Abstract：Now transparent plastic wrap packaging gains great popularity because of its characteristics like convenience, economy and sanitation and be widely used in supermarket stores and daily life, which increases difficulties in detecting food and agricultural products. Thus a rapid nondestructive detecting method to detect agricultural products covered with transparent film is urgently needed. Chlorophyll is one of the vital factors which affect cucumber quality. The research mainly makes a thorough inquiry in the influence of food plastic wrap(material and number of plies) to Raman characteristic peaks of chlorophyll in cucumber. In the research, point-to-point Raman detecting system is used to gather Raman spectrum of cucumber covered with no plastic wrap and several layers of plastic wrap. Fluorescence background of Raman spectrum of cucumber is deducted with Savitzky-Golay five-spot smoothing and adaptive iterative least square method to investigate the influence of PE plastic wrap (1 to 6 layers) to Raman characteristic peaks of chlorophyll in agricultural products like cucumber. One detecting spot is detected three times to get its average value after covering a layer of plastic wrap. And nine detecting spots is got from a cucumber sample. The Raman spectrum of cucumber covered with plastic wraps is gathered and processed. Then the prediction model between reduction value of Raman characteristic peaks of chlorophyll (in the position of 1 158 and 1 528 cm-1) and layers of plastic wrap can be built. And then predictive effect of the model can be evaluated. With the increase of layers of plastic wrap, linear relationship is clear between layers of transparent package and intensity of Raman characteristic peaks of chlorophyll in cucumber. And as a reliable validation method, unary linear regression is used to judge the degree of correlation between the reduction value and layers of transparent package. It can be extracted that the reduction value of intensity of Raman characteristic peaks of chlorophyll in 1 158 and 1 528 cm-1 respectively are 81.4 and 103.1 which occupy 7.98% and 8.56% of intensity of Raman characteristic peaks of chlorophyll in cucumber without plastic wrap. In addition, the correlation index of verification result of several groups are all more than 0.95. And the correlation index of the results when verifying the change rulealso researches 0.94. From the research we know thatin the detection of chlorophyll in cucumber, rape and celery, the reduction value of intensity of Raman characteristic peaks of chlorophyll will also occupies 7.9%～8.6% and 8.1%～8.6% of the intensity value after covering a layer of plastic wraprespectively. And with Chlorophyll concentration of samples increasing, the detection effects become obvious. It is assumed that the scattering to exciting laser by plastic wrap is the reason that makes the intensity of Raman characteristic peaks of chlorophyll decrease with a linear relationship. The Raman characteristic peaks of plastic make no effect to the detection results. And it can be speculated the intensity of Raman characteristic peaks of chlorophyll also decreases with a linear relationship in detecting agricultural products covered with PVC or PVDC wrap. Similar results also will be got when detecting chlorophyll in other agricultural products. The research provides a new method in detecting the quality of fruits and vegetables with transparent package.
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