Identification of volatile organic compounds and formulation of white-nest swiftlet (aerodramus fuciphagus) aroma attractant

Swiftlets (Aerodramus fuciphagus) are small insectivorous birds that breed throughout Southeast Asia and can produce edible birds' nest (EBN) from the secreted saliva. EBN industries in Malaysia expand greatly and the aroma is one of the factors believed to attract swiftlets to enter and build nests in the birdhouse. However, the use of existing aroma products has not been scientifically proven and the products also contain chemicals which are harmful to swiftlets and humans. This study focused on the identification of volatile organic compounds (VOCs) from the aroma of EBN, feather, and guano as reference samples in a successful swiftlet birdhouse. E-nose technology was used to determine the VOC similarity index based on the reference samples collected. Further validation and chemical profile identification were done using the headspace technique coupled with gas chromatography/mass spectrometry (HS-GC/MS). Then, samples solubilization for aroma formulation was developed using enzymatic hydrolysis and aqueous extraction. The VOCs of the formulated product were compared with the e-nose database. The results from the e-nose showed the similarity index of the feather (87.06%), guano (67.15%), and EBN (60.23%) to the area concentrated with the swiftlet population. Next, HS-GC/MS using four different types of solid-phase microextraction (SPME) fibers were used in the analysis. PDMS fiber showed the highest efficiency in extracting the VOCs from the reference samples. 2,4-Di-tert-butylphenol (10.41%) was the main compound from 16 compounds identified in EBN. Eleven compounds were identified in the feather sample with heptadecane (7.26%) and pentadecane (6.14%) as the main compounds, followed by ten compounds extracted from the guano sample, with 2,4-Di-tert-butylphenol (3.35%) and hexadecane (7.39%) as the main compounds. Next, enzymatic hydrolysis was used to facilitate the solubility of the EBN and feather sample for product formulation. Meanwhile, 24-h aqueous extraction was conducted on the guano sample to obtain the extract for aroma formulation. UV-Vis analysis was carried out to obtain the optimum condition for EBN hydrolysis, which was achieved at 80 °C for 90 min with 4% alcalase concentration, while feather hydrolysis was the best at 80 °C for 120 min with 5% keratinase concentration. Based on the similarity index obtained from the e-nose analysis previously, the aroma formulation was produced using the ratio of 80 (feather hydrolysate): 15 (guano extract): 5 (EBN hydrolysate). Further analysis using HS-GC/MS showed that 2,4-di-tert-butylphenol (26.5%) was the main compound obtained from the formulated product. This research provides much beneficial information regarding the use of attractant aroma toward the success of swiftlet ranching in Malaysia and increasing productivity of the EBN industry