Time-of-flight near-infrared spectroscopy for nondestructive measurement of internal quality in grapefruit

We proposed a technique combining time-of-flight (TOF) and near-infrared spectroscopy (NIRS), termed TOF-NIRS, capable of measuring the time-resolved profiles of near-infrared (NIR) light with nanosecond resolution. Analysis of the variation in time-resolved profiles was used to estimate soluble solids concentration (SSC) and acidity in grapefruit (Citrus paradisi)*and the prediction accuracy was compared with the conventional NIR measurement device. In data processing*the cross-correlation function*which evaluated the similarity between the reference and transmitted beams*was introduced as an explanatory variable for partial least squares regression. TOF-NIRS predicted both SSC and acidity in grapefruit with higher precision than the conventional NIR measurement with respective r values of 0.72 and 0.85. Specifically*the superiority of TOF-NIRS was attributed to measurement time and prediction accuracy in determining acidity.