What should be paid attention to in acid value testing oils?

Determination of acid value I. Principle Free fatty acids in oils and fats.

A neutralization reaction is produced with potassium hydroxide, and the amount of free fatty acids can be calculated from the consumption of potassium hydroxide standard solution. The reaction formula is as follows: rcooh+koh rcooh+h2o Second, the reagent neutral alcohol ether mixture or neutral phenol alcohol.

Mixture: take chemically pure 95% ethanol.

Mix with ether in a 2:1 volume, or benzene and 95% ethanol in equal volumes, then add a few drops of phenolphthalein indicator, and neutralize with potassium hydroxide solution until reddish. 1% phenolphthalein indicator.

Potassium hydroxide standard solution. 3. Operation method Accurately weigh the oil sample and place it in a beaker.

, add 50 ml of mixture, shake to dissolve (warm if necessary), add 3 4 drops of phenolphthalein indicator, and titrate with potassium hydroxide standard solution until light red and do not fade within 1min. Calculated using the following formula: Acid value = where:

n--- equivalent concentration of the standard alkali solution; v--- the amount of standard alkali solution consumed; the amount of potassium hydroxide contained in 1ml of alkali solution, mg; w--- weight of the sample, g.

The reddish color of the titration endpoint is indeed not easy to judge, what is the best way?

Summary. 1.The acid value of oils and fats is determined by titration.

Its principle is to use the characteristics of fats and fatty acids that can be dissolved in organic drops, mix neutral ether - ethanol to dissolve the free fatty acids in the oil sample, and then use the standard solution for titration, calculate the fatty acid according to the quality of the oil sample and the volume of alkali consumption, and judge the indication of the titration endpoint is phenol, and the endpoint color is pink. In order to make the endpoint easy to observe and reduce the breaking error, for the samples with darker color than the tung itself, the dosage can be increased accordingly, so as to reduce the color effect of the oil sample itself on the results.

2. The instrument used in the experiment needs to be dried to carry the water medium.

Ringing results. 3.Ethanol is a solvent that dissolves oil to prevent the occurrence of turbidity.

Bear. Determination of the acid value of fats and fats.

1.The acid value of oils and fats is determined by titration. The principle is to use the characteristics of fats and fatty acids that can be dissolved in the dissipation of the attack, and the free fatty acids in the oil sample are dissolved with neutral ether-ethanol mixture, and then titrated with a standard solution, and the fat acid is calculated according to the quality of the oil sample and the volume of alkali consumption.

In order to make the end point easy to observe and reduce the breaking error, for the darker color of the tung itself, the dosage can be increased accordingly, so as to reduce the color of the oil sample itself on the results of the color 2 The instrument needs to be dried, and the water medium effect result 3 is carried by the instrumentEthanol is a solvent that dissolves oil to prevent the occurrence of turbidity.

Determination of soybean urease activity (GB).

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There are several methods: colorimetry, titration, pH value-added method, rapid detection method.

Determination of soybean urease activity (rapid test method).

There are two methods for rapid determination, you can refer to the figure below.

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The method of determining the acid number of the oleoacid is as follows:

Acid and alkali neutralization titration is commonly used for the determination of acid number. For oils and fats with high acid value, dark color, and difficult to neutralize titration, pH meter can also be used to measure filial piety.

Determination principle: After dissolving the oil sample with a mixed solvent of neutral ether and ethanol, the free fatty acids in the oil are titrated with potassium hydroxide standard solution, and the size of the calculated acid value is calculated according to the amount of substances consumed in the potassium hydroxide standard solution and the quality of the oil.

Regardless of whether potassium hydroxide or sodium hydroxide solution is used in the determination process, the formula constant for the result is , not the molar mass of sodium hydroxide (40), because the result expression of the acid number is expressed in terms of the mass of potassium hydroxide (mg).

Oleoacid number:

The acid value of oil, also known as "oil acid value", is a sign of the content of free fatty acids in oils and fats, and is an important indicator to test the quality of oils and fats, which is expressed in milligrams of potassium hydroxide required to neutralize free fatty acids in each gram of oil. If the content of free fatty acids in the oil is large, the acid value is high and the quality is poor; If the content is low, the acid value is low and the quality is good.

Freshly harvested and fully mature oilseed seeds have very little free fatty acids; The content of oil seedlings that are not hot or have germinated and moldy is more. Therefore, by measuring the acid value, the freshness of the oil can be determined, and the quality of the raw materials for oil production can also be explained, whether the conditions are suitable for storage, and whether the process is reasonable during processing.

1.This tester is fully suitable for the determination of the acid value of animal fats, only need to use a balance to weigh the oil sample grams and add them to the bottom solution, put the titration flask in a 50 600C hot water bath to heat the oil sample to dissolve, take out the titration flask from the hot water bath and shake and mix well, and after cooling to room temperature, it is determined according to the above determination procedures Another simple method is to take an appropriate amount of animal oil in a beaker, place the beaker in a hot water bath and wait for the oil sample to melt, and then use a syringe to absorb 0 40 ml of animal oil sample for determination After the syringe is used, it should be sucked up in time and washed under hot water to avoid the syringe being blocked and damaged by grease

2.Do not wash the two alloy pieces of the sensor with strong acid, soak them in the hypo solution for 1 2 minutes after the test is completed, wipe them with filter paper pieces for later use, if the sensor is not used for a long time, it is advisable to coat the two electrodes with a thin layer of neutral oil protection.

The instrument should be used in a moisture-proof, moth-proof, dust-proof, shock-proof, dry, and ventilated environment.

Acid value refers to the number of milligrams of potassium hydroxide standard solution consumed per gram of vegetable oil by titration of free fatty acids in vegetable oil with potassium hydroxide standard solution, and the unit is mg koh g. It is a measure of the number of free carboxylic acid groups in a compound (such as fatty acids) or mixtures, and is a marker of the free fatty acid content in lipid fats. Acid value is one of the important indicators to evaluate the stability and reasonable processing technology of edible oil.

The size of the acid value of oils and fats is related to the raw materials for making oils, the processing technology of oils and fats, and the storage and transportation methods and conditions of oils and fats. During the storage period, the oil is slowly hydrolyzed due to the action of microorganisms, moisture, temperature, light, lipase and other factors, and free fatty acids are produced, which are placed in the oil to increase the acid value and reduce the storage stability. The acid value can be used as an indicator of the degree of hydrolysis of fats and fats, and can also be used as an indicator of the degree of rancidity.

The lower the acid value, i.e. the better the quality of the oil, the better the refinement and freshness. Generally, the acid value of edible vegetable oil should not be 5 mg koh g, and a slightly higher acid value will not cause damage to human health; However, if the acid value is too high, it will cause gastrointestinal discomfort, diarrhea and damage to the liver, so the accuracy of the acid value measurement results is very important for human health.

Why is acid value determination very important in the industrial production of oils and fats?

Because the acid resistance or acid value is the most basic and important indicator to measure the quality of the oil, the higher the acid value, the higher the degree of oxidation and decay of the oil, and the worse the quality.

1.Take 7 ml of isopropanol and put it in the titration flask, take 0 40 ml of oil sample with a syringe and put it in the titration flask (the density of the liquid oil sample is generally gram ml, that is, equivalent to the weight of the oil sample), shake the titration bottle to fully dissolve the oil sample, then add 1 ml of bottom solution and place it in the titration flask, place the sensor head in the test solution, and insert the sensor wire plug into the jack of the tester and connect with the tester.

2.Set the calibration and measurement switch to the calibration position at the measured position, press the "reset button" to reset the acid value display table to zero, press the "measurement and stop button" to continuously shake the test solution, pay attention to observe the microscopic pink color of the test solution in the titration bottle for 30 seconds, press the "measure, stop" button, and the value displayed in the acid value display table is the value of oil-like acid

3.Take the sensor out of the test solution, wipe the test solution remaining on the sensor head with a filter paper piece, soak it in a hypo solution for 1 to 2 minutes, take out the sensor and fully rinse the two metal sheets with distilled water, and then wipe them with filter paper for use again, 4After the test is completed, turn off the power, remove the sensor from the tester, clean the sensor as described in the previous item, and store it in the carton for later use.

5.Please do a blank test when measuring low acid value oils: (A quick pre-cut operation is as described in the measurement method, but the oil is not added to the sample.) ）