應用螢光檢測稻米新鮮度之研究

Abstract

本研究的目的是以螢光光譜儀探討貯藏期間稻米品質的變化情形，並自製螢光感測裝置進行稻米新鮮度檢測試驗。本研究之樣本為收集自台灣北中南不同農業改良場之稻穀。實驗用稻穀經過碾米加工為白米之後貯藏於10℃、25℃與35℃之恆溫箱中，進行白米老化處理。本研究使用Jasco FP-6300螢光光譜儀以波長365nm激發光進行光譜掃描，掃描範圍之波長介於400nm到600nm，並利用PCA分析獲得特徵波長為450nm。本研究使用BTB-MR多粒米試管法與單粒米新鮮度檢測器來量測團粒米與單粒米之酸鹼度。螢光光譜實驗結果指出團粒樣本因為外形所產生的螢光強度之變異性高於粉末樣本。含水率高的樣本米螢光強度較弱。當舊米混入乳白米與新米混入腹白米之混入比率高於20%時，才會影響新舊米判別結果。掃描不同碾白米率之白米樣本之結果指出精米次數愈多其螢光強度較高。白度介於34 ~ 40之間（市售白米白度範圍）的白米樣本螢光強度不受白度影響。白米貯藏溫度愈高，其貯藏白米之螢光強度亦愈高。利用PCA針對不同溫度下貯藏1個月之螢光光譜進行分析可得到第一主成分具有95%解釋變數量，可辨別出新鮮米與老化米之螢光差異。MLR分析結果指出螢光強度會受到貯藏樣本含水率、產區與品種的影響。白米螢光強度衰減量和酸鹼值之間具有正相關性，其迴歸決定係數為0.57，迴歸結果顯著（p < 0.01）。本研究所開發之螢光感測裝置針對單粒白米樣本進行螢光偵測之實驗結果顯示單粒白米螢光強度平均值與樣本團粒米酸鹼值之間呈現負相關性，其決定係數為0.22，迴歸結果顯著（p < 0.05）。

The objective of this study was to apply fluorescence method for detection of the rice freshness by using spectrofluorometer and fluorescent sensing system. The paddy samples of different crop years were obtained from local district agricultural research and extension stations and farmers' associations. The paddy was processed by laboratory huller and the milled white rice was stored in incubators at temperatures of 10℃, 25℃ and 35℃. The BTB-MR method and a commercial rice grain freshness tester were used to evaluate the pH value of group-kernel rice sample and single kernel rice sample respectively. The fluorescence responses of white rice samples were measured by Jasco FP-6300 Spectrofluorometer. The rice fluorescence spectra excited by a light source at 365 nm were obtained in the range between wavelength 400 nm and 600 nm. The results show that the variation of fluorescence intensity of different crop year rice flour sample is smaller than those of group-kernel sample. The rice fluorescence intensity is low at high moisture content. The rice fluorescence intensity is not affected by chalky kernel if the ratio of chalky kernel mixed in normal rice is less than 20%. The rice fluorescence intensity is not influenced by rice whiteness at the range between 34 and 40. The fluorescence intensity of stored rice at high temperature is higher than those stored at low temperature. The coefficient of determination (R2) of regression of fluorescence intensity attenuation against pH value was 0.57 for group-kernel rice. The fluorescence sensing system developed in this study is consisted of a high power UV LED and a digital color light sensor. The coefficient of determination (R2) of regression of fluorescence intensity against pH value was 0.22 for single kernel rice.