The Effect of Different Drying Temperatures on the Transformation of Polyphenols and Volatile Aroma Components in Pu-erh Tea
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Abstract:
Acceleration of the fermentation of pu-erh tea by the addition of alanine and xylose was analyzed; in addition, the effect of different drying temperatures (air-drying at, and drying at 40 ℃, 60 ℃, 80 ℃, 100 ℃, and 120 ℃) on the quality and volatile aroma components of Pu-erh tea following pile fermentation were explored in this study. Drying at different temperatures was observed to have different effects on the transformation of polyphenols. The tea polyphenol, catechins and theabrownins content in Pu-erh tea was higher in the low-temperature drying group (below 60 ℃) than in the other groups; however, the polyphenol content was significantly lower in the high-temperature drying group (above 80 ℃) than in the other groups. Analysis of the volatile aroma components of Pu-erh tea revealed similarities in the major aroma components in each temperature group; these included (+)-cyclosativene, hexanal, heptanal, 5-methyl furfural, benzaldehyde, phenylacetaldehyde, and natural nonylaldehyde. The aroma components of Pu-erh tea dried at low-temperatures (air-drying, 40 ℃ and 60 ℃) showed a relatively high percentage of olefins, while tea dried at high temperatures (80 ℃, 100 ℃, and 120 ℃) displayed relatively higher aldehyde content. The low-temperature drying group displayed a relatively higher percentage of benzene-related and heterocyclic aroma components than the high-temperature drying group; the highest percentage was observed in the air-drying group. In general, the quality of air-dried Pu-erh tea was determined to be the best, and good quality Pu-erh teas were those dried at temperatures below 60 ℃.
