Study on the Homogeneity of Tea Powder by Infrared Spectral Similarity Evaluation
WU Xian-xue1, 2, LI Ming2, LI Liang-xing2, DENG Xiu-juan1, MA Xian-ying3, LI Ya-li1, ZHOU Hong-jie1*
1. College of Longrun Pu-erh Tea, Yunnan Agricultural University, Kunming 650201, China
2. College of Chemistry, Biology and Environment, Yuxi Normal University, Yuxi 653100, China
3. Kunming YiwuHongqing Tea Industry Co. Ltd., Kunming 650000, China
Abstract：Sufficient homogenization pretreatment of heterogeneous solid samples is the prerequisite for obtaining reliable analysis results, which is particularly important for infrared spectrum (IR, KBr) analysis with just about 1 mg needed in a single test. Through the multi-angle infrared spectral similarity evaluation of tea samples including different tea types and particle sizes, the relationship between particle size and the degree of homogenization was revealed and used to guide the tea pulverization to ensure that the followed IR spectra could accurately reflect the chemical composition information of tea powder. Three kinds of Yunnan tea production, including Raw Pu-erh tea (Raw-PE), DianHong (YNBT), Riped Pu-erh tea (Riped-PE), were selected to be prepared into four tea samples with different particle sizes respectively. The IR (KBr) and attenuated total reflection method (ATR-IR) spectra of the prepared tea powder were collected 5 times in parallel. The similarity evaluations by Cosine(i) of the infrared spectra obtained were carried out to investigate the influence of pulverized particle size, spectral collection method, tea type and other factors on the spectral correlation coefficient (r). The spectral similarity evaluation results based on different tea types showed that the r value from Raw-PE was significantly higher than that of Riped-PE and YNDH. The r values from the tea powder of YNDH with different meshes fluctuated by up to 18%. The results from different spectral test mode showed that the r values based on ATR spectra were more concentrated, while the results based on KBr spectra were dispersed. The results based on tea powder with different particle sizes showed that the smaller the particle size was, the higher the r value was. Moreover, the r value from tea samples with more than 250 mesh was usually a good result over 0.999. The results show that the r values based on ATR spectra showed good reproducibility and the results from KBr spectra displayed stronger difference recognition ability. The latter is more suitable for the comparative analysis of the composition differences between highly similar samples. The homogeneity of tea powder is closely related to the pulverized particle size and related to the substrate of the tea sample itself. Whatever it can be improved by reducing the pulverized particle size. Generally, the particle size of tea powder less than 60 mesh is difficult to meet the infrared spectroscopy analysis’s homogeneity requirements. An r value over 0.995 based on IR spectra (KBr) of tea powder above 120 mesh could be given, but for the ATR spectra, the tea sample needs to be shredded by more than 250 mesh to give the same evaluation result.
Key words：Tea; Particle size; Infrared spectrum; Coefficient of correlation; Homogeneity
伍贤学，李 明，李亮星，邓秀娟，马宪英，李亚莉，周红杰. 茶粉均质性的红外光谱相似度评价研究[J]. 光谱学与光谱分析, 2021, 41(05): 1417-1423.
WU Xian-xue, LI Ming, LI Liang-xing, DENG Xiu-juan, MA Xian-ying, LI Ya-li, ZHOU Hong-jie. Study on the Homogeneity of Tea Powder by Infrared Spectral Similarity Evaluation. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2021, 41(05): 1417-1423.
[1] SUN Su-qin, ZHOU Qun, CHEN Jian-bo(孙素琴, 周 群, 陈建波). ATC 009 Infrared Spectral Analysis Technology(ATC 009 红外光谱分析技术). Beijing: Standard Press of China, China Quality and Standards Publishing & Media Co. Ltd.(北京: 中国标准出版社，中国质检出版社), 2013.
[2] Sun Suqin, Chen Jianbo, Zhou Qun, et al. Planta Medica，2010, 76: 1987.
[3] SUN Su-qin, ZHOU Qun, CHEN Jian-bo(孙素琴, 周 群, 陈建波). Infrared Spectroscopy for Complex Mixtures: Application in Food and Traditional Chinese Medicine(复杂混合物的红外光谱学：在食品和中药分析中的应用). Beijing: Chemical Industry Press(北京: 化学工业出版社), 2011.
[4] WANG Qiu-quan, ZHANG Xin-rong, ZHUANG Qian-kun(王秋泉, 张新荣, 庄乾坤). Chinese Journal of Analytical Chemsitry(分析化学), 2005, 33(3): 2651.
[5] Wu Xiaohong, Zhu Jin, Wu Bin, et al. Computers and Electronics in Agriculture, 2018, 147(4): 64.
[6] Cai Jianxiong, Wang Yuanfeng, Xi Xionggang, et al. International Journal of Biological Macromolecules, 2015, 78(7)：439.
[7] Xu Lu，Deng Dehua, Cai Chenbo. Journal of Agricultural and Food Chemistry，2011, 59(19)：10461.
[8] WU Quan-jin, DONG Qing-hua, SUN Wei-jiang(吴全金, 董青华, 孙威江). Journal of Tea Science(茶叶科学), 2014, 34(1): 63.
[9] Wu Xianxue, Xu Changhua, Li Ming, et al. Journal of Molecular Structure, 2014, 1069(7): 133.
[10] MA Jing, WU Xian-xue, TAI Xi, et al(马 晶, 伍贤学, 台 希，等). Spectroscopy and Spectral Analysis(光谱学与光谱分析), 2014, 34(10): 2833.
