Classification of High Acid Satsuma Mandarins by Near Infrared Transmittance Spectroscopy

Abstract

On-line measurement of sugar content in satsuma mandarins was already achieved using NIR transmittance spectroscopy. The feasibility of simultaneous measurement of citric acid content was investigated. The citric acid content determined by titration with NaOH and the second derivative absorption values autoscaled in the 710-930 nm region were analyzed by PLS1 using Unscrambler software. The spectra of peeled fruits measured by an NIR Systems Model 6250 were analyzed, and the model composed of 12 factors indicated the highest accuracy; R was 0.93, the mean residual (Bias) was -0.013% and the standard error of prediction (SEP) was 0.146%. The citric acid content in intact satsuma mandarins was regressed by the same method using an on-line instrument. The model composed of 5 factors calibrated from 689 samples showed the highest accuracy; R=0.83, Bias=0.024% and SEP=0.147% as a prediction result from 548 samples. It was possible to classify nondestructively the high acid fruits using near infrared (NIR) transmittance spectroscopy at about 20% error rate.