Ion Chromatography Analysis: Nitrites in Edible Birds Nests

Edible Birds Nests, made from the saliva of several Swiftlet species, have been used in Chinese cooking for over 400 years, most commonly in Birds Nest soup. This is an expensive delicacy in China and is believed to provide many health benefits. Now, the nests have become big business, with Hong Kong and the United States being the largest importers of these nests, and China being the highest end user.

Last summer, when this story broke, China’s Zhejiang Provincial Administration for Industry and Commerce found nitrite levels in the rare red Birds Nest imported from Malaysia averaged 4,400 mg/kg, far above the allowed maximum of 70 mg/kg. The administration said that the contamination was the result of adulteration—dying white Birds Nests and selling them as the rare and more expensive blood-red Birds Nests.

This contamination is of concern because nitrite can react with secondary amines in food products or in the digestive system to form nitrosoamines (link to a Wikipedia page), a class of carcinogenic compounds. Nitrate, although more stable than nitrite, can act as a reservoir for nitrite. Also, nitrate can readily be converted into nitrite by microbial reduction. Thus, both nitrate and nitrite must be monitored to ensure the quality and safety of meat products.

A few months later, it was reported on China.org.cn that the Chinese government was mulling over chemical standards for edible Birds Nest. Then, as recently as December of 2011, the CHINADAILY.com.cn reported that again nitrite had been found in Birds Nests originating from Malaysia.

Ion Chromatography Analysis: Nitrites in Edible Birds Nests

With vast experience with nitrite and nitrate analyses, we offer the following three methods as solid starting points for the analysis of nitrites and nitrates in edible Birds Nests and other food products.

• Application Note 154, Inorganic Anions in Environmental Waters Using a Hydroxide-Selective Column (downloadable PDF)
• Application Note 131, Nitrite and Nitrate in Drinking Water Using Chemically Suppressed Ion Chromatography (downloadable PDF)
• Application 132, Nitrite and Nitrate in Drinking Water Using Ion Chromatography with Direct UV Detection (downloadable PDF)
Let us know of your food testing challenges in the comments field below.

How to clean raw Birds Nests?

Please have a look at our instruction with 03 steps as below :

A. Preparation of tool:

01 small-top and long-body tweezer (for plucking the feathers easily)
01 big white bowl or brass basin (easy to see the black feathers)
01 sieve with small hole (note: the hole should not be too small)
01 spoon
01 clean dish (to put raw Birds Nest in after cleaned)

B. Taking steps as follows:

Step 1:
Put unprocessed raw Birds Nest in white bowl (or brass basin), then soak it in cold water around 1-3 hours (subject to the structure of nest) and wait until the nest becomes loose.
Note: The nest should not be soaked in hot water
Step 2:
Put the loose Birds Nest in a sieve to dry it out (Note: avoid dropping nest out). Take the nest sieve and put it under light water tap, using spoon (or hand) to press softly and take a bowl to catch the nest chip in case it is dropped out). This method helps remove callows and dirty particles out of the sieve.
After cleaning feathers and dirty particles, put nest sieve in bowl (or brass basin) with full of water, then shake the sieve regularly to wash away the remaining small feathers and dirty particles. This action is repeated for a few times until the Birds Nest is cleaned completely. And now, put the processed cleaned nest in a dish and go to Step 3.
Step 3:
Use a spoon or finger top to flatten the nest into a thin layer in order to observe easily the remaining feathers. At this step, there are only some big feathers or callows sticking on nest, so a tweezer shall be used to quickly pluck it out. When plucking feather, we will put the tweezer into water bowl (or basin) to get feathers out. This action is repeated until feathers cleaned completely.
Notes:
Clean edible Birds Nest which is not used immediately should be dried out before preservation in the refrigerator.