Progress In Terahertz Technique For Quality Inspection Of Agro-Food Products

The safety and quality of agro-food has attracted increasing attentions. Due to the problems of traditional detection methods, such as being time-consuming, operation complicated, solvent-consuming and high-cost, it is essential to develop rapid and non-destructive detection methods. Terahertz(THz) ,which lies between the mid-infrared and microwave ranges, has unique properties such as transient, transmission, broadband, coherence and low-energy. THz wave can indicate structures and characteristics of many biomolecules, and be used in the quantitative and qualitative analysis of organic biomolecules as "fingerprint". Therefore, compared with other spectroscopy techniques such as NIR, Raman and X-ray, THz has become an extremely competitive tool for agri-food products inspection. In this paper, the characteristics of THz wave and the principles of THz spectroscopy and imaging technique were introduced at first. Then THz data analysis process and the commonly used methods in its main steps were given, in which the quantitative and qualitative model construction and evaluation were emphatically introduced. Thirdly, the application and research progress of THz technique in the agro-food quality inspection which contains the detection of pesticide residues, antibiotic, toxins, identification of adulteration, transgenetic agro-food and foreign body, and prediction of the content of nutrient contents were discussed. Finally, the challenges that THz technique in the agro-food quality detection has to face were discussed systematically, based on which the research directions were pointed out, and the future outlook for THz technique was also discussed. The published literatures have indicated that THz technique is an effective solution in the agro-food quality inspection, especially THz wave can penetrate many commonly used nonpolar dielectric materials, which gives it superiorities in detection of packaged agro-food products. With the development of information technology, such as machine learning and intensive learning, on one hand, the THz data analysis technique needs to be strengthened. Through data self-learning, we can reveal the scientific rule from the data point of view, and build an analytical model with higher accuracy, lower computation cost, stronger real-time performance and better generalization ability. On the other hand, based on molecular vibration theory and combined with knowledge of chemistry and Physics, the mechanism of the terahertz spectroscopic characteristics is studied, which can be used in the model construction. Thereby through the combination of these two sides, the soft power of the terahertz will be improved. Meanwhile developing cost-effective and portable THz spectrometer with high sensitivity is a future research trend. It is expected that the application of terahertz technique will gradually begin from the laboratory state to the engineer application.