Metabolomics Provides A Novel Interpretation of the Changes in Main Compounds during Black Tea Processing through Different Drying Methods

Abstract

This study aimed to compare the effect of hot roller (HR) drying and hot air (HA) drying on the sensory evaluation, chemical quality, antioxidant activity, and metabolic profile of Yihong Congou black tea processed from E'cha NO1. The Yihong Congou black tea dried with HA obtained higher sensory scores and better chemical qualities such as the hue of tea brew color (a and b), content of theaflavins, thearubigins, water extract, free amino acids, tea polyphenol, and the ratio of polyphenol to amino acids as well as higher antioxidant capacities compared to that dried with HR. The HA drying tea increased the contents of volatile compounds that had positive correlation with sweet and flowery flavor, while the HR drying tea increased the contents of volatile compounds related to fruity flavor. Moreover, non-targeted metabolomics data indicated that the levels of most free amino acids significantly increased, while the levels of most soluble sugars reduced in the HA drying method compared to the HR drying method. The metabolic analysis was also consistent with the above results and revealed that D-ribose and gallic acid were the main characteristic metabolites of HA drying. Our results could provide a technical reference and theoretical guide to processing a high quality of Yihong Congou black tea.

Keywords: E’cha NO1; black tea; drying methods; metabolite; non-targeted metabolomics.

Figure 1

Scavenging rates of Congou black tea processed by hot air (HA) and hot roller (HR) treatments at various concentrations on DPPH free radicals.

Figure 2

(a) Score plots from principal component analysis. (b) Partial least squares discrimination analysis. (c) Orthogonal partial least squares discrimination analysis. (d) Its permutations test. The dataset comprised 966 filtered ion features. Stars in blue show samples from the HR treatment group, spots in yellow indicate the samples from the HA treatment group, Stars in blue show samples from the HR treatment group, spots in yellow indicate samples from the HA treatment group.

Figure 3

(a) Heat map of metabolites in tea samples dried by the HA and HR treatments. Group A, Yihong Congou black tea processed by HA drying; Group B, Yihong Congou black tea processed by HR drying. Warm color and cold color indicate increased and decreased expression of the metabolites, respectively. (b) Loading plot of metabolites in tea samples dried by the HA and HR treatments, based on the criteria of VIP > 1, p < 0.05, and match score ≥ 700. D-ribose and gallic acid were considered as the most influential characteristic metabolites.