Non-destructive Detection of Insect Foreign Bodies in Finishing Tea Product Based on Terahertz Spectrum and Image.

Xudong Sun,Wenping Li,Jiajun Li,Yun Shen

doi:10.3389/fnut.2021.757491

Abstract

Non-destructive testing of low-density and organic foreign bodies is the main challenge for food safety control. Terahertz time-domain spectroscopy (THz-TDS) and imaging technologies were applied to explore the feasibility of detection for insect foreign bodies in the finishing tea products. THz-TDS of tea leaves and foreign bodies of insects demonstrated significant differences in terms of time domain and frequency signals in the range of 0.3–1.0 THz. These signals were corrected by the use of adaptive iteratively reweighted penalized least squares (AirPLS), asymmetric least squares (AsLS), and baseline estimation and de-noising using sparsity (BEADS) for reducing baseline drift and enhancing effective spectral information. The K-nearest neighbor (KNN) and partial least squares discrimination analysis (PLS-DA) models showed the best performance after AirPLS correction with the prediction accuracy of 98 and 100%, respectively. In addition, the locations and outlines of insect bodies could be clearly presented via the THz-TDS image. These results suggested that THz-TDS spectroscopy and imaging provide an alternative tool for the detection of insect foreign bodies in finishing tea products.

Highlights

During processing, the food matrix is easy to be contaminated by foreign bodies, such as insects, metal, sand, plastics, hair, and so on, resulting in physical pollution [1]
It could be observed that the spectrum of the pure insect sample had lower intensity than that of the pure tea sample, and the spectral intensity of the sample with insect foreign material was between the pure tea and the pure insect
Terahertz time-domain spectroscopy and imaging were applied to investigate the feasibility of non-destructive testing of insect foreign matters in finishing tea products

Summary

Introduction

The food matrix is easy to be contaminated by foreign bodies, such as insects, metal, sand, plastics, hair, and so on, resulting in physical pollution [1]. Food foreign contamination issues will cause conflicts between manufacturers and consumers, and importers and exporters, which can only be reduced rather than eradicated. Non-destructive testing technologies used to scan and exclude foreign bodies will be one of the hot issues for future food analysis. As a current mainstream technology, X-ray imaging is conducted based on the density difference between food matrix and foreign bodies. This method can be applied to detect metal and extended to high-density plastics. The low-density and organic foreign bodies are beyond their limitation [3], which poses big challenges for foreign bodies detection in food processing

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Conclusion