拉曼高光谱成像系统中光在奶粉层的穿透深度研究

摘要

The use of Raman hyperspectral imaging technique can obtain not only the spatial distribution information of samples, but also the spectral information of each pixel on the image.It has been applied in food safety testing for its abundant informa-tion.This study was aimed at quantitatively analyzing of light penetration depth through milk powder in Raman hyperspectral imaging,and exploring the influences of system parameters and types of milk powders.The attenuation of Raman signal in milk powder layer was also discussed.Milk powder layers with five different thicknesses ranging from 0.8 ~4.0 mm were prepared on the top of a melamine layer with 5 mm thick.The penetration depth of light was evaluated by detecting the characteristic peaks of melamine.The results showed that the Raman characteristic signal was enhanced with a bigger laser intensity and lon-ger exposure time at the same thickness of milk powder layer.When the laser intensity was not less than 2 W and the exposure time was not less than 500 ms,the light penetration depth in whole milk powder was 4 mm at least.The peak intensities of mel-amine decayed in exponent with the thickness of milk powder layer increasing from 0.8 to 4.0 mm.The light penetration depths in whole milk powder,low fat milk powder and skim milk powder were all 4 mm at least when the laser intensity was 8 W and the exposure time was 1000 ms.The Raman signal through the skim milk powder layer was weaker than those through the whole milk powder layer and the low fat milk powder layer at the same thickness.Therefore,the light penetration depth of the skim milk powder layer was less than those of the whole milk powder layer and the low fat milk powder layer.The results pro-vide a useful reference for the pretreatment of milk powder in safety and quality detection by Raman hyperspectral imaging.%拉曼高光谱成像技术不仅可以获取样本的空间分布信息,图像上每个像素点还包括了完整的光谱信息,因其信息量丰富的特点已在食品安全检测方面得到了应用.本研究探索拉曼高光谱成像系统中光在奶粉层中的穿透深度,以及采集参数和奶粉类型对穿透深度的影响.实验选取均匀奶粉层样品放置于厚度为5 mm的三聚氰胺样本之上,检测奶粉层厚度为0.8~4.0 mm时的三聚氰胺特征峰强度,以此评估光在奶粉层中的穿透性和信号衰减情况.结果显示当奶粉层厚度一定时,随着激光功率变大,拉曼特征峰值随之增加,此外更长的曝光时间也可以使拉曼信号得到增强.在激光功率不小于2 W且曝光时间不小于500 ms时,光在全脂奶粉层的穿透深度可达4 mm.奶粉层厚度在0.8~4.0 mm范围内,穿透奶粉层的拉曼信号随着奶粉层厚度增加呈指数式衰减.在激光功率为8 W、曝光时间为1000 ms的条件下,光在全脂、低脂和脱脂奶粉层的穿透深度均达到了4 mm.在相同测量厚度下,通过脱脂奶粉层接收的拉曼信号弱于通过全脂和低脂奶粉层接收的拉曼信号强度.研究结果为拉曼高光谱检测中奶粉样品的前处理提供了有益参考.