A portable dual-gear device for non-destructive testing on multi quality of citrus

Rapid and non-destructive testing is of great significance for the quality grading in the citrus industry. This study was focused on the actual needs of on-site real-time detection on the internal quality of citrus fruits with different fruit diameters (25-95mm) in China. The spectral variation coefficient of citrus fruits was determined with different fruit diameters at the same point. A systematic investigation was made to explore the impact of the incident light angle on the spectral information of citrus fruits. A dual-gear probe was then designed for the local diffuse transmission spectral acquisition. A portable non-destructive testing device was developed for the internal quality of citrus fruits with multiple fruit diameters. Four modules included a light source, a spectrum acquisition, a control and display, as well as a power supply module. The size of entire device was 160mm × 80mm × 65mm, weighing 390g. Taking sugar orange (fruit diameter 25.35-48.61mm) and Wuming Wo orange (fruit diameter 53.24-94.71mm) as the research objects, the spectra were collected every 120 ° at the equator using the dual range probe, and then the average spectrum was used as the original spectrum of the citrus. Competitive adaptive weighted sampling (CARS) was used to filter feature wavelengths after preprocessing with standard normal variable transformation (SNV) and multiple scatter correction (MSC). A partial least squares (PLS) prediction model was established for the soluble solids content (SSC) and moisture content of citrus. The correlation coefficients of the SSC and moisture prediction model validation set for Wogan were 0.937 and 0.951, respectively, with the root mean square errors (RMSE) of 0.382°Brix and 0.491%, respectively; The correlation coefficients of SSC and moisture prediction model validation set for sugar orange were 0.921 and 0.935, respectively, with the RMSE of 0.460°Brix and 0.673%, respectively. A real-time analysis and control software was written for the device using C/C++language in the QT development tool. One click, real-time, and non-destructive testing was achieved in the multiple qualities of citrus fruits with different diameters. Finally, the experimental verification was conducted on the stability and accuracy of the developed device. The results showed that the average coefficient of variation of SSC and water content predicted by the device for Wogan were 0.024% and 0.022%, respectively; The average coefficient of variation (CV) of SSC content and water content in sugar orange were 0.014% and 0.020%, respectively; The maximum absolute residual values of SSC and moisture device predictions and standard physicochemical values for Wogan were 1.15% and 1.37%, respectively, while those of sugar orange were 1.71% and 1.58%, respectively. Therefore, the portable dual-gear device can fully meet the requirements of on-site and real-time spectral detection on the multiple quality of citrus, particularly for the stability and accuracy of internal quality detection of citrus fruits with different fruit diameters.