应用FLS920P型稳态和时间分辨荧光光谱仪, 对三种品牌不同脂肪含量的纯牛奶和鲜奶(共9种)进行了荧光光谱的测量。 9种牛奶样品的三维荧光光谱显示, 牛奶的荧光峰值波长为349 nm左右, 半高宽为66 nm左右, 最佳激发波长为291 nm左右, 平均寿命为4.6 ns左右, 实验表明9种牛奶的荧光光谱除荧光强度外基本一致。 实验测得酪蛋白溶液的荧光峰值波长为344 nm, 半高宽为66 nm, 最佳激发波长为295 nm, 荧光寿命为4.1 ns。 酪蛋白的荧光峰值波长和荧光寿命与牛奶基本一致, 对比牛奶中其他荧光物质后, 推断牛奶的主要荧光物质为酪蛋白。 进一步探究9种牛奶荧光强度的差别, 对比9种牛奶最佳激发波长下的荧光发射光谱, 相同品牌的全脂牛奶荧光强度明显低于脱脂牛奶。 对比全脂牛奶、 脱脂牛奶和离心处理的全脂牛奶归一化后的荧光光谱, 离心后的全脂牛奶荧光强度介于全脂和脱脂之间, 离心使得脂肪减少, 散射降低, 从而导致荧光强度的增强。 牛奶的荧光发射全谱显示全脂牛奶的瑞利散射强度明显高于脱脂牛奶, 全脂牛奶的脂肪含量高, 散射强, 激发光入射全脂牛奶后更多地被散射, 导致全脂牛奶的瑞利散射强度高于脱脂牛奶。 光透过率曲线显示全脂牛奶的透过率都低于脱脂牛奶, 入射光通过全脂牛奶时, 除了一部分被酪蛋白吸收以外, 还有一部分因脂肪的散射而损失, 透过率减小, 使得全脂牛奶的透过率都低于脱脂牛奶。 使用荧光光谱技术在不进行预处理的情况下对牛奶进行检测, 确定了牛奶的主要荧光物质, 并对全脂牛奶和脱脂牛奶荧光强度存在差别的原因进行了解释。

Three-dimensional fluorescence spectra of milk of three brands (9 types) were measured by FLS920P fluorescence spectrometer, including pure milk and fresh milk, whole milk and skim milk. The fluorescence peak wavelength of milk is about 349 nm, the full width at half maximum (FWHM) is about 66 nm, the optimal excitation wavelength is about 291 nm, and the average lifetime is about 4.6 ns, the results show that the fluorescence spectrum of 9 kinds of milk is basically the same except the fluorescence intensity. The fluorescence peak wavelength of the casein solution is 344 nm, the FWHM are 66 nm, the optimal excitation wavelength is 295 nm, and the fluorescence lifetime is 4.1 ns. The fluorescence peak wavelength and fluorescence lifetime of casein are similar to that of milk. After comparing other fluorescent substances in milk, it is inferred that casein is the main fluorescent substance in milk. In order to explore the differences in fluorescence intensity of 9 types of milk, the fluorescence emission spectra under the optimal excitation wavelength of 9 types of milk are compared. The fluorescence intensity of the whole milk of the same brand is significantly lower than that of skim milk. By comparing the normalization fluorescence spectra of whole milk, skim milk and centrifuged whole milk, the fluorescence intensity of centrifuged whole milk is between that of whole milk and that of skim milk. Centrifugation of milk results in less fat and less scattering and increase fluorescence intensity. The full fluorescence emission spectrum of milk shows that the Rayleigh scattering intensity of whole milk is significantly higher than that of skim milk, whole milk has a high-fat content and strong scattering, the excitation light is scattered more after it enters the whole milk, resulting in the Rayleigh scattering intensity of the whole milk being higher than that of skim milk. The light transmittance curve shows that the transmittance of whole milk is lower than that of skimmed milk, when incident light passes through whole milk, in addition to the part of it being absorbed by casein, part of it is lost due to fat scattering, and the transmittance is reduced, so that thetransmittance of whole milk is lower than that of skim milk. In this paper, the main fluorescent substances of milk are determined by using fluorescence spectroscopy without pretreatment. Moreover, the reason for the difference in fluorescence intensity between whole milk and skim milk is explained.