Non-destructive measurement of dry matter in mature 'Long-lab-lae' durian fruits using portable NIR spectrometer

Durian fruit 'Long-lab-lae' originated in AmphoeLub-lae, Uttaradit province, Thailand. It is a very popular cultivar among consumers. Mature durian fruits are very difficult to determine from the external appearance. For local market, the maturity of durian is identified by using sound from knocking on the peel of fruits. However, this method is subjective nature based on skill of durian growers and sellers. According to Thai Agricultural Standard (TAS) 3-2013 for durian, numbers of days from anthesis (harvesting period is about 105-110 days after anthesis) and dry matter (DM) are also used as parameters of maturity. This method is a destructive measurement method and time consuming (48 h). NIR technique is an interesting method which is non-destructive and has fast analysis. Therefore, this research aimed to study the determination of DM at upper fruit stem, lower fruit stem and the center of durian fruit by using portable NIR spectrometer over the wavelength range of 700-1,100 nm. The calibration equations were developed from correlation between NIR spectra and DM of aril using multiple linear regression analysis (MLR). From the results, the equation derived from the spectrum of the center of durian fruit provided the best DM of 'Long-lab-lae' prediction with the highest multiple correlation coefficient (R) at 0.78, the lowest standard error of prediction (SEP) at 1.67% and no bias.