专家对话燕窝之亚硝酸盐

长达40多页的综述文章“A Comprehensive Review of Edible Bird's Nest”投稿影响因子4.972的杂志。某评审专家对燕窝中亚硝酸盐的问题颇有兴趣，两次提出相关问题：

**次：

Using nitrate as an inspection criterion, this is questionable. As the edible bird's nest is built with swiftlets' saliva. Saliva has a high nitrate content. With the assistance of reducing reagents, nitrate could be reduced to nitrite. If this is the common method in the EBN, the validation of this method should be questioned.

第二次：

The authors revised the manuscript and answered most of the questions appropriately. But they skipped one of my questions I raised in the last version, the concerns of regulation of nitrate/nitrite content in bird's nest. The endogenous metabolism of nitrite was found in humans and mammals from the last century. Some vegetables, such as celery, cauliflowers, all have a relatively high content of nitrate. Nitrate reductase activity of bacteria on the tongue generates nitrate and nitrite can be metabolized to NO in the stomach and circulation. NO also is important to humans. In the meat industry, sodium nitrite is the formation of carcinogenic nitrosamines if it is exposed under high temperatures. If the temperature is correctly controlled, nitrosamine is not an issue.

As the authors already mentioned the steps of processing bird's nest, the saliva of swiftlet plays a very important role as a glue, which could be the factors contributing to the higher nitrite/ nitrate content in bird's nest. Meanwhile, the author also wrote in the manuscript, Line 923-928, the addition of nitrite to white edible bird's nest under acidic condition could turn white one to red one. Red edible bird nest is considered a rare species in the market and it is at a higher price. The nitration of the tyrosyl residue to the 3-nitrotyrosyl residue in the glycoprotein and the oxidation of iron ions is proved to be a pathway for the artificial red color in edible bird's nest (Shim and Lee, 2018; Wong, Chan, Dong, et al., 2018). However, it could be the pathway in the natural one. My concerns include the following questions:

1) Whether it is necessary to include nitrite or nitrate as a testing criterion in an edible bird's nest?

2) How much nitrite or nitrate can be found in the saliva of swiftlet?

3) If nitrite or nitrate can be found in the saliva of swiftlet, what resource of this nitrite and nitrate? From their diet or soil contamination?

4) What are the mechanisms of forming red color in the natural edible bird's nest? Is it the same as the artificial one? If not, please detail. If it is the same, where is the resource of the nitrite? Which edible bird's nest has higher nitrite/ nitrate residues, white one, red one?

我们回复如下：

Q：将亚硝酸盐或硝酸盐作为燕窝的检测标准是否有必要？

A：有必要。因为燕窝中亚硝酸盐的含量不仅可以从侧面反映出燕屋的管理水平，还可以从一定程度提示燕窝的真伪情况。但是重新考虑亚硝酸盐的限值十分必要。目前在中国，燕窝中亚硝酸盐的临时限量值为30ppm，这就要求工厂要用一些操作来降低燕窝中亚硝酸盐的含量。这些操作一方面使工厂的投资增加，另一方面也会降低燕窝中的营养物质含量。由于燕窝只能在炖煮之后食用，而研究发现炖煮之后的燕窝中几乎检测不到亚硝酸盐。因此，适当放宽燕窝中亚硝酸盐的含量限度不会损害消费者的健康。

参考文献：Zhang, Y. Z., Dong, T. X., Chen, J. L., Chou, J. Y., Li, G., Lai, X. P. & Zhan, H. Q. (2017). Content Determination of Nitrite and Effects of Soaking and Stewing on Its Content in 48 Batches of Edible Bird’s Nest. Evaluation and analysis of drug-use in hospitals of China. 17(11), 1441-1447.

Q：金丝燕的唾液中可以发现多少亚硝酸盐或硝酸盐？

A：金丝燕唾液中亚硝酸盐和硝酸盐的含量变化很大。Zhang等测定了48批燕窝中的亚硝酸盐，发现其含量从0到6429.58mg/kg不等。

参考文献：Zhang, Y. Z., Dong, T. X., Chen, J. L., Chou, J. Y., Li, G., Lai, X. P. & Zhan, H. Q. (2017). Content Determination of Nitrite and Effects of Soaking and Stewing on Its Content in 48 Batches of Edible Bird’s Nest. Evaluation and analysis of drug-use in hospitals of China. 17(11), 1441-1447.

Q：如果在金丝燕唾液中发现了亚硝酸盐或硝酸盐，那它的来源是哪里？来自饮食或土壤污染？

A：正如文章所述，洞穴或燕屋的特殊环境条件，例如高温高湿，光线昏暗和空气不流通等，会导致燕窝中的氨基酸转变为亚硝酸盐。此外，粪便的积累和高亚硝酸盐含量的食物的摄入（例如海藻），也会导致燕窝中亚硝酸盐的增加。

Q：天然燕窝的红色形成机理是什么？和人造燕窝的一样么？如果不同，请详述。如果相同，亚硝酸盐的来源是哪儿？白色燕窝和红色燕窝中哪个的亚硝酸盐/硝酸盐含量高?

A：天然燕窝红色形成的机理和人造燕窝红色并不完全相同。除了亚硝酸盐含量和燕窝颜色深浅具有高度相关性之外，Wong等提出AMCase样蛋白中铁离子的氧化对燕窝颜色的变化也有显著影响。

参考文献：

1.Paydar, M., Wong, Y. L., Wong, W. F., Hamdi, O. A. A., Kadir, N. A., & Looi, C. Y. (2013). Prevalence of nitrite and nitrate contents and its effect on edible bird nest’s color. Journal of Food Science, 78(12), 1940-1947.

2.Wong, Z. C. F., Chan, G. K. L., Dong, T. T. X., & Tsim, K. W. K. (2018). Origin of red color in edible bird’s nests directed by the binding of Fe ions to Acidic Mammalian Chitinase-like protein. Journal of Agricultural and Food Chemistry, 66, 5644–5653.

最后，该评审专家的回复：

The authors answered my questions appropriately. It can be accepted now.