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Study on the compositions of the peel essential oil of Kao Nam Pueng pomeloes at different harvesting date and storage duration using near infrared spectroscopic technique Student Miss Jittra Duangchang Student ID. 50061202 Degree Master of Engineering Program Agricultural Engineering Year 2009 Thesis Advisor Assoc. Prof. Dr. Panmanas Sirisomboon Thesis Advisor (Co.) Dr. Sumaporn Kasemsamran Thesis Title

ABSTRACT The near infrared spectroscopy (NIRS) appears as a prominent technique for fruit quality assessment. The objective of this study was to evaluate the use of NIR short wavelength 600-1,100 nm to predict composition of the peel essential oil of pomeloes (Citrus maxima (J. Burm.) Merr. cv. Kao Num Peung) at different harvesting date at 190, 200, 210 and 220 days after blooming and storage duration at 0, 15, 30, 45, 60, 75, 90, 105 and 120 days (10째C and 70% relative humidity). The composition of the oil was analyzed by Gas Chromatography-Mass Spectrometry (GC-MS) after it was extracted by a cold-press method. To establish the relationship between NIR spectral measurements and the major component peel essential oils (e.g. limonene, the highest composition in %w/w, beta-phellandrene and nootkatone). The partial least square regression (PLSR) was used. Before calibration, a principal component analysis (PCA) technique was applied to check outliers. NIR models were developed based on PLSR using raw spectra, and full multiplicative scatter correction (MSC) or second derivative (SavizkyGolay algorithm, second order polynomial) pre-processing spectra. Among the component of oil at different harvesting date and storage duration, beta-phellandrene with the raw spectra and nootkatone with full MSC had the highest correlation coefficient between predicting and reference values (r) of 0.89 and 0.82, standard error of prediction (SEP) of 0.39 and 0.11 %w/w and bias of 0.39 and 0.01 %w/w, respectively.