Protein extraction and identification by gel electrophoresis and mass spectrometry from edible bird's nest samples

Edible bird’s nest (EBN) is a delicacy rich in protein and carbohydrate from the salivary secretion of swiftlets. There are limited studies on the protein profile of EBN, mainly due to its complexity in chemical composition and diversity of species, as well as the capacity of analytical techniques. The protein extraction methods, namely, ultrasonic and detergent (Triton X-100 and SDS)-assisted methods, as well as Tris–HCl buffer solubilization were used to compare the protein profiles of EBNs harvested from two locations (Batu Pahat and Kota Tinggi) in Malaysia. Ultrasonic assisted extraction produced the highest protein content because EBN contains mostly water-soluble protein. The electrophoretic gels revealed that EBNs from Batu Pahat (17–150 kDa) exhibited more protein bands than those samples from Kota Tinggi (25–154 kDa). The difference could be explained by the variance in the geographical origin of EBNs. Additional protein bands (25, 27, and 92 kDa) were detected for the detergent-assisted methods. These could be poorly water-soluble membrane proteins that were released after cell lysis by detergents. The mass spectra revealed that acidic mammalian chitinase precursor is the most abundant protein. The other proteins include trypsinogen, inter-alpha-trypsin inhibitor heavy chain H2 precursor, tumor necrosis factor receptor superfamily member 5 precursor, and phospholipase A2-like. There are also collagen and co-enzyme Q-binding proteins which are important for skin complexion in line with the traditional belief of Chinese community. The protein extraction methods could produce good quality of proteins for affirmative confirmation using gel electrophoresis and mass spectrometric identification