Enhancement of flavor components of oolong tea and dark tea based on graphene heating film

Abstract

Reheating is crucial for improving tea quality, and graphene heating film provides a stable, uniform heating surface. This study used graphene heating film to heat oolong and dark tea at medium (M, 65 °C) and high (H, 75 °C) temperatures for 10, 20, and 30 min to assess the impact on flavor compounds. The results showed that the optimal parameters are as follows: the content of ester catechins decreased, the content of non-ester catechins increased, and the concentrations of woody and fruity compounds (Cedrol, Limonene, trans-Isoeugenol, Indole) significantly increased at M10 or H10 in oolong tea. The ester catechin content decreased at H20, the non-ester catechin content increased at M20, and the concentration of Floral compounds (trans-β-ionone) increased at H30 in dark tea. This study explores the potential of graphene heating film in tea processing, offering a theoretical basis for new technology in tea flavor enhancement.

Keywords: GC–MS; Graphene heating film; Quality; Tea; Volatile component.

Fig. 1

Graphene Heating Film Usage.

Fig. 2

Differences in dry weight of non-volatile matter in different combinations. (A) Non-volatile matter content of oolong tea. (B) Non-volatile matter content of dark tea. The letters on the bar graphs represent significant levels, where capital letters indicate: differences in the effects of different heating times on tea under the same gear heating; and lower case letters indicate: differences in the effects of different heating gears on tea under the same time heating. Error bars represent the mean ± SD and letters (A, B, C, a, b, c) indicate the differences obtained according to the Turkey HSD comparison method (p < 0.05), n = 3.

Fig. 3

Effects of different gears and different treatment times of graphene heating film on the changes of volatile substances in oolong tea. (a) represents the total concentration of volatile substances in oolong tea under different treatments of graphene heating film; (b) represents the changes in the concentration of different types of volatile substances identified; (c) represent the changes in the quantity of different types of volatile substances identified; (d) Radar chart of aroma and flavor of oolong tea under different treatments; (e-m) represent the changes in the concentration of the nine types of volatile substances with the highest concentration identified; (l-r) Concentration of potential key aroma substances of oolong tea under different treatments; (s) Total concentrations of potential key aroma compounds in oolong tea under different treatments. The letters on the bar graphs represent significant levels, where capital letters indicate: differences in the effects of different heating times on tea under the same gear heating; and lower case letters indicate: differences in the effects of different heating gears on tea under the same time heating. Error bars indicate Mean ± SD, and letters (A, B, C, a, b, c) indicate differences obtained according to the Turkey-HSD comparison method (p < 0.05), n = 3.

Fig. 4

Effects of different gears and different treatment times of graphene heating film on the changes of volatile substances in dark tea. (a) represents the total concentration of volatile substances in dark tea under different treatments of graphene heating film; (b) represents the changes in the concentration of different types of volatile substances identified; (c) represent the changes in the quantity of different types of volatile substances identified; (d) Radar chart of aroma and flavor of dark tea under different treatments; (e-m) represent the changes in the concentration of the nine types of volatile substances with the highest concentration identified; (l-r) Concentration of potential key aroma substances of dark tea under different treatments; (s) Total concentrations of potential key aroma compounds in dark tea under different treatments. The letters on the bar graphs represent significant levels, where capital letters indicate: differences in the effects of different heating times on tea under the same gear heating; and lower case letters indicate: differences in the effects of different heating gears on tea under the same time heating. Error bars indicate Mean ± SD, and letters (A, B, C, a, b, c) indicate differences obtained according to the Turkey-HSD comparison method (p < 0.05), n = 3.

Fig. 5

Multivariate statistical analysis of the volatile components of oolong tea and dark tea treated with graphene heating film at different temperature grades and time. (A) PLS-DA score plot of the volatile components of oolong tea; (B) Cross-validation results: the intercept of the Q2 replica line of the cross-validated model for 200 comparisons was less than 0, which indicated that there was no overfitting in the PLS-DA discriminant model, and that the model was relatively reliable; (C) VIP score plot: the pink color indicated the volatile compounds with VIP > 1; and the blue color indicated the volatile compounds with VIP < 1; (D) PLS-DA score plot of volatile components of dark tea; (E) Cross-validation results: the intercept of the Q2 replica line of the cross-validated model for 200 comparisons is less than 0, indicating that the PLS-DA discriminant model is not overfitted and the model is relatively reliable; (F) VIP score plot: pink bars indicate volatile compounds with VIP > 1; blue color indicates volatile compounds with VIP < 1. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 6

Schematic diagram of sensory evaluation and aroma enhancement of oolong tea and dark tea by graphene heating film.