Tuesday, 3 July 2012

Chemistry of food preservatives

Preservative


A preservative is a natural or synthetic substance that is added to products such as foods, pharmaceuticals, paints, biological samples, wood, etc. to prevent decomposition by microbial growth or by undesirable chemical changes.

Contents

1.       Preservatives in wood
2.       Preservatives in food
3.       Natural food preservatives
4.       Health concerns

1-Preservatives in wood

Preservatives may be added to wood to prevent the growth of fungi as well as to repel insects and termites. Typically arsenic, copper, chromium, borate, and petroleum based chemical compounds are used. For more information on wood preservatives, see timber treatment.

2-Preservatives in foods


Preservative food additives can be used alone or in conjunction with other methods of food preservation. Preservatives may be:-

       I.            antimicrobial preservatives : The chemicals which inhibit the growth of fescies or fungi, including mold, or antioxidants such as oxygen absorbers, which inhibit the oxidation of food constituents.Antimicrobial preservatives include calcium propionate, sodium nitrate, sodium nitrite, sulfites (sulfur dioxide, sodium bisulfite, potassium hydrogen sulfite, etc.) and disodium EDTA.

    II.            Antioxidants :  include BHA and BHT. Other preservatives include ethanol and methylchloroisothiazolinone..


What are BHA and BHT ?

Butylated hydroxyanisole (BHA) and the related compound butylated hydroxytoluene (BHT) are phenolic compounds that are often added to foods to preserve fats.

 

Chemical structure of BHA.

BHA Characteristics:

  • BHA is a mixture of the isomers 3-tert-butyl-4-hydroxyanisole and 2-tert-butyl-4-hydroxyanisole. Also known as BOA, tert-butyl-4-hydroxyanisole, (1,1-dimethylethyl)-4-methoxyphenol, tert-butyl-4-methoxyphenol, antioxyne B, and under various trade names
  • Molecular formula C11H16O2
  • White or yellowish waxy solid
  • Faint characteristic aromatic odor

BHT Characteristics:

  • Also known as 3,5-di-tert-butyl-4-hydroxytoluene; methyl-di-tert-butylphenol; 2,6-di-tert-butyl-para-cresol
  • Molecular formula C15H24O
  • White powder

How do they preserve food?

BHA and BHT are antioxidants. Oxygen reacts preferentially with BHA or BHT rather than oxidizing fats or oils, thereby protecting them from spoilage. In addition to being oxidizable, BHA and BHT are fat-soluble. Both molecules are incompatible with ferric salts. In addition to preserving foods, BHA and BHT are also used to preserve fats and oils in cosmetics and pharmaceuticals.

What foods contain BHA and BHT ?

BHA is generally used to keep fats from becoming rancid. It is also used as a yeast de-foaming agent. BHA is found in butter, meats, cereals, chewing gum, baked goods, snack foods, dehydrated potatoes, and beer. It is also found in animal feed, food packaging, cosmetics, rubber products, and petroleum products.

BHT also prevents oxidative rancidity of fats. It is used to preserve food odor, color, and flavor. Many packaging materials incorporate BHT. It is also added directly to shortening, cereals, and other foods containing fats and oils.

Are BHA and BHT safe ?

Both BHA and BHT have undergone the additive application and review process required by the US Food and Drug Administration. However, the same chemical properties which make BHA and BHT excellent preservatives may also be implicated in health effects. The oxidative characteristics and/or metabolites of BHA and BHT may contribute to carcinogenicity or tumorigenicity; however the same reactions may combat oxidative stress. There is evidence that certain persons may have difficulty metabolizing BHA and BHT, resulting in health and behavior changes. BHA and BHT may have antiviral and antimicrobial activities. Research is underway concerning the use of BHT in the treatment of herpes simplex and AIDS.

3-Natural food preservation


Natural substances such as salt, sugar, vinegar, alcohol, and diatomaceous earth are also used as traditional preservatives. Certain processes such as freezing, pickling, smoking and salting can also be used to preserve food. Another group of preservatives targets enzymes in fruits and vegetables that start to metabolize after they are cut. For instance, citric and ascorbic acids from lemon or other citrus juice can inhibit the action of the enzyme phenolase which turns surfaces of cut apples and potatoes brown.

4-Health concerns


Some modern synthetic preservatives have become controversial because they have been shown to cause respiratory or other health problems. Some studies point to synthetic preservatives and artificial coloring agents aggravating ADD & ADHD symptoms in those affected. Older studies were inconclusive, quite possibly due to inadequate clinical methods of measuring offending behavior. Parental reports were more accurate indicators of the presence of additives than clinical tests. Several major studies show academic performance increased and disciplinary problems decreased in large non-ADD student populations when artificial ingredients, including preservatives were eliminated from school food programs.. Allergenic preservatives in food or medicine can cause anaphylactic shock in susceptible individuals, a condition which is often fatal within minutes without emergency treatment.

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