Study on Interference from the Peel to Predict Apple Firmness by Near Infrared Spectroscopy

摘要

The near infrared spectra of apples with peel and peeled were collected by FT-NIR spectrometer. In order to reduce the influence on the model of apple firmness, the useful wavelengths were selected and the outlier samples were deleted. To analyze the difference between the models with peel and peeled, the calibration and prediction samples were divided for ten times and were used to build the ten different firmness models for both peel and peeled. In the models of peeled apple, the correlation coefficient (r) and the relative standard deviation of prediction (RSDp) were all around 0.84 and 12.6%, respectively, indicating that the peeled models were stable. For the peel model, r and RSDp were 0.74-0.86 and 13.5-17.7%, respectively, suggesting that the stability of the peel model was not very good. The t-test for ten groups of RSDp showed that the difference was significant between the peel and peeled models (P<0.0001). In addition, the results from Magness-Taylor puncture test only represented the firmness of flesh. However, the near infrared diffuse reflectance spectra of peel apples contained the information of pectin substance from both peel and flesh. The pectin substance content was closely related to the apple's firmness. Therefore, the spectra and reference firmness data were not corresponded and the absorbance spectra of peel became the interference for the near infrared spectra of peel apple. It was obtained the reason for the prediction ability of peel apple model for the firmness reducing.