1. Types of preservatives detected

At present, the commonly used food preservative testing can be divided into two categories: organic preservative testing and inorganic preservative testing.The permissible organic preservatives in China include benzoic acid and its sodium salts, sorbic acid and its potassium salts, dehydroacetic acid and acetic acid derivatives.Inorganic preservatives tested include sulfites and their salts, hydrogen peroxide, free chlorine and hypochlorite.These preservatives are relatively toxic, benzoic acid and sorbic acid can be eliminated through the body's metabolic process, and are less harmful to the human body.

Two, common preservative detection methods

There are many methods for the detection of food preservatives. The main methods for the detection of several common preservatives are as follows:

1. Preservative - hydrogen peroxide detection method

At present, there are two commonly used methods for detecting hydrogen peroxide at home and abroad, which are chemical solvent titration analysis and instrumental analysis.

(1) chemical titration

Our country commonly used detection method is chemical solvent titration analysis method, such as potassium permanganate titration, indirect iodine titration, cerium sulfate titration.Potassium permanganate titration method is the simplest, the cost is low, and because of its own color, do not need to make

Use other indicators, but some foods contain some organic matter, will be oxidized by potassium permanganate, resulting in a large error in the detection results.Indirect iodimetry method is also more economical, the use of catalase is less, but to ensure the activity of the enzyme

The test environment selection is more strict, more difficult to control, the determination of the results are also prone to errors.The results of ceric sulfate method are accurate, the standard solution of ceric sulfate is stable, the reaction is less in the test process, and the intermediate product is not generated

The requirements are not high, but the cost is high.In a word, chemical titration analysis has many deficiencies, such as time consuming and material consuming, and the color change at the end of the test is not obvious, so microanalysis cannot be carried out.

(2) Instrumental analysis

The commonly used instrumental analysis methods for detecting hydrogen peroxide in food include titanium solution spectrophotometry, atomic absorption method, fluorescence analysis method, chromatography and so on.Titanium solution spectrophotometric method is simple, easy operation, high accuracy, the main use of acidic hydrogen peroxide with titanium ions in the solution produces chemical reaction, generate stable complex of orange, to a certain concentration range, the complex of absorbance and hydrogen peroxide content in the samples present linear relationship, which can calculate the content of hydrogen peroxide.Relatively speaking, the operation of atomic absorption method is relatively complex, and the test conditions are harsh, so the detection results are easily affected and errors are formed.Fluorescence analysis is a common analytical method with high sensitivity and high selectivity. Hydroxyl radicals are generated by the reaction of hydrogen peroxide and ferric ion under acidic conditions, and then the fluorescent substance hydroxyl benzoic acid is generated by the reaction with benzoic acid which does not produce fluorescence itself. Hydrogen peroxide content is indirectly measured according to the fluorescence reaction.

2, preservatives - sorbic acid, benzoic acid test method

Sorbic acid and benzoic acid are widely used in food preservative treatment. The detection methods of sorbic acid and benzoic acid in kitchen condiments, soy sauce, drinks, fruit juices and other foods are mainly used by gas chromatography and high performance liquid chromatography.After sampling by gas chromatography, acidification is carried out first, and then organic solvents such as diethyl ether are used for extraction and concentration for several times, and then the detection is carried out. This method consumes more organic solvents, and has high working intensity, time-consuming and laborious, and is not economical.High performance liquid chromatography (HPLC) is also widely used. Relatively speaking, this method does not require the use of organic solvents, it is easy to operate, high separation efficiency, and high detection accuracy.Meat products in China are not allowed to add benzoic acid, only allows you to add a small amount of sorbic acid, are to be scientific and reasonable and sorbic acid in meat products, is different from the juice drinks, pretreatment of the samples need to work, gas chromatograph, hydrogen flame ionization detector is the separation of detection of sorbic acid in meat products, effective measures to detect process is relatively simple, high accuracy,Can carry out trace detection, to meet the requirements of China.

3, preservative-dehydroacetic acid detection method

Dehydroacetic acid is one of the necessary inspection items in QS certification, due to the toxicity of dehydroacetic acid is relatively large, the control of dehydroacetic acid is relatively strict at home and abroad, China is only allowed in fermented bean curd, assorted pickles in a small amount of use.The main detection method of dehydroacetic acid in pickles and fermented bean curd is gas chromatography, which mainly requires extraction of organic solvents and repeated concentration. Although this method has a high degree of separation and can detect a variety of preservatives at the same time, the operation process is more complex and time-consuming.