LU502373B1

LU502373B1 - Method for preparing agar with low melting point

Info

Publication number: LU502373B1
Application number: LU502373A
Authority: LU
Inventors: Xianqing Yang; Laihao Li; Shaoling Yang; Bo Qi
Original assignee: South China Sea Fisheries Res Inst Chinese Acad Fishery Sciences
Priority date: 2022-06-28
Filing date: 2022-06-28
Publication date: 2022-12-29

Abstract

The application discloses a method for preparing agar with low melting point, which comprises the steps: Taking a mass of agar, adding an ethanol solution, adjusting the pH to pH8.0-pH10.0, adding a 30% hydrogen peroxide solution, reacting at a constant temperature of 20-30℃, adjusting the ph to be neutral, dispersing the filter residue with 50-60% ethanol; (2) adding the obtained agar into an ethanol alcohol solution with the same volume as in step (1), adding sodium hydroxide, and stirring at a temperature between 40 and 45℃ until the sodium hydroxide is dissolved; (3) adding sodium hydroxide with the same amount as in step (2), and adding chloroacetic acid or sodium chloroacetate; (4) putting the mixture of step (3) into a microwave reactor, adjusting the microwave power to 300-500 W, the temperature to 45-60℃ and the reaction time to 35-60 min; (5) performing suction filtration.

Description

DESCRIPTION LU502373

METHOD FOR PREPARING AGAR WITH LOW MELTING POINT

TECHNICAL FIELD The application belongs to the technical field of food additives and food processing, and in particular to a method for preparing agar with low melting point.

BACKGROUND Agar is a natural high molecular polysaccharide. It has been widely used in food, biology, medicine and other fields due to its good gel properties and gel temperature hysteresis. However, the ordinary agar has poor solubility, which can only be completely dissolved at above 90 C. Besides, the solution has poor clarity and transparency, which greatly limits its application process and application range. How to reduce the dissolution temperature of agar and improve its solubility to effectively exert its application value and process adaptability has become one of the problems to be solved.

The application aims to provide a method for preparing agar with low melting point. The method comprise that following step of: firstly, treating with hydrogen peroxide under an alkaline condition to improve the gel strength of the agar, and then using chloroacetic acid or sodium chloroacetate combined with microwave auxiliary technology for preparing through alkylation reaction in alkaline solution of non-aqueous solvent.

SUMMARY The application aims to provide a method for preparing agar with low melting point. The method adopts microwave-assisted technology to esterify agar with chloroacetic acid or sodium chloroacetate to synthesize agar with low dissolving temperature and high and low transparency.

To realize the purpose of the application, the following technical scheme 1s adopted: (1) taking edible agar, adding ethanol solution, then adjusting pH to 8.0-10.0, then adding 30% hydrogen peroxide solution, reacting at a constant temperature of 20-3°C, and then adjusting pH to 7.0; suction filtering the reaction mixture, dispersing the filter residue with ethanol, and suction filtering for 3 times; LUS02373 (2) Adding the agar obtained in the step (1) into the ethanol solution with the same volume as that in the step (1), adding NaOH, and stirring at 40-45 °C until the NaOH is completely dissolved: (3) In the reaction system of step (2), adding sodium hydroxide with the same quality as that of step (2), also adding chloroacetic acid or sodium chloroacetate; (4) Putting the mixture of step (3) into a microwave reactor for stirring reaction; (5) Performing suction filtration on the reaction solution in step (4), taking filter residue, cleaning the filter residue with ethanol solution, and performing suction filtration until the filtrate is negative by silver nitrate solution; drying the filter residue to obtain agar with low melting point.

The method of the application adopts hydrogen peroxide to moderately oxidize agar before esterification, and under the condition of controlled oxidation, the gel strength of agar is improved. Meanwhile, the method of the application esterifies agar under the microwave condition, so that the reaction rate is accelerated, the reaction time is obviously shortened, and the reaction yield is improved.

The volume of the ethanol solution added in the step (1) is 8-12 times (v/m, mL/g) of the mass of agar, and the concentration of the ethanol solution is 40-55% (v/v); the volume ratio of the hydrogen peroxide solution to the ethanol solution in the step (1) is 1: 15-1: 30.

The reaction time of the step (1) is 3-4 h.

The volume fraction of the ethanol solution in the step (2) is 70-90% (v/v); the mass ratio of sodium hydroxide to agar (the molecular weight of agar is calculated based on the amount of agar 306) is 0.3: 1-0.7: 1.

The ratio of chloroacetic acid or sodium chloroacetate added in the step (3) to the mass of agar (the molecular weight of agar is calculated based on the amount of agar 306) is 1: 1-1.5: 5.

The reaction conditions of step (4) are as follows: microwave power is 300 - 500 W, the temperature is 45-60°C, and reaction time is 35-60°C.

The drying temperature of step (5) is 50-80°C.

The application has the following beneficial effects:

In the application, the agar is subjected to esterification reaction with chloroacetic acid bF502373 sodium chloroacetate by a microwave auxiliary technology to prepare the modified agar, and the prepared modified agar has the advantages of good low-temperature solubility, high transparency, stability to heat and pH, and good water holding property.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a graph showing the relationship of heat stability of agar.

FIG. 2 is a graph showing the relationship between pH and jelly strength of agar.

DESCRIPTION OF THE APPLICATION The following examples are only used to illustrate the present application, and the scope of protection of the present application is not limited to the following examples. Those of ordinary skill in the technical field can realize the purpose of the present application according to the above disclosed contents of the present application and the ranges of various parameters.

Embodiment 1 Weighing 1 kg of edible agar powder, adding 8 L of 45% ethanol, adjusting pH to pH8.0 with NaOH, slowly adding 0.4L of 30% hydrogen peroxide solution, stirring uniformly, and reacting at 25°C for 3 h. Then adjusting the pH value to pH7.0 with acetic acid, performing suction filtration, taking filter residues, dispersing the filter residues with a 50% ethanol solution, performing suction filtration, and repeating for 3 times.

Adding 8 L of 80% ethanol solution to the filter residue, adding 50 g of sodium hydroxide, heating to about 40°C, and continuously stirring until the sodium hydroxide is completely dissolved.

Adding 50 g of sodium hydroxide and 310 g of chloroacetic acid into the mixture, and reacting in a microwave reactor at a microwave power of 400 W and a temperature of 50 °C for 50 min under stirring; after the reaction, filtering, taking the filter residue, then dispersing the filter residue with 60% ethanol and filtering until the filtrate is negative by silver nitrate solution. Then drying the filter residue at 60 °C to obtain about 990 g of agar with low melting point. The dissolution temperature of agar is determined to be 69°C.

Embodiment 2

Weighing 2 kg of edible agar gel strip, adding 20 L of 50% ethanol, adjusting pH to pHOl4/502373 with NaOH, slowly adding 1.2 L of 30% hydrogen peroxide solution, stirring uniformly, and reacting at 25°C for 3 h. Then adjusting the pH value to pH7.0 with acetic acid, performing suction filtration, taking filter residues, dispersing the filter residues with a 60% ethanol solution, performing suction filtration, and repeating for 3 times.

Adding 20 L of 85% ethanol solution to the filter residue, adding 150 g of sodium hydroxide, heating to about 45°C, and continuously stirring until the sodium hydroxide is completely dissolved.

Adding 150 g of sodium hydroxide and 910 g of sodium chloroacetate into the mixture, setting the microwave power at 450 W and the temperature at 45°C to react for 50 min under the condition of stirring; after the reaction, filtering, taking the filter residue, then dispersing the filter residue with 60% ethanol and filtering until the filtrate is negative by silver nitrate solution. Then drying the filter residue at 60 °C to obtain about 1.9 kg of agar with low melting point. The dissolution temperature of agar is determined to be 58°C.

Test of physical and chemical properties of agar The physicochemical properties of the agar and original agar from Embodiment 1 are tested, and the results are shown in Table 1 and Figs. 1- 2.

Table 1 physicochemical properties of agar Dissolution Gel Gel re-melting Jelly Samples temperature temperature temperature strength Franspare ney oC oC oC g/em? (%) Original agar 98.0 39 94.0 1004 26.9 Agar with 52-68 31-35 61-66 123-326 81.2-84.8 low melting point As can be seen from Table 1, the dissolution temperature, gel temperature, gel re-melting temperature and jelly strength of the prepared agar with low melting point are all significantly reduced, especially the dissolution temperature is reduced from the original 98°C to 52-68°C and the gel re-melting temperature is reduced from 94°C to 61-66°C; the transparency of the gel is obviously improved from 26.9% to 81.2-84.8%.

As can be seen from FIG. 1, the jelly strength of low-melting-point agar has a small change range after being heated in boiling water bath for different time, and the low-melting-point agar is basically not affected by boiling water heating time within 1 h; however, with the prolongatidr"502373 of boiling time, the gel strength of the original agar decreases continuously, which indicates that the low melting point agar has higher thermal stability than the original agar.

The application may be embodied in other specific forms that do not depart from the spirit or essential characteristics of the application. The above-described embodiments of the present application are to be considered as illustrative of the present application and not restrictive. Therefore, all slight modifications, equivalent changes and modifications to the above embodiments according to the essential technology of the present application are within the scope of the technical scheme of the present application.

Claims

CLAIMS LU502373

1. A method for preparing agar with low melting point, characterized by comprising the following steps: (1) taking edible agar, adding ethanol solution, then adjusting pH to 8.0-10.0, then adding 30% hydrogen peroxide solution, reacting at a constant temperature of 20-30°C, and then adjusting pH to 7.0; suction filtering the reaction mixture, dispersing the filter residue with ethanol, and suction filtering for 3 times; (2) adding the agar obtained in the step (1) into the ethanol solution with the same volume as that in the step (1), adding NaOH, and stirring at 40-45 °C until the NaOH is completely dissolved: (3) in the reaction system of step (2), adding sodium hydroxide with the same quality as that of step (2), also adding chloroacetic acid or sodium chloroacetate; (4) putting the mixture of step (3) into a microwave reactor for stirring reaction, (5) performing suction filtration on the reaction solution in step (4), taking filter residue, cleaning the filter residue with ethanol solution, and performing suction filtration until the filtrate is negative by silver nitrate solution; drying the filter residue to obtain agar with low melting point.

2. The method for preparing agar with low melting point according to claim 1, characterized in that the volume of the ethanol solution added in the step (1) is 8-12 times (v/m, mL/g) of the mass of agar, and the concentration of the ethanol solution is 40-55% (v/v); the volume ratio of the hydrogen peroxide solution to the ethanol solution in the step (1) is 1: 15-1: 30.

3. The method for preparing agar with low melting point according to claim 1, characterized in that the reaction time of the step (1) is 3-4 h.

4. The method for preparing agar with low melting point according to claim 1, characterized in that the volume fraction of the ethanol solution in the step (2) is 70-90% (v/v); the mass ratio of sodium hydroxide to agar (the molecular weight of agar is calculated based on the amount of agar 306) is 0.3: 1-0.7: 1.

5. The method for preparing agar with low melting point according to claim 1, characterized in that the ratio of chloroacetic acid or sodium chloroacetate added in the step (3) to the mass of agar (the molecular weight of agar is calculated based on the amount of agar 306) is 1: 1-1.5: 1.

6. The method for preparing agar with low melting point according to claim 1, characterizéd/202373 in that the reaction conditions of step (4) are as follows: the microwave power is 300 - 500 W, the temperature is 45-60‘C, and the reaction time is 35-60°C.

7. The method for preparing agar with low melting point according to claim 1, characterized in that the drying temperature of step (5) is 50-80°C.