A cross-linked emulsified modified starch and its preparation method and application

Abstract

The invention discloses a cross-linked emulsified modified starch and its preparation method and application, and belongs to the field of modified starch technology. Its preparation method includes: waxy potato starch is configured into 30-40wt% starch milk, pH is adjusted to 8-9, sodium hypochlorite is added, so that the effective chlorine concentration in the solution is 600-9000ppm of the weight of starch dry matter, pH is maintained at 8-9, until starch cross-linking is complete; Residual effective chlorine is removed, 2-4wt% of octenyl succinic anhydride of starch dry weight is added, pH is maintained at 8-8.5 for 6-10h, pH is adjusted to 5-5.5, washing, dehydration, drying, crushing and sieving are obtained. The preparation method of the present invention is simple, and on the basis of conventional wet synthesis of sodium octenyl succinate starch, a low-concentration sodium hypochlorite solution is used to cross-link starch before treatment, and the finished product whiteness is higher, and better transparency and glossiness can be given to frozen food, and whether tofu antifreeze performance can be given. It has a high practical application value.

Description

Technical Field

[0001] The invention relates to the technical field of modified starch, and in particular to a cross-linked emulsified modified starch and a preparation method and application thereof. Background Art

[0002] In order to improve the sensory properties of frozen tofu, currently, additives are usually added or mechanical equipment such as colloid mills are used in the preparation process. Although this can improve the properties of some frozen tofu, there are still problems such as poor boiling resistance, rough taste and poor rehydration during the processing process.

[0003] Japanese patent JP3167105B2 uses tapioca starch, potato starch or marshmallow starch as raw materials to prepare etherified starch with a substitution degree in the range of 0.04 to 0.2, thereby giving tofu antifreeze properties. Currently, there is no report on adding waxy starch cross-linked emulsified as an additive to tofu to make tofu have antifreeze properties.

[0004] In summary, there is an urgent need to develop a starch cross-linking emulsification modification method using waxy starch as raw material. Summary of the invention

[0005] In order to overcome the above-mentioned deficiencies in the prior art, the present invention provides a cross-linked emulsified modified starch and a preparation method and application thereof. The cross-linked emulsified modified starch provided by the present invention solves the problem of poor antifreeze performance of tofu in the prior art.

[0006] In order to achieve the above object, in a first aspect of the present invention, a method for preparing a cross-linked emulsified modified starch is provided, which comprises the following steps:

[0007] The waxy potato starch is prepared into a 30-40 wt% starch milk, the pH is adjusted to 8-9, sodium hypochlorite is added so that the effective chlorine concentration in the solution is 600-9000 ppm of the starch dry matter weight, and the pH is maintained at 8-9 until the starch is completely cross-linked; the residual effective chlorine is removed, 2-4 wt% of the starch dry weight of octenyl succinic anhydride is added, the pH is maintained at 8-8.5, the reaction is carried out for 6-10 hours, the pH is adjusted to 5-5.5, washing, dehydrating, drying, crushing and sieving to obtain the product.

[0008] It should be noted that the present application does not limit the reagents for adjusting / maintaining pH. As long as it does not affect the cross-linking and emulsification process, conventional acid-base reagents can be used, such as NaOH, Na2CO3, H2SO4, HCl, etc. NaOH and H2SO4 are preferred. More preferably, the concentration of the NaOH solution is 2.5-3.5wt%.

[0009] Furthermore, the waxy potato native starch includes any one of waxy cassava starch and waxy potato starch.

[0010] Furthermore, the effective chlorine concentration is 1200-7200 ppm based on the weight of starch dry matter.

[0011] Furthermore, the cross-linking temperature is 25-40°C.

[0012] Furthermore, the sodium hypochlorite is a sodium hypochlorite solution, wherein the effective chlorine concentration is 10wt%.

[0013] It should be noted that the starch cross-linking is completely referred to as the carboxyl content in the starch being controlled below 0.1 wt%.

[0014] In the second aspect of the present invention, a cross-linked emulsified modified starch prepared by the above preparation method is provided.

[0015] Furthermore, the viscosity of the cross-linked emulsified modified starch is 800-3000cp.

[0016] In the third aspect of the present invention, there is provided a tofu comprising the above cross-linked emulsified modified starch, wherein the amount of the tofu is 1-8 wt % of the total amount.

[0017] In the present application, the soy milk used to produce bean curd can be any soy milk used to prepare bean curd, but preferably the soy milk solid content is 10-18%. Waxy starch treated with sodium hypochlorite and octenyl succinic anhydride can be added to the soy milk, a coagulant can also be added, and heating and sterilization can be performed, and a mixture of soy milk and waxy starch treated with sodium hypochlorite and octenyl succinic anhydride can be heated, and then a coagulant can be added for sterilization. The coagulant is not particularly limited as long as it is a coagulant commonly used in the production of bean curd, such as calcium sulfate, magnesium chloride, gluconolactone, calcium chloride, magnesium sulfate, etc. In addition, if necessary, defoamers and sugars can be added as auxiliary effects for imparting antifreeze properties.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The invention adopts a low-concentration sodium hypochlorite solution to perform cross-linking pre-treatment on starch on the basis of synthesizing sodium starch octenyl succinate by a conventional wet method, and does not require pre-gelatinization. The finished product has higher whiteness and can give frozen food better transparency and glossiness.

[0020] The preparation method of the present invention introduces hydrophobic groups into the starch molecular chain, and can form more microporous structures during the tofu preparation process. The microporous structures can inhibit the generation of large ice crystal structures during the freezing process, so that the structure of the frozen tofu is not destroyed during the thawing process.

[0021] The raw materials used in the present invention are waxy raw materials with high branched-chain starch content, such as waxy cassava and waxy potato. The high branched-chain starch can prevent the short straight-chain molecules in the starch molecular chain from rearranging, aging and water precipitation during the freezing process. Meanwhile, the waxy cassava and waxy potato starch can give the product a Q-elastic texture. DETAILED DESCRIPTION

[0022] In order to make the present invention easier to understand, the present invention is further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. Specific experimental methods not mentioned in the following examples are usually carried out according to conventional experimental methods in the art; specific reagents and equipment not mentioned are usually conventional reagents and equipment in the art.

[0023] The following are specific examples.

[0024] Example 1

[0025] A method for preparing cross-linked emulsified modified starch, the steps of which are as follows:

[0026] A waxy cassava starch suspension having a concentration of 30-40% by weight of dry starch is prepared, and the pH value is adjusted to 8.0-9.0 with a 2.5-3.5% sodium hydroxide solution, and a sodium hypochlorite solution having an effective chlorine concentration of 10% is added to the starch suspension, and the effective chlorine concentration is 600ppm by weight of the starch dry matter, and the starch suspension is treated at 30-35° C. for 30 minutes to keep the pH value at 8.0-9.0, and an appropriate amount of starch milk is taken, and the pH value is adjusted to 5.0 with a 10% sulfuric acid aqueous solution until the starch suspension stops changing color when it is dripped into potassium iodide, and a 10% sodium sulfite solution is added to remove the effective chlorine remaining in the starch suspension; the pH value is adjusted to 8.0-8.5 with a 2.5-3.5% sodium hydroxide solution, and the temperature is controlled at 30-35° C., and 3% of the dry weight of the starch is added to the starch suspension. Octenyl succinic anhydride is added, and the pH value is maintained at about 8.5 for reaction for 8 hours, and after the reaction is completed, the starch suspension is neutralized again with a 10% sulfuric acid aqueous solution to a pH value of 1. 5.0, dehydrate, dry and obtain starch samples.

[0027] Example 2

[0028] A method for preparing cross-linked emulsified modified starch, the steps of which are as follows:

[0029] A waxy cassava starch suspension with a concentration of 30-40% by weight of dry starch is prepared, and the pH value is adjusted to 8.0-9.0 with a 2.5-3.5% sodium hydroxide solution, and a sodium hypochlorite solution with an effective chlorine concentration of 10% is added to the starch suspension, and the effective chlorine concentration is 1200ppm by weight of the starch dry matter, and the starch suspension is treated at 30-35° C. for 30 minutes to keep the pH value at 8.0-9.0, and an appropriate amount of starch milk is taken, and the pH value is adjusted to 5.0 with a 10% sulfuric acid aqueous solution until the starch suspension stops changing color when it is dropped into potassium iodide, and a 10% sodium sulfite solution is added to remove the residual effective chlorine in the starch suspension; the pH value is adjusted to 8.0-8.5 with a 2.5-3.5% sodium hydroxide solution, and the temperature is controlled at 30-35° C., and 3% of the dry weight of the starch is added to the starch suspension. Octenyl succinic anhydride is added, and the pH value is maintained at about 8.5 for reaction for 8 hours. After the reaction is completed, the starch suspension is neutralized again with a 10% sulfuric acid aqueous solution to a pH value of 1. 5.0, dehydrate, dry and obtain starch samples.

[0030] Example 3

[0031] A method for preparing cross-linked emulsified modified starch, the steps of which are as follows:

[0032] A waxy cassava starch suspension having a concentration of 30-40% by weight of dry starch is prepared, and the pH value is adjusted to 8.0-9.0 with a 2.5-3.5% sodium hydroxide solution, and a sodium hypochlorite solution having an effective chlorine concentration of 10% is added to the starch suspension, and the effective chlorine concentration is 1800ppm by weight of the starch dry matter, and the starch suspension is treated at 30-35° C. for 30 minutes to keep the pH value at 8.0-9.0, and an appropriate amount of starch milk is taken, and the pH value is adjusted to 5.0 with a 10% sulfuric acid aqueous solution until the starch suspension stops changing color when it is dripped into potassium iodide, and a 10% sodium sulfite solution is added to remove the effective chlorine remaining in the starch suspension; the pH value is adjusted to 8.0-8.5 with a 2.5-3.5% sodium hydroxide solution, and the temperature is controlled at 30-35° C., and 3% of the dry weight of the starch is added to the starch suspension. Octenyl succinic anhydride is added, and the pH value is maintained at about 8.5 for reaction for 8 hours, and after the reaction is completed, the starch suspension is neutralized again with a 10% sulfuric acid aqueous solution to a pH value of 1. 5.0, dehydrate, dry and obtain starch samples.

[0033] Example 4

[0034] A method for preparing cross-linked emulsified modified starch, the steps of which are as follows:

[0035] A waxy cassava starch suspension having a concentration of 30-40% by weight of dry starch is prepared, and the pH value is adjusted to 8.0-9.0 with a 2.5-3.5% sodium hydroxide solution, and a sodium hypochlorite solution having an effective chlorine concentration of 10% is added to the starch suspension, and the effective chlorine concentration is 3600ppm by weight of the starch dry matter, and the starch suspension is treated at 30-35° C. for 30 minutes to keep the pH value at 8.0-9.0, and an appropriate amount of starch milk is taken, and the pH value is adjusted to 5.0 with a 10% sulfuric acid aqueous solution until the starch suspension stops changing color when it is dripped into potassium iodide, and a 10% sodium sulfite solution is added to remove the effective chlorine remaining in the starch suspension; the pH value is adjusted to 8.0-8.5 with a 2.5-3.5% sodium hydroxide solution, and the temperature is controlled at 30-35° C., and 3% of the dry weight of the starch is added to the starch suspension. Octenyl succinic anhydride is added, and the pH value is maintained at about 8.5 for reaction for 8 hours, and after the reaction is completed, the starch suspension is neutralized again with a 10% sulfuric acid aqueous solution to a pH value of 1. 5.0, dehydrate, dry and obtain starch samples.

[0036] Example 5

[0037] A method for preparing cross-linked emulsified modified starch, the steps of which are as follows:

[0038] A waxy cassava starch suspension with a concentration of 30-40% by weight of dry starch is prepared, and the pH value is adjusted to 8.0-9.0 with a 2.5-3.5% sodium hydroxide solution, and a sodium hypochlorite solution with an effective chlorine concentration of 10% is added to the starch suspension, and the effective chlorine concentration is 7200ppm by weight of the starch dry matter, and the starch suspension is treated at 30-35° C. for 30 minutes to keep the pH value at 8.0-9.0, and an appropriate amount of starch milk is taken, and the pH value is adjusted to 5.0 with a 10% sulfuric acid aqueous solution until the starch suspension stops changing color when it is dropped into potassium iodide, and a 10% sodium sulfite solution is added to remove the residual effective chlorine in the starch suspension; the pH value is adjusted to 8.0-8.5 with a 2.5-3.5% sodium hydroxide solution, and the temperature is controlled at 30-35° C., and 2% of the dry weight of the starch is added to the starch suspension. Octenyl succinic anhydride is added, and the pH value is maintained at about 8.5 for reaction for 8 hours. After the reaction is completed, the starch suspension is neutralized again with a 10% sulfuric acid aqueous solution to a pH value of 1. 5.0, dehydrate, dry and obtain starch samples.

[0039] Example 6

[0040] A method for preparing cross-linked emulsified modified starch, the steps of which are as follows:

[0041] A waxy cassava starch suspension with a concentration of 30-40% by weight of dry starch is prepared, and the pH value is adjusted to 8.0-9.0 with a 2.5-3.5% sodium hydroxide solution, and a sodium hypochlorite solution with an effective chlorine concentration of 10% is added to the starch suspension, and the effective chlorine concentration is 9000ppm by weight of the starch dry matter, and the starch suspension is treated at 30-35° C. for 30 minutes to keep the pH value at 8.0-9.0, and an appropriate amount of starch milk is taken, and the pH value is adjusted to 5.0 with a 10% sulfuric acid aqueous solution until the starch suspension stops changing color when it is dropped into potassium iodide, and a 10% sodium sulfite solution is added to remove the residual effective chlorine in the starch suspension; the pH value is adjusted to 8.0-8.5 with a 2.5-3.5% sodium hydroxide solution, and the temperature is controlled at 30-35° C., and 4% of the dry weight of the starch is added to the starch suspension. Octenyl succinic anhydride is added, and the pH value is maintained at about 8.5 for reaction for 8 hours. After the reaction is completed, the starch suspension is neutralized again with a 10% sulfuric acid aqueous solution to a pH value of 1. 5.0, dehydrate, dry and obtain starch samples.

[0042] Comparative Example 1

[0043] A method for preparing cross-linked modified starch, comprising the following steps:

[0044] The waxy cassava starch suspension with a concentration of 30-40% by weight of dry starch is prepared, and the pH value is adjusted to 8.0-9.0 with a 2.5-3.5% sodium hydroxide solution, and a sodium hypochlorite solution with an effective chlorine concentration of 10% is added to the starch suspension, and the effective chlorine concentration is 1200ppm by weight of the starch dry matter, and the starch suspension is treated at 30-35° C. for 30 minutes to keep the pH value at 8.0-9.0, and an appropriate amount of starch milk is taken, and the pH value is adjusted to 5.0 with a 10% sulfuric acid aqueous solution until the starch suspension stops changing color when it is dripped into potassium iodide, and a 10% sodium sulfite solution is added to remove the effective chlorine remaining in the starch suspension; the starch suspension is neutralized to pH 5.0 with a 10% sulfuric acid aqueous solution, and the starch sample is dehydrated and dried to obtain a starch sample.

[0045] Comparative Example 2

[0046] A method for preparing emulsified modified starch, comprising the following steps:

[0047] A waxy cassava starch suspension with a concentration of 30-40% by weight of dry starch is prepared, the pH value is adjusted to 8.0-8.5 with a 2.5-3.5% sodium hydroxide solution, the temperature is controlled at 30-35° C., 3% of octenyl succinic anhydride based on the dry weight of starch is added to the starch suspension, the pH value is maintained at about 8.5 and the reaction is carried out for 8 hours. After the reaction is completed, the suspension is neutralized again with a 10% sulfuric acid aqueous solution to a pH value of 5.0, dehydrated, and dried to obtain a starch sample.

[0048] Comparative Example 3

[0049] A method for preparing emulsified modified starch, comprising the following steps:

[0050] A waxy cassava starch suspension with a concentration of 30-40% by weight of dry starch is prepared, the pH value is adjusted to 11.0-11.5 with a 2.5-3.5% sodium hydroxide solution, the temperature is controlled at 30-35° C., 0.1% sodium trimetaphosphate based on the dry weight of starch is added to the starch suspension, and then 3% octenyl succinic anhydride based on the dry weight of starch is added, the pH value is maintained at about 8.5, and the reaction is carried out for 8 hours. After the reaction is completed, the mixture is neutralized again with a 10% sulfuric acid aqueous solution to a pH value of 5.0, dehydrated, and dried to obtain a starch sample.

[0051] Example 7

[0052] A method for preparing cross-linked emulsified modified starch, the steps of which are as follows:

[0053] Prepare a waxy potato starch suspension with a concentration of 30-40% by weight of dry starch, adjust the pH to 8.0-9.0 with a 2.5-3.5% sodium hydroxide solution, add a sodium hypochlorite solution with an effective chlorine concentration of 10% to the starch suspension, the effective chlorine concentration is 600ppm by weight of the starch dry matter, treat at 30-35°C for 30 minutes, keep the pH value at 8.0-9.0, take an appropriate amount of starch milk, adjust the pH to 5.0 with a 10% sulfuric acid aqueous solution, until the starch suspension stops changing color when it is added dropwise to potassium iodide, add a 10% sodium sulfite solution to remove the residual effective chlorine in the starch suspension; adjust the pH to 8.0-8.5 with a 2.5-3.5% sodium hydroxide solution, control the temperature at 30-35°C, add 3% of the dry weight of the starch to the starch suspension octenyl succinic anhydride, maintain the pH at about 8.5 for 8 hours, and after the reaction is completed, neutralize again with a 10% sulfuric acid aqueous solution to a pH of 5.0, dehydrate, dry and obtain starch samples.

[0054] Example 8

[0055] A method for preparing cross-linked emulsified modified starch, the steps of which are as follows:

[0056] Prepare a waxy potato starch suspension with a concentration of 30-40% by weight of dry starch, adjust the pH to 8.0-9.0 with a 2.5-3.5% sodium hydroxide solution, add a sodium hypochlorite solution with an effective chlorine concentration of 10% to the starch suspension, the effective chlorine concentration is 1200ppm by weight of the starch dry matter, treat at 30-35°C for 30 minutes, keep the pH value at 8.0-9.0, take an appropriate amount of starch milk, adjust the pH to 5.0 with a 10% sulfuric acid aqueous solution, until the starch suspension stops changing color when it is dropped into potassium iodide, add a 10% sodium sulfite solution to remove the residual effective chlorine in the starch suspension; adjust the pH to 8.0-8.5 with a 2.5-3.5% sodium hydroxide solution, control the temperature at 30-35°C, add 3% of the dry weight of the starch to the starch suspension octenyl succinic anhydride, maintain the pH at about 8.5 for 8 hours, and after the reaction is completed, neutralize again with a 10% sulfuric acid aqueous solution to a pH of 5.0, dehydrate, dry and obtain starch samples.

[0057] Comparative Example 4

[0058] A method for preparing cross-linked modified starch, comprising the following steps:

[0059] A waxy potato starch suspension with a concentration of 30-40% by weight of dry starch is prepared, and the pH value is adjusted to 8.0-9.0 with a 2.5-3.5% sodium hydroxide solution, and a sodium hypochlorite solution with an effective chlorine concentration of 10% is added to the starch suspension, and the effective chlorine concentration is 1200ppm by weight of the starch dry matter, and the starch suspension is treated at 30-35° C. for 30 minutes to keep the pH value at 8.0-9.0, and an appropriate amount of starch milk is taken, and the pH value is adjusted to 5.0 with a 10% sulfuric acid aqueous solution until the starch suspension stops changing color when it is dripped into potassium iodide, and a 10% sodium sulfite solution is added to remove the effective chlorine remaining in the starch suspension; the starch suspension is neutralized to pH 5.0 with a 10% sulfuric acid aqueous solution, and the starch sample is dehydrated and dried to obtain a starch sample.

[0060] Comparative Example 5

[0061] A method for preparing emulsified modified starch, comprising the following steps:

[0062] A waxy cassava starch suspension with a concentration of 30-40% by weight of dry starch is prepared, the pH value is adjusted to 8.0-8.5 with a 2.5-3.5% sodium hydroxide solution, the temperature is controlled at 30-35° C., 3% of octenyl succinic anhydride based on the dry weight of starch is added to the starch suspension, the pH value is maintained at about 8.5 and the reaction is carried out for 8 hours. After the reaction is completed, the suspension is neutralized again with a 10% sulfuric acid aqueous solution to a pH value of 5.0, dehydrated, and dried to obtain a starch sample.

[0063] Comparative Example 6

[0064] A method for preparing emulsified modified starch, comprising the following steps:

[0065] A waxy potato starch suspension with a concentration of 30-40% by weight of dry starch is prepared, the pH value is adjusted to 11.0-11.5 with a 2.5-3.5% sodium hydroxide solution, the temperature is controlled at 30-35° C., 0.1% sodium trimetaphosphate based on the dry weight of starch is added to the starch suspension, and then 3% octenyl succinic anhydride based on the dry weight of starch is added, the pH value is maintained at about 8.5 and the reaction is carried out for 8 hours. After the reaction is completed, the solution is neutralized again with a 10% sulfuric acid aqueous solution to a pH value of 5.0, dehydrated, and dried to obtain a starch sample.

[0066] Comparative Example 7

[0067] A method for preparing cross-linked emulsified modified starch, the steps of which are as follows:

[0068] A waxy potato starch suspension with a concentration of 30-40% by weight of dry starch is prepared, anhydrous sodium sulfate in an amount of 10% by weight of the dry starch is added as a swelling inhibitor, a pH value of 11.0-11.5 is adjusted with a 2.5-3.5% sodium hydroxide solution, propylene oxide in an amount of 6% by weight of the dry starch is added as an etherifying agent, and the mixture is treated at 40-42° C. for 16 hours; the pH value is adjusted to 8.0-8.5 with 10% dilute sulfuric acid, the temperature is adjusted to 30-35° C., octenyl succinic anhydride in an amount of 3% by weight of the dry starch is added to the starch suspension, the pH value is maintained at about 8.5, and the mixture is reacted for 8 hours. After the reaction is completed, the mixture is neutralized again with a 10% aqueous sulfuric acid solution to a pH value of 5.0, dehydrated, and dried to obtain a starch sample.

[0069] Comparative Example 8

[0070] A method for preparing cross-linked emulsified modified starch, the steps of which are as follows:

[0071] Prepare a waxy potato starch suspension with a concentration of 30-40% by weight of dry starch, adjust the pH to 11.0-11.5 with a 2.5-3.5% sodium hydroxide solution, add a sodium hypochlorite solution with an effective chlorine concentration of 10% to the starch suspension, the effective chlorine concentration is 1200ppm by weight of the starch dry matter, treat at 30-35°C for 30 minutes, and keep the pH value at 11.0-11.5, take an appropriate amount of starch milk, adjust the pH to 5.0 with a 10% sulfuric acid aqueous solution, until the starch suspension stops changing color when it is dropped into potassium iodide, add a 10% sodium sulfite solution to remove the residual effective chlorine in the starch suspension; adjust the pH to 8.0-8.5 with a 2.5-3.5% sodium hydroxide solution, control the temperature at 30-35°C, add 3% of the dry weight of the starch to the starch suspension octenyl succinic anhydride, and maintain the pH After the reaction was completed, the mixture was neutralized again with 10% sulfuric acid aqueous solution to pH 5.0, dehydrated, and dried to obtain a starch sample.

[0072] Comparative Example 9

[0073] A method for preparing cross-linked emulsified modified starch, the steps of which are as follows:

[0074] Prepare a waxy potato starch suspension with a concentration of 30-40% by weight of dry starch, adjust the pH to 8.0-9.0 with a 2.5-3.5% sodium hydroxide solution, add a sodium hypochlorite solution with an effective chlorine concentration of 10% to the starch suspension, the effective chlorine concentration is 300ppm by weight of the starch dry matter, treat at 30-35°C for 30 minutes, keep the pH value at 8.0-9.0, take an appropriate amount of starch milk, adjust the pH to 5.0 with a 10% sulfuric acid aqueous solution, until the starch suspension stops changing color when it is added dropwise to potassium iodide, add a 10% sodium sulfite solution to remove the residual effective chlorine in the starch suspension; adjust the pH to 8.0-8.5 with a 2.5-3.5% sodium hydroxide solution, control the temperature at 30-35°C, add 3% of the dry weight of the starch to the starch suspension octenyl succinic anhydride, maintain the pH at about 8.5 for 8 hours, and after the reaction is completed, neutralize again with a 10% sulfuric acid aqueous solution to a pH of 5.0, dehydrate, dry and obtain starch samples.

[0075] Comparative Example 10

[0076] A method for preparing cross-linked emulsified modified starch, the steps of which are as follows:

[0077] Prepare a waxy potato starch suspension with a concentration of 30-40% by weight of dry starch, adjust the pH to 8.0-9.0 with a 2.5-3.5% sodium hydroxide solution, add a sodium hypochlorite solution with an effective chlorine concentration of 10% to the starch suspension, the effective chlorine concentration is 12000ppm by weight of the starch dry matter, treat at 30-35°C for 30 minutes, and keep the pH value at 8.0-9.0, take an appropriate amount of starch milk, adjust the pH to 5.0 with a 10% sulfuric acid aqueous solution, until the starch suspension stops changing color when it is dropped into potassium iodide, add a 10% sodium sulfite solution to remove the residual effective chlorine in the starch suspension; adjust the pH to 8.0-8.5 with a 2.5-3.5% sodium hydroxide solution, control the temperature at 30-35°C, add 3% of the dry weight of the starch to the starch suspension octenyl succinic anhydride, and maintain the pH After the reaction was completed, the mixture was neutralized again with 10% sulfuric acid aqueous solution to pH 5.0, dehydrated, and dried to obtain a starch sample.

[0078] Peak Viscosity Measurement Method

[0079] Starch milk concentration: water is used as solvent, and the starch dry matter concentration is 5%.

[0080] Temperature conditions:

[0081] (1) Heating: from 30°C to 95°C (heating rate 6°C / min)

[0082] (2) Hold: 95°C for 30 minutes

[0083] (3) Cooling: from 95°C to 50°C (temperature rate 6°C / min)

[0084] (4) Keep: Keep at 30°C for 10 minutes

[0085] The weight of the starch suspension during measurement was 20.0 g, and the rotation speed of the paddle in the measuring cup was set to 160 rpm. The results are shown in Table 1.

[0086] Table 1 Comparison of raw material dosage and viscosity of the embodiment and the comparative example

[0087]

[0088]

[0089] After the waxy potato starch is treated with a low concentration of sodium hypochlorite solution, the peak viscosity increases first and then gradually decreases. The reason is that in the low concentration of sodium hypochlorite solution, the aldehyde groups produced during the starch oxidation process cross-link with the hydroxyl groups in the adjacent starch molecules to form new ether bonds. The result of this cross-linking leads to an increase in the viscosity of the oxidized starch paste from a macroscopic perspective. The aldehyde groups after starch oxidation should be a dynamic equilibrium, and they may form three structures in the aqueous solution: free point aldehyde groups, forming a ring structure or hydration with water molecules, and forming cross-links with the hydroxyl groups of adjacent starch molecules. However, as the dosage of the oxidant gradually increases, the strength of the glycosidic bonds in the starch molecules weakens, the molecules degrade, and the viscosity tends to decrease.

[0090] Performance Testing

[0091] 1. Tofu production

[0092] Using untreated waxy cassava starch and waxy potato starch as blank controls, the samples prepared in the above embodiments and comparative examples were used to produce tofu according to the following procedures.

[0093] Untreated waxy tapioca starch, waxy potato starch and starch samples prepared in the embodiment were dispersed into soy milk with a solid content of 14%, starch accounting for 4% of the weight of the dry matter of tofu, stirred and heated to 65-70°C, and then 3g of water and calcium sulfate (mass ratio 1:1) suspension were added to the mixture (300g), 50g of the mixture was poured into 6 cylindrical heat-resistant containers respectively, and allowed to stand for about 10 minutes, and then the tofu was steamed and heated at 90°C for 10 minutes to obtain tofu. The obtained tofu was immersed in cold water together with the entire container, three of which were used as "pre-frozen samples", and the remaining three were frozen in a refrigerator for one week, and then naturally thawed at 25°C to obtain "freeze-thaw samples".

[0094] 2. Fracture strength and deformation rate

[0095] The breaking strength and deformation rate of tofu were measured using a texture analyzer. The workbench rising speed was 60 mm / min. The breaking strength and deformation rate when a 10 mm spherical plunger penetrated were measured. Each sample was measured three times and the average value was taken. The results are shown in Table 2.

[0096] Table 2 Breaking strength and deformation rate of tofu

[0097]

[0098] It can be concluded from the data in the table that the changes in the breaking strength and deformation rate of the tofu before freezing and after thawing in Examples 2-5 and 10-11 are relatively small, indicating that the addition of modified starch under this condition helps to improve the storage stability of frozen tofu.

[0099] 3. Change rate before and after freezing and thawing

[0100] The breaking strength change rate and deformation rate before and after freezing and thawing were calculated according to the following formula:

[0101] Breaking strength change rate (%) = 100-(breaking strength before freezing (10 -1 N) / breaking strength after freeze-thaw (10 -1 N))×100

[0102] Deformation rate change rate (%) = 100-(deformation rate before freezing (%) / deformation rate after freezing and thawing (%)) × 100

[0103] The smaller the absolute value of this change rate is, the smaller the change in physical properties caused by freeze-thaw is. The results are shown in Table 3.

[0104] Table 3 Change rate before and after freezing and thawing

[0105]

[0106] Note:

[0107] A: Change rate is less than ±10%

[0108] B: Percentage change is more than ±10% and less than 30%

[0109] C: Percentage change ±30% or more, less than 50%

[0110] D: Percentage change ±50% or more

[0111] The examples rated two A's indicate that the tofu after thawing can maintain the ideal hardness and smooth texture comparable to the pre-frozen tofu. In addition, the tofu rated B can suppress the release of water to a certain extent, but cannot maintain the smoothness before freezing. The tofu rated C or D indicates that water is released from the tofu, the texture is uneven, and it cannot maintain its state before freezing.

[0112] 4. Effect of starch addition on the frost resistance of tofu

[0113] The starch samples prepared in Production Example 3 were used, and the starch concentrations in the tofu were 0.5%, 1%, 2%, 4%, 6% and 8%. Table 4 shows the measurement results of the breaking strength and deformation rate of the tofu obtained according to the analytical method.

[0114] Table 4 Breaking strength and deformation rate of tofu with different starch addition amounts

[0115]

[0116]

[0117] Table 5 shows the results of the increase and decrease ratios of the breaking strength and deformation rate of tofu before and after freeze-thawing.

[0118] Table 5 Breaking strength and deformation rate of tofu before and after freezing and thawing at different amounts of cross-linked starch added

[0119]

[0120] Tofu rated two A's also maintained an ideal hardness and smooth texture comparable to that before freezing after thawing. In addition, tofu rated A and B overall maintained a sufficiently smooth texture, with a hardness and deformation rate slightly different from that before freezing. On the other hand, tofu rated C or D overall would be dehydrated and have an uneven texture, failing to maintain the hardness and smooth texture of the tofu before freezing.

[0121] The starch concentration in the tofu was increased by 4% by dry weight using the sample prepared in Production Example 3, and as a comparative example, waxy corn starch, glutinous rice starch, and waxy wheat starch treated in the same denaturing manner as in Example 3 were used. Table 6 shows the measurement results of the breaking strength and deformation rate of the prepared tofu.

[0122] Table 6 Breaking strength and deformation rate of tofu prepared with different cross-linked starches

[0123]

[0124] Table 7 shows the results of the increase and decrease ratios of the breaking strength and deformation rate of tofu before and after freeze-thawing.

[0125] Table 7 Breaking strength and deformation rate of tofu prepared with different cross-linked starches before and after freezing and thawing

[0126]

[0127] From the above results, it can be seen that when waxy corn starch, glutinous rice starch and waxy wheat starch treated with sodium hypochlorite and OSA were added to tofu, the evaluation showed C or D, indicating that the tofu was dehydrated, the texture was uneven, and it was unable to maintain its pre-freezing state. On the other hand, tofu with an overall rating of two A's can still maintain the ideal hardness and smooth texture comparable to the tofu before freezing even after freeze-thawing. This shows that the cross-linked emulsified starch prepared in this application using waxy potato starch as raw material can improve the antifreeze properties of tofu.

[0128] According to the disclosure and teaching of the above description, those skilled in the art to which the present invention belongs may also make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the invention should also fall within the scope of protection of the claims of the present invention. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation to the present invention.

Claims

1. A method for preparing cross-linked emulsified modified starch, characterized in that: The steps include: The waxy potato starch is prepared into a 30-40wt% starch milk, the pH is adjusted to 8-9, sodium hypochlorite is added so that the effective chlorine concentration in the solution is 1200-7200ppm of the starch dry matter weight, and the pH is maintained at 8-9 until the starch is completely cross-linked; the residual effective chlorine is removed, 2-4wt% of the starch dry weight octenyl succinic anhydride is added, the pH is maintained at 8-8.5 for 6-10 hours, the pH is adjusted to 5-5.5, and the starch is washed, dehydrated, dried, crushed and sieved to obtain the waxy potato starch; the waxy potato starch comprises any one of waxy cassava starch and waxy potato starch.

2. The method for preparing the cross-linked emulsified modified starch according to claim 1, characterized in that: The crosslinking temperature is 25-40°C.

3. The method for preparing the cross-linked emulsified modified starch according to claim 1, characterized in that: The sodium hypochlorite is a sodium hypochlorite solution.

4. The cross-linked emulsified modified starch prepared by the method for preparing the cross-linked emulsified modified starch according to any one of claims 1 to 3.

5. The cross-linked emulsified modified starch according to claim 4, characterized in that: The viscosity of the cross-linked emulsified modified starch is 800-3000cp.

6. A tofu, characterized in that: The cross-linked emulsified modified starch as claimed in claim 4 or 5 is used in an amount of 2-8wt% of the total amount.

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