A method for detecting anisidine value of fish meal

Abstract

The invention relates to a method for detecting anisidine value of fish meal. The method comprises the following steps: firstly, mixing a fish meal sample with activated carbon and anhydrous sodium sulfate, extracting the mixture in petroleum ether, filtering the mixture, and rotary distilling the mixture at 40°C to obtain fish meal crude fat; then mixing the mixture with isooctane to obtain a test solution; mixing the test solution with glacial acetic acid to obtain an unreacted solution; mixing the test solution with anisidine to obtain a reaction solution; mixing isooctane with anisidine to obtain a blank solution; and finally, using isooctane as a control, respectively detecting the absorbances of the unreacted solution, the reaction solution, and the blank solution at 350nm, and calculating the anisidine value AV of the fish meal sample according to the following formula: #imgabs0# wherein A0 is the absorbance of the blank solution, A1 is the absorbance of the unreacted solution, and A2 is the absorbance of the reaction solution; Q is the concentration of the test solution in the reaction solution, 0.01g / mL; m is the mass of the fish meal crude fat, g; and V is the amount of isooctane in the test solution, mL. Compared with the prior art, the present invention has the advantages of simple operation and high accuracy in detecting anisidine values.

Description

Technical Field

[0001] The invention belongs to the technical field of fish meal detection methods and relates to a method for detecting the anisidine value of fish meal. Background Art

[0002] Fish meal contains 7-10% crude fat. During transportation and storage, the crude fat in fish meal is susceptible to oxygen, water, light, heat, microorganisms, etc., and will gradually hydrolyze or oxidize and become rancid, causing neutral fat to decompose into glycerol and fatty acids. The unsaturated chain segments in the fatty acids then form peroxides, which in turn decompose into lower fatty acids, aldehydes, ketones and other substances, producing odors and smells, further accelerating the deterioration of the color, aroma, taste and nutrition of the fish meal. However, the fish oil standard SC / T3502-2016 does not set a limit for the anisidine value index of crude fish oil products. Therefore, the anisidine value can be used to measure the level of aldehydes (mainly α, β-unsaturated aldehydes) generated during the oxidation of crude fish meal fat, and is an important indicator for evaluating the content of secondary oxidation products in fish meal. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for detecting the anisidine value of fish meal.

[0004] The purpose of the present invention can be achieved by the following technical solutions:

[0005] A method for detecting the anisidine value of fish meal comprises the following steps:

[0006] 1) Mix the fish meal sample with activated carbon and anhydrous sodium sulfate, then add petroleum ether and let it stand for extraction. Filter the filtrate and evaporate the petroleum ether at 40°C to obtain the crude fish meal fat.

[0007] 2) Mixing the crude fat from fish meal with isooctane to obtain a test solution;

[0008] 3) Mix the test solution with glacial acetic acid and let it stand to obtain an unreacted solution; mix the test solution with anisidine and let it stand to obtain a reaction solution; mix isooctane with anisidine and let it stand to obtain a blank solution;

[0009] 4) Using isooctane as a control, the absorbance of the unreacted solution, the reaction solution, and the blank solution at 350 nm was measured using a spectrophotometer. The anisidine value (AV) of the fish meal sample was calculated according to the following formula:

[0010]

[0011] Wherein, A0 is the absorbance of the blank solution, A1 is the absorbance of the unreacted solution, and A2 is the absorbance of the reaction solution; Q is the concentration of the assay solution, 0.01 g / mL; m is the mass of the crude fat of the fish meal, g; and V is the amount of isooctane used in step 2), mL.

[0012] Furthermore, in step 1), the mass ratio of the fish meal sample to activated carbon and anhydrous sodium sulfate is 10:10:(1-2).

[0013] Furthermore, in step 1), the amount of petroleum ether added is 2-3 times the total volume of the fish meal sample, activated carbon, and anhydrous sodium sulfate.

[0014] Furthermore, in step 1), during the static extraction process, the static temperature is room temperature and the static time is 12-24 hours. If the static time exceeds 24 hours, petroleum ether may evaporate, and the crude fat content may be reduced.

[0015] Furthermore, in step 1), during the filtration process, the pouring speed of the extract is consistent with the filtration speed.

[0016] Furthermore, in step 1), the petroleum ether evaporation method includes rotary evaporation and water bath evaporation.

[0017] Furthermore, in step 3), in the unreacted solution, the volume ratio of the test solution to glacial acetic acid is (4-6):1.

[0018] Furthermore, in step 3), in the unreacted solution, the volume ratio of the test solution to anisidine is (4-6):1.

[0019] Furthermore, in step 3), the volume ratio of isooctane to anisidine in the unreacted solution is (4-6):1.

[0020] Furthermore, in step 3), during the standing process, the standing temperature is 23±3° C. and the standing time is 6-8 minutes.

[0021] Compared with the prior art, the present invention has the following characteristics:

[0022] 1) The present invention overcomes the problem of low fish oil extraction yield from fish meal by increasing the volume of petroleum ether and extending the fat extraction time. Anhydrous sodium sulfate is added to remove the effect of moisture on the reaction equilibrium, and the pouring speed of the extract is controlled to be consistent with the filtration speed, so that the moisture content of the extracted fish oil does not exceed 0.1%. Activated carbon is added to absorb the color of the extracted fish oil, reducing the interference of the fish oil color on the absorbance of the reaction system and avoiding the problem of inaccurate results caused by excessive color.

[0023] 2) To improve the accuracy of anisidine value detection, the present invention evaporates petroleum ether at a temperature below 40°C, and the residue is the crude fish meal fat. On the one hand, this avoids cumbersome operation (GB / T 6433 requires cumbersome operation, and the oil is treated at high temperature). On the other hand, this method uses room temperature extraction and evaporates petroleum ether in a water bath below 40°C to avoid accelerating fat oxidation under high temperature conditions (>40°C), which would cause irreversible effects on the anisidine value (research shows that the anisidine value of oil increases with temperature above 40°C). DETAILED DESCRIPTION

[0024] The present invention is described in detail below with reference to specific embodiments.

[0025] A method for detecting the anisidine value of fish meal comprises the following steps:

[0026] 1) Mix a fish meal sample with activated carbon and anhydrous sodium sulfate in a mass ratio of 10:10:(1-2), then add petroleum ether 2-3 times the bulk volume of the above components, let it stand at room temperature for 12-24 hours, filter the filtrate, and remove the petroleum ether by heating at 40°C in a water bath or rotary evaporation to obtain crude fish meal fat;

[0027] Among them, during the filtration process, the pouring speed of the extract is consistent with the filtration speed;

[0028] 2) Mixing the crude fat from fish meal with isooctane to obtain a test solution;

[0029] 3) Mixing the test solution with glacial acetic acid at a volume ratio of (4-6):1 and allowing to stand to obtain an unreacted solution; mixing the test solution with anisidine at a volume ratio of (4-6):1 and allowing to stand to obtain a reaction solution; and mixing isooctane with anisidine at a volume ratio of (4-6):1 and allowing to stand to obtain a blank solution;

[0030] During the standing process, the standing temperature was 23±3°C and the standing time was 6-8 minutes.

[0031] 4) Using isooctane as a control, the absorbance of the unreacted solution, the reaction solution, and the blank solution at 350 nm was measured using a spectrophotometer. The anisidine value (AV) of the fish meal sample was calculated according to the following formula:

[0032]

[0033] Wherein, A0 is the absorbance of the blank solution, A1 is the absorbance of the unreacted solution, and A2 is the absorbance of the reaction solution; Q is the concentration of the assay solution, 0.01 g / mL; m is the mass of the crude fat of the fish meal, g; and V is the amount of isooctane used in step 2), mL.

[0034] This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0035] The reagents and instruments used in the following examples include:

[0036] Petroleum ether: boiling range 30-60°C, AR; anhydrous sodium sulfate: AR; isooctane: absorbance measured with water as a reference within the wavelength range of 300-350 nm should not exceed 0.01; glacial acetic acid: water content by mass should not exceed 0.1%, AR; anisidine reagent: accurately weigh 0.125 g of 4-anisole into a 50 mL volumetric flask and dilute to the mark with glacial acetic acid. Avoid direct sunlight and prepare immediately before use. The absorbance of the anisidine reagent should not exceed 0.2 (at 350 nm, using isooctane as a blank).

[0037] Volumetric flask: 25mL or 50mL, 100mL; black centrifuge tube: 10mL; pipette: 1mL, 5mL, etc.

[0038] Example 1:

[0039] A method for detecting the anisidine value of fish meal comprises the following steps:

[0040] S1: Extraction and concentration of crude fat from fish meal: Take a fish meal sample, mix it evenly and transfer it to a wide-mouth bottle. Add activated carbon and anhydrous sodium sulfate and mix thoroughly (for every 10g of fish meal sample, add 10g of activated carbon and 1-2g of anhydrous sodium sulfate). Add 2-3 times the volume of petroleum ether, shake well, and let it stand for 12h.

[0041] Filter with filter paper, control the pouring speed of the extract to be consistent with the filtration speed, take the filtrate, and evaporate the petroleum ether under reduced pressure using a rotary evaporator in a water bath below 40°C. The residue is the crude fat of the fish meal;

[0042] At the same time, take fish meal crude fat with a moisture content (refer to GB 5009.236-2016 National Food Safety Standard - Determination of Moisture and Volatile Matter in Animal and Vegetable Oils and Fats) not higher than 0.1% as the sample to be processed in the next step. The crude fish meal fat should be measured as soon as possible after extraction and concentration;

[0043] S2: Preparation of the test solution: Weigh approximately 1 g of crude fish fat to the nearest 0.0001 g, record as m, directly into a 100 mL volumetric flask, dissolve with 5-10 mL of isooctane, and dilute to the mark to obtain the test solution;

[0044] S3: Construction of reaction system:

[0045] Blank solution (A0): Add 5 mL of isooctane and 1 mL of anisidine reagent to a 10 mL black centrifuge tube, seal, and shake thoroughly;

[0046] Unreacted solution (A1): Add 5 mL of the test solution and 1 mL of glacial acetic acid to a 10 mL black centrifuge tube, seal, and shake thoroughly;

[0047] Reaction solution (A2): Add 5 mL of the test solution and 1 mL of anisidine reagent to a 10 mL black centrifuge tube, seal, and shake thoroughly;

[0048] After the above solution is fully shaken, it is placed at 23±3℃ for 8 minutes to react. Then, the solution is transferred to a clean, dry cuvette of the spectrophotometer within 2 minutes. The total time is controlled within 10±1 minutes. The spectrophotometer zero point is calibrated at 350nm with isooctane. With isooctane as the control, the absorbance of the blank solution A0 (A0<0.2), the unreacted solution A1, and the reaction solution A2 (0.2 <A2<0.8)。

[0049] S4: The anisidine value (AV) of the fish meal sample is calculated according to the following formula:

[0050]

[0051] Where A0 is the absorbance of the blank solution, A1 is the absorbance of the unreacted solution, and A2 is the absorbance of the reaction solution; Q is the concentration of the test solution, 0.01 g / mL; m is the mass of the crude fishmeal fat, approximately 1 g; V is the amount of isooctane used in step S2, 100 mL; and 1.2 is the correction factor for diluting the test solution with 1 mL of anisidine reagent or glacial acetic acid solution. The experimental results are shown in Tables 1, 2, and 3.

[0052] Table 1

[0053]

[0054] Table 2

[0055]

[0056] Table 3

[0057]

[0058] By adding activated carbon and anhydrous sodium sulfate, this embodiment can remove the effect of moisture generated during the fish meal extraction process on the reaction equilibrium, control the pouring speed of the extract and the filtration speed to be consistent, and ensure that the moisture content of the extracted fish oil does not exceed 0.1%. At the same time, the addition of activated carbon can absorb the color of the extracted fish oil, reducing the interference of the fish oil color on the absorbance of the reaction system and preventing excessive color from darkening, which may lead to inaccurate results.

[0059] The method in this embodiment also offers the advantages of accurate and objective testing: GB / T 19164 fish meal standards for evaluating fish meal freshness include volatile basic nitrogen (protein breakdown), oil acid value (free fatty acids), and histamine (protein breakdown). The anisidine value can be used to measure the level of aldehydes (primarily α- and β-unsaturated aldehydes) generated during the oxidation of crude fat in fish meal, making it an important indicator for evaluating the content of secondary oxidation products in fish meal. The anisidine value of fish meal is closely related to the production process and transportation and storage conditions. Therefore, testing the anisidine value of fish meal can more comprehensively and accurately assess the freshness of fish meal, preventing adulteration of fish meal that could affect product quality.

[0060] For example, the acid value test is used to determine the free fatty acid content in fish meal. This is calculated by consuming a standard potassium hydroxide solution. The extraction process produces a darker color, making the titration endpoint difficult to determine and prone to subjective errors. Volatile basic nitrogen, on the other hand, is produced by enzymes and bacteria through the breakdown of proteins, producing ammonia and other alkaline nitrogen-containing substances such as amines. This can be a source of adulteration and artificial adjustments by suppliers. The anisidine value test, however, uses a spectrophotometer to directly read absorbance, providing a more accurate and objective assessment of fish meal freshness and reducing human error.

[0061] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for detecting the anisidine value of fish meal, characterized in that: The method comprises the following steps: 1) Mix the fish meal sample with activated carbon and anhydrous sodium sulfate, then add petroleum ether and let it stand for extraction. Filter the filtrate and evaporate the petroleum ether at 40°C to obtain the crude fish meal fat. 2) Mixing the crude fat from fish meal with isooctane to obtain a test solution; 3) Mixing the test solution with glacial acetic acid and letting it stand to obtain an unreacted solution; mixing the test solution with anisidine and letting it stand to obtain a reaction solution; mixing isooctane with anisidine and letting it stand to obtain a blank solution; 4) Using isooctane as a control, the absorbance of the unreacted solution, the reaction solution, and the blank solution at 350 nm was measured using a spectrophotometer. The anisidine value (AV) of the fish meal sample was calculated according to the following formula: Wherein, A0 is the absorbance of the blank solution, A1 is the absorbance of the unreacted solution, and A2 is the absorbance of the reaction solution; Q is the concentration of the test solution in the reaction solution, 0.01 g / mL; m is the mass of the crude fat of the fish meal, g; and V is the amount of isooctane used in step 2), mL.

2. The method for detecting the anisidine value of fish meal according to claim 1, wherein In step 1), the mass ratio of the fish meal sample to activated carbon and anhydrous sodium sulfate is 10:10:(1-2).

3. The method for detecting the anisidine value of fish meal according to claim 1, wherein In step 1), the amount of petroleum ether added is 2-3 times the total volume of the fish meal sample, activated carbon, and anhydrous sodium sulfate.

4. The method for detecting the anisidine value of fish meal according to claim 1, wherein In step 1), during the static extraction process, the static temperature is room temperature and the static time is 12-24 hours.

5. The method for detecting the anisidine value of fish meal according to claim 1, wherein In step 1), during the filtration process, the pouring speed of the extract is consistent with the filtration speed.

6. The method for detecting the anisidine value of fish meal according to claim 1, wherein In step 1), the petroleum ether evaporation method includes rotary evaporation and water bath evaporation.

7. The method for detecting the anisidine value of fish meal according to claim 1, wherein In step 3), the volume ratio of the test solution to glacial acetic acid in the unreacted solution is (4-6):

1.

8. The method for detecting the anisidine value of fish meal according to claim 1, wherein In step 3), in the unreacted solution, the volume ratio of the test solution to anisidine is (4-6):

1.

9. The method for detecting the anisidine value of fish meal according to claim 1, wherein In step 3), the volume ratio of isooctane to anisidine in the unreacted solution is (4-6):

1.

10. The method for detecting the anisidine value of fish meal according to claim 1, wherein: In step 3), during the standing process, the standing temperature is 23±3° C. and the standing time is 6-8 minutes.

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