Sulfur dioxide (also sulphur dioxide) is the chemical compound with the formula SO2. It is produced by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide. Further oxidation of SO2, usually in the presence of a catalyst such as NO2, forms H2SO4, and thus acid rain. This is one of the causes for concern over the environmental impact of the use of these fuels as power sources.
Sulfur dioxide can be liquefied under moderate pressures at room temperatures; the liquid freezes at -73° C (-99.4° F) and boils at -10° C (+14° F) under atmospheric pressure.
1-Serving both as antimicrobial substance and as antioxidant.
2-Sulfur dioxide is a gas that can be used in compressed form in cylinders.
3-It is liquid under pressure of 3.4 atm and can be injected directly in liquids.
4-It can also be used to prepare solutions in ice cold water.
5-It dissolves to form sulfurous acid.
As a preservative
Food preservation methods of preparing food so that it can be stored for future use.
Many chemicals will kill micro-organisms or stop their growth but most of these are not permitted in foods. Chemical food preservatives are those substances which are added in very low quantities (up to 0.2%) and which do not alter the organoleptic and physico-chemical properties of the foods at or only very little.
Sulfuring has the advantage of producing an excellent quality product .Fruit treated with sulfur will maintain color, flavor, vitamins A and C, and sulfuring will discourage insect infestation during drying. The heat during drying and subsequent cooking dissipates the sulfur.
Sulphur dioxide and its various sulphites dissolve in water, and at low pH levels yield sulphurous acid, bisulphite and sulphite ions. The various sulphite salts contain 50-68% active sulphur dioxide. A pH dependent equilibrium is formed in water and the proportion of SO2 ions increases with decreasing pH values. At pH values less than 4.0 the antimicrobial activity reaches its maximum.
Sulphur dioxide is used as a gas or in the form of its sulphite, bisulphite and metabisulphite salts which are powders. The gaseous form is produced either by burning Sulphur or by its release from the compressed liquefied form.
Methamphetamine are more stable to oxidation than plebiscites, which in turn show greater stability than sulphites.
Sulfur dioxide in drying food
Bulk Fruits are sulfured with sulfur dioxide (SO2) or meta bisulfate to keep them from oxidizing during and after the drying process. This preserves their original color. When fruits are dried with no sulfur they oxidize and change to a brown to black color as they dry. Golden raisins are always sulfured and that is why they are golden in color.
Typically all white, yellow and orange colored fruits have been sulfured.
Fruits that are sulfured are:
•Light Brown Calimyrna Figs
•Cantaloupe, Crystallized Ginger
Raisinsare driedgrapes. Raisins may be eaten raw or used in cooking and baking.
A raisin that is treated with sulphur dioxide, which help to prevent oxidation and prevent the raisin from darkening. Golden raisins are dried with artificial heat, which results in a moister, plumper product. They have a sweet but tangier flavor than the dark raisins.
Golden raisin:This kind is oven dried and then sulfur is added in order to saving its color.
Sulfur Dioxide Use in raisins
Raisins retain their light color because of sulfur dioxide (SO2) treatment after dipping and before dehydration. It retards both enzymatic and nonenzymatic browning, preserves the natural flavor, and retards the loss of pro-vitamin A and ascorbic acid. Sulfur dioxide is a reducing agent that prevents the enzymatic conversion of the phenolic compounds. Sulfur dioxide gas is injected into sulfur houses from pressurized tanks to achieve a total rate of about 5 to 8 pounds per ton of fruit. The fruit is left for 5 to 8 hours to absorb the SO2.
Traditionally, the goal was to achieve an SO2 concentration high enough to give the processed fruit a minimum of 2,000 ppm for golden color retention through distribution and marketing. However, some markets such as the European Economic Community and Japan will not accept dried fruit containing more than 2,000 ppm SO2. Dehydrator operators may have to decrease dosages or modify practices to meet these requirements in the future.
* Recommended storage conditions are at 45ºF / 7ºC at 45-55% RH.
Raisins freeze well for long periods of time and thaw quickly at room temperature prior to use.
If the temperature exceeds 50ºF / 10ºC, the relative humidity should be kept below 55%.
When stored as recommended, raisins will keep their flavor and nutritional value for up to 15 months.
*Products which contain sulfur dioxide as the active ingredient are formulated as a liquid under pressure which forms a gas upon release for grape fumigation. These products are stored in steel cylinders and applied to the treatment area via a hose system with a detector tube at a maximum rate of 1% concentration (based on measured volume of the fumigation chamber) for the initial fumigation, and up to 0.5% gas concentration for maintenance fumigations.
SO2 is added to meat products as a preservative. It increases the lag phase of bacteria (the period of time before they begin to grow in a new environment), slows their growth rate, and selects against the species of bacteria that traditionally dominate in meat and eventually cause the putrid off-odours of spoilage. It is effective against Salmonella spp and many other Enterobacteriaceae, Pseudomonas spp, Lactobacillus spp and various species of yeasts.
In sausages and other finely comminuted fat-protein-water meat emulsions, it is an effective antioxidant. It also acts as a reducing agent for preventing the grey-brown discolouration of minced meat and fresh sausages.
Permitted levels in meat products
Less than 500mg/kg of the finished product.
In the meat industry, sulphur dioxide can only be used in:
Some processed meat, poultry and game products that are produced using comminuted meats (e.g. chopping, dicing, etc.).
•Mortadella, chicken loaf, turkey loaf, frankfurters, luncheon meats, Polish salami, devon and manufactured hams.
•Raw unprocessed sausage and sausage meat.
•Sausages, sausage meat and sausage rissoles – sausages must contain at least 500g/kg of fat free meat and fat cannot exceed 500g/kg of the fat free meat content – chipolatas, BBQ sausages, beef and pork sausages, chicken sausages.
•Hamburger patties made from sausage meat.
Sulfur dioxide is an important compound in winemaking.
Roles of SO2 in Wine
–knock down yeast (esp. wild) and bacteria
–Wild yeast and bacteria potential source of off flavors
–Oxidation of wine leads to brown color, decrease in varietal aromas, development of nutty and sherry aromas.
–In juice, SO2 inhibits enzymatic oxidation (PPO).
–In wine, SO2 reacts with chemical oxidation intermediates & oxidized compounds to reduce apparent effect.
The uses of sulfur dioxide are many, some of which are: preservative for beer and in the manufacture of sulfite and hydrogen sulfites, solvent extraction and as a refrigerant in the ice industry.