Dynamic Formation of Green Tea Cream and the Identification of Key Components Using the "Knock-Out/Knock-In" Method

Abstract

The composition of green tea cream is extremely complex, and identification of key components is a prerequisite for elucidating its microstructure formation mechanism. This study examined the dynamic changes in the content of components and properties of colloid particles during the formation process of tea cream by chemical analysis and dynamic laser scattering (DLS). A "knock-out/knock-in" method was developed and used to further explore the relationship between the interaction of these components and the microstructure formation of tea cream. The results revealed that polysaccharides, proteins, epigallocatechin gallate (EGCG), and caffeine were the main components involved in tea cream formation. These components participated in the formation process in the form of polysaccharide-protein and EGCG-caffeine colloidal particles. Consequently, there were synchronized dynamic changes in the levels of polysaccharides, proteins, EGCG, and caffeine. The "knock-out/knock-in" experiment revealed that the interactions between EGCG or caffeine and macro-molecule components were not the key factors in tea cream microstructure formation. However, it was found that the complexation between EGCG and caffeine played a crucial role in the formation of tea cream. The findings suggested that decreasing the concentrations of EGCG and caffeine could be useful in controlling tea cream formation during tea beverage processing and storage.

Keywords: colloid particles; dynamic formation process; green tea cream; key components; “knock-out/knock-in” method.

Figure 1

(A) Transformation of original tea infusion during storage at 4 °C. Changes in turbidity (B) and tea cream content (C) in original tea infusion stored at 4 °C. Data are shown as the mean ± SD, n = 3.

Figure 2

Changes in major chemical component contents (µg/mg) (A) and metal element contents (mg/kg) (B) during the green tea cream formation process. (C) Distribution coefficients of major chemical components of green tea cream stored at 4 °C for 4 h. Data are shown as the mean ± SD, n = 3. Different lower-case letters denote significant differences (p < 0.05) at each variable.

Figure 3

Electrophoretic pattern of proteins in green tea cream.

Figure 4

Changes in size distributions during green tea cream formation at 4 °C.

Figure 5

(A) Changes in the z-average hydrodynamic diameter, PDI, and zetapotential of dialyzed tea infusion recorded at 4 °C. (B) Changes in the turbidity of the samples recorded after adding EGCG and caffeine into dialyzed tea infusion at 4 °C. (C) Schematic illustration for the EGCG–caffeine-nanoparticle precipitation process. Data are presented as the mean ± SD, n = 3. Different lower-case letters denote significant differences (p < 0.05) at each variable.