Identifying CPPU-Treated Kiwifruits Using Near-Infrared Hyperspectral Imaging Technology

The application of forchlorfenuron (N-(2-chloro-4-pyridyl)-N′-phenylurea), short form CPPU, on kiwifruits has become an important factor that influences kiwifruit economic efficiency and the health development of kiwifruit industry. This study aims to investigate the feasibility of using hyperspectral imaging technology to identify kiwifruits treated with CPPU (named as treated kiwifruits) from kiwifruits without CPPU treatment (named as untreated kiwifruits), and to investigate which model, developed for a single variety or for two varieties together, has better identification performance. Two hundred and forty “Xixuan” kiwifruits and 240 “Huayou” kiwifruits (120 treated kiwifruits and 120 untreated kiwifruits for each variety) were used to obtain hyperspectral from 865.11 to 1711.71 nm. The samples were divided into calibration set and prediction set based on Kennard–Stone method as the ratio of 3:1. Standard normal variate transformation was used to preprocess obtained spectra. Successive projections algorithm (SPA) was applied to extract the characteristic wavelengths from full spectra (FS). Support vector machine (SVM) and extreme learning machine (ELM) modeling methods were used to establish identification models of treated kiwifruits based on FS, characteristic wavelengths extracted by SPA, and universal wavelengths (UWs) extracted from characteristic wavelengths selected by SPA for “Xixuan,” “Huayou,” and two varieties together, respectively. The results showed that the number of characteristic wavelengths selected by SPA were 18, 18, and 21 for “Xixuan,” “Huayou,” and two varieties together, respectively. Five UWs were found for the three different samples. The best model was SPA-ELM for both “Xixuan” (99.8 % accuracy rate for predication set) and “Huayou” (100.0 % accuracy rate for predication set). Models of SPA-SVM and SPA-ELM, whose accuracy rate reached 100 % for both calibration and predication sets, had the best performance when the two varieties were used together. The performances of models built for two varieties together were better than that for “Xixuan,” but they were worse than that for “Huayou.”.The study indicates that NIR hyperspectral imaging technique can be used as a noninvasive method for identifying CPPU-treated kiwifruits from untreated ones, and it is potential to develop a model based on multi-varieties together.