Empirical reduction of rind effect on rind and flesh absorbance for evaluation of durian maturity using near infrared spectroscopy

Durian possesses a thick-spiky rind that limits light penetration into the flesh and makes models based on rind and flesh absorbance measurements ineffective for prediction of flesh dry matter content (DMC). An empirical technique to adjust the rind and flesh absorbance to be closer to that of the flesh by reducing the effect of rind absorbance was developed. The difference in absorbance obtained by subtracting the flesh absorbance from that of the rind and flesh absorbance at each wavelength was partially related with the dry matter content of the flesh depending on wavelength. A regression equation partial least squares regression model (PLSR) for each wavelength was developed to relate the difference spectra with the DMC. The dry matter content was used to compute the difference absorbance at each wavelength which was subtracted from the rind and flesh absorbance to create the adjusted rind and flesh absorbance. The PLSR models were compared based on the flesh, rind and flesh and adjusted rind and flesh absorbance for prediction of the DMC. The adjusted rind and flesh model performed better than the original rind and flesh model. The results showed the advantage of the empirical technique in reducing the effect of rind absorbance on that of the rind and flesh absorbance.