Sunday, September 18, 2011

Poison in our Foods : Nitrite

In August 2011, surveillance conducted by
Zhejiang Provincial Administration for Industry and Commerce found that excessive nitrite 亚硝酸盐 was present in culibose imported from Malaysia.  It was unsure how nitrite could occurred in bird’s nests燕窝. The Malaysian exporters claims no additives were added to bird’s nest, especially nitrite.

Experts says it is normal to have trace amount of nitrite in bird’s nest, but 4400 mg/kg is totally unacceptable.  Expert says nitrite may occure naturally due to chemical reaction.  Some studies suggested that It could be from the bird droppings, or other environmental contaminant.
Traces of nitrite is also found naturally in some vegetables, eg. beetroot, broccoli, cabbage, carrot, celery, cucumber, lettuce, potato, spinach, tomato etc. 

Processed meat, such as sausages, smoked meats and fishes, fermented meats, hams, canned meats, etc and cheeses may contain nitrite not exceeding 200mg/kg.  

Nitrite are permitted preservatives in many countries for processed meat, but do not include bird’s nest.

Bird’s nest is a prized delicacies, especially for the Chinese.  Bird’s nest is produced by swiftlets, Aerodramus fuciphagus ( synonym Collocalia fuciphaga ), and German’s swiftlets, Aerodramus germani.  The swiftlets used a glutinous secretion to bind together materials for nest building, or construct a whole nest with it.  

Bird’s nests are among the most expensive animal products consumed by humans.  A 100g of bird’s nest cost about USD1,000.  bird’s nest is believed to be very nourishing and contains unknown properties.  It is claimed that bird’s nests can help maintain a youthful, radiant and wrinkle-free complexion.  

Bird’s nest has a translucent appearance.  It smells similar to the scent of egg white.  It contains mainly carbohydrates ( sialic acid, galactoamine, glucosamine, galactose, fucose ) , amino acids ( aspartic acid, blutamic acid, praline, threonine, valine, etc ) and minerals ( copper, iron, zinc, manganese, potassium, sodium, etc ). 

It is very disturbing that such a premium delicacy contains nitrites.  Nitrites, when consumed, will go into the blood stream and react with hemoglobin ( Hb ) to form methemoglobin ( metHb ).  MetHb cannot bind oxygen, which decrease the capacity of the blood to transport oxygen to body tissues, thus causing a condition known as methemoglobinemia.   Methemoglobinemia may cause bluish tinge on lips and skin, tiredness, coma and even death.  However, metHb formation is reversible.  Nitrite in blood is rapidly oxidized to nitrate, and excreted via the urinal tract.  

The China health authority thus announced the maximum of nitrite in bird’s nest to be 30mg/kg ,  adopted from the existing rule on processed meats.

Still, it is recommended that bird’s nest should be thoroughly washed and soaked before stewing.  Washing and soaking for few hours can in general remove substantial quantity of nitrite.  The water used for soaking should also be discarded and replace once or twice during the soaking process. 


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