| Selenium is a daily essential trace element for human body.It is of practical significance to improve selenium nutrition by drinking selenium-enriched tea.Wanyuan city of Sichuan province is an important production area of selenium-enriched tea in China.It mainly uses raw materials in spring to produce selenium-enriched green tea and selenium-enriched black tea,but no selenium-enriched yellow tea has been developed.Yellow tea is currently a hot spot of development,and Sichuan is the traditional yellow tea production area.Therefore,in this paper,firstly,the raw materials of fresh leaves in Wanyuan from different regions,tenderness and seasons were screened,and determine selenium-enriched raw materials;then single factor test and orthogonal test were carried out on the key process parameters to establish the processing technology of Wanyuan selenium-enriched yellow tea;finally,the changes of quality components in the processing of Wanyuan selenium-enriched yellow tea were studied to explore the formation mechanism of the quality of Wanyuan selenium-enriched yellow tea.This can not only provide a basis for processing selenium-enriched yellow tea,but also has important guiding significance for enriching the varieties of yellow tea in Sichuan and improving the utilization rate of Wanyuan tea resources.The main research results of this paper are as follows:（1）The selenium content of fresh leaves in different regions,tenderness and seasons was determined,the results show that:From a regional perspective,among the six sampling points,the selenium content of tea at four sampling points in Gujun town,Baiyang town and Qinghua town in the southwest of Wanyuan was between 0.05 and 0.1mg/kg,only the selenium content of tea at the sampling point of Xiaoheba,Dazhuhe town was between 0.2-4mg/kg,meeting the requirements of selenium-enriched tea GH/T1090-2014;In terms of seasons,because of sufficient accumulation in spring and autumn,the selenium content of fresh leaves in spring and autumn is significantly higher than that in summer.In terms of tenderness,the content of selenium in one bud with a leaf and one bud with two leaves was higher,and the content of selenium in fresh leaves of one bud with three leaves was lower.Because of the low utilization of raw materials of Wanyuan summer tea,moreover,the selenium content of one bud with a leaf（0.22mg/kg）and one bud with two leaves（0.23mg/kg）was the highest in summer,and the difference between them was not significant（P<0.05）.Therefore,considering the requirements of famous tea raw materials,processing and product appearance,one bud with a leaf were selected as the raw material of selenium-enriched yellow tea fresh leaves at the sampling point of Xiaoheba in Dazhuhe town in summer.（2）Taking one bud with a leaf as raw materials in summer,the processing of Wanyuan selenium-enriched yellow tea was carried out,and the key technological parameters（heaping for yellowing temperature,heaping for yellowing time and drying temperature）were orthogonal optimized,the results show that:Amino acid content was used as the evaluation index,among the three different factors,the primary and secondary factors are A（heaping for yellowing temperature℃）>B（heaping for yellowing time min）>C（drying temperature）,among them,there was a significant difference between the two groups in heaping for yellowing temperature（P<0.01）.,and the heaping for yellowing temperature was the key factor affecting the quality of Wanyuan yellow tea;According to the SPSS variance processing results and the comprehensive comparison of other inclusion component analysis results,the optimal combination of the key processing parameters of Wanyuan selenium-enriched yellow tea was selected as A2B2C2（the heaping for yellowing temperature was 45±2℃,the heaping for yellowing time was 120min,and the drying temperature was 70±2℃）.（3）The quality components in the processing of the selenium-enriched yellow tea were analyzed and detected,the results show that:With the processing process,from the sensory point of view,the appearance of color from pale green to yellow green to yellow with brown,soup color from pale green to green yellow to yellow bright,aroma from green grass to sweet and then to high fragrance with flowers;In terms of quality components,the total amount of tea polyphenols,catechins and total chlorophyll content decreased by 22.25%,17.51%and 35.08%respectively compared with fresh leaves,the astringent ester catechin EGCG and ECG were converted into simple catechin C and EC,which reduced the astringency and bitterness of the tea.The contents of water extract,total amino acid and soluble sugar increased,and the increases of finished products were16.78%,27.77%and 45.58%.respectively,compared with fresh leaves.The bitter amino acid components gradually decreased,and the sweet and fresh amino acid components gradually increased,however the contents of tea caffeine and selenium did not change during processing.（4）The main components of color,fragrance and flavor of yellow tea from Wanyuan were analyzed,the results show that:In terms of color,due to the destruction of chlorophyll by high temperature,the chlorophyll content of yellow tea decreased by 23.53%compared with that of green tea,it was beneficial to yellow leaves of yellow tea.In terms of flavor,the contents of water extract,tea polyphenols green tea are higher than that of yellow tea,but the contents of free amino acids and soluble sugars are higher than that of green tea.Besides,the bitter taste of esterified catechin EGCG and ECG in yellow tea decreased by 9.91%and 8.41%,respectively,compared with green tea.In addition,the amino acid components of yellow tea（18.88mg/g,1.81mg/g）with fresh and sweet taste are better than green tea（16.79mg/g,1.26mg/g）,making Wanyuan yellow tea more mellow than green tea.In terms of aroma,20 and 26 aroma components were detected in yellow tea and green tea,respectively.In this study,the content of linalool in yellow tea decreased by 42.16%compared with green tea,and the reduction of linalool weakened the sense of freshness.However,the content of nonanal,limonene and heptanal in yellow tea with rose aroma,lemon aroma and fruit aroma were significantly higher than that in fresh leaves and green tea,which was the main reason for Wanyuan selenium rich yellow tea with flower fragrance. |
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