TIME-SERIES ANALYSIS OF POSTHARVEST RIPEN ING OF PLUM FRUIT BY NEAR-INFRARED SPECTROSCOPY

Time series analysis was performed on ripening process of picked plum 'OoishiWase' fruit by near infrared (NIR) spectroscopy. Accompanying r ipening after picking, base lines of NIR spectra of intact fruits were shifted up remarkably. It was suggested that these shift up of spectr a was caused by an increase of transmittance of NIR ray into the intac t fruit which was attributable to loosening of middle lamella in tissu e structure. On the other hand, an absorption peak at vicinity of 1 41 0 nm became larger regardless of shift up of NIR spectrum. Therefore, 1 410 nm was considered to be a key wavelength to evaluate ripening af ter picking of plum fruit. Ripening of plum fruit affected the measure ment of soluble solid (degrees Brix), acidity (%) and hardness (kg) va lues of the fruit by NIR spectroscopy and increased the standard error of prediction (SEP) of measurement by NIR spectroscopy to analyze fru its with different ripeness after picking. By using a calibration curv e based on samples with different ripeness, accurate measurement by NI R spectroscopy was successfully performed. It was considered that the principle of measurement of hardness in plum fruit by NIR spectroscopy was based both on shift up of base line of NIR spectrum and on change s of chemical components in AIS.