基于拉曼光谱技术的茶树叶片中类胡萝卜素含量的无损快速检测

叶片中类胡萝卜素是植被环境胁迫、光合能力和植被发育阶段的指示器。基于叶片的原位拉曼光谱响应特性对龙井43叶片的类胡萝卜素含量进行了研究，建立了两者之间的定量模型。本文共对315个龙井43叶片样本进行了拉曼光谱采集和分光光度检测。为排除检测过程中受噪声、基线漂移等因素的干扰，运用和比较了五种光谱数据预处理方法提取原始拉曼光谱中与茶叶中类胡萝卜素含量有关的有效信息。基于预处理后的数据建立了偏最小二乘(PLS)回归模型，拉曼光谱与类胡萝卜素含量的建模集和预测集的相关系数(r)分别为0.817和0.786。为进一步研究类胡萝卜素的拉曼光谱响应机理，本文采用连续投影算法(SPA)优选了17个拉曼特征波数建立相应的特征波数模型，模型的建模集和预测集的相关系数(r)分别为0.808和0.777。根据已建立的模型，探究了茶树四个不同叶位的叶片类胡萝卜素含量的变化。发现茶树叶片随着叶龄的增加，类胡萝卜素浓度呈先增后减的趋势。以第2位叶的类胡萝卜素含量最高。进一步验证了模型的可行性以及探索了将该模型应用于茶树叶片树龄和叶位探测的可能性。采用拉曼光谱技术可以实现茶树叶片中类胡萝卜素含量的原位、无损、定量检测。

Determination of Carotenoids Contents in Tea Leaves Based on Raman Spectroscopy

Carotenoids are one of the most important components to reflect the physiological state of plant,such as environmental stress,photosynthesis as well as growing state.An effective and nondestructive detection method for the contents of carotenoids in Longjing-43 leaves was established based on Raman spectroscopy in this research.A total of 315 tea sample were used for the spectral collection and spectrophotometry determination.Quantitative models were established to predict the content of carote-noids.Firstly,in order to eliminate the interference from noise,5 preprocessing methods were applied before calibration stage. Partial least square regression (PLS)was applied as calibration method to establish the Raman spectra quantitative model of the carotenoids in Longjing-43's leaves.The results of PLS models based on these methods were used to evaluate the performances of these pretreatments.The best performance was achieved with wavelet transformed spectra,obtaining correlation coefficient (r)value of 0.817 and 0.786 for validation and prediction,respectively.Secondly,to further explore the Raman spectral re-sponse properties of carotenoids in tea,Successive Projections Algorithm (SPA)was applied to extract the characteristic wave-numbers for carotenoids in tea.Then,the selected 17 wavenumbers were used to build PLS model and good results are reached, obtaining R v of 0.808 and R p of 0.777.Based on the PLS model,this article studied the carotenoids content of tea leaves in 4 dif-ferent growth periods.Results indicated that the content of carotenoids was firstly increased then decreased.The above results revealed that it was feasible to apply Raman spectroscopy for the determination of the carotenoids content in Longjing-43 leaves.