Recently, the team of Professors Wan Xiaochun and Wang Yijun at the laboratory published online in the internationally renowned journal Food Hydrocolloids (IF=11, a CAS Tier-1 TOP journal) a research paper entitled “Discovery and identification of the temperature dependent EGCG and β-lactoglobulin covalent conjugate in green tea and milk mixture”. The study discovered covalent binding between β-lactoglobulin, the main soluble protein in milk, and EGCG, the main catechin in green tea, and revealed its binding conditions and binding sites. Related covalent conjugates were also found in milk tea products, providing a new scientific understanding of the combination of milk and tea.

At 25 °C and 90 °C, the study analysed the interaction between these two compounds using a series of advanced technical approaches, such as fluorescence spectroscopy, Fourier transform infrared spectroscopy, circular dichroism, SDS-PAGE, NBT staining, LC-MS/MS, Western blot, ¹H NMR and molecular docking. The study found that heating significantly promoted the covalent reaction between β-LG and EGCG, forming two main stable complexes with molecular weights of 18.3 kDa and 37.6 kDa, a monomer and a dimer respectively. When heated at 90 °C, the monomer is formed by the binding of glutamine at position 35 of β-LG to the B ring of EGCG. Heating was also found to promote the covalent reaction in milk tea systems. The formation of covalent protein–polyphenol complexes does not significantly affect protein digestibility, but reduces IgG/IgE binding capacity, which may reduce the allergenicity of milk.

Anhui Agricultural University is the first completing institution. Doctoral student Zhang Kangyi of the National Key Laboratory of Tea Plant Biology and Resource Utilization is the first author of the paper, and Professor Wan Xiaochun and Professor Wang Yijun are the corresponding authors. The research was supported by the National Natural Science Foundation of China (32372337), the National Key R&D Program (2021YFD1601105-2, 2022YFD2101100-3) and the Joint Research Centre for Food Nutrition and Health of the Health and Medical Research Institute of the Hefei Comprehensive National Science Center (2023SJY02).