Emerging non-destructive terahertz spectroscopic imaging technique: Principle and applications in the agri-food industry

The safety and quality of agri-food products is a critical public concern over the years. In order to guarantee human heath, it is essential to develop a rapid and non-destructive tool for assuring high-quality agri-food products in the market. Terahertz (THz) spectroscopic imaging is an emerging non-destructive technique. THz wave with the frequency range between the infrared and the microwave can penetrate many commonly used nonpolar dielectric materials and indicate vibrational modes of many biomolecules, which make it an extremely attractive tool for agri-food products inspection. This current paper presents the THz sources and fundamentals of THz spectroscopic imaging technique and discusses chemometric methods applied in THz spectra for qualitative and quantitative analysis. In addition, recent advances in its applications for the safety and quality control of agri-food products over the years 2012–2017 are reviewed. Finally, some perspectives on the current situation and future trends of using THz technique are addressed. It is expected that THz technique combined with chemometric methods has great potential for agri-food products evaluation, and continuous wave THz imaging performs better for identifying low-density foreign bodies embedded in foodstuffs as compared to X-ray imaging. Additionally, THz technique shows the ability to detect packaged agri-food products. The future development of cost-effective and portable THz spectrometer with high sensitivity will make this technique in practical applications.