Abstract: In order to explore the applicability of FT-NIR technique for rapid and non-destructive evaluation of apple quality in terms of titratable acidity (TA), pH and solid soluble content (SSC), NIR spectra in the wavelength range of 12000 to 8000 cm-1 were acquired from 40 samples including Fuji and Pink Lady apples during the storage period of 30 days. Universal mathematical models of TA, pH and SSC for both apple varieties were established using partial least square (PLS) regression. The results showed that a stable model of TA was developed in the wavelength range of 7502 to 4247 cm-1. The coefficient of correlation (R2) of calibration and root mean square error of estimation (RMSEE) were 0.9231 and 0.0263%, respectively. Meanwhile, the coefficient of correlation of prediction (R2) and the root mean square error of cross-validation (RMSECV) were 0.9071 and 0.0266%, respectively. In addition, a stable model of pH was achieved by PLS＋FD model based on NIR spectra in the wavelength range of 11995 to 4247 cm-1. The R2 of calibration and RMSEE were 0.9263 and 0.0700, respectively, and the R2 of prediction and RMSECV were 0.9113 and 0.0772, respectively. A good model of SSC was obtained by min-max normalization pretreatment in the wavelength range of 6102 to 5446 cm-1. The R2 of calibration and RMSEE were 0.9212 and 0.3570%, respectively, and the R2 of prediction and RMSECV were 0.9130 and 0.370%, respectively. The models of TA, pH and SSC were stable in evaluating the quality of Fuji and Pink Lady apples and could meet the requirements for rapid and non-destructive evaluation of fruit quality.

Key words: apple, near infrared spectra, non-destructive measurement, titratable acidity, pH, SSC