Watchdogs yesterday collected samples of red cubilose - the main ingredient of the most sought-after type of bird's nest soup - from local health food stores for quality testing.

Red cubilose.[File phot]

This action by the Shanghai Industrial and Commercial Administrative Bureau comes as red cubilose is at the center of a health scare in neighboring Zhejiang Province.

Officials there found red cubilose on sale was actually cheaper white cubilose dyed red, resulting in excessive levels of carcinogenic nitrites.

Cubilose - mostly made from the saliva nests of swiftlets - is an expensive delicacy used in Chinese cooking for hundreds of years.

The product, boasting a high protein and mineral content, is popular with women aiming to maintain a youthful appearance. Usually eaten as a sweet soup, it is also made into snacks.

Red cubilose is the rarest variety. It occurs when nests are built on rock where minerals - especially iron - permeate them, coloring nests red.

Yesterday, at the Kaixuanmen Health Food Market near the Shanghai Railway Station, one of the biggest health food markets in the city, many vendors claimed not to sell red cubilose.

The Shenjirong Health Food Co Ltd, which owns a booth in the market, was selling red cubilose on Monday, but yesterday said it only had the more common white cubilose.

Officials still managed to find red cubilose in the store's refrigerator.

Vendors said genuine red cubilose was hard to find and it was impossible to get enough to satisfy demand.

The results will be announced in three days. Officials will then carry out a risk assessment, said the bureau.

Its Zhejiang Province counterpart said on Monday that almost all the red cubilose in the Zhejiang market failed its quality test.

The Zhejiang Province Industrial and Commercial Administrative Bureau tested more than 200 kilograms of red cubilose and found it to have an average nitrite content of 4.4 grams per kilogram, with some having as much as 11 grams per kilogram.

Several brands, including Ying-huang, Yanzhiwu, Zhengji and Qinghetang, contained more than 10 grams per kilogram.

Nitrites have been linked to stomach and esophagus cancer.