中国天然茶叶硒的含量特征及其质量标准探讨

Characteristics of Organic Selenium Contents in Natural Tea of China and Discussion on the Quality Standard

摘要: [目的]通过建立我国天然茶叶有机硒数据库，分析茶叶总硒含量、有机硒含量及其比例特征，探讨我国天然茶叶硒的质量划分标准。[方法]本研究从中、英文数据库文献中共遴选出茶叶/茶汤有机硒数据记录65/15条，重点分析了不同种类、产地、硒提取测定方式天然茶叶有机硒的含量与比例及其与总硒含量之间的关系，同时，结合我国有关硒质量标准，初步提出了我国天然茶叶和天然有机富硒茶的质量标准。[结果]自2013年来关于茶叶特别是绿茶有机硒的研究相对较多。总体上，我国茶叶有机硒的含量为0.74 ± 0.94 mg kg⁻¹ (0.03~5.54 mg kg⁻¹, n = 65)，约占总硒(0.85 ± 1.07 mg kg⁻¹, n = 65)的87.6%。相似地，茶汤中有机硒均值为0.43 ± 0.27 μg/100ml (0.15~0.99 μg/100ml, n = 15)，约占总硒(0.40 ± 0.28 μg/100ml, n = 15)的91.2%。虽然绿茶有机硒含量较高，但是，各类茶叶之间并无明显差异(P > 0.05)。除湖北恩施茶叶中的有机硒含量及其比例相对较高外，其它各产地茶叶之间并无明显差异(P > 0.05)。此外，硒提取测定方式(直接法或间接法)均可能对茶叶有机硒含量有一定的低估。茶叶或茶汤中的有机硒含量与总硒含量具有显著正相关关系(P < 0.05)，而茶叶有机硒的比例随总硒含量升高则呈先升高而后逐步趋于稳定的趋势。考虑到上述结果及我国茶叶硒有关质量标准，将我国天然有机硒茶分为5级：V (<0.20 mg kg⁻¹，以总硒计，下同)、IV (0.20~0.40 mg kg⁻¹)、III (0.40~0.60 mg kg⁻¹)、II (0.60~1.00 mg kg⁻¹)和I (≥1.00 mg kg⁻¹)，同时，茶叶或茶汤有机硒比例 ≥ 70%。由于天然富硒茶叶或茶汤总硒含量、有机硒含量及其比例均高于普通茶叶(P < 0.05)，本研究参照有关富硒茶质量标准又将天然富硒有机茶分为3级，即III级(0.40~0.60 mg kg⁻¹)、II 级(0.60~1.00 mg kg⁻¹)和I级(1.00~4.00 mg kg⁻¹)，且有机硒的比例不低于80%。[结论]以茶叶总硒含量为基础并结合茶叶或茶汤有机硒比例进行分级的办法易于操作且结果可靠，它不仅有利于我国天然富硒茶叶的良性发展和市场监管，也有利于保证人体的健康和安全。

Abstract: [Objective] In order to discuss the classification of quality standard of selenium (Se) in tea natu-rally produced in China, contents of the total Se, the organic Se and its percents were analyzed based on the bibliographic database. [Method] This study totally selected 65/15 pieces of organic Se data records for tea/tea soup from the database, analyzed contents and percents of organic Se in natural tea grouped by types, areas and the Se extracted and measured methods, and their relationships to the total Se, and primarily put forward the quality standards of the natural tea and Se-enriched tea. [Result] More studies had been conducted upon the organic Se in tea especially the green tea since 2013. In general, content of the organic Se in tea was 0.74 ± 0.94 mg kg⁻¹ (0.03~5.54 mg kg⁻¹, n = 65), accounting for 87.6% of the total Se (0.85 ± 1.07 mg kg⁻¹, n = 65). Similarly, the average of the organic Se in tea soup was 0.43 ± 0.27 μg/100ml (0.15~0.99 μg/100ml, n = 15), which approximately accounted for 91.2% of the total amount (0.40 ± 0.28 μg/100ml, n = 15). Though the organic Se content was relatively higher in green tea, its percent was not so, and no significant differences were found between different types of tea (P > 0.05). The contents of organic Se and their percents in tea produced in Enshi, Hubei were much higher, but no significant differences were observed among other areas (P > 0.05). The Se extracted and measured methods, direct or indirect, would probably underestimate the contents of organic Se in tea to a certain extent. A positive correlation existed between the organic Se and total Se contents in tea or tea soup (P < 0.05), nevertheless, the organic Se percents firstly increased with the total Se and then tended to be stable gradually. Five grades, namely, V (<0.20 mg kg⁻¹), IV (0.20~0.40 mg kg⁻¹), III (0.40~0.60 mg kg⁻¹), II (0.60~1.00 mg kg⁻¹) and I (≥1.00 mg kg⁻¹), with a percent of ≥70% for organic Se in tea or soup, were validated according to the total Se contents in natural tea based on our results and some issued quality standards of tea in China. As the contents of total Se, organic Se and its percent in the natural Se-enriched samples were higher than those in the ordinary samples (P < 0.05), this study further divided the natural Se-enriched tea into 3 grades, namely III (0.40~0.60 mg kg⁻¹), II (0.60~1.00 mg kg⁻¹) and I (1.00~4.00 mg kg⁻¹), with a percent of not less than 80% for organic Se. [Conclusion] The established grading method based on the total Se contents combined with the organic percents in tea or tea soup is easily operated and the results are reliable, which will not only be benefit to better development and market supervision of natural tea, but also assure the health and safety of human body.