Characterization of the edible bird's nest the "Caviar of the East"

A few species of swiflets (genus Aerodramus) build edible nests that are consumed by humans worldwide, as a delicacy known as the "Caviar of the East" or as a medicinal food. This study reports on the compositional properties of two types of nest, the white nest and the red "blood" nest. The order of composition (from lowest to highest) was found to be identical for both types of nests, i.e., lipid (0.14-1.28%), ash (2.1%), carbohydrate (25.62-27.26%) and protein (62-63%). It was also found that both nests share a common 77 KDa protein that has properties similar to those of the ovotransferrin protein in eggs. This protein may be partially responsible for the severe allergic reactions that sometimes occur among young children who consume edible bird's nest products. It was found that SDS-PAGE electrophoretic fingerprinting might serve as a useful analytical technique for differentiating between white and red nests and for determining if the more expensive "blood" nest was adulterated with the less expensive white nest. Also evaluated were different analytical methodologies for detecting adulterants. Three of the most common adulterants found in retail bird's nests are karaya gum, red seaweed, and tremella fungus, and they are routinely incorporated during commercial processing prior to final sale. Using crude protein determination, it was found that these adulterants (which typically accounted for 2-10% of the finished nest), reduce the overall crude protein content of the genuine white bird's nest by as much as 1.1-6.2%. A modified xanthoproteic nitric acid test for proteins proved to be a rapid, and simple test to detect adulteration in both whole and finely ground nests, and would be suitable in the field where analytical facilities are not readily available. After simple nitric acid treatment, visual examination and comparison of whole nests adulterated with karaya gum, red seaweed, and Tremella fungus against the authentic white nest revealed that levels of adulteration as low as 1.7%, 1.8%, and 3.5%, respectively, could be identified visually. In the case of finely ground nests, the visual detection level was higher for all three adulterants: 1.1% for karaya gum, 1.2% for red seaweed, and 2.0% for Tremella fungus. The use of a reflectance colourmeter rendered this test even more sensitive, allowing detection at even lower levels.