Preliminary exploration on identification of probiotics in terahertz time-domain spectroscopy

Three kinds of probiotics in the biological food additives which are respectively Bacillus licheniformis, Bacillus subtilis and Bacillus coagulans have been tested and investigated with the terahertz time-domain spectroscopic(THz-TDS) technique at room temperature in nitrogen environment in the paper. The absorption coefficient and refraction index of three probiotics samples were calculated in the frequency of 0.2-1.6 THz. Test reveal that the absorption coefficients is increased as frequency increases and has considerable different absorption trend and characteristic absorption peaks among the samples, which means the vibration information made up of different molecular vibration and multi-molecular group is different in the THz spectrum of three samples. Furthermore, the average refractive indices were 1.71, 1.67 and 1.64 corresponding to Bacillus licheniformis, Bacillus subtilis and Bacillus coagulans, respectively. The refractive value indicates that abnormal dispersion, which meant three samples had the characters of strong selective absorption in this wave band. In contrast, the Fourier transform infrared spectroscopy(FTIR) in the 400-4000 cm-1 was utilized to measure the IR absorption spectra, and the results revealed that the probiotics is more active in the range of Terahertz than in the IR band and terahertz can be a good supplementary means of IR test. Meanwhile, some explanation on mechanism was put forward in this paper. The experiments showed that THz-TDS is a powerful tool to complement the conventional analytical approaches and can be applied to detect and identify the features of the constituent in probiotics or other biological food additives.