茶粉均质性的红外光谱相似度评价研究

非均质固态样品的充分均质化前处理是取得可靠分析结果的前提，这对于单次测试取样量约1 mg的红外光谱（KBr）分析而言尤为重要。通过对不同茶类、粒径茶粉的多角度红外光谱相似度评价，揭示茶粉粒径与均质化程度的关系并用于指导茶叶的均质化粉碎，确保采集的红外光谱能准确反映茶粉的化学组成信息。选取普洱生茶（Raw-PE）、普洱熟茶（Riped-PE）、滇红茶（YNBT）三类茶制成的A，B，C和D四种不同粒径茶样，以透射法（KBr）及衰减全反射法（ATR）分别平行五次采集茶样的红外光谱（FTIR），利用夹角余弦值（r）对所得红外光谱开展相似度评价研究，考察粉碎粒径、光谱采集方式、茶叶类别等因素对r值的影响。不同茶类光谱相似度评价结果显示，基于普洱生茶所得的r值明显高于普洱熟茶和滇红茶，不同粒径滇红茶的r值波动幅度高达18%。不同光谱采集方式评价结果显示，基于ATR谱所得的r值更为集中，而基于KBr谱的结果则更分散。不同粒径茶粉评价结果显示，粒径越小，所得的r值越高，250目以上的茶样对应的r值通常大于0.999。ATR谱具有更好的重现性，而KBr谱则具有更强的差异识别能力，后者更适于组成高度相似的样本间的差异分析。茶粉的均质性不仅与粉碎粒径密切相关，还可能与茶样本身的基质相关，但均可以通过缩小粉碎粒径提高均质性。一般而言，60目以下的粉碎粒径难以满足红外光谱分析方法对茶叶均质性的要求。120目以上的茶粉粒径可让平行KBr谱间r＞0.995，但若基于ATR谱进行分析，最好将茶样粉碎至250目以上。

Study on the Homogeneity of Tea Powder by Infrared Spectral Similarity Evaluation

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 agood 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.