| Edible bird's nest (EBN; Yan Wo) is a glue-like substance secreted by the specific glands of the swiftlets (e.g. Aerodramus fuciphagus ), which is valuable Chinese delicacy for several hundreds of years. Despite of the long history of human consumption, the detailed chemical compositions and biological functions of EBN are largely unknown. In this report, a comprehensive research on EBN including food safety, quality control and potential biological functions was performed.;A high content of nitrite (NO2-), a toxic food additive, was found in EBN, which aroused the public concern on the safety of EBN consumption. Here, the nitrite content of EBN selling in the market of Hong Kong was investigated. The traditional processing method in EBN cooking was evaluated for the efficiency of the nitrite removal. The highest content of nitrite found in EBN was 6,400 ppm, and Red EBN contained the highest nitrite content, followed by Yellow EBN and White EBN. Up to98% of nitrite was removed in the first step of soaking. Further removal of nitrite from EBN after stewing was found. The origin of nitrite found in EBN was investigated by the EBN samples collected directly from their production sites. The nitrite content of EBN collected from the production sites were similar to that of EBN purchased from Hong Kong market. The high content of nitrate (NO3 -) found in the environment of production sites suggested that nitrate might be involved in the cause of high content of nitrite found in EBN. By proteomic analysis, a protein was isolated from Red EBN, which was identified as nitrate reductase deriving from microbes, and this enzyme converted nitrate to nitrite within EBN. The addition of specific inhibitor of nitrate reductase successfully abolished the formation of nitrite in EBN. In addition, the changed in colour of EBN (i.e. from white to red) was shown to be related to the nitrite content in EBN. Taken together, the nitrite found in EBN was derived from natural environment, which should be originated from the conversion of nitrate by a nitrate reductase.;Fake EBN, or low-grade EBN, sold as the price of high-grade EBN is commonly happened in Hong Kong. Here, the currently established EBN authentication methods were reviewed; however, these methods failed to distinguish EBN with different quality. Therefore, an advanced and reliable authentication method for EBN was developed. By using free N-acetyl-D-neuraminic acid (NANA) as indicative marker, a new method of EBN authentication was developed. Under negative charged mode of a QQQ-LC-MS/MS system, the precursor ion of NANA (308 m/z) was split into two product ions (87 and 170 m/z). The higher abundant product ion (87 m/z) was applied for quantitative analysis. This developed method successfully differentiated fake EBN materials from the genuine EBN in a fast and reliable manner. Furthermore, the method could classify different classes of EBN quantitatively.;Besides chemical identification, the skin whitening and water retention functions of EBN were analyzed. The activity of tyrosinase was the first step of melanogenesis, and therefore the inhibitory effects on tyrosinase by NANA and EBN were studied. The IC50 of NANA which behaved as mixed type-I reversible inhibitor on mushroom tyrosinase activity was 16.93 microM. Different types of EBN also showed different degrees of inhibitory effects on tyrosinase activity. In the water retention assay in cultured keratinocytes, the transcripts encoding aquaporin 3 and filaggrin 2 were determined: no significant variation at the expression level on both genes after the treatment of EBN.;Overall, the current study definitely enhanced the knowledge of EBN. In addition, the framework of this comprehensive research, including food safety, quality assurance and potential medical functions, can be served as an example for oriental nutraceuticals' study. Furthermore, the pioneer works on the skincare function of EBN successfully opened up the clue for this unproven medicinal function. |
