Application of FT-NIR spectroscopy to the measurement of fruit firmness of "Fuji" apples

This paper indicates the possibility of using near infrared (NIR) spectroscopy as a rapid method of predicting quantitatively fruit firmness of apple. A hundred "Fuji" apples were used as the study target in the experiment. A partial least square (PLS) algorithm was used to perform the calibration. To decide upon the number of PLS factors included in the PLS model, the model was chosen according to the lowest root mean square error of cross-validation (RMSECV) in training. The correlation coefficient R between the NIR predicted and the reference results for the test set were used as an evaluation parameter for the models. The best experimental results were obtained as follows: the PLS calibration model in fruit firmness determination was achieved with 12 PLS factors under MSC preprocessing method. The correlation coefficient between the NIR spectroscopy prediction results and reference measurement result was R = 0.74893. The study demonstrates that NIR spectroscopy technology with multivariate calibration analysis could be successfully applied as a rapid method to predict fruit firmness of apples.