistance. Whether it is partially replacing conventional starch or completely replacing conventional starch, the higher the resistant starch content, the better the digestion resistance is.

[0131] It can be seen from the results of Table 1 that the starch gel prepared by the method (embodiment) of the present invention has a good anti-digestion effect. It can be seen that the starch gel of Examples 1-4 has a better anti-digestion effect than the starch gel of Examples 5-11. It is shown that when the preferred water-soluble hemicellulose and the preferred starch gel preparation conditions of the present invention are adopted, the resistance effect will be better. The starch gel in the present invention can completely replace ordinary wheat starch, which can significantly reduce the fast digestion rate and increase the slow digestion rate.

[0132] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing starch gel, characterized in that: The method comprises: mixing starch and water-soluble hemicellulose to obtain a mixed solution, and heat-treating the mixed solution; The mass ratio of starch to water-soluble hemicellulose is (8-15):1; Among them, in starch, the mass of amylose accounts for more than 60wt% of the total mass of starch.

2. The method according to claim 1, wherein: The mass ratio of starch to water-soluble hemicellulose is (10-12):1; and / or, in the starch, the mass of amylose is 65-75wt% of the total mass of the starch; And / or, the weight average molecular weight of starch is (1×10 6 )-(8×10 7 )g / mol; and / or, in the mixed solution, the mass content of starch is 7.2-9.2wt%; and / or, the weight average molecular weight of the water-soluble hemicellulose is (3.5-8.5)×10 5 Da, molecular weight distribution index is 1-130.

3. The method according to claim 1, wherein: The heat treatment method comprises: heating the mixed solution to a constant temperature, then maintaining the constant temperature, and then cooling the mixed solution to room temperature; The constant temperature is 80-150°C, more preferably 90-145°C.

4. The method according to claim 3, wherein: The heating method includes: first heating the mixed solution to 45-55°C at a heating rate of 20-25°C / min; and then heating the mixed solution to a constant temperature at a heating rate of 4-7°C / min; Preferably, the second heating rate is 5-6°C / min.

5. The method according to claim 3 or 4, wherein: The constant temperature time is 3-8 minutes, preferably 4-6 minutes.

6. The method according to claim 3 or 4, wherein: The cooling method includes: first cooling the mixed solution to 45-55°C at a cooling rate of 4-7°C / min, keeping the temperature for 1-3 minutes, and then naturally cooling the mixed solution to room temperature; Preferably, the first cooling rate is 5-6°C / min.

7. The method according to claim 1, wherein: The preparation method of the water-soluble hemicellulose comprises: (1) subjecting a material liquid containing corn bran to a first enzymatic hydrolysis in the presence of α-amylase; subjecting the material after the first enzymatic hydrolysis to a second enzymatic hydrolysis in the presence of alkaline protease, and performing a first solid-liquid separation after inactivating the enzyme; (2) mixing the solid phase obtained in step (1) with an alkali to obtain an alkali-containing mixed liquid, and subjecting the mixed liquid to an alkali treatment; subjecting the alkali-treated material to a second solid-liquid separation, and taking a supernatant; (3) The supernatant is mixed with an organic reagent to obtain a precipitate.

8. The method according to claim 7, wherein: In step (1), in the feed liquid containing corn bran, the average particle size of corn bran is 0.01-0.5 mm, preferably 0.1-0.3 mm; And / or, in step (1), the weight content of corn bran in the corn bran-containing liquid is 5-10 weight %; And / or, in step (1), relative to 100g of corn bran, the amount of α-amylase used is 45000-70000U, and the amount of alkaline protease used is 200000-450000U; And / or, in step (1), the conditions of the first enzymatic hydrolysis include: temperature of 50-60°C, time of 1.5-2.5h, pH of 6-6.6; And / or, in step (1), the conditions of the second enzymatic hydrolysis include: temperature of 50-60°C, time of 1.5-2.5h, pH of 8.8-9.3; And / or, in step (2), the mass concentration of the alkali in the alkali-containing mixed solution is 2-7wt%, preferably 2.5-6.5wt%; And / or, in step (2), the conditions of the alkali treatment include: temperature of 75-85°C and time of 1.5-2.5h.

9. The method according to claim 1 or 8, wherein: Before mixing the supernatant and the organic reagent, the method further comprises: adjusting the pH of the supernatant to 6-7, and sequentially concentrating and dialyzing the supernatant; Preferably, the specific method of concentration is: rotary evaporation concentration at 40-65° C. and a stirring speed of 50-100 rpm; Preferably, the specific method of dialysis is: the concentrated supernatant is dialyzed at room temperature for 6-12 hours using a dialysis bag with a molecular weight cutoff of 500-3000Da; And / or, the organic reagent is selected from at least one of ethanol and acetone; and / or, in step (3), the volume ratio of the supernatant to the organic reagent is 1:(2-4); And / or, in step (3), after mixing the supernatant and the organic reagent, the method further comprises: performing a third solid-liquid separation on the material.

10. Starch gel prepared by the method described in any one of claims 1-9.

Images