Sulfur dioxide is the most common and simplestSulfur oxide, chemical formula SOtwo, which is colorless and transparent gas with irritating odor.Soluble inwater、ethanolandEther。Sulfur dioxide is one of the main air pollutants.Volcano eruptionThe gas will be ejected when, and sulfur dioxide will also be produced in many industrial processes.becausecoalandpetroleumIt usually contains sulfur element, so sulfur dioxide will be generated during combustion.When sulfur dioxide is dissolved in water, it will formSulfite。If sulfite is further oxidized in the presence of PM2.5, it will be rapidly and efficiently generatedsulphuric acid(One of the main components of acid rain)[5]。This is one of the reasons for concern about the environmental effects of using these fuels as energy sources.
On October 27, 2017, the list of carcinogens published by the International Agency for Research on Cancer of the World Health Organization (WHO) was preliminarily sorted out for reference, and sulfur dioxide was included in the list of category 3 carcinogens.[4]
Sulfur dioxide is colorless and transparent gas with irritating odor.Soluble in waterethanolandEther。
Three Resonance Structures of Sulfur Dioxide
Liquid sulfur dioxide is relatively stable and inactive.Gaseous sulfur dioxide will not decompose when heated to 2000 ℃.It does not burn and does not form explosive mixture with air.[1]
inorganic compoundasbromine 、Boron trichloride、carbon disulfide、Phosphorus trichloridePhosphoryl chlorideIodine chlorideAnd various sulfite chlorides can be mixed with liquid sulfur dioxide in any proportion.The solubility of alkali metal halide in liquid sulfur dioxide is as per I->Br－>Cl－The order of decreases.Most metal oxides, sulfides, sulfates, etc. are insoluble in liquid sulfur dioxide.[1]
O-O bond length (120.7 pm) in.Average of sulfur dioxideBond energy（548 kJ·mol-1）It should be greater than the average bond energy of S-O (524 kJ · mol-1）, and
Average bond energy of (297 kJ · mol-1）Less than OtwoAverage bond energy of (490 kJ · mol-1）。These evidences led chemists to conclude that the S-O bond in sulfur dioxideKey levelAt least 2, andozoneThe O-O bond in ozone is different, and the bond order of O-O bond in ozone is 1.5.
Molecular structure and polarity: V-shaped molecules,Polar molecule。
PH: 2/3 sulfur dioxide dissolved in waterSulfite（HtwoSOthree）, the pH value of the solution becomes 2 or 3.
At room temperature, wet sulfur dioxide andhydrogen sulfideThe reaction precipitates sulfur.Under the condition of high temperature and the presence of catalyst, it can be reduced by hydrogen to hydrogen sulfide and carbon monoxide to sulfur.Strong oxidant can oxidize sulfur dioxide intoSulfur trioxideOnly in the presence of catalyst can oxygen oxidize sulfur dioxide to sulfur trioxide.It is self igniting and non combustion supporting.Liquid sulfur dioxide can dissolve organic compounds such as amine, ether, alcohol, phenol, organic acid, aromatic hydrocarbon, and most saturated hydrocarbons cannot be dissolved.It has a certain degree of water solubility, and reacts with water and steam to generate toxic and corrosive steam.[1]
The chemical properties of sulfur dioxide are extremely complex, and different temperatures can be used as aprotic solventLewis acid、reducing agent, oxidant, redox reagent, etc.Liquid sulfur dioxide can also act as a free radical acceptor.If inAzodiisobutyronitrileIt is obtained by reacting with ethylene compound in the presence of free radical initiatorpolysulfone。Liquid sulfur dioxide can be mixed with chlorine and alkanes under lightChlorosulfonation reaction, generate sulfonic acid in the presence of oxygen.Liquid sulfur dioxide shows reduction at low temperature, but shows oxidation above 300 ℃.[1]
Sulfur dioxide bleaching fuchsin solution
Sulfur dioxide can makeFuchsin solutionFading, color reduction after heating, because the bleaching principle of sulfur dioxide is that sulfur dioxide reacts with the bleached substance to produce colorless and unstable compounds, which destroys the paraquinone formula that plays the role of color generation in magenta. When heated, the compound decomposes to restore the original color, so sulfur dioxide bleaching is also called temporary bleaching.
It can fade the acid potassium permanganate solution.
Sulfur dioxide can be used insulfurGenerated under combustion conditions:
Sulfur dioxide is bleachable.Sulfur dioxide is commonly used in industry to bleach pulp, wool, silk, straw hat, etc.The bleaching effect of sulfur dioxide is due to its (sulfite) ability to form unstable colorless substances with some colored substances.This colorless material is easy to decompose and make the colored material restore its original color, so the straw hat braid bleached with sulfur dioxide turns yellow again after a long time.The bleaching effect of sulfur dioxide and some sulfur compounds has also been illegally used by some illegal manufacturers to process food to whiten food.Eating this kind of food will cause serious damage to the liver and kidney of the human body and cause cancer.
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.
Chemical equation
Use limit
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GB 2760-96: It can be used for wine and fruit wine as preservative, 0.25g/kg.The residual amount of sulfur dioxide shall not exceed 0.05g/kg.
The allowable residue of bleached dried fruits, preserved fruits, dried vegetables, vermicelli and candied fruits by sulfur fumigation refers to "sulfur".Sulfur fumigation means burning sulfur to produce sulfur dioxide, which can destroy the surface cells of fruit slices and promote drying. At the same time, due to its reduction, it can destroy the oxidation system of enzymes and prevent oxidation.The tannins in the fruit will not be oxidized and become brown.Vitamin C in fruits can also be preserved.The concentration of sulfur dioxide in the sulfur fuming room is generally 1%~2%, and the maximum is 3%.The sulfur fumigation time is 30-50 min, and the longest time can reach 3 h.
FAO/WHO（1984；Mg/kg): white granulated sugar 20 (specification A), 70 (specification B);Sugar powder, fructose, glucose powder 20 (amount taken in);Soft white sugar 40;Anhydrous glucose, glucose monohydrate 20;Glucose syrup 40;400 for confectionery;High concentration glucose syrup 40, 150 for confectionery;Bleached raisins 1500;Jam, jelly, orange peel jelly 100, amount of introduction;Dried apricot 2000;Pickled cucumber 50, brought in from initial products;Pineapple juice 500 with preservatives (for manufacturing only).
EEC（1990；Mg/kg): dried coconut 50;Beer 70;Candied fruit and canned coconut 100;Apple juice 200;Most dried fruits 2000;Thousand papain and papain 30000.
EEC-HACSG recommends not to be used in children's food.
FDA, 182.3862 (2000): Not for meat and vitamin B.Source food.
Refer to "sodium hydrosulfite" according to the maximum dosage specified by Japan.
3. Sulfur dioxide is the reducibility allowed in Chinableaching agents。Bleaching for food and bleaching for vegetable foodoxidaseIt has a strong inhibitory effect.Chinese regulations can be used forWineandfruit wineThe maximum use amount is 0.25g/kg, and the residual amount shall not exceed 0.05g/kg.
6. According to Claude Ribbon's book "Napoleon's Crime", sulfur dioxide was used as a poison by some monarchs in Haiti in the early 19th century to suppress slave rebellion.
Risk analysis
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The food and drug supervision department found that some vegetables, fruit products, white granulated sugar and other sulfur dioxide content exceeded the standard through sampling inspection.So, what is sulfur dioxide?How to apply it to the food industry?Is it harmful to human health?Can it be used in fruit and vegetable products, white granulated sugar and related products?What are the relevant regulations and standards at home and abroad?A few days ago, the State Food and Drug Administration released the 14th issue of 2016 Food Safety Risk Analysis, and organized relevant experts to interpret it.
1、 Sulfur dioxide is a food additive allowed to be used at home and abroad. It plays a role in color protection, corrosion prevention, bleaching and oxidation resistance in the food industry
Sulfur dioxide is a food additive that is allowed to be used at home and abroad. Generally, this substance is added to food in the form of potassium pyrosulfite, sodium pyrosulfite, sodium sulfite, sodium bisulfite, low sodium sulfite and other sulfites, or used in food treatment by sulfur fumigation to protect color, prevent corrosion, bleach and resist oxidation.For example, in the drying of fruits and vegetables, the production of candied fruits and preserved fruits, the processing of white granulated sugar, and the storage and processing of fresh edible fungi and algae, oxidative browning or microbial pollution can be prevented.Using sulfur dioxide gas to fumigate raw materials of fruits and vegetables can inhibit the activity of oxidase in raw materials and make products bright and beautiful.In white granulated sugar processing, sulfur dioxide can combine with colored substances to achieve bleaching effect.
2、 Reasonable use of sulfur dioxide according to the standard will not cause harm to human health, but long-term excessive exposure to sulfur dioxide may lead to human respiratory system diseases and multi tissue damage
Each food additive shall be subject to strict risk assessment before being listed in the standard.It is safe as long as it is approved through risk assessment and used in accordance with the standards and corresponding quality specifications.The food additives allowed to be used in the National Food Safety Standard for the Use of Food Additives (GB2760-2014) are all subject to safety assessment, and the sulfur dioxide used when meeting the standard will not harm the health of consumers.
Taking sugar processing as an example, the residual sulfur dioxide in sugar is mainly due to the use of sulfur dioxide as a processing aid in the sugar manufacturing process to clarify and decolorize the sulfur dioxide. Sulfur in sugar raw materials and other processing aids may also be one of the reasons for the residual sulfur dioxide in sugar.A small amount of sulfur dioxide enters the body and finally generates sulfate, which can be discharged from the urine after normal detoxification without toxic effect.However, if the human body ingests too much sulfur dioxide, it is easy to produce allergies, which may cause dyspnea, diarrhea, vomiting and other symptoms, and may also cause varying degrees of damage to the brain and other tissues.
3、 The use limit and residual amount of sulfur dioxide in many international countries and regions are clearly stipulated
Many countries and regions in the world have clear regulations on the use of sulfur dioxide.The regulations and standards of the Codex Alimentarius Commission (CAC), the European Union, the United States, Australia, New Zealand, Canada and other international organizations, countries and regions allow sulfur dioxide to be used in the corresponding food categories.The Joint Expert Committee on Food Additives of FAO/WHO (JECFA) has conducted safety assessment on sulfur dioxide and formulated the ADI of 0-0.7mg/kg bw.The International Codex Alimentarius (CODEX STAN 212-1999) also has a limit requirement for sulfur dioxide in sugar, and the residual amount of sulfur dioxide in white granulated sugar should be ≤ 15 mg/kg.
4、 The relevant standards and regulations of China have defined the categories of food that can use sulfur dioxide and the corresponding use limits and residues
The National Food Safety Standard for the Use of Food Additives (GB2760-2014) clearly stipulates that sulfur dioxide is used as a bleaching agent, preservative and antioxidant for surface treated fresh fruits, dried fruits, preserved fruits, dried vegetables, pickled vegetables, canned vegetables (bamboo shoots and pickled vegetables only), dried edible fungi and algaeCanned edible fungi and algae (limited to canned mushrooms only), preserved beancurd (including preserved beancurd, oil skin, etc.), canned nuts and seeds, cocoa products, chocolate and chocolate products (including cocoa butter substitute chocolate and products), and candy, wet flour products (such as noodles, dumpling skin, wonton skin, and roasted wheat skin) (limited to ramen only), edible starchFrozen rice and flour products (only for flavor pie), biscuits, sugar, starch sugar (fructose, glucose, maltose, partial invert sugar, etc.), flavoring syrup, semi-solid compound seasoning, fruit and vegetable (pulp), fruit and vegetable juice (pulp) drinks, sweet wine and fruit wine, beer and malt drinks.
At the same time, in order to ensure its safe use, with reference to the Joint Expert Committee on Food Additives (JECFA) of FAO/WHO, the original announcement of the Ministry of Health in 2011 No. 6 specifies the quality specification requirements for sulfur dioxide as a food additive.In addition, according to the provisions of the National Food Safety Standard General Principles for the Labeling of Prepackaged Food (GB7718), whenever sulfur dioxide is used in food, it must be identified on the food label.
Therefore, experts suggest that: First, food production enterprises should strictly comply with relevant standards and regulations.The relevant food production enterprises should strictly comply with the requirements of GB2760, and try to reduce the use of sulfur dioxide in food as much as possible on the premise of achieving the expected effect. It is not allowed to use sulfur dioxide beyond the range, the limit or add it in violation of regulations.Through innovation of process and adoption of new technology, browning, pollution and reproduction of harmful microorganisms are controlled technically and technologically, and the use of sulfur containing food additives is reduced.If sulfur dioxide is added to the food, the manufacturer shall carry out standard identification in accordance with GB7718.Second, the regulatory authorities need to further strengthen the supervision of the use of food additives.It is suggested that the relevant regulatory authorities should further strengthen the publicity of food additive use standards and other relevant regulations, and at the same time, strengthen the supervision, and severely punish enterprises that use sulfur dioxide beyond the limit and scope.Third, consumers should establish a correct view of consumption and carefully study food labels.Consumers should choose food with a correct attitude and avoid excessive pursuit of the appearance of food, such as bright day lily and white tremella.In addition, the food label reflects the name, ingredients, food additives and other information of the food. According to the provisions of GB7718, if the manufacturer adds sulfur dioxide to the food, it should be identified on the food label.Before choosing a food, consumers can identify whether sulfur dioxide is added to the food by studying the food label.[2]
matters needing attention
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endanger one's health
Forest corroded by acid rain
In the atmosphere, sulfur dioxide will be oxidized into sulfuric acid mist or sulfateaerosol, Yesenvironmental acidification The importance ofPrecursor。The concentration of sulfur dioxide in the atmosphere above 0.5 ppm has potential impact on human body;At 1~3ppm, most people begin to feel stimulated;At 400-500ppm, people will suffer from ulcer and pulmonary edema until death due to asphyxia.Sulfur dioxide and atmosphericsmokeThere is synergy.When the concentration of sulfur dioxide in the atmosphere is 0.21ppm and the concentration of smoke dust is greater than 0.3mg/L, the incidence of respiratory diseases will increase and the condition of patients with chronic diseases will deteriorate rapidly.asLondon smog incident、Meuse Valley fog And Donora and other smog events are all caused by this synergy.
First aid measures
Exposure
First aid measures
Skin contact
Take off contaminated clothes immediately and wash with plenty of flowing water.Get medical attention.
Eye contact
Lift the eyelids and wash them with flowing water or normal saline.Get medical attention.
inhalation
Quickly leave the site to fresh air.Keep the respiratory tract unobstructed.If breathing is difficult, give oxygen.If breathing stops, perform artificial respiration immediately.Get medical attention.[1]
Poisoning
The patient should be immediately moved to a place with fresh air, unfastened tight clothes, quickly inhaled oxygen, washed eyes and nasal cavity, and rinsed with 2% soda solution.If it accidentally splashes into the eyes, wash it with plenty of warm water.Those who are serious should be sent to hospital immediately.
Fire fighting measures
Hazard characteristics: non combustible.In case of high heat, the internal pressure of the container will increase, which may cause cracking and explosion.
Hazardous combustion products: sulfur oxide.
Fire extinguishing method: the product is non combustible.Firefighters must wear filter type gas masks (full face masks) or isolated respirators, and wear full body fire and gas clothing to extinguish the fire in the windward direction.Cut off the air supply.Spray water to cool the container, and move the container from the fire site to an open place if possible.Extinguishing agent: spray water, foam, carbon dioxide.[1]
Leakage emergency treatment
Evacuate the personnel in the leakage contaminated area to the windward place quickly and isolate them immediately. Isolate 150 m for small leakage and 450 m for large leakage, and strictly restrict access.It is recommended that emergency personnel wear self-contained positive pressure respirators and anti poison clothing.Enter the site from the upwind.Cut off the leakage source as much as possible.Cover the sewer and other places near the leakage point with industrial coating or adsorption/absorbent to prevent gas from entering.Reasonable ventilation to accelerate diffusion.Dilute and dissolve with spray water.Build a dike or dig a pit to collect a large amount of wastewater generated.If possible, use a trap to make the gas pass throughsodium hypochloriteSolution.Leaking containers shall be properly treated, repaired and inspected before reuse.[1]
Operation, disposal, storage and transportation
Precautions for operation: it shall be strictly sealed, and sufficient local exhaust and general ventilation shall be provided.Operators must be specially trained and strictly abide by the operating procedures.It is recommended that operators wear self-priming filter gas masks (full face masks), polyethylene gas suits and rubber gloves.Keep away from flammable and combustible materials.Prevent gas leakage into the air of the workplace.Avoid contact with oxidants and reducing agents.The cylinder and accessories shall be handled with care to prevent damage.Provide leakage emergency treatment equipment.
Precautions for storage: store in a cool and ventilated warehouse.Keep away from kindling and heat sources.The warehouse temperature should not exceed 30 ℃.It shall be stored separately from combustible (combustible) materials, oxidants, reducing agents and edible chemicals, and mixed storage is strictly prohibited.The storage area shall be equipped with leakage emergency treatment equipment.[1]
Precautions for transportation: The railway transportation time limit for this product is to use the tank car provided by the pressure resistant liquefied gas enterprise for shipment, and it needs to be reported to the relevant department for approval before shipment.The railway transportation shall be carried out in strict accordance with the dangerous goods loading table in the Dangerous Goods Transportation Rules of the Ministry of Railways.When steel cylinders are used for transportation, safety helmets on steel cylinders must be worn.Cylinders are generally placed horizontally, and the mouth of the cylinder should be in the same direction, not crossed;The height shall not exceed the protective fence of the vehicle, and shall be firmly clamped with triangular wood pad to prevent rolling.It is strictly prohibited to mix with combustibles or combustibles, oxidants, reducing agents, edible chemicals, etc.Transport in the morning and evening in summer to prevent sunlight exposure.Road transportation shall be carried out according to the specified route, and it is forbidden to stay in residential areas and densely populated areas.It is forbidden to slip during railway transportation.[1]
It shall be tightly sealed to provide adequate local ventilation and overall ventilation.Provide safety shower and eyewash equipment.
respiratory system protection
When the concentration in the air exceeds the standard, wear a self-priming filter type gas mask (full face mask).It is recommended to wear positive pressure self-contained breathing apparatus during emergency rescue or evacuation.
Eye protection
The respiratory system has been protected.
Body protection
Wear polyethylene gas protective clothing.
Hand protection
Wear rubber gloves.
Other protection
Smoking, eating and drinking are prohibited at the work site.After work, take a shower and change clothes.Keep good hygiene habits.[1]
Hazard prevention
Personal protection: First, education on labor protection and production safety should be strengthened.The operator can saturate several layers of gauzesodium carbonateSolution andglycerolClamp it in gauze mask after wetting to absorb SOtwo。Rinse mouth with 2% sodium carbonate solution before and after work.
Routine treatment SOtwoMethods: While paying attention to the personal protection of workers, effective measures should be taken to deal with SOtwoFlue gas.Since the 1950s, China has focused on low concentration SO in nonferrous smelting flue gastwoA series of experiments and researches have been carried out and some progress has been made.
Ammonium sulfite method: treat SO with ammonium sulfite methodtwoYesammoniaAbsorb SOtwo, by-product ammonium sulfite.Although the technology of ammonium sulfite process is relatively mature, the by-product produced is ammonium sulfite in liquid state, which is difficult to store and transport. It is only applicable to small smelters with ammonia sources.
Sodium sulfite process: it can be used by small and medium-sized smelterssodium sulfite Method for flue gas desulfurization.The sodium sulfite method usescaustic sodaOr soda ash absorbs SOtwoAt the same time, the by-product sodium sulfite is produced.For example, Shanghai Smelter uses this method to treat flue gas.The sodium sulfite process is simple in process, convenient in operation, low in system resistance, and low in investment and operation cost.The desulfurization efficiency is up to about 95%.However, soda ash and caustic soda need to be consumed. Each ton of anhydrous sodium sulfite consumes 0.8 t of soda ash and 0.1 t of caustic soda.The by-product sodium sulfite can not be widely used because of its limited use.
Zinc oxide method: can be used for lead and zinc smelterszinc oxideProcess SOtwo。For example, the Fourth Smelter of Hunan Shuikoushan Mining Bureau adopts this method.The zinc oxide process uses zinc oxide as an absorbent to producezinc sulfateAll slag is returned to zinc concentrate fluidized bed furnaceroasting , decompose to SOtwoGas can be used to produce concentrated SOtwo。
VtwoOfiveOxidation method: SO generated during smelting of non-ferrous metalstwoThe concentration is generally lower than 3.15%, which is not suitable for direct recovery and manufacturing of SOtwo。In order to realize SO, Shenyang SmeltertwoGovernance.The production process has been reformed, the closed blast furnace has been adopted, and the smoke exhaust system has been reformed, the negative pressure of the furnace mouth and flue has been strictly controlled, the air leakage rate has been reduced, thus improving the SOtwoThe concentration (4%~5%) meets the requirements of acid production.Using VtwoOfiveAs catalyst, SOtwoOxidation to SOthreeAbsorb SO with dilute sulfuric acidthree, Manufacturing HtwoSOfour, the reaction is as follows:
As the flue gas contains AstwoOthree, causing catalyst poisoning and reducing SOtwoConversion rate of.
Treatment of SO by activated carbon adsorptiontwoIn view of the problems existing in the above treatment methods, the treatment of SO produced in the smelting process of non-ferrous metals by activated carbon adsorption is systematically studiedtwoAnd overcome the shortcomings and limitations of the above governance methods.
When containing SOtwoExhaust gas andActivated carbonSO at contacttwoIt is adsorbed when there is OtwoIn the presence of water vapor, chemical adsorption occurs simultaneously with physical adsorption.
When a certain amount of H is adsorbed on the activated carbontwoSOfourThen, the activated carbon is regenerated by washing with water to obtain by-product HtwoSOfour。
SOtwoConvert to SOthreeIt is completed under the catalysis of activated carbon. The traditional activated carbon adsorption method only uses the catalyst performance of activated carbon itself, which has low catalytic activity, slow reaction speed and huge equipment.This activated carbon treatment method uses the characteristics of activated carbon as the catalyst carrier, and there is some active component on the activated carbon to form a higher active activated carbon catalyst, so that SOtwoConvert to SOthreeThe reaction speed ofActivated carbon adsorption methodHandling SOtwoOther influencing factors.
From the experimental results, the desulfurization effect is the best at 25 ℃, followed by 100 ℃.Although the desulfurization efficiency at 25 ℃ is the highest, the temperature of flue gas after desulfurization is low, and the thermal buoyancy of flue gas is reduced, which is not conducive to the diffusion of flue gas, and the flue gas is easy to return to the ground, causing nearby ground pollution.If desulfurization at 100 ℃ is adopted, although the desulfurization effect is not as good as that at 25 ℃, the desulfurization efficiency has reached a higher value, and after desulfurization, the flue gas temperature is higher, which is easy to exhaust smoke. Therefore, desulfurization at 100 ℃ should be adopted.
Various factors affecting the desulfurization efficiency are mutually restricted. When the desulfurization temperature is 100 ℃, HtwoO/ SOtwo= 1～2，Otwo/ SOtwo=10-14, airspeed 3600h-1The desulfurization efficiency can reach 96%.
SO generated during smelting of non-ferrous metalsx, which has the greatest impact on the health of operators, must take effective prevention and control measures to ensure the health of workers.Treatment of SO Produced in Nonferrous Metal Smelting with Activated CarbontwoIt has the characteristics of high desulfurization efficiency, simple process, easy operation control, renewable and reusable activated carbon, no secondary pollution, etc. It overcomes the limitations and shortcomings of ammonium sulfite method, sodium sulfite method and zinc oxide method in application, and also avoids the use of VtwoOfiveThe catalyst poisoning of oxidation method is an effective method with wide application prospects.
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Exogenous addition as food additive
As a food additive, sulfur dioxide is widely used in food processing. Driven by the interests of some illegal traders, a large number of sulfur dioxide and its salts are added to food, which is the main source of excessive sulfur dioxide.
Sulfur dioxide and sulfite are added to food for the following purposes: during food processing, the oxidation of sulfur dioxide and sulfite can effectively inhibit non enzymatic browning during food processing;Using its reducibility and bleachability, it can also be used as a preservative to inhibit the growth of mold and bacteria.Therefore, during the production and processing of food, sulfur dioxide and sulfite 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 include sodium sulfite, sodium bisulfite, low sodium sulfite and sodium pyrosulfite.
For example, in fresh vegetable foods such as fruits and vegetables, sulfite 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.During the fermentation of wine, sulfur dioxide is filled or water dissolved with sulfur dioxide is used as preservative.In order to maintain flavor stability during beer production, sulfur dioxide is often added as an antioxidant before filling.However, sulfur dioxide and sulfite are easy to interact with sugars, proteins, pigments, enzymes, vitamins, aldehydes, ketones, etc. in food, and remain in food as free and combined sulfur dioxide.
Once these additives are used excessively and there is no sequential sulfur dioxide removal technology, the sulfur dioxide residue will inevitably exceed the standard.This will not only damage the quality of food, but also seriously affect the health of consumers.[3]
Endogenous production of food
Although the excessive residue of sulfur dioxide and its salts is mainly caused by excessive addition, the sulfur dioxide produced by food itself is another important source that cannot be ignored.
It was found that some foods would produce sulfite during fermentation without any additives such as sulfite.The content of sulfite naturally produced in the fermentation process of wine and fruit wine can reach 300 mg/kg at most, and it can reach 40 mg/kg even under normal circumstances, which is far beyond the safety range of sulfite content in food stipulated by the US FDA.
In addition, on the basis of a large number of studies, our laboratory found that shiitake mushroom would also produce sulfur dioxide due to its own metabolism after harvest, and seriously exceeded the residue standards set by many countries, resulting in serious obstacles to its export.
On the other hand, since a considerable part of food is plant, during the growth of plant, sulfur dioxide in the atmosphere will enter the plant through the leaf stomata of the plant, and sulfur dioxide in other soil or water will also enter the plant through the absorption of the plant.Sulfur dioxide entering the plant is easy to react with aldehyde and ketone compounds in the plant, especially sugar compounds, to generate bound sulfite, so there is a certain amount of free and bound sulfur dioxide in the plant.
During the growth of animals, they will also accumulate a certain amount of sulfur dioxide due to eating plants.Therefore, both animal food and plant food contain a certain amount of sulfur dioxide from natural sources.[3]
Limit standard of sulfur dioxide in food
In view of the serious harm of sulfur dioxide to human body, in order to avoid adverse reactions such as poisoning caused by excessive sulfur dioxide residues in food, all countries have formulated a series of standards to strictly control the use and residues of sulfur dioxide.
The US FDA requires that foods with sulfite consumption higher than 10 mg/kg should be marked. Japan has a limit of 30 mg/kg for sulfur dioxide in salty vegetables, starch and other foods, and Germany has a limit of 50 mg/kg for garlic products.In view of the use of sulfite in beer, many countries have also stipulated the limit of sulfur dioxide residue in beer.
China's Hygienic Standard for Fermented Liquor (GB2758 - 1981) stipulates that free SOtwoResidual SO measuredtwoLimit of.China's Hygienic Standard for the Use of Food Additives has made clear provisions on the scope of use, amount of use and maximum allowable residue of sulfur dioxide in various foods.For example, sulfur is limited to fumigation of candied fruits, dried fruits, dried vegetables, vermicelli and sugar;Low sodium sulfite can be used for candied fruits, dried fruits, dried vegetables, vermicelli, glucose, sugar, rock sugar, maltose, candy, liquid glucose, bamboo shoots, mushrooms and canned mushrooms, with the maximum use amount of 0.40 g/kg;Sulfur dioxide can be used for wine, fruit wine, etc. The maximum amount of sulfur dioxide should not exceed 0.25 g/kg, and the residual amount of sulfur dioxide should not exceed 0.05 g/kg;Sesame, milk, beans, vegetables and raw edible fresh fish and shellfish are prohibited.
The Joint FAO and WHO Expert Committee on Food Additives (JECFA) assessed the risk of sulfur dioxide as a food additive as follows: the daily allowable intake (ADI) of sulfur dioxide is 0~0.7 mg/kg body weight, that is, an adult with a body weight of 60 kg, and the daily intake of sulfur dioxide is not more than 42 mg.[3]
Determination of sulfur dioxide in food
Due to the difference of food matrix, sulfur dioxide detection requires different methods and detection principles.The detection methods of sulfur dioxide in food include colorimetry, titration and chromatography.
colorimetry
The national standard GB/T5009.34-2003 stipulates that the pararosaniline hydrochloride method is used to detect the content of sulfur dioxide in food. The main principle is to use the reaction of sulfite and mercury tetrachloride to generate a stable complex, and then react with formaldehyde and pararosaniline hydrochloride to generate a purplish red complex. The absorbance of the solution is measured at the wavelength of 550 nm, and compared with the standard series for quantification.
Titration, as the main method for the determination of trace sulfur dioxide in food, has the advantages of simple operation, high sensitivity and good reproducibility, and is the most commonly used method in practical detection.However, the linear range of this method is narrow. For the samples with high sulfite content, it is necessary to dilute the samples for determination;Secondly, the toxic reagent sodium tetrachloride is used in this method, and the amount is large, which is easy to cause mercury pollution to the environment.
In addition, for some samples with red or rose red color, such as wine, interference will occur at 550 nm, and there is no rule to follow due to deviation, so interference cannot be deducted.In order to reduce the environmental pollution of toxic reagent sodium tetrachloride and eliminate this deficiency, other substances with lower toxicity are often used to replace sodium tetrachloride solution as the absorption solution of sulfur dioxide.Sulfur dioxide in white granulated sugar was determined by formaldehyde solution absorption pararosaniline hydrochloride spectrophotometry.The sulfur dioxide in food was determined by EDTA sodium buffer instead of sodium tetrachloride, and the results were consistent with the national standard method.
In order to avoid the dark color of some samples and interference with the determination wavelength at 550 nm, distillation is often used to pretreat the samples.The "distillation colorimetric method" in the method of the Japanese Food Hygiene Association is to heat and distill the sample in nitrogen flow after acidification, receive it with sodium hydroxide solution, and color develop the receiving solution with the mixture of basic fuchsin and formaldehyde.
Titrimetry
The common titration methods are direct titration iodometry, distillation iodometry, distillation alkali titration.
Direct titration
The principle of direct titration iodometry is that the measured components (including free and combined sulfur dioxide) in the sample lose their binding force in the alkaline solution, are fixed as sulfites, and are free again under the action of sulfuric acid, and titrated with iodine standard solution.When the titration end point is reached, the excess iodine reacts with the starch indicator to form a blue iodine starch complex.Calculate the total sulfur dioxide content from the titration amount of iodine standard solution.The direct titration iodometry is simple and fast, especially suitable for the determination of sulfite in wine.However, for dehydrated garlic, ginger products, etc., due to the presence of more volatile aromatic substances, the color of the titration end point is often unstable, easy to fade, and can not be kept for 30 seconds, so it is difficult to determine the end point.
Distillation iodometry GB/T5009134 - 1996 (2)
The "distillation iodometry" method is used to acidify and distill the sample. The sulfur dioxide in the sample escapes, is received by the lead acetate solution, acidified with concentrated hydrochloric acid, and titrated with iodine standard solution.The pretreatment of samples by distillation can effectively avoid the interference of sample background, but it takes a long time. Generally, it takes more than one hour to distill a sample, which is not suitable for the detection of large batches of samples.
Distillation alkali titration
This method uses the principle of acid-base neutralization titration. After the sample is acidified, it is heated and distilled in nitrogen flow, received with excess sodium hydroxide, acidified and oxidized to sulfuric acid, and titrated with standard sodium hydroxide solution to determine the total amount of sulfite in the sample.This method is a rapid determination method, and is widely used in the detection of various foods.The method of Japan Food Hygiene Association (A), IS05522 (1981) and the routine law of the International General Administration of Wine are all of this kind.The distillation time is short, and the receiving solution can be titrated with alkali standard solution 10~15min after the solution boils, 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 poor repeatability of results caused by uneven distribution of sulfites in the sample.However, this method requires a customized all glass distillation device with the specified size, which is easily damaged.Degassed water shall be used during operation, and nitrogen filled shall be of high purity.For samples with high organic acid content, volatile organic acids will be generated, which will cause errors in the determination.
Chromatography
Gas chromatography
After the free sulfite and total sulfite in food are extracted with tartaric acid extract respectively, a certain amount is taken out and turned into acid volatile sulfite in a sealed container. The headspace gas is taken and injected into a gas chromatograph with a flame photometric detector (FPD) for quantitative determination.Wang Xiaoyun et al. [13] converted the bound sulfur dioxide in the expanded jujube into sulfur dioxide gas under acidic conditions, and took the headspace gas for gas chromatography analysis.The sulfur dioxide content in the sample is indirectly determined by measuring the sulfur dioxide content in the gas phase. The relative standard deviation of the experimental results is 1.65%.
This method is simple, fast, accurate and sensitive.
Ion chromatography
Ion chromatography, which is simple and sensitive, is a research hotspot in the analysis of sulfur dioxide in food.The principle is: under the condition of 20% phosphoric acid, the sulfite in the sample is separated in 90 ℃ water bath with nitrogen, collected in triethanolamine solution, and determined by IC (ion chromatography).Ion chromatography is suitable for the determination of residual sulfite and natural sulfite in foods.It includes ICE pulse amperometric detection, ICE single potential or pulse amperometric detection, ICE indirect UV photometric detection and ion exchange UV detection.However, food samples are complex in composition and contain more organic macromolecules such as protein, oil, pigment and cellulose. These components interact with the packing of the separation column and affect the performance and life of the column.
Some sulfites exist in food in a combined state. For direct determination, the storage time of sample solution during sample processing has a greater impact on the determination results.However, the error can be avoided by distilling the sample under acidic conditions.[3]
Other test methods
Chemiluminescence method
Chemiluminescence (CL) has attracted much attention due to its high sensitivity and simple operation.Chemiluminescence analysis of sulfur dioxide has long been reported.It was suggested that
Chemiluminescence reaction mechanism, some oxidants can be oxidized in acid medium
Generates luminescence, which can enhance chemiluminescence in the presence of certain compounds.Therefore, chemiluminescence method is used to determine sulfite.Balasubramanian et al. reported a simple and sensitive extraction photometric method, that is, fixed sulfur dioxide with formaldehyde solution, and reacted with iodate to produce I in the medium of pH 4.76 acetatetwo，ItwoAnd excessive Cl-Form stable ICl-Then, it reacts with 2,7-dichlorofluorescein to generate iododichlorofluorescein which is easy to be extracted by organic solvent.
Electrochemical method and sensor
Soak copper or gold electrodes coated with graphite/epoxy resin/curing agent in saturated 4-methylpiperidine potassium dithiocarbamate aqueous solution and saturated mercuric nitrate aqueous solution for 1h respectively.Then use this electrode to measure
-Its linear range is 5 × 10- 6~0.1 mol/L。Oxidation with iodine produced by constant current coulometer
, indirectly by detecting excessive iodine
Its linear range is 0.015~25 mg/L.The sulfur dioxide sensor mainly uses electrochemical method.In addition, piezoelectric crystal sensor is used to simultaneously measure sulfur dioxide and relative humidity, and surface acoustic wave sensor is used to measure sulfur dioxide.The electrochemical sensor has the advantages of high sensitivity and convenient use.
Enzyme photometry
Sulfite was determined by enzyme spectrophotometry.The principle is that sulfite is oxidized to
Under the action of catalase, use 3,3,5,5-tetramethylbenzidine (TMB) to develop color, and indirectly determine the content of sulfite at 650 nm wavelength.The method has high sensitivity and can detect trace sulfur dioxide, but the sample pretreatment is tedious.
Quick test kit.There are also on-site rapid detection kits and instruments for sulfur dioxide in food on the market. The principle is that sulfur dioxide in food reacts with chromogenic agent to produce colored compounds. The content of sulfur dioxide in food is read directly on the sulfur dioxide rapid detection color scale card by visual colorimetric analysis.The instrument has the advantages of simple operation, convenient use, portable, real-time on-site detection, fast detection speed (10-15 min), less sample and reagent consumption, no pollution, and has broad application prospects.[3]
security information
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Safety terminology
S9：Keep container in a well-ventilated place.
Keep the container in a well ventilated place.
S26：In case of contact with eyes，rinse immediately with plenty of water and seek medical advice.
In case of contact with eyes, please immediately flush with plenty of water and seek medical advice.
S36/37/39：Wear suitable protective clothing，gloves and eye/face protection.
Wear appropriate protective clothing, gloves and goggles or mask.
S45：In case of accident or if you feel unwell，seek medical advice immediately.（show the label whenever possible).
In case of accident or discomfort, seek medical advice immediately (show the label if possible).
Risk terminology
R23：Toxic by inhalation.
Toxic by inhalation.
R34：Causes burns.
Causes burns.
Common rumors
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rumor:Sulfur dioxide is harmful to human body and cannot be used as food bleach.
refute: Excess sulfur dioxide is really harmful to human health, but it can be used as an additive for certain foods according to the national standard. It comes from the designated standard issued by the Ministry of Health in 2011 No. 19, and the number 3 in the standard is sulfur dioxide.
