Feasibility and Performances of a New, Multiplexed, Fast and Low-Cost Fiber-Optic NIR Spectrometer for the On-Line Measurement of Sugar in Fruits

Abstract

This paper describes an attempt to develop a new NIR spectrometer to sort fruits according to the sugar content in the conditioning stations. This spectrometer, ranging from 800 to 1050 nm, is based on diode array technology. It is coupled with fiber optics, which allow multiplexing; 20 fibers have been detected by the camera, showing the potential multiplexing of 20 different points. The acquisition time is 40 ms per image (i.e., 2 ms per spectrum). A good signal-to-noise ratio has been recorded in the 820–1010 nm range. This spectrometer has been tested with a set of 79 peaches. Partial least-squares processing is applied to different wavelength ranges. The best coefficient of correlation, achieved with a reduced wavelength range (from 847 to 977 nm), is 0.81, and the standard error of prediction is 1.04°Brix. With this calibration, the fruits can be sorted into three maturity classes with a reliability of 76%. This performance, as well as the other characteristics of the instrument, is in accordance with the requirements of the conditioning station managers.