Extraction and identification of proteins from edible bird’s nest

Abstract

Edible bird’s nest (EBN) is a delicacy rich in proteins and carbohydrates 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 bird species, as well as the limitation of analytical techniques. Therefore, in the current study, a number of protein extraction methods, including water sonication, Triton X-100 (non-ionic) and sodium dodecyl sulfate (SDS, ionic) detergent-assisted methods, and Tris-HCl buffer solubilization were used to compare the protein profiles of EBN harvested from Batu Pahat and Kota Tinggi in Malaysia. The yields of protein extracted from the EBN samples were determined by using Bradford assay. The water sonication and Triton X-100 extraction methods produced higher protein content (6.44-12.88 mg/g) than the SDS assisted and Tris-HCl buffer extraction methods (3.47-8.60 mg/g). Based on gel electrophoresis, EBN 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 difference in environment and food sources of swiftlets. Additional protein bands (25, 27 and 92 kDa) which were observed in the detergent-assisted methods were suggested to be either membrane or transmembrane proteins. After trypsin digestion, the presence of proteins was analyzed by liquid chromatography coupled with tandem mass spectrometry. The mass spectra revealed that acidic mammalian chitinase was the most abundant protein. The newly found proteins include pre-rRNA-processing protein TSR1 homolog isoform X3, collagen alpha-1(VII) chain-like, lysyl oxidase homolog 3 and phospholipase A2-like. As a summary, the protein extraction methods used in this study could produce good quality of proteins for affirmative confirmation using gel electrophoresis and mass spectrometric identification.