Effects on the Quality of Wuyi Rock Tea with Different Airing Thicknesses

In order to explore the effect on the quality of Wuyi rock tea with different leaf spreading thickness during airing, the leaf temperature, leaf ambient CO₂ concentration, volatile metabolites, polyphenols, and amino acids composition of primary tea during airing stage under 6, 12, 18 cm leaf spreading thickness, and traditional airing were detected, the shoots of the third and fourth leaves of Rougui (the Camellia sinensis var. Rougui) was selected as raw materials, headspace solid-phase microextraction combined with gas chromatography-time-of-flight mass spectrometry (HS-SPME-GC-TOF-MS) and targeted metabolomics were used as method. The results showed that the leaf temperature of 6 and 12 cm thickness was relatively stable, and the CO₂ concentration of each leaf spreading thickness was significantly lower than that of traditional airing after the second airing (P<0.05). The sensory quality of raw tea showed a downward trend with the increase of thickness, and the comprehensive quality score was highest (94.1) under 6 cm leaf spreading thickness. Meanwhile, there was no significant difference in the total catechins among different leaf spreading thickness was observed. However, the total catechins in treatments were significantly higher than the control (normal leaf spreading thickness, P<0.05), and the content of catechin in raw tea under the 6 cm leaf spreading thickness was higher. In addition, there was no significant difference in the total amino acids and fresh tast amino acid among 6, 12 and 18 cm leaf spreading thickness, but 12 and 18 cm were significantly higher than traditional airing (P<0.05). Alcohols accounted for the largest proportion of volatile substances in each raw tea. Meanwhile, some important ester volatiles, such as cis-3-hexenyl hexanoate, 4-hexanolide and hexyl hexanoate were significantly higher in 6 and 12 cm leaf spreading thickness than that in 18 cm and traditional leaf spreading thickness treatment (P<0.05). In conclusion, airing with 6 and 12 cm leaf spreading thickness enhance the soup thickness and the formation of pleasant aroma substances of Wuyi rock tea, 12 cm can be used as a reference leaf spreading thickness to Wuyi rock tea airing considering both quality and yield.