Quantitative and qualitative measurement of pear firmness based on near infrared spectroscopy and chemometrics

Firmness is one of the most important characteristics to estimate fruit maturity and quality. This research was to study the potential of near-infrared (NIR) diffuse reflectance spectroscopy as a nondestructive way for pear firmness evaluation of three varieties (‘Cuiguan’, ‘Xueqing’ and ‘Xizilv’), both quantitatively and qualitatively. NIR models were established using partial least square (PLS) methods in the spectral range of 800 to 2500 nm. For quantitative analysis, the correlation coefficient r increased with more varieties involved in the model. Best results were obtained in the model for all three varieties: rcal was 0.934, root mean square error of calibration (RMSEC) and root mean square error of prediction (RMSEP) were 2.06 N and 3.14 N, respectively. For qualitative analysis, the overall accuracies of discriminant PLS models for classifying pears into three firmness levels: low, medium and high firmness level were not so good, percentage of samples correctly classified ranged from 70.63% to 81.25% for calibration and from 56.25% to 74.38% for validation. The results of this study indicate that NIR spectroscopy together with PLS chemometrics method is feasible for quantitative analysis of pear firmness, however, the classification accuracy were too low to put into practical application.