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Nitrite in Bird's Nest

Nitrite in Bird’s Nest

Introduction

  1. In 2011, surveillance conducted by Mainland authority and local studies found that nitrite was present in various bird’s nests, in particular blood-red bird’s nest, available at the market.
  2. Nitrite occurs in the environment, in food and water, and is produced inside living organisms. It can be used as a food additive, mainly as a preservative and colour fixative in foods such as cheese and cheese products as well as cured and fermented meats.
  3. Some scientific studies have shown that nitrite may naturally form in bird's nests due to fermentation under certain temperature and humidity. Some studies also suggested that high level of nitrite in bird’s nest may due to environmental contamination e.g. from bird droppings which contain high level of nitrate. However, the exact mechanism for the presence of nitrite in bird’s nest is not entirely clear at this stage.

Safety and Public Health Significance

  1. The safety of nitrite in food has raised concern because of its possible implication for the adverse health effects such as methaemoglobinaemia and cancers.
  2. In the body, nitrite can oxidise haemoglobin in blood and make it unable to carry oxygen to the body tissues. Having insufficient oxygen, the person may develop blue or purple colouration in the lip and skin and the condition is called methaemoglobinaemia. Population subgroups such as young infants and people with glucose-6-phosphate dehydrogenase (G6PD) deficiency are more susceptible to the above condition. According to the Centre for Health Protection record, since 2003 there were two cases of nitrite related food poisoning and both were related to consumption of vegetables with high levels of nitrate in infants and young children.  
  3. The International Agency for Research on Cancer (IARC) of the World Health Organization has evaluated the carcinogenicity of ingested nitrite and concluded that ingested nitrite under conditions that result in endogenous nitrosation (i.e. conversion into nitroso compounds such as nitrosamines) is probably carcinogenic to humans (i.e. Group 2A). However, JECFA * considered that there was no evidence for an association between nitrite exposure in humans and the risk of cancer.
  4. JECFA has evaluated the safety of nitrite and allocated an acceptable daily intake (ADI) of 0-0.07 mg per kg body weight (bw), expressed as nitrite ion and the ADI does not apply to infants below the age of 3 months. According to the results from recent local studies, any adverse health effect due to the consumption of thoroughly washed, soaked and stewed bird’s nest is not likely.

Regulatory Control

  1. Like other countries, nitrites (potassium nitrite and sodium nitrite) are permitted preservatives in a number of food categories e.g. cured meats, fermented meats, cheeses and cheese products, but do not include bird’s nests in Hong Kong . However, Section 3(10) of the Preservatives in Food Regulation stated that it does not apply to an article of food containing any food additive that is naturally present in that food.
  2. For bird’s nests containing naturally formed nitrite, there is no international consensus on their reference and regulatory levels.

Recommended Preparation Method for Bird’s Nest

  1. In practice, dried bird’s nest should be thoroughly washed and soaked before stewing. Both local and Mainland studies have showed that thoroughly washing and soaking for a few hours can in general remove substantial quantity (up to more than 90%) of nitrite in bird’s nest. However, since nitrites are dissolved into the soaking water, they should be discarded after soaking. Water used for soaking bird’s nests should also be replaced once or twice during the soaking process. The public can also refer to the suppliers’ recommendation when preparing bird’s nest.

Advice to the Public

  1. Buy bird’s nests from reliable premises.
  2. Since nitrite is water-soluble, washing and soaking bird’s nests thoroughly can in general remove up to more than 90% of nitrite.
  3. Water used for soaking bird’s nests should be replaced once or twice and should be discarded after use.
  4. Young infants are not recommended to take bird’s nest.

Advice to the Trade

  1. Source bird’s nests from reliable suppliers.  
  2. According to the Preservatives in Food Regulation, nitrites should not be added in bird’s nest.
  3. Provide clear instruction to consumers on proper way of preparation of bird’s nest.
Risk Assessment Section
Centre for Food Safety
September 2011

* Joint Food and Agriculture Organization/ World Health Organization Expert Committee on Food Additives

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Last Revision Date : 27-09-2011