| Summary: | 碩士 === 國立臺灣大學 === 農業機械工程學系研究所 === 87 === Near infrared spectroscopy (NIR) and nuclear magnetic resonance (NMR), which are non-destructive and rapid inspection techniques, were used to determine the fat content in milk powder successfully in this study. In near infrared spectroscopy research, multiple linear regression (MLR) and partial least square regression (PLSR) were used to develop models for three kinds of spectrum treatments (original, first derivative and second derivative). The range of the spectra was from 700 to 2498nm with a wavelength increment of 2 nm. Seventy-nine milk powder samples were used for analysis in this study. In MLR analysis, the best equation of calibration was obtained by using first derivative spectra with five-wavelengths (1790nm，1314nm，2352nm，948nm and 742nm)； the results of calibration and prediction were rc=0.9993, SEC=0.263, rp = 0.998, SEP=0.425, RPD=19.040. In PLSR analysis, the best equation of calibration was also obtained by using first derivation spectra (700~2498nm, factors = 9)； the results of calibration and prediction were rc = 0.9999, SEC = 0.066, rp = 0.998, SEP = 0.455, RPD = 17.785. Since all the wavelengths in the specified range (700~2498nm) were included in PLSR analysis, the results of PLSR analysis in original, first derivative and second derivative spectra were all better compared to MLR analysis. Appropriate spectrum treatments, such as smoothing and gap techniques could eliminate the spectrum error effectively, and give better accuracy in calibration and prediction.
In nuclear magnetic resonance research, since the major source of hydrogen nuclei in the milk powder is associated with fat, the response of hydrogen nuclei were measured by Free Induction Decay (FID) and Spin Echo. Regarding the determination of fat content in milk powder, the performance of FID was better than that of Spin Echo. The FID results of calibration and prediction were rc=0.9902, SEC=1.027, rp=0.995, SEP=0.820, RPD=9.873. Since milk powder at low fat level (below 4%) adsorbs moisture more easily, thus error was introduced in both FID and Spin Echo measurements due to hydrogen nuclei in the moisture.
Non-destructive and rapid measurement was the common advantage for both near infrared spectroscopy and nuclear magnetic resonance methods. However, regarding the accuracy, near infrared spectroscopy is better than nuclear magnetic resonance, because near infrared spectroscopy uses multi-variable statistics (MLR and PLSR) and the wavelengths could be such selected that other constituents in milk powder would not have influence. On the other hand, nuclear magnetic resonance only depends on the signal from the hydrogen nuclei''s resonance and may be affected by water, which is the major constituent in the food.
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