Relationship between Colors and Iron's Content and Oxidation State in Edible Bird's Nest

Edible birdís nests (EBNs) are known as a medical food with abundant mineral and nutrition. Their colors vary from white, yellow and red according to their production sites. White EBNs are produced by swiftlets living in both natural caves and man-made birdís houses. Red EBNs, on the other hand, can be only found in a certain caves. Due to the higher price of red EBNs in comparison with the white EBNs, artificial red EBNs are made by exposing white EBNs with vapor from a solution of sodium nitrite in hydrochloric acid solution. According to ICP-OES, red cave EBNs displayed higher amount of iron (2.52 ± 1.46 mg/100g dry matter), compared to white EBNs from both cave (0.74 ± 0.35 mg/100g dry matter) and house (0.85 ± 0.29 mg/100g dry matter). Fe K-edge XAS demonstrated the presence of iron(II) and iron(III) species in all EBNs. Both red cave EBNs and artificial red EBNs from both cave and house showed significantly higher amount of iron(III) (97.33 ñ 99.72 %) than white EBNs from both cave and house (69.46 ñ 74.83 %). This study suggests that the red color in EBNs of both authentic red cave and artificial red EBNs are associated with their iron (III)