| Food sciences |
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| Quality evaluation and price discrimination of jasmine-scented tea |
| Zhang Jun, Gong Shuying, Tang Desong, Zhang Yingbin, Chen Meili |
| (1. Tea Research Institute, Zhejiang University, Hangzhou 310058, China; 2. Hangzhou Tea Research Institute, All China Federation of Supply and Marketing Cooperatives, Hangzhou 310016, China; 3. Tea Research Institute, Chinese Academy of Agricultural Sciences, Hangzhou 310008, China; 4. Research Institute of Forestry Science of Liuzhou, Liuzhou 545300, Guangxi, China) |
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Abstract Jasmine-scented tea is a mainstream product of scented tea, which is very popular in Chinese northern tea market. Until nowadays, tea quality evaluation still mainly depends on the sensory assessment, which is potentially affected by individual preference and physical and mental conditions of tasters. It is necessary to search for objective and quantifiable methods for quality evaluation and discrimination. Factor analysis and discriminant analysis are statistical methods widely used in natural science, medicine, economics, sociology and many other fields. There have been some researches about application of these two methods in evaluating tea quality or discriminating the locality, variety and grade of tea. In this paper, factor analysis and discriminant analysis were used for quality evaluation and price discrimination of jasmine-scented tea. Compared with the sensory evaluation, extraction is an usual method to get tea liquor for tea quality research, which is considered to be a time and energy consuming method. In the present paper, brewing method for sensory analysis was introduced in the price discrimination study, aiming at simplifying the method for preparing tea liquor.
One hundred and twelve samples of jasmine-scented tea with price ranging from 28 to 3 000 Yuan RMB per kilogram were purchased from tea market or supplied by tea companies of Wuyutai, Zhangyiyuan, Yuanchanghou and Jinghua. The tea liquor was prepared by brewing and extracting methods respectively. Brewing method for sensory analysis, 3.0 g jasmine-scented tea was infused with 150 mL freshly boiled water for 5 min and then filtered while hot. The concentrations (mg/mL) of 13 main chemical components were measured. Total extracting method, the tea liquor was prepared according to the method of China national standard GB/T 8312—2002. Extracting 3.0 g jasmine-scented tea powder with 450 mL boiled water for 45 min in boiling water bath and shaking it in every 10 min. The liquor was pressure filtered while hot and diluted with distilled water to 500 mL when cooled. The contents (%) of 13 main chemical components were measured. Concentrations and contents of polyphenols, amino acids and water soluble extract were determined by the methods of China national standard GB/T 8313—2002, GB/T 8314—2002 and GB/T 8305—1987, respectively. While concentrations and contents of caffeine, gallic acid (GA) and the composition of catechins including gallocatechin (GC), epigallocatechin (EGC), catechin (C), epicatechin (EC), epigallocatechin gallate (EGCG), gallocatechin gallate (GCG), epicatechin gallate (ECG), catechin gallate (CG) were determined by high performance liquid chromatography (HPLC). Factor analysis and discriminant analysis were carried out based on the 32 variables using SPSS 16.0 for Windows.
The models for quality evaluation and price discrimination of jasmine-scented tea samples were established by factor and discriminant analysis based on the data obtained from brewing and extracting methods. For brewing and extracting methods, 5 factors with cumulative variance of 91.825% and 93.858% were obtained along with factor analysis, and 5 factor score functions and 1 comprehensive evaluation function were obtained. Three Bayes discrimination functions were obtained along with discriminant analysis. For the two methods, recognition accuracy of back substitution was 85.7% and 83.9%, respectively; meanwhile the recognition accuracy of the cross-validation was 84.8% and 81.3%, respectively. On the whole, the discrimination results are satisfactory and the brewing method for sensory analysis is better.
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Published: 20 September 2015
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茉莉花茶的品质评定与价格判别
以茉莉花茶为研究对象,采用审评冲泡法和全量浸提法,通过因子分析和判别分析建立基于化学成分的品质评定和价格区间判别模型。结果表明:通过因子分析,审评冲泡法和全量浸提法分别得到累积解释变异量达91.825%和93.858%的5个因子,并均由此得到5个因子得分函数和1个综合评定函数;通过判别分析,审评冲泡法和全量浸提法均得到3条贝叶斯(Bayes)判别函数,回代总正判率分别为85.7%和83.9%,交叉验证总正判率分别为84.8%和81.3%。这说明2种方法的正确判别力较高,且审评冲泡法的判别效果更好。
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