Sulfur dioxide

Sulfur dioxide

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.

As a preservative

Food preservation methods of preparing food so that it can be stored for future use.

Chemical preservation:

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.

Sulfur dioxide

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.

Metabisulphite are more stable to oxidation than bisulphites, which in turn show greater stability than sulphites.

>> Sulphur 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:-

  • Golden Raisins
  • Dates
  • Orange Apricots
  • Light Brown Calimyrna Figs
  • Cantaloupe, Crystallized Ginger
  • Mango
  • Papaya
  • Peaches
  • Pears
  • Pineapple.

In meat

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.).

For example:

  • 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

Raisins

Raisins are dried grapes. 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.