introduction
Under today's rapid social and economic development, the living standards of the people are getting higher and higher, and there are higher requirements for the quality of food safety, and people are anxious about the outbreak of a food safety incident. Among them, there are also many problems of sulfur dioxide content exceeding the standard in food, such as sulfur star anise, vermicelli noodles and dried fruit preserves, which are related to the excessive residual amount of sulfur dioxide, so that people are looking forward to these foods containing sulfur dioxide. The following reviews are made on the properties of sulfur dioxide, sources, roles, hazards, limiting standards and testing methods in food.
Chapter 1: Physicochemical Properties and Sources of Sulfur Dioxide
1.1 Physicochemical properties of sulfur dioxide
1.1.1 Physical Properties
Sulfur dioxide is the most common sulfur oxide, a colorless transparent gas with a pungent odor. Soluble in water, ethanol and ether. [1]
Fig. A.1 Three resonant structures of sulfur dioxide
Liquid sulfur dioxide is relatively stable and inactive. Gaseous sulfur dioxide is heated to 2000 °C without decomposition. Does not burn, nor does it form an explosive mixture with air.
1.1.2 Chemical properties
At room temperature, humid sulfur dioxide reacts with hydrogen sulfide to precipitate sulfur. At high temperatures and in the presence of catalysts, hydrogen can be reduced to hydrogen sulfide and carbon monoxide to sulfur. Strong oxidants can oxidize sulfur dioxide to sulfur trioxide, and oxygen can oxidize sulfur dioxide to sulfur trioxide only in the presence of a catalyst. It has spontaneous combustion and no combustion. Liquid sulfur dioxide can dissolve organic compounds such as amines, ethers, alcohols, phenols, organic acids, aromatic hydrocarbons and other organic compounds, and most saturated hydrocarbons cannot be dissolved. It has a certain degree of water solubility, and reacts with water and water vapor to generate toxic and corrosive vapors.
Bleaching of sulfur dioxide: Sulfur dioxide can bleach certain colored substances. The magenta solution fades (the compound is heated to form an unstable compound and then returns to the original red), so the bleaching of sulfur dioxide is also called temporary bleaching. This phenomenon is used to test for the presence of sulfur dioxide. Sulfur dioxide is bleached. Industrially, sulfur dioxide is commonly used to bleach pulp, wool, silk, straw hats, etc. The bleaching effect of sulfur dioxide is due to its (sulfurous acid) ability to form unstable colorless substances with certain colored substances. This colorless substance is easy to decompose and the colored substance returns to its original color, so the straw hat braid that has been bleached with sulfur dioxide turns yellow over time. The bleaching effect of sulfur dioxide and some sulfur-containing compounds is also illegally used by some unscrupulous manufacturers to process food to whiten food. Eating such foods has serious damage to the liver and kidneys of the human body, and has a carcinogenic effect.
Fig. A.2 Sulfur dioxide is generated under sulfur combustion conditions
Sulfur dioxide preservative: In addition, sulfur dioxide can also inhibit the growth of mold and bacteria, and can be used as a preservative for food and dried fruits. However, it must be used in strict accordance with the relevant national scope and standards.
Reducibility of sulfur dioxide: sulfur dioxide can fade chlorine water, bromine water, KMnO4 solution, reflecting the strong reducibility of sulfur dioxide rather than bleaching.
Oxidation of sulfur dioxide: sulfur dioxide has a weak oxidation, and the ratio of oxidation products to the amount of reducing product substances is 2:1.
1.2 Sources of sulfur dioxide
Sulfur dioxide present in food comes from two sources.
1.2.1 Exogenous Sources
As a food additive, sulfur dioxide is widely used in food processing, and some unscrupulous traders are driven by interests to add sulfur dioxide and its salts in large quantities in food is the main source of sulfur dioxide exceeding the standard.
Sulfur dioxide and sulfites are added to food for the following purposes: in the food processing process, the use of sulfur dioxide and sulfite oxidation, can effectively inhibit the non-enzymatic browning in the food processing process; using its reductivity and bleaching, can also be used as a preservative, inhibit the growth of mold and bacteria. Therefore, in the production and processing process of food, sulfur dioxide, sulfites, etc. are often added to make the food fade and avoid browning, improve the appearance quality, and extend the shelf life. Commonly used sulfur dioxide additives are sodium sulfite, sodium bisulfite, sodium hyposulfite and sodium metabisulfite. For example, in fresh plant foods such as fruits and vegetables, sulfites can inhibit the activity of polyphenol oxidase and prevent browning of apples, potatoes, mushrooms, etc., so dried foods are often used to control the browning of fruits and vegetables. Wines are filled with sulfur dioxide during fermentation or use water dissolved in sulfur dioxide as preservatives. In order to maintain flavor stability in the beer production process, sulfur dioxide is often added as an antioxidant before filling. Moreover, sulfur dioxide and sulfites are easy to interact with sugars, proteins, pigments, enzymes, vitamins, aldehydes, ketones, etc. in food, and remain in food with free and bound sulfur dioxide. Once these additives are used in excess, and there is no sequence of sulfur dioxide removal technology, it will inevitably lead to excessive sulfur dioxide residues and destroy the quality of food. [2]
1.2.2 Endogenous Sources
Although the residue excess of sulfur dioxide and its salts is mainly caused by artificial over-addition, sulfur dioxide produced by the food itself is also another important source that cannot be ignored. Studies have found that some foods also produce sulfites during fermentation without the addition of any additives such as sulfites. The naturally occurring sulfite content of wine and fruit wine fermentation can reach up to 300 mg/kg, and even in general, it will reach 40 mg/kg, which far exceeds the safety range requirements of the us FDA for the sulfite content in food. On the one hand, since a considerable part of the food is plant bodies, during the growth of plant bodies, sulfur dioxide in the atmosphere will enter the plant through the foliar stomata of the plant body, and the combined sulfur dioxide in other soils or water will also enter the plant body through the absorption of the plant. Sulfur dioxide that enters the plant body is easy to react with the aldehyde and ketone compounds in the plant body, especially the sugar compounds, to form a bound state of sulfurous acid, so the plant body has a certain content of free and bound sulfur dioxide. During the growth process of animals, due to eating plants, a certain amount of sulfur dioxide will also accumulate in the body. So both animal and plant foods contain a certain amount of sulfur dioxide from natural sources. [4]
Chapter 2: The Role of Sulfur Dioxide
2.1 Sulfur dioxide acts as a bleach
2.1.1 Principle of bleach
China allows the use of bleaching agents, mainly sodium sulfite, sodium bisulfite, sodium hyposulfite, sodium metabisulfite and sulfur dioxide generated by sulfur combustion, these bleaches are used in food dissociation into sulfurous acid, sulfurous acid has reducibility, combined with colored substances to form colorless substances, showing bleaching effect. Sulfur dioxide is a colorless, irritating odor gas, bleaching and antiseptic effect on food, sulfur is commonly used in food processing to generate sulfur dioxide as a bleach and preservative. The use of sulfur dioxide can achieve the effect of bright and white outside the product. [3] Substances bleached by sulfur dioxide can change color due to its disappearance, so a certain amount of sulfur dioxide should usually remain in food. However, if the residue is too high, it will make the products with sulfur dioxide, which has adverse effects on the added spices, pigments, etc., and is not good for the human body, so it is necessary to strictly control its residual amount when using. Reducing bleach can only function when it is present in food, and once it disappears, it can be oxidized again due to the presence of oxygen in the air. In daily life, sulfur dioxide is often used for the bleaching of grains, starches, and sugars, for the bleaching of tea leaves, and to prevent browning of color when peeling and slicing. These uses are often because we prefer to buy clean white fresh food when purchasing. In fact, white does not actually mean clean, and some foods cannot be stored for a long time due to their easy discoloration and deterioration. In order to attract consumers and ensure that the fresh products in the sales process remain "shiny and shiny", some sulfur dioxide preservatives and bleach agents are added. In short, because the application of sulfur dioxide can make dried fruit, preserved fruit, etc. have a beautiful appearance, and some people call it a cosmetic additive. [6]
2.1.2 Bleach application
Sulfur dioxide, produced by sodium sulfite, can be applied to fruit juices to prevent changes in the color of fruit juices. Sulfur dioxide, which is produced by sodium metabisulfite, can be used for mushroom color protection, and the treated mushrooms have excellent color and flavor. Sulfur dioxide, which is generated by sulfur, can be used for dried fruits, dried vegetables, vermicelli, preserves, and sugar (only for fumigation, not directly added to food). [5]
After the raw materials of mushrooms are harvested, they are soaked with low concentration of sulfur dioxide to protect the color, which is certain for maintaining and improving the quality of raw materials and finished products. With the current use of low concentration sulfur dioxide solution to soak the mushroom color protection, with the extension of the soaking time, although the sulfur dioxide content increased slightly, but after adding acid pre-cooking, canning and sterilization, the residual amount of sulfur dioxide of the finished product is almost the same, only 1.4ppm higher than the control group that does not protect the color, so it can be considered that the current color protection concentration (about 0.1%), the color protection time (5 to 30 minutes) does not seem to affect the finished sulfur dioxide, the residual amount. The low-concentration sulfur dioxide soaking method used in many production plants today can improve the quality of the finished product and is simple and easy to implement. The impact on the residual amount of sulfur dioxide in the finished product is almost negligible, and there is no significant difference between the corrosion of the empty tank in the experiment and the unprotected color control group, so it is feasible to use sulfur dioxide color protection from the perspective of food hygiene or safety. Before there is a better color protection method to replace it, it is still a safe and reliable mushroom color preservation method.
Sulfur treatment can prevent fruit browning, maintain nutrients China's traditional specialty food dried fruit, preserved fruit processing mostly using sulfur smoking method or sulfite solution impregnation method for color protection, to prevent browning. After the sulfur treatment of the fruit pieces before drying, the oxidase in the fruit is destroyed, the oxidation effect is prevented, and the tan substances in the fruit are not oxidized and appear tan. At the same time, the vitamin C in the fruit can also be destroyed by oxidation. For preserved fruit production, sulfur treatment of the fruit blocks before sugar boiling can keep the product light yellow, prevent browning, and facilitate the endosmosis of sugar in sugar boiling. When smoking sulfur, the raw materials after grading, peeling, cutting and pitting are plated and sent to the sulfur chamber. The amount of sulfur used is generally 0.03% of the weight of the fruit, or 200 grams of sulfur according to the volume of 1 cubic meter. The sulfur smoking time of various fruits varies, generally 8 to 16 hours. If treated with sulfur immersion, soak with about 0.2% sulfite solution for several hours. The effect of sulfur treatment on the preservation of vitamin C in fruits is very obvious, and the preservation rate of sulfur-treated vitamin C in dried dates is 65%, while the control and other treatments are lower. In addition, apples, pears and other fruits are peeled and cut and immediately put into a dilute sulfurous acid solution, which can effectively prevent browning. [13]
2.2 Sulfur dioxide acts as a preservative
2.2.1 Principle of preservatives
Due to the long-term storage, long-distance transportation and sealed packaging needs of food, food corrosion has become an important issue in the development of the food industry. The use of preservatives can not only extend the storage period and shelf life of food, but also prevent the production of toxic microorganisms in food, thus playing a huge role in the development of the food industry. Preservatives are divided into organic chemical preservatives and inorganic chemical preservatives according to their source and properties. When sulfur dioxide is an inorganic chemical preservative, sulfur dioxide will first transform into sulfurous acid, and sulfuric acid has a strong inhibitory effect on oxidase, and reacts with sugar, and the substance formed by the reactants can block the condensation reaction between carbonyl-containing compounds and amino acids, so it can prevent enzymatic browning and prevent the occurrence of non-enzymatic browning, inhibit microbial reproduction, and thus play an antiseptic role. However, the sulfurous acid produced by sulfur dioxide is unstable, and if it is not sealed, it is easy to decompose, and heating will quickly decompose to release sulfur dioxide.
2.2.2 Preservative application
Sulfur dioxide is preserved in two ways during the preservative process of grapes.
Sulfur dioxide drug pack storage. Sulfur dioxide drug pack storage: put human sodium bisulfite and hygroscopic silicone mixed powder in the grape fruit box. The amount of sodium bisulfite is 0.3% of the weight of the fruit spike and 0.6% of the silicone. The two are divided into 5 packs after mixing at the time of application, placed on the fruit spikes in the box according to the diagonal method, and stored fresh with the sulfur dioxide generated during the moisture absorption reaction. Generally, the medicine package is changed once every 20 to 30 days, and it can be stored after the Spring Festival under the condition of 0 °C.
Sulfur dioxide fumigation preservative. It is used to fumigate the cellar, which has a good effect on the gray mold bacteria that cause decay during the storage period. After one person cellars, it is immediately smoked with 4 grams of sulfur dioxide, burned and fumigated for 30 to 60 minutes, and then smoked once every 10 days, and smoked once every other month when the temperature is 0 to 1 °C. It should be noted that when the temperature is too high, the release rate of sulfur dioxide is too fast, which is easy to produce poisoning and bleaching, forming white patches on the fruit surface, affecting the appearance of the fruit. Therefore, when conditions permit, try to use the first method as much as possible to be safer and more reliable. [7]
Some experimental results show that the control group without sulfur dioxide antiseptic preservation treatment, at the 60th time the fruit has been seriously decayed, can not continue to sample, and the sulfur dioxide antiseptic preservation treatment of the group, the fruit can be stored for up to nearly 140 days, it can be seen that sulfur dioxide plays a key role in maintaining the storage quality of the fruit. There are also some grape varieties like red earth grapes that need long-term storage and preservation, due to the long-term high sulfur dioxide concentration environment, the fruit absorbs a large amount of sulfur dioxide, which may cause the residue of sulfur dioxide to exceed the standard, through the various real storage and transportation processes after the harvest of olive red earth grapes, the sulfur dioxide residues under different origins, different years, different distances of transportation and the use of a variety of preservatives under different temperature storage conditions have been analyzed, According to the residual amount and risk providers in different situations, a dietary safety risk assessment was carried out. The results show that sulfur dioxide has been detected in various types of products, the residue value range is 2.97 ~ 40.95mg / kg, which is less than the minimum sulfur dioxide residue standard of the Ministry of Agriculture and Rural Affairs of China, and the dietary safety risk assessment results show that the residual amount of sulfur dioxide in red earth grapes in different storage and transportation environments is extremely low, will not cause damage to the person, consumers can eat with confidence, these results provide a scientific basis for the practical production and application of sulfur dioxide preservatives. [8]
2.3 Sulfur dioxide acts as an antioxidant
2.3.1 Principle of antioxidants
The antioxidant capacity of antioxidants essentially refers to their ability to capture free radicals or inhibit the production of free radicals. Antioxidant intake can be obtained from natural vegetables or fruits, or it can be chemically synthesized. Sulfur dioxide meets water to form sulfurous acid. Sulfites react with acids to produce sulfur dioxide, which forms sulfurous acid when exposed to water. Sulfurous acid is a strong reducing agent, which can consume oxygen in fruit and vegetable tissues and destroy its oxidase system, so it has antioxidant effect. The average person knows that eating garlic or onions is good for the body, because this type of vegetable is rich in various fat-soluble sulfides, and the more sulfur it contains, the stronger the ability to scavenge free radicals. The sulfides that are distributed on the surface of garlic after crushing are the root cause of the garlic odor. The heavier the garlic odor, the stronger the antioxidant capacity; the antioxidant capacity of the onion is because it is quite rich in sulfur-containing amino acids and sulfites with strong antioxidant capacity. Sulfites are characterized by a unique spicy taste and a strong bactericidal ability.
2.3.2 Antioxidant application
Application in beer: sulfur dioxide itself has reducibility, it is an antioxidant and bacteriostatic agent, can be coupled with the reaction product, the affinity for oxygen is very large, the reaction speed is fast, in a very short period of time can be removed oxygen. It has three main roles in beer: first, it can reduce the aging rate of beer, slow down the rate of oxidative turbidity and aging flavor substances; second, it and carbonyl compounds plus synthesis of carbonyl-sulfonate, such substances can inhibit the effects of aging flavor, and have the effect of eliminating free radicals; third, sulfur dioxide is dissolved in water to form sulfurous acid, which has a preservative effect. Therefore, sulfur dioxide is an effective antioxidant in the beer industry, but the residual sulfur dioxide content in beer should not be too high, otherwise it will not be detrimental to the human body and will also bring the irritating taste of sulfur dioxide to beer. China's fermented wine hygiene standards do not stipulate the limit of sulfur dioxide in beer, and the food safety law of the United States requires that when the sulfur dioxide content in beer exceeds 10mg/L, it should be marked on the label of the packaging. In actual production, sulfur dioxide is mostly added in the form of sulfites, bisulfites or partial sulfites. [9]
Application in dried fruits: The antioxidant capacity of sulfur dioxide was analyzed by DPPH, FARP, ABTS and ORAC methods at the same time, which confirmed that sulfur dioxide (aqueous sodium sulfite solution) has antioxidant capacity, and the antioxidant capacity is linearly related to the concentration, of which the antioxidant capacity of the ORAC method is the best. Through the determination of sulfur dioxide content in dried fruits, it was found that 5 kinds of dried fruits contained sulfur dioxide, of which the sulfur dioxide content of Huangti and Goji berries exceeded the national food safety limit standards, especially the sulfur dioxide in Huangti reached 1.45g/kg DW. From the existing results, sulfur dioxide may be the main reason for the abnormal antioxidant capacity of some dried fruits. Therefore, in the quality analysis of dried fruits or other samples that may use sulfur dioxide, the influence of sulfur dioxide on the relevant indicators should be considered in order to objectively evaluate its nutritional and functional value. [12]
In recent years, sulfur dioxide has a new understanding of the antioxidant properties of wine. The antioxidant effect of sulfur dioxide in wine is sulfite, and in the pH range of wine, its sulfur dioxide concentration is very low and generally 1-3 μmol/L. The antioxidant properties of sulfur dioxide in red wine are generally considered to be the inhibition of oxidase activity in wine by sulfur dioxide and the rapid consumption of dissolved oxygen. [10] A growing body of research has questioned this and agreed that sulfur dioxide shows little antioxidant performance in red wines under the condition of the amount of addition, and that the phenols in wine are more easily absorbed and consume dissolved oxygen than sulfur dioxide. Therefore, the tradition holds that sulfur dioxide in wine has antioxidant properties that need to be investigated. [11]
Chapter 3: The Hazards of Sulfur Dioxide in Food
3.1 Hazards of sulfur dioxide in food
Sulfur dioxide in food is mainly formed when burning sulfur fumigation food. Burning sulfur produces sulfur dioxide, which can destroy surface cells and promote their drying, and at the same time, due to its reducing effect, it can destroy the oxidation system of enzymes and prevent oxidation in order to improve food color and prolong storage time, so as to achieve the purpose of preventing deterioration. And if the purity of sulfur is not high, it may also contain harmful trace elements such as arsenic, which can also cause harm to the human body. Food experts believe that sulfur dioxide into the human body after the production of sulfite, and by the tissue cells in the sulfite oxidase to oxidize it into sulfate, through normal detoxification and eventually excreted by the urine, therefore, a small amount of sulfur dioxide into the body can be considered safe and harmless, but excess will cause harm to the human body. However, there are still many unscrupulous traders who often use sulfur dioxide additives in excess of standard restrictions in order to preserve the bright color of food and prevent rot, resulting in the residual amount of sulfur dioxide in food exceeding the standard. Eating such foods with excessive sulfur dioxide, it is easy to produce gastrointestinal reactions such as nausea and vomiting, in addition, it can also affect calcium absorption and promote the loss of calcium in the body; acute poisoning caused by excessive eating can cause symptoms of eye and nasal mucosa irritation, and in severe cases, laryngeal spasm, laryngeal edema, bronchospasm, etc., can also be transformed into a carcinogen in the human body - nitrosamine. Therefore, in the process of purchasing food, it is necessary to pay attention to whether the color of the purchased food is too bright or shallow, whether there is a pungent odor when the sealed food is opened, etc., so as to avoid buying food with sulfur dioxide exceeding the standard and affecting health. [16]
Taking sugar processing as an example, the sulfur dioxide residue in the sugar is mainly due to the use of sulfur as a processing aid in the sugar making process to use sulfur as a processing aid to clarify and decolorize, and the sulfur content of sugar raw materials and other processing aids may also be one of the reasons for the presence of sulfur dioxide residue in the sugar. A small amount of sulfur dioxide enters the body and eventually produces sulfates, which can be excreted from the body by urine after normal detoxification and will not produce toxic effects. However, if the human body consumes too much sulfur dioxide, it is easy to produce allergies, which may cause symptoms such as breathing difficulties, diarrhea, vomiting, etc., and may also cause different degrees of damage to the brain and other tissues.
Limit standards for sulfur dioxide
4.1 Allowable use range and maximum usage
<col style="width: 123px;">
<col>
Food classification number
Food name
Maximum usage/(g/kg)
remark
04.01.01.02
Fresh fruit with surface treatment
0.05
The maximum amount of use is recorded in the residual amount of sulfur dioxide
04.01.02.02
Dried fruits
0.1
04.01.02.08
Candied cold fruit
0.35
04.02.02.02
Dried vegetables
0.2
Dried vegetables (dehydrated potatoes only)
0.4
04.02.02.03
Pickled vegetables
continue
<col style="width: 120px;">
<col style="width: 311px;">
04.02.02.04
Canned vegetables (bamboo shoots, sauerkraut only)
04.03.02.02
Dried edible mushrooms and algae
04.03.02.04
Canned mushrooms and algae (canned mushrooms only)
04.04.01.04
Humus (including humus bamboo, oil skin, etc.)
04.05.02.03
Canned nuts and seeds
05.0
Cocoa products, chocolate and chocolate products (including cocoa butter substitutes and products) and confectionery
06.03.02.01
Raw and wet noodle products (e.g. noodles, dumpling skins, wonton skins, roasted wheat husks) (ramen only)
06.05.01
Edible starch
0.03
06.08
Frozen rice noodles (flavor pie only)
07.03
biscuits
11.01
sugar
11.02
Starch sugars (fructose, grape sugar, caramel, partial invert sugar, etc.)
0.04
11.05
Season the syrup
<col style="width: 105px;">
<col style="width: 125px;">
12.02.01
Semi-solid compound seasoning
14.02.01
Fruit and vegetable juice (pulp)
The maximum amount of use is measured by the residual amount of sulfur dioxide, the concentrated fruit and vegetable juice (pulp) is converted according to the concentration multiple, and the solid drink is increased by the dilution multiple
14.02.03
Fruit and vegetable juice (pulp) drinks
15.03.01
wine
0.25g/L
The maximum use of sweet wine and fruit wine series products is 0.4g/L, and the maximum use is measured by the residual amount of sulfur dioxide
15.03.03
wine
15.03.05
Beer and malt drinks
0.01
Detection method of sulfur dioxide in food
5.1 Colorimetry
5.1.1 Absorption of para-rose aniline hydrochloride colorimetry
Para-rose aniline hydrochloride colorimetric method China's national standard method is the colorimetric method of para-rose aniline hydrochloride with sodium tetrachloromercury as the extract agent, which stipulates the determination method of nitrite in food, which is suitable for the determination of sulfur dioxide residue in food. The method uses sulfites to react with sodium tetrachloromercury to generate a stable complex, and then reacts with aldehyde and para-rose aniline hydrochloride to generate a purple-red complex, which is quantitative with the standard series, and the detection limit is 1mg/kg but the method is not suitable for colored samples (such as wine, which will cause interference in determining the wavelength at a certain wavelength), the analysis time is more than 4h, and the absorption solution has a high mercury content, which is difficult to recycle, which is easy to cause environmental pollution and affect the operator's physical health. [14]
5.1.2 Mercury-free absorption para-rose aniline hydrochloride colorimetric method
Para-rose aniline hydrochloride colorimetric method has a long processing time and is also prone to environmental pollution, so the new technology adopts mercury-free pararose aniline colorimetric method of para-rose hydrochloride. After the sulfur dioxide in the sample is absorbed by the formaldehyde buffer solution, a stable hydroxymethylsulfonic acid is generated, and after alkali is added, it reacts with para-rose aniline hydrochloride to form a purple-red compound, which is quantitative in colorimetric. The conclusion shows that the ultrasonic extraction centrifugal treatment method of this test determines the sample extraction and measurement conditions for rapid detection of sulfur dioxide residue in food, which greatly shortens the analysis time. The use of formaldehyde absorber instead of sodium tetrachloromercury absorber avoids the toxicity and pollution of mercury. The color rendering time and color stability required for different temperatures are investigated, which can provide reference basis for the determination of different seasons and different room temperatures. The method determined in this test can be applied to the field rapid inspection of sulfur dioxide residues in sulfur fumigation foods in supermarket farmers' markets and other places. [15]
5.2 Titration
5.2.1 Distillation- iodine dosing method
The "distillation of one iodine quantity method" is to acidify and distill the sample in a closed container, and the distillate is absorbed with a solution of lead acetate. The absorbed solution is acidified with hydrochloric acid, titrated with an iodine standard solution, and the sulfur dioxide content in the sample is calculated according to the amount of iodine standard solution consumed. The use of distillation method to pretreat the sample, can effectively avoid the interference of the sample background, is currently widely used, but the time required is longer, the general distillation of a sample takes about an hour, not suitable for large-scale sample detection. [1]
5.2.2 Distillation-base titration
Distillation-base titration. This method uses the principle of acid-base neutralization titration, the sample acidifies, heats, and then passes into the nitrogen gas stream to carry the released sulfur dioxide out and through the neutral hydrogen peroxide solution, sulfur dioxide is absorbed by the hydrogen peroxide solution and generates sulfuric acid, and the total amount of sulfite in the sample can be determined by titration with standard sodium hydroxide solution. Barium chloride can also be added to the titrated solution to precipitate sulfate ions, and the resulting sulfate ions can be verified by barium sulfate gravimetric or turbidity determination. This method belongs to the rapid determination method and is widely used in the detection of various types of food. The Japan Food Sanitation Association Method (A), IS05522 (1981) and the General Administration of International Wine Are of this category. Its distillation time is short, and the solution can be titrated with alkali standard solution after boiling for 10 to 15 minutes, and the end point is easy to judge. The sampling volume can be flexibly controlled from 1g to 100g, and the detection range is wide, which can avoid the phenomenon of poor reproducibility of results due to uneven sulfurite distribution in the sample. However, this method requires a customized set of all-glass distillation units according to the specified size, which is easy to damage. Degassed water is used during the operation, and the nitrogen filled with nitrogen also needs to be of high purity. For samples with a high content of organic acids, volatile organic acids are produced, and errors are generated in the measurement. [1]
5.3 Chromatography
5.3.1 Ion chromatography
Ion chromatography is a food with sulfites added under acidic conditions, which is absorbed and released by hydrogen peroxide, so that sulfur dioxide is converted into sulfuric acid, and then determined by ion chromatography. Ion chromatography can accurately determine sulfur dioxide in food, and has the characteristics of simplicity, speed, high sensitivity, less interference, and less pollution. Ion chromatography: Take 5.0 g of uniformly crushed sample and wash the sample into a distillation bottle with 150 ml of pure water. Attach the condensing device, insert the bottom of the volumetric flask containing 20 ml (1 + 9) hydrogen peroxide at the lower end of the condensing tube, then add 5 ml (1 + 1) hydrochloric acid to the distillation bottle, immediately cap the plug, heat distillation. Collect about 90 ml of filtrate, stop distillation, add pure water to fix the volume to 100 ml. After the volume fixation, the distillate is filtered by a 0.22μm microporous filter membrane, the sample is injected, and the standard sulfate solution is used as the standard curve, and the measurement result is integrated by peak height or peak area to calculate the sulfate method in the sample solution: content. Ion chromatography is simple and sensitive to use, and is a hot research topic for analyzing sulfur dioxide in food. [17]
5.3.2 Gas chromatography
Gas chromatography: After the free sulfurous acid and total sulfurous acid in the food are extracted with tartaric acid extract, a certain amount is removed in a sealed container to make it an acidic volatile sulfurous acid, the air body is taken, and the gas chromatograph attached to the flame photometric detector (FPD) is injected for quantification. Gas chromatography was performed by converting the bound sulfur dioxide in the puffed jujube into sulfur dioxide gas under acidic conditions. By determining the content of sulfur dioxide in the gas phase and indirectly determining the sulfur dioxide content in the sample, the relative standard deviation of the experimental results is 1.65%. This method has the advantages of simple operation, fast, accurate and high sensitivity. [18]
summary
In recent years, the phenomenon of excessive use and abuse of sulfur dioxide in food is very serious, and strengthening the supervision and detection of sulfur dioxide in food has become an urgent problem to be solved, standardizing the application of sulfur dioxide, with GB2760-2014 food safety national standard food additive use standards. [19] Deeply understand the application of sulfur dioxide in what fields. The study of rapid determination technology of sulfur dioxide content is one of the effective measures to achieve supervision and management. With the improvement of the quality of life of our people, food safety issues have attracted increasing attention. Food safety assurance relies on reliable quality monitoring, so food safety issues are gradually occupying a large position, making people must have a deep understanding of the application of sulfur dioxide in food.
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